Adipose-derived stem cells (ADSCs) are rapidly becoming the gold standard cell source for tissue engineering strategies and hold great potential for novel breast reconstruction strategies. However, their use in patients with breast cancer is controversial and their oncological safety, particularly in relation to local disease recurrence, has been questioned. In vitro, in vivo, and clinical studies using ADSCs report conflicting data on their suitability for adipose tissue regeneration in patients with cancer. This review aims to provide an overview of the potential role for ADSCs in breast reconstruction and to examine the evidence relating to the oncologic safety of their use in patients with breast cancer. Increasing patient expectations for improved aesthetic outcomes means that surgeons are persistently attempting to optimise surgical technique and investigating new and improved approaches to breast reconstruction. This has driven research in the direction of tissue engineering strategies in an effort to develop superior breast reconstruction alternatives. Adipose-derived stem cells (ADSCs) have become the gold standard as a cell source for tissue engineering.10 They are particularly attractive for breast reconstruction as they exhibit potential for proliferation, preferential differentiation to adipocytes, and maintenance of mature adipose graft volume. However, the oncological safety of their use for adipose tissue regeneration, particularly in patients who have had a malignancy has been questioned.1115 Concern stems from the characteristics that make ADSCs attractive for tissue engineering, namely, their proliferative and differentiation capacity along with stromal support of cancer cells and delivery of locally inflammatory cytokines and/or growth factors. The aim of this review is to examine the current use of ADSCs in adipose tissue engineering, specifically related to breast reconstruction with a focus on cellular biology; use in breast surgery; oncological safety; and the effect of adjuvant therapies on the regenerative potential of ADSCs.Breast cancer represents a significant health care burden, with an estimated 1.7 million new cases diagnosed worldwide annually.16 Contemporary breast reconstruction approaches can be categorised as follows:The National Institute of Clinical Excellence (NICE) guidelines recommend that all suitable patients undergoing mastectomy for breast cancer should be offered immediate breast reconstruction.Implant-based reconstruction. Encompassing (a) implant-only reconstructions performed as a 2-stage procedure with placement of a tissue expander which is subsequently replaced with a permanent implant at a later operation or (b) single-stage, direct to fixed-volume permanent implant reconstruction with or without an acellular dermal matrix (ADM);Autologous reconstruction. Using pedicled tissue flaps , which tend to be myocutaneous, or free tissue transfer , which may be composed of myocutaneous tissue or solely adipose tissue along with perforating vasculature.1721 possibly explained by shorter and less complicated procedures and increased use of ADMs which have been shown to improve cosmetic outcomes by allowing for better definition of the infra- and lateral mammary folds, reduced capsular contracture rates, and the provision of an additional biocompatible layer between the prosthesis and the overlying skin.22 Traditionally, single-stage immediate implant-based reconstruction with total muscle coverage of the implant was only achievable in small-breasted women as it is limited by the degree of expansion of the overlying pectoral muscles. This may be overcome by placement of a tissue expander prosthesis which can be inflated over time and replaced by a permanent implant at a second surgery, or alternatively using an ADM with the permanent implant, obviating the need for total muscle coverage.23 Short-term complications of implant-based reconstructions include seroma, haematoma, infection, and skin necrosis, with implant extrusion and rupture being long-term possibilities.25 A significant longer term complication of implants is capsular contracture; the formation of a firm, fibrous tissue capsule surrounding the implant. This constricts over time, resulting in a spherical appearance of the breast which feels firmer than desired, chronic chest wall discomfort, and restricted shoulder rotation. The increasing use of ADMs in implant-based reconstruction has reduced the rate of capsular contracture; however, it remains a significant problem. Capsular contracture has a cumulative incidence of 6% to 18% in non–ADM-assisted implant reconstructions, compared with <5% in ADM-assisted procedures.26 Post-mastectomy radiation therapy (PMRT) has deleterious effects on aesthetic outcomes and complication rates in implant-based reconstruction as it can affect the symmetry, volume, and projection initially achieved at the time of reconstruction. Post-mastectomy radiation therapy also increases the rates of grade 3 and 4 capsular contracture and reduces the skin quality of the mastectomy flaps27 leading to an increased risk of necrosis and implant loss.Until recently, autologous flap procedures were the most common reconstructive approach. Contemporary trends have seen implant-based reconstruction become more common in the United States and Europe,28 The most widely used pedicled flap was traditionally the LD flap29; however, this is now being surpassed by the DIEP flap, although LD reconstruction is still popular as a salvage or delayed breast reconstruction technique.31 Free flaps include DIEP flaps and transverse rectus abdominis muscle (TRAM) flaps, which is also used as a pedicled flap. More recently developed flaps include the superior and inferior gluteal artery perforator flaps, transverse upper gracilis flap, superficial inferior epigastric artery flap, and profunda artery perforator flap. Autologous reconstructions are more cosmetically natural in shape and texture than implants. They provide skin coverage in cases of poor quality of the mastectomy flaps or delayed breast reconstruction. It is believed that DIEP reconstruction is more suitable in patients who will require PMRT as muscular atrophy is a significant complication of LD reconstruction that may occur post-radiotherapy.32Although the number of autologous reconstructions being performed has been surpassed by implant-based approaches, this approach still has a prominent role in post-mastectomy breast reconstruction, particularly in patients who have poor skin quality of the mastectomy flaps or for whom delayed reconstruction is preferred.33 Unfortunately, autologous reconstruction is associated with morbidity at the donor and reconstruction site. Tissue flap necrosis and loss may occur secondary to ischaemia of transferred tissue. Complications may arise from the donor site in the form of, eg, an incisional hernia in the case of a TRAM flap (incidence of 1.2%-8%) or donor site seroma in LD flaps (incidence of 70%-80%).35 These operations require longer admissions and recovery times.36 Autologous flap procedures are also longer and more technically challenging, particularly in the case of DIEP flaps which require the formation of a microvascular anastomosis.37Although initial complication rates for autologous reconstructions may be higher, they provide a more consistent and durable reconstruction over time.Due to the complications associated with current breast reconstruction methods, there is an urgent need to develop superior alternatives that will achieve the aesthetic goal of establishing a natural appearing breast shape. The preferred approach would include an autologous or biocompatible component to minimise foreign body reactions but without the requirement for extensive surgical resection at a donor site. Regenerative medicine approaches hold exciting potential in this regard, and recent efforts have focused on cell-based regeneration of adipose tissue.38 Recent scientific interest has focused on the potential for adipose tissue engineering to generate sufficient volumes of fat for breast reconstruction. Adipose tissue engineering requires a stem cell with the capacity for differentiation into mature adipocytes.There has been increasing interest the potential of autologous fat as a donor source for effective breast reconstruction. Autologous fat is thought to be a superior method of soft tissue augmentation due to a range of properties including biocompatibility and versatility; it is non-immunogenic, has similar mechanical properties to breast tissue, appears more natural than implants or pedicled flaps, and is associated with minimal donor site morbidity.40 Adult/somatic stem cells are multipotent cells within adult tissues which maintain and repair the tissue in which they are found and are capable of differentiating into mature cell types such as osteoblasts, adipocytes, and chondroblasts, in addition to a lack of expression of HLA-DR surface molecules.41 Adult/somatic stem cells are more abundantly available and avoid the ethical considerations associated with the use of embryonic stem cells (ESCs) for tissue regeneration.42 Adult stem cells are found in almost all adult tissues; mesenchymal stem cells (MSCs) have been harvested from tissues such as trabecular bone and periosteum, synovial membrane, skeletal muscle, skin, teeth, and periodontal ligaments.4349 However, the most widely harvested and studied adult stem cells are those from bone marrow, adipose tissue, and peripheral blood.50 Adipose-derived stem cells are rapidly becoming the gold standard as a cell source for tissue engineering and regenerative medicine. They are contained within the stromal vascular fraction (SVF) of adipose tissue and hypothesised to improve wound healing, tissue regeneration, and graft retention.51 According to the International Federation for Adipose Therapeutics and Science (IFATS) and International Society for Cellular Therapy (ISCT) joint statement on ADSCs, these cells are identified phenotypically as a CD45−, CD235a−, CD31−, and CD34+ cell population. They differ from bone marrow–derived cells (BMSCs) in that they are positive for CD36 and negative for CD106. They are also capable of trilineage differentiation.52Stem cells are an undifferentiated cell type with multipotent capacity.53 have significant proliferative capacity in culture with a longer life span in culture than BMSCs,54 and possess multi-lineage potential .5558 Adipose-derived stem cells also have a shorter doubling time and later in vitro senescence than BMSCs.12Adipose-derived stem cells possess certain advantages over BMSCs and ESCs. They are isolated with less invasive techniques, offer a higher cell yield than bone marrow aspirates (>1000× stem cell number per gram of tissue) or umbilical cord blood,40 To isolate ADSCs, adipose tissue is digested with collagenase, filtered, and centrifuged. The resulting cell pellet is the SVF, containing stromal cells, including ADSCs, which do not contain the lipid droplet in mature adipocytes and have a fibroblast-like morphology.38 Other cell types present include endothelial cells, smooth muscle cells, pericytes, fibroblasts, and circulating cells such as leucocytes, haematopoietic stem cells, and endothelial progenitor cells. White adipose tissue (WAT) depots vary in stem cell content and properties depending on anatomical site. Adipose-derived stem cells of visceral origin have a higher self-renewal capacity59 and ADSCs from abdominal superficial regions are more resistant to apoptosis than those from the arm, thigh, or trochanteric depots.10 This is hypothesised to be secondary to different levels of apoptotic regulators within cells from different depots, such as the Bcl-2 family, in addition to variations in production of paracrine/autocrine factors, eg, insulinlike growth factor 1 (IGF-1).60 A recent study demonstrated that superficial abdominal cells have higher G3PD activity, aP2, peroxisome proliferator–activated receptor γ (PPAR-γ), and C/EBP-α expression compared with other depots, which may contribute to their resistance to apoptosis.61 However, the greatest numbers of stem cells are isolated from the arm when compared with depots such as the thigh, abdomen, or breast, postulated to be secondary to this depot having the highest PPAR-γ2 expression.62 The optimum WAT depot ADSC harvest and recovery has yet to be elucidated.63Adipose-derived stem cells are typically isolated from lipoaspirates obtained at liposuction procedures, of which, approximately 400 000 are conducted in the United States annually. Each procedure yields approximately 100 mL to 3 L of lipoaspirate, in which 90% to 100% of ADSCs are viable, which is usually discarded following routine liposuction.14 One significant difference between the cell types is the presence of the glycoprotein CD34 on the ADSC cell surface.6365 Adipose-derived stem cells show uniformly positive expression for stem cell markers CD34, CD44, CD73, CD90, and CD10512 and are negative for CD19, CD14, and CD45. They are positive for pericytic markers CD140a and CD14b and the smooth muscle marker α-smooth muscle actin. Adipose-derived stem cells secrete growth factors such as vascular endothelial growth factor (VEGF), hepatocyte growth factor, fibroblast growth factor 2 (FGF-2), and IGF-1, all of which are involved in angiogenesis and adipose tissue regeneration.64 As ADSCs exhibit a similar cell surface immunophenotype as pericytes, it is thought that ADSCs reside within the perivascular region of adipose tissue, between mature adipocytes and adipose extracellular matrix (ECM) near small capillaries.66The immunophenotype of ADSCs is >90% identical to that of BMSCs.54 This is regulated by the nuclear transcription factor PPAR-γ. The transcriptional programme activated by PPAR-γ is responsible for the regulation of expression of hormone-sensitive lipase, adiponectin, and fatty acid–binding protein 4 (FABP-4).11 Insulinlike growth factor 1 stimulates the first stage of adipogenesis. Glucocorticoids, insulin, and growth hormone play a role in the stimulation of the early and late phases of adipogenesis.40 Mature adipocytes are terminally differentiated cells with limited capacity for self-renewal and replacement of mature adipocytes.63 The responsibility for tissue homeostasis and cell renewal as a result of cells lost due to maturation, damage, or ageing in mature adipose tissue lies with ADSCs.67 As ADSCs originate from the SVF of digested adipose tissue, they also have the ability to differentiate into vascular endothelial cells and also produce the pro-angiogenic growth factor VEGF, which would be advantageous in the process of vascularising an engineered tissue construct.10The transition of a multipotent ADSC into a mature adipocyte occurs in 2 stages. First, by determination and differentiation of the stem cell into a preadipocyte, with subsequent terminal differentiation into a mature adipocyte characterised by accumulation of a single lipid droplet within the cell.Due to these characteristics, ADSCs hold considerable potential for the regeneration of fat tissue in reconstructive surgery and can be used as both autologous and allogenic grafts in this context.6872 and contour defects in implant-based breast reconstructions.74 Although promising aesthetic outcomes have been demonstrated in this setting, the larger volume of adipose tissue required to reconstruct the breast mound post-mastectomy is more challenging.75 Autologous fat grafting has had limited success in breast reconstruction with resorption rates ranging from 25% to 80% and complications such as fat necrosis, oil cyst formation, and microcalcifications in patients receiving autologous fat transfer in addition to a primary reconstructive procedure, eg, LD flap76 or as a filler for small-volume defects post-BCS.7779 In an attempt to reduce the rate of resorption, cell-assisted lipotransfer, first described by Matsumoto et al80 in 2006, involves enrichment of autologous lipoaspirates with ADSCs prior to grafting. Enrichment of autologous fat lipoaspirates with ADSCs which have been expanded ex vivo has had more successful outcomes in terms of volume retention, likely as a result of superior graft maintenance due to increased vascularisation and collagen synthesis within the graft.14 Kolle et al demonstrated residual fat volume of >80% in 10 patients over 121 days using abdominal lipoaspirate enriched with ADSCs that had been expanded ex vivo for 14 days prior to reimplantation into the upper posterior arm. Compared with controls, there were higher amounts of adipose tissue, less necrotic tissue, and newly formed connective tissue in grafts enriched with ADSCs.81 Yoshimura et al conducted a study in 40 healthy patients undergoing cosmetic breast augmentation, where a mean volume of 270 mL of ADSC-enriched fat was injected into the breast. They reported minimal post-operative atrophy of the injected fat which did not change significantly more than 2 months. Small cystic formations and microcalcifications were observed in some cases; however, the microcalcifications were readily distinguished as benign radiologically. Post-operative computed tomographic and magnetic resonance imaging images showed that transplanted fat tissue survived and breast volume stabilised 2 to 3 months post-operatively. These data indicate that cell-assisted lipotransfer is effective for small-volume breast defects.82Autologous fat grafting has been successfully used in the clinical setting for breast augmentation, filling small-volume defects post–breast-conserving therapy28 There has been limited success with ‘scaffold free’ techniques. This approach involves inducing ADSCs to differentiate into adipocytes and supplementation of culture media with ascorbic acid, to stimulate the production and organisation of ECM to form manipulatable sheets which can be assembled into thicker adipose constructs. Such constructs produced a thickness of 140 ± 14 µm after superimposing 3 adipose sheets.83 For scaffold-based tissue-engineered constructs, correct scaffold material and design selection will be paramount in overcoming the obstacles of volume retention and vascularisation. Current tissue engineering strategies involve 2-dimensional or 3-dimensional (3D) natural or synthetic scaffold biomaterials that may or may not be seeded with MSCs.54Recreating the breast mound post-mastectomy is likely to require long-term maintenance of larger tissue volumes in engineered grafts supported by a biocompatible scaffold.54 The ideal scaffold is also biocompatible, preventing the occurrence of a long-term immune reaction. A highly porous structure is required for vascular ingrowth and cell differentiation. Adipose-derived stem cells undergo morphologic alterations during differentiation to mature adipocytes which includes an increase in diameter from approximately 10 to 100 µm.84 Pores within the scaffold must be of adequate size to accommodate changes such as these. A scaffold’s stiffness is an important consideration, in that it must be capable of maintaining its structural integrity despite handling during surgical insertion and physiological forces in vivo, yet flexible so that ingrowth of new tissue and vascular structures is possible. In addition to this, biomaterial stiffness influences ADSC differentiation, eg, when stem cells are encapsulated in polycaprolactone (PCL), they are more likely to differentiate towards bone, tendon, and cartilage over other tissue types.85 Biomechanical properties of the biomaterial must be adjustable to regulate the cellular microenvironment. Degradation properties of a biomaterial are imperative; an ideal scaffold should remain intact for sufficient time for new tissue to form but degrade at a sufficient rate that new ECM can be formed and tissue regenerated.86 Generally, scaffolds are composed of biomaterials in the form of sponges, hydrogels, 3D or bioprinted constructs, and electrospun scaffolds  and subcutaneously implanted in athymic nude mice for 24 weeks. Explanted samples were well-vascularised constructs of adipose tissue without necrosis, inflammation, or cysts. There was an increase in adipose tissue produced from 37.17% to 62.3% between weeks 5 and 15. This further increased to 81.2% between weeks 15 and 24.113Synthetic scaffolds studied in this field include polyglycolic acid (PLGA), polyethylene glycol, PCL, and poly-tic acid . Propert127 successfully bioprinted a 3D cell laden construct with dECM that showed high cell viability and functionality. A similar biomaterial adipose tissue construct was implanted into a mouse model, which demonstrated positive tissue infiltration, constructive tissue remodelling, and adipose tissue formation. Decellularised adipose tissue (DAT) also holds promise as an adipogenic bioscaffold. One study seeded ADSCs onto DAT bioscaffolds and implanted them into female Wistar rats. At explantation at 12 weeks, 56.1% ± 9.2% of the ADSC-seeded DAT had been remodelled into mature adipose tissue. There was a higher density of blood vessels within the areas of the implant that had been remodelled into mature adipose tissue.128More recently, biological scaffolds such as decellularised ECM (dECM) have been studied . They ge133 In addition, ADSCs themselves are implicated in the regulation of neovascularisation through their modulation of the ECM, or scaffold, by matrix metalloproteinases (MMPs).134 Some studies have sought to aid vascularisation by the addition of HUVECs to ADSC and scaffold constructs.136 Chhaya et al seeded HUVECs onto their adipose tissue construct prior to implantation into a murine model. They observed a 62.3% increase in adipose tissue with the formation of a functional capillary network within the tissue.113 Vascular pedicles have been used as additional support for an engineered adipose construct within a chamber to facilitate large-scale adipose tissue engineering.137 In this setting, a chamber allows the vascular pedicle to induce intense vasculogenesis to maximise cell survival.84 Dolderer et al138 demonstrated a 10% to 15% increase in adipose tissue volume over a 20-week period using this approach; there was no evidence of hypertrophy, fat necrosis, or atypical changes in the regenerated tissue. Findlay et al114 was successful in generating up to 56.5 mL of adipose tissue by implanting bilateral 78.5-mL chambers subcutaneously in the groin of a pig which enclosed a fat flap based on the superficial circumflex iliac pedicle for 22 weeks. Implantation of a scaffold prior to ADSC/adipose tissue to allow for ingrowth of new vessels among the scaffold has been investigated. ‘Additive biomanufacturing’ used delayed fat injection into a custom-made scaffold implanted in minipigs for 24 weeks after a period of prevascularisation. The prevascularisation + lipoaspirate group had the highest relative area of adipose tissue on explantation (47.32% ± 4.12%) which was similar to native breast tissue (44.97%±14.12%).122 These studies represent the largest volumes of adipose tissue engineering in vivo.Vascularisation of regenerated tissue is one of the primary challenges of tissue engineering. Several methods of providing these constructs with adequate blood supply have been investigated. The scaffold within regenerated tissue can play a prominent role in this regard, as scaffold stiffness and porosity are known to influence angiogenesis.39The transition to large animal studies and the generation of larger, more clinically relevant volumes of adipose tissue present an exciting prospect for translation of a tissue-engineered breast reconstruction to the clinical setting. However, the evidence for the oncological safety of using ADSCs in patients who have been treated for breast cancer is limited and requires further investigation before the knowledge and techniques generated through these studies can be considered for application in post-mastectomy reconstruction.Despite the promising early results of ADSCs in breast lipofilling and small-volume reconstruction, its application towards post-oncologic reconstruction should be approached with caution. The concern regarding use of autologous ADSCs in this setting stems from the very same characteristics which make them so attractive for tissue regeneration. Adipose-derived stem cells may potentially contribute to stromal support for cancer cells and deliver locally inflammatory cytokines and/or growth factors, thus facilitating residual cancer cell survival and growth.46 It is composed of all cells surrounding the tumour including endothelial, inflammatory and immune cells, adipocytes, myoepithelial cells, and fibroblasts in conjunction with their ECM.140 Understanding the complexity of tumour-stromal interactions will enhance our understanding of how ADSCs may interact with the tumour microenvironment. Numerous autocrine, paracrine, and exocrine pathways in this environment have been described as a role-playing factor in breast cancer.47Breast cancer grows in close anatomical proximity to adipose tissue. The ‘tumour microenvironment’ consists of a complex signalling network which influences the behaviour of both resident stem cells and tumour cells.141 Cancer-associated adipocytes are mature adipocytes that have dedifferentiated into preadipocytes through loss of their lipid droplet and adopted a fibroblastic morphology.11 This cell type increases tumour growth, tumour invasion via greater epithelial-mesenchymal transition (EMT)14 and results in a radio-resistant breast cancer phenotype.13 Several inflammatory cytokines are thought to be involved in this process, eg, tumour necrosis factor α (TNF-α), interleukin (IL)-1, IL-6, IL-11, leukaemia inhibitory factor, IFN-γ, oncostatin M, and ciliary neurotrophic factor. They have been observed to both inhibit stem cell commitment and differentiation towards adipogenesis and may be implicated in adipocyte dedifferentiation.67A subset of adipocytes known as ‘cancer-associated adipocytes’ (CAAs) have been shown to play an active role in tumour progression and metastasis.142 Adipose-derived stem cells have a role in angiogenesis and localise to sites of injury and contribute to revascularisation.64 Epithelial-mesenchymal transition plays a major role in tumour development and benign resident and stromal cells recruited to the area are implicated in early cancer development and metastasis.39 These stromal cells within the tumour microenvironment are collectively known as ‘cancer-associated fibroblasts’. They secrete pro-angiogenic and anti-apoptotic factors, contributing to tumour development. Zhang et al59 demonstrated that ADSCs mobilise and migrate through the systemic circulation to distant tumours resulting in acceleration of tumour growth. This action appears to be unique to ADSCs and is not observed in similar models using bone marrow-derived or lung-derived MSCs.143 It remains unclear whether ADSCs used in wound repair are capable of migration to distant tumours. Altman et al investigated whether ADSCs had any effect on the growth and progression of distant tumours when applied to a skin wound; comparing tumour growth in vivo (murine model) when breast cancer cells and ADSCs were co-injected and when the ADSCs were introduced on an ADM at a distant skin wound. Although there was an increase in tumour volume when ADSCs were co-injected, there was no such effect observed in cases where the ADSCs were introduced at the skin wound, indicating that that the wound microenvironment is capable of retaining ADSCs and preventing their migration to distant malignant sites.144In order for cancer to progress, it requires stem cells and partly differentiated progenitor cells to be recruited from local and distant sites and angiogenesis, both of which occur due to release of factors by the inflammatory and hypoxic tumour microenvironment.145 Coculture of breast cancer cells and preadipocytes prevents adipogenic differentiation, supporting the hypothesis that ADSCs are part of the CAA population within breast cancer tumours.146Adipose-derived stem cells, both local and those recruited to a breast tumour site, are capable of dedifferentiation into CAAs. Several genes involved in cell growth, ECM deposition/remodelling, and angiogenesis are expressed at higher levels in local breast ADSCs than those isolated from adipose tissue or bone marrow, suggesting that the breast adipose depot plays a more intimate role in breast cancer progression.147150 Adipose tissue ECM is rich in collagen VI,151 which is upregulated in tumorigenesis and promotes GSK3β phosphorylation and increased β-catenin activity in breast cancer cells. Breast tumour growth has been shown to be reduced in a collagen VI–deficient murine model. Breast cancer cells cocultured with adipocytes and injected subcutaneously in the mammary fat pad of a nude mouse resulted in larger tumours than breast cancer cells cocultured with fibroblasts and Matrigel.152 Matrix metalloproteinases are enzymes involved in the degradation of ECM proteins during growth and tissue turnover. Higher levels of MMP-11 are expressed by adipocytes at the invasive front of human breast cancers secondary to ECM remodelling in this area. MMP-11 is a negative regulator of adipogenesis and may be responsible in part for the ‘dedifferentiation’ of adipocytes.13 Certain cell surface markers, eg, CD44, mediate reorganisation of ECM components, by anchoring MMPs to the cell surface. Therefore, ADSCs play a direct role in ECM remodelling occurring during tumour growth.12 Adipose-derived stem cells are involved in the desmoplastic reaction occurring within tumours through their involvement with MMPs. Desmoplasia results in the recruitment of myofibroblasts, a cell type frequently detected in breast cancer tumour stroma. Adipose-derived stem cells express α-smooth muscle actin, a marker for myofibroblasts, suggesting that ADSCs are a source of tumour myofibroblasts.14 These intricate interactions within the tumour microenvironment illustrate how ADSCs may create a favourable milieu for tumour growth.Extracellular matrix secreted by adipocytes also has a role in breast cancer progression.140 Adipose tissue secretes cytokines known as adipokines, eg, TNF-α, IL-6, IL-8, PAI-1, MCP-1, adiponectin, resistin, leptin, insulin growth factor, and steroid hormones, some of which have been studied in relation to cancer,142 eg, leptin upregulates activity in signalling pathways in breast cancer tumours that play a role in proliferation , TNF-α, and VEGF.39Many adipokines are pro-inflammatory, are secreted in increasing amounts in obese individuals, and are involved in the promotion of tumour growth, locally at the tumour site and, via communication with distant sites, in particular TNF-α, IL-6, IL-8, and MCP-1.152Adipokines induce transcriptional programmes implicated in promoting tumorigenesis which include increased cell proliferation through IGF-2, FOS, JUN, and cyclin D1; invasive potential through MMP-1 and AFT3l; cell survival via A20 and nuclear factor κB; and angiogenesis.2, TGF-β1, indoleamine 2,3-dioxygenase, hepatocyte growth factor (HGF), and inducible nitric oxide synthase. Adipose-derived stem cells may be responsible for abnormal CD4+ T-cell activation and function.15 Razmkhah et al investigated the expression of IL-4, IL-10, and TGF-β1 in ADSCs isolated from breast tissue in patients with cancer and healthy controls and whether these cytokines had an influence on peripheral blood lymphocytes. Messenger RNA expression of IL-10 and TGF-β1 in ADSCs from patients with cancer was higher than those isolated from healthy patients. The conditioned media from ADSCs of patients with stage III disease was used to culture ADSCs from healthy patients and caused IL-4 and IL-10 expression to increase. Therefore, ADSCs may assist in protecting the breast cancer from anti-tumour immune responses by providing a source of anti-inflammatory cytokines within the tumour microenvironment and their potential to act as regulatory T cells.15Adipose-derived stem cells may also influence tumour growth and progression through exertion of immunomodulatory effects on T cells within the tumour microenvironment due to the secretion of cytokines such as prostaglandin E153 Oestrogen upregulates growth factors such as epidermal growth factor receptor and Akt phosphorylation, sustaining breast cancer growth.154 Oestrogen plays a role in the increased aggressiveness of breast cancer in obese individuals.155 Adipose-derived stem cells isolated from abdominal adipose tissue of those with a body mass index >30 enhance breast cancer cell line proliferation and tumorigenicity in vitro and in vivo. Changes in the oestrogen receptor alpha and progesterone receptor gene expression profile correlated with these changes. Obesity caused changes in several adipogenic genes including leptin, and women with ER+/PR+ tumours that had high leptin expression had a poorer prognosis.156Breast adipose tissue functions in oestrogen biosynthesis and high local levels of oestrogen are related to breast cancer development and progression.As discussed above, ADSCs have the potential to influence the behaviour of breast cancer cells due to secreted adipokines and their effect on the tumour microenvironment. However, there are conflicting reports on the manner in which this influence is exerted.141 who reported increased invasiveness of both human and murine breast cancer cells associated with overexpression of proteases, including MMP-11, and pro-inflammatory cytokines , when cocultured with adipocytes. Zhang et al157 demonstrated that ADSCs increased the motility of MCF-7 breast cancer cells in vitro through the secretion of the chemokine CCL5.The role of adipokines was demonstrated by Dirat et al158However, it has been suggested that ADSCs may only promote the growth and progression of active breast cancer cells and do not activate dormant residual breast cancer cells; therefore, the use of ADSC regenerative therapies should therefore be delayed until there is no evidence of active disease.inhibit tumour growth in vitro. Adipose-derived stem cells are capable of inducing cell death in pancreatic adenocarcinoma, hepatocarcinoma, colon, and prostate cancers.160 Adipose-derived stem cells cultured at high density and their conditioned media have been shown to be capable of suppressing the growth of MCF-7 cells in vitro, as a result of IFN-β expression by ADSCs in high-density culture.161Indeed, there is a lack of consensus on the reported effects of ADSCs on tumour behaviour as some studies have demonstrated an ability by ADSCs to + WAT ADSCs, suggesting that most of the tumour progression effects of human WAT are due to the ADSC fraction. A follow-up metastasis study demonstrated that mice which had a primary breast cancer tumour removed and were injected with ADSCs alone had a higher rate of axillary and lung metastasis than mice which had CD34− cells injected post-resection. Immunohistochemistry revealed that human cells generated from ADSCs were incorporated into the tumour vasculature. These effects have never been observed using bone marrow–derived stem cells, suggesting that these functions are unique to ADSCs.53There is a similar discordance in results from in vivo studies. Increased tumour growth and metastasis in a murine model was observed when ADSCs from WAT were co-injected with triple-negative human breast cancer cells. Tumour progression was similar in the groups that were co-injected with human breast cancer cells and unprocessed lipoaspirate and those co-injected with human breast cancer cells and purified CD34162 The authors using a murine cancer model similar to prior studies demonstrated that ADSCs did not appear to increase tumour progression or metastasis and actually had the effect of inhibiting breast cancer cells by apoptosis.Conversely, the ability of ADSCs to inhibit MDA-MB-231 breast adenocarcinoma cells was demonstrated by Sun et al.Experimental data, both in vitro and in vivo, are conflicting regarding the effect of ADSCs on breast cancer, and there is a lack of consensus on this subject. Data from their use in the clinical setting must also be considered when evaluating the oncological safety of their use in patients with breast cancer.164 In addition to experimental mechanistic data, the clinical evidence relating to the safety of ADSC use in patients with breast cancer has been assessed in both retrospective and prospective series of patients undergoing ADSC-enhanced fat grafting .166 Although the results of these studies are significant, they are retrospective series in a single centre with small numbers of patients. Several other explanations may exist for this increased rate of recurrence: there was a higher rate of recurrence in those patients with close or positive surgical margins in the study group, and there was an increased rate of recurrence in those with a higher grade tumour. There is no other published study that reports such an increased rate of breast cancer recurrence after autologous fat grafting. Further prospective investigation of the risk that intraepithelial neoplasia poses in autologous fat grafting is required, in larger numbers of patients with longer follow-up. The largest retrospective study to date which focused on ADSCs use in patients with a history of breast cancer was conducted by Kronowitz et al. The authors conducted a retrospective matched controlled study of 719 patients undergoing lipofilling of the breast post-tumour resection. There was no increase in locoregional or systemic recurrence or of a second breast cancer.168 In a separate retrospective study conducted by Petit et al,169 which focused on local recurrence consisted of 370 patients who underwent mastectomy (1.35%) and 143 patients who underwent BCS (2.19%), the authors concluded that there was no difference in recurrence rate of either group when compared with controls. Several other studies showed similar rates of recurrence in patients who solely underwent BCS when compared with controls.170 Therefore, there does not appear to be any difference in the rate of recurrence in patients undergoing autologous fat grafting post-BCS or mastectomy and reconstruction.The oncological safety of autologous fat grafting has been assessed in multiple prospective and retrospective series of patients who had undergone BCS or mastectomy . Petit e121The RESTORE-2 trial prospectively assessed the oncological safety of ADSC-enriched fat grafting in patients undergoing BCS with defects of up to 150 mL. In total, 67 patients reported high levels of satisfaction with the cosmetic outcomes. No incidences of local recurrence were reported within 12 months of the procedure; however, this is not a sufficient follow-up time to adequately investigate the oncologic safety of this technique.77 They also reported that the radiological appearance of the breasts post-lipofilling was usually of normal breast tissue; however, some images showed fat necrosis, which was easily distinguished from neoplastic lesions. Systematic reviews on the topic conclude that autologous fat grafting appears to be oncologically safe with low rates of complications and satisfactory patient and surgeon satisfaction.186189 However, questions remain with many of these previous mentioned studies as limited information is given about tumour size, lymph node status, and chemotherapy regimens, all of which would affect the locoregional recurrence (LRR) rate. Another key factor is the follow-up time, which varied considerably between studies. The largest study published by Kronowitz et al had a follow-up time of 5 years; in comparison, Petit et al reported a follow-up time of a little more than 2 years.169 The timing of the autologous fat grafting after surgery is another area for consideration; deciding on an optimal time point post primary surgery for autologous grafting with ADSCs may indeed be the primary decision in preventing recurrence. It is due to these issues that all authors call for well-designed randomised controlled trials with adequate follow-up to adequately address these issues and to exercise caution in performing these procedures in high-risk patients. A phase 3 multicentre randomised controlled trial is currently underway in France with the goal of investigating this issue (GRATSEC NCT01035268).Delay et al analysed outcomes in 880 patients in a retrospective review, who underwent fat grafting. This review of the practice of 4 surgeons demonstrated that after 10 years of follow-up, there was no increased risk of cancer recurrence or new cancer development.189191One further suggested explanation for the discrepancies between basic science and clinical studies in relation to oncological safety is the higher concentration of ADSCs used in vitro than clinically, which raises further concerns for the use of ADSCs in tissue engineering strategies which would require high concentrations of ADSCs to generate large volumes of adipose tissue.If ADSC-based breast reconstruction/regeneration approaches are to be translated to the clinical setting for patients with breast cancer, in addition to addressing oncologic safety, the potential effect of tissue regeneration using ADSCs on the efficacy of adjuvant therapy and the effects of adjuvant therapy on the success of tissue regeneration and breast reconstruction also require investigation.192 Harris et al treated ADSCs isolated from human periumbilical fat with paclitaxel at various concentrations in vitro. Adipose-derived stem cells from rats treated with paclitaxel were also investigated. Paclitaxel treatment resulted in increased ADSC apoptosis and decreased cell proliferation and migration and inhibited ADSC multipotent differentiation in both human and rodent cell populations. However, human and rodent ADSCs recovered differentiation abilities after cessation of paclitaxel treatment.193 Chen et al194 demonstrated that ADSCs induce doxorubicin resistance in MDA-MBA-231 triple-negative breast cancer cells through IL-8 secretion. However, ADSCs are shown to cause increased chemosensitivity to doxorubicin and 5-flourouracil in SKBR3 Her2 breast cancer cell lines.195 Beane et al discovered that vincristine, cytarabine, and etoposide all inhibited the proliferative ability of ADSCs, although the authors did note that variability did exist between drug type and concentration. In direct comparison, it was found that ADSCs’ growth or viability was not inhibited by any concentration of methotrexate.196After neoadjuvant chemotherapy for breast cancer, poor wound healing is a significant problem for patients undergoing subsequent tumour resection and reconstruction. It is postulated that chemotherapy influences ADSC’s ability to function effectively. Charon et al were the first to investigate the effect of paclitaxel on ADSCs. They found that paclitaxel inhibits proliferation and differentiation of ADSCs and can induce apoptosis. Paclitaxel can also impair wound healing in chemotherapy patients due to its inhibition of endothelial differentiation in ADSCs.Overall, it would appear that each chemotherapeutic agent interacts with ADSCs in a distinct manner and each would warrant investigation. What is clear, however, is that harvesting and storing ADSCs prior to beginning any chemotherapeutic regime may be the best approach to maximise their benefit in terms of adipose regeneration.197An in vitro coculture study and in vivo analysis of Her2 breast cancer found that adipocytes play a role in resistance of Her2-overexpressing breast cancer cells to trastuzumab. Whether this effect is exclusive to mature adipocytes or whether ADSCs are capable of similar promotion of breast cancer cell resistance to trastuzumab requires further investigation.198 Pike et al isolated human ADSCs and treated them with various concentrations of tamoxifen. This resulted in increased apoptosis, decreased proliferation of human ADSCs, and a decrease in differentiation capability into adipocytes and osteocytes and inhibited ability to form cords in Matrigel, suggesting that patients treated with tamoxifen may have decreased ADSC graft survival.199 This is a cause for concern and could potentially mean women may not be suitable for ADSC-based tissue regeneration while being treated with tamoxifen. In the clinical setting, Kronowitz et al167 showed a significant increased risk of LRR in patients who received hormonal therapy after autologous fat grafting. Although it is unclear what this increased risk is due to, Waked et al47 hypothesised that it may be due to a stimulatory effect of hormonal therapy on the communication between breast cancer cells and ADSCs or more worryingly that hormone receptor–positive patients with breast cancer may be at increased risk of LRR post-autologous grafting. This is a hypothesis that also requires further investigation.Tamoxifen is the most widely used adjuvant hormonal therapeutic agent for the treatment of breast cancer.200 This may be secondary to a superior ability of MSCs to retain their proliferative capacity due to their enhanced repair mechanisms for damaged DNA compared with terminally differentiated cells. Lower metabolic demands of ADSCs compared with mature adipocytes result in protection from hypoxia and apoptosis, preserving them to perform regenerative functions.200 There are several possible mechanisms by which injection of ADSCs into a previously irradiated area can overcome radiation-induced injury: ADSC adipogenic differentiation; increasing perfusion of injured tissues through induction and paracrine promotion of angiogenesis; exerting an anti-oxidant effect against hypoxia, ischaemia reperfusion, and reactive oxygen species–induced damage by adipokine release; modulating immune responses, inflammation, and improving wound healing; modulating granulation tissue, fibrosis, ECM remodelling, and improve epithelialisation; secreting lymphangiogenic factors, improving or reversing lymphoedema in damaged tissues; and recruiting endogenous stem cells via a homing chemokine gradient.200 A study of cocultured ADSCs and normal human fibroblasts (NHF) exposed to radiation shows promise for the use of ADSCs in breast reconstruction. Monocultures of ADSCs and NHFs showed reduced cell proliferation after radiation exposure; however, reduced impairment of cell proliferation was seen in the cocultured cells after radiation exposure. Gene expression of MMPs was also improved in the cocultured group.201 Microvascular endothelial cells were then added to the coculture. The levels of cytokines and adhesion molecules, IL-6, bFGF, ICAM-1, and VCAM-1, in the coculture supernatants were significantly less affected by irradiation than monocultures.202Post-mastectomy radiotherapy can result in complications such as recurrent infection, impaired healing, fibrosis, contracture, and lymphoedema. Adipose-derived stem cells display an element of radio-resistance in comparison with other components of the SVF.203 In a study of the effect of ADSCs on flap survival in irradiated tissues in rats, increased flap viability was observed in the ADSC-injected irradiated group compared with the control radiation only group. The mechanism may be both neovascularisation and vasodilation in addition to endothelial repair.204 A clinical study of the treatment of radiotherapy-induced injury by lipoaspirate-containing ADSCs showed improved outcomes for 20 grade 3 or 4 patients on the Late Effects Normal Tissue Task force - Subjective, Objective, Management, Analytic (LENT-SOMA) scale measuring severity of radiation effects, with improvement or remission of symptoms in all 20 patients.205Adipose-derived stem cells improve graft retention in irradiated scalps of mice. Fat grafts supplemented with ADSCs demonstrated superior volume retention, structural qualities, and vascularity.Further investigation of the effects of adjuvant cancer therapies, both cytotoxic and targeted on ADSC-based tissue regeneration, is required before this method of breast reconstruction can be considered for translation into the clinical setting.206 However, as of yet, there is no consensus on the protocol for adipose aspiration.207 The optimal adipose depot also needs to be identified. First, as the source of greatest ADSC cell yield, and second, as the one that is oncologically safe. As previously discussed, several genes involved in cell growth, ECM deposition, or remodelling and angiogenesis are expressed at higher levels in local breast ADSCs than those isolated from adipose tissue or bone marrow, suggesting that the breast adipose depot plays a more intimate role in breast cancer progression.Although there has been significant advancement made in the field of adipose tissue engineering, and in the use of ADSCs as a cell source in this regard, there are several outstanding issues that need to be addressed before adipose tissue engineering can be used to its full potential in breast reconstruction. Most basically, the isolation techniques used to produce lipoaspirate require refinement to optimise cell yield, survival, and viability. Investigation of this has thus far revealed that high-speed centrifugation is harmful to lipoaspirates and that washing the adipose tissue to separate it from blood and infiltration solutions may improve outcomes.The question of oncological safety of ADSCs needs to be definitively answered through investigation of the adipokines produced by this cell type and elucidating the role that these adipokines play in EMT and the tumour microenvironment. The role of ADSCs in stromal support for tumours will also require scrutiny in future experiments. Patient factors will also influence the oncological safety of ADSCs. Many adipokines are pro-inflammatory and are secreted in increasing amounts in obese individuals and are involved in the promotion of tumour growth, which begs the question, whether ADSCs are used in breast reconstruction, are obese individuals are greater risk of cancer recurrence? In addition, are there any other patient characteristics that place them at a greater recurrence risk?Timing of reconstruction with ADSCs also requires careful consideration. It has been suggested that ADSCs may only promote the growth and progression of active breast cancer cells and not dormant residual breast cancer cells. Therefore, should the use of ADSC regenerative therapies be delayed until such time that there is no evidence of active disease, and what is the optimal time point post-curative surgery for reconstruction with ADSC technology to prevent recurrence?Several clinical studies and systematic reviews have concluded that reconstruction techniques using autologous fat and ADSCs are oncologically safe with no increased rate of LRR. However, data such as tumour size, lymph node status, and adjuvant therapy regimens are scant. These factors are highly influential on the rate of recurrence and so need to be studied in greater detail in clinical trials of breast reconstruction techniques involving ADSCs.Finally, there has been limited investigation of the relationship between ADSCs, adjuvant therapies, such as chemotherapy and radiotherapy, and cosmetic and oncological outcomes. The potential effect of tissue regeneration using ADSCs on the efficacy of adjuvant therapy and the effect of adjuvant therapy on the success of tissue regeneration and breast reconstruction requires elucidation.With rates of mastectomy showing no sign of decline, novel, safe, functional, and cost-effective methods of breast reconstruction are required. Adipose tissue has been shown to be a valuable source of MSCs that hold immense potential for modern tissue engineering strategies in the field of breast reconstruction. However, there are still several pertinent research questions outstanding regarding the best adipose tissue depot from which to isolate ADSCs and how to generate and sustain volumes of mature adipose tissue to reconstruct the breast mound. Furthermore, the oncological safety of implanting ADSCs into patients with breast cancer due to the risk of cancer recurrence and what effects do adjuvant therapies have on ADSC isolation and their function on implantation remain to be fully elucidated. Well-designed randomised controlled trials will be required to accurately answer these issues. However, it is currently widely believed that ADSCs will be central to the development of novel future techniques in adipose tissue engineering.


Autoimmune disease has affected up to 50 million Americans, according to the American Autoimmune Related Diseases Association (AARDA) and 75 percent of those affected are women. These inflammatory diseases have variable activity and a lot of women will have to undergo major therapies during and after pregnancy. Many of the women suffering from these disease will improve during gestation. However a lot of women will require continuation of disease-modifying therapies  throughout pregnancy and post-partum involving many risks. In the past decade all gaze turned to biological therapies, as an attempt, to obtain even more effective medications in order to suppress the exacerbation of autoimmune disease, even at the most unfit circumstances such as pregnancy. The results are both satisfying and promising since increasingly proven thoughts prevail on making anti-TNF agents first-line medications, clearing up the limited knowledge over human influence. The purpose of this review is to summarize the results of the reports with the highest and representative range of patients of the last decade involving the use of anti-TNF agents during pregnancy. Autoimmune disease affects up to 50 million Americans, according to the American Autoimmune Related Diseases Association (AARDA) and 75 percent of those affected are women. These inflammatory diseases have variable activity and a lot of women will have to undergo major therapies during and after pregnancy. The majority of these women suffering from these diseases will improve during pregnancy. However, a lot of women will require the continual administration of these drugs.α promoted the role of TNF in the development of polyarthritis and that anti-TNF therapies could be effective against the human disease [Tumor necrosis factor (TNF) is a substance that is secreted primarily by cells of the immune system and plays a central role in the inflammatory process. It was associated with the pathogenesis of bacterial sepsis when the first preclinical studies using anti-TNF antibodies were performed on animal models (mice) of sepsis . However disease .Today, since therapeutic options are limited during pregnancy, most age- and gender- related incident rates of inflammatory diseases occur during the peak reproductive years and seeing that certain DMARDs are proven to be teratogenic , studies on other types of immunosuppressive drugs had to be conducted, making anti-TNF drugs the most possible therapy. In the last years more and more data regarding exposure to anti-TNF therapy during pregnancy has been published. Since pregnant patients face a disease both persistent and active, treatment with these agents may be required. Thus, it is crucial to review the available information on the safety of anti-TNF therapies , 4.α (TNFα) drugs are a preferable therapeutic option for patients with most autoimmune deceases since they are considered category B drugs by the FDA and they are often well tolerated by patients (even though the inconvenience of intravenous administration (IV), the high costs, and the adverse effects associated with these drugs limit their wide use as first-line medications) [Antitumor necrosis factor-cations) .Thanks to modern biotechnology various types of compositions have been produced that selectively inhibit the action of TNF. These compounds include antibodies to TNF  or agents that block the TNF receptor (etanercept), that is, the substance with which the TNF needs to be connected to exert its action.α currently licensed are available [The cytokine inhibitors affecting TNFvailable .Infliximab is a chimeric monoclonal antibody that counters tumor necrosis factor alpha (TNFα) and is approved by the US Food and Drug Administration (FDA) as treatment for autoimmune diseases such as inflammatory bowel disease (Crohn's disease and ulcerative colitis), psoriasis, psoriatic arthritis, ankylosing spondylitis, and rheumatoid arthritis [rthritis . Inflixirthritis .α and decreases its role in disorders involving excess inflammation in ankylosing spondylitis, adolescent rheumatoid arthritis, psoriasis, psoriatic arthritis, and rheumatoid arthritis and, potentially, in a variety of other disorders mediated by excess TNFα [Etanercept is a dimeric molecule, an inhibitor acting as a soluble receptor. It binds to TNFess TNFα .α) receptors and it is also used as a treatment for inflammatory bowel disease (Crohn's disease and ulcerative colitis), rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis, moderate to severe chronic psoriasis, moderate to severe hidradenitis suppurativa, and adolescent idiopathic arthritis. In rheumatoid arthritis, adalimumab has a response rate similar to methotrexate and, in combination, almost doubles the response rate of methotrexate alone [Adalimumab is a monoclonal antibody that also targets the TNF alpha , which is expressed in Escherichia coli and conjugated with polyethylene glycol (PEG). It is used for the treatment of Crohn's Disease and rheumatoid arthritis [Certolizumab pegol is a recombinant, humanized antibody Fab fragment against tumor necrosis factor alpha  are structurally complete IgG1 monoclonal antibodies that interact with neonatal Fc receptor (RnFc) and can transfer IgG from mother to fetus through the placenta . EtanercSince these biological agents are either fully chimeric or humanized antibodies, they can cross the placenta at the end of the second and the third trimester.As mentioned before the United States Food and Drug Administration (FDA) classifies all 5 biologic agents as pregnancy category B drugs; animal reproduction studies have not demonstrated a fetal risk but have no corresponding human studies or animal studies that have shown adverse effects that have not been confirmed in controlled studies of women in the first trimester (or subsequent trimesters) .As mentioned, since the highest age- and gender-related incidence rates of inflammatory bowel disease  occur during the peak reproductive years , a lot oIn 2004 Katz et al. published in The American Journal of Gastroenterology a study of 131 women administered infliximab during pregnancy. The results were unequivocal. Of the 146 identified pregnancies, 131 involved women exposed directly to infliximab and resulting data was available for 96 of these women. With miscarriages in only 14 of the 96 pregnancies (15%), therapeutic termination in 18 out of 96 (19%), and live births in 64 out of 96 (67%), the authors stated that the results of pregnant women in the US population exposed to infliximab during pregnancy do not differ from pregnant women with CD not exposed to infliximab and also that no increased risk of adverse outcome was detected but in order to exclude any fetal risk, follow-up of larger numbers of pregnant women exposed to infliximab proved to be necessary .In the same year (2004) Chambers et al. presented data of the Organisation of Teratology Information Services of 33 women in gestation (divided in 2 groups depending on the treatment administered). 29 out of 33 pregnant were treated with etanercept while 4 were on infliximab, all of whom were in their first trimester. Even though out of the 29 pregnancies exposed to etanercept one ended in trisomy 18 and 3 in spontaneous abortion, the authors concluded that no significant differences in the rate of malformation were observed between those two groups [It was in 2005 that Mahadevan et al. conducted the first study on intentional use of infliximab during gestation to maintain remission of Crohn's disease. In this study 10 participants received infliximab infusions for induction and maintenance of remission of Crohn's disease during pregnancy . The results were 4 women exhibiting no symptoms (from conception to labor), 2 women showing improvement of their symptoms, and 2 patients that relapsed. Furthermore, those 10 women gave birth to live fetuses without congenital or other abnormalities associated with infliximab .α agents . All pregnancies resulted in expected range with no miscarriages or other complications associated with the use of the anti-TNF drugs [In 2005 Joven et al. presented, among women exposed to biological therapies in rheumatic diseases, 13 women (14 pregnancies) treated with anti-TNFIn 2007 Strangfeld et al. analyzed the data of 545 patients treated with biologic agents either during pregnancy or before conception, from a prospective cohort study, involving patients with rheumatoid arthritis, conducted by the German biologics register (RABBIT). The authors compared data from patients who were exposed to biologic agents during pregnancy to those who stopped either biologic or conventional DMARD treatment before conception. 37 pregnancies in 29 women could be analyzed. Anti-TNF agents were given to 27 of these pregnant women before conception . The authors did not find a relation between the use of anti-TNF agents prior to conception and miscarriages, higher congenital malformations, or low birth weight .α therapy at the time of conception had a higher spontaneous abortion rate in contrast to patients without prior exposure (17%) and those in the control group (10%). Thus, the authors concluded that even though the results are promising it is preferable to avoid anti-TNF therapy at the time of conception [The British Society for Rheumatology Biologics Register in 2011 published a review by Verstappen et al. of 130 pregnancies concerning patients receiving anti-TNF agents before or during pregnancy. All data was collected and summarized with regard to adverse effects including pregnancies with rheumatoid arthritis patients treated with anti-TNF . The patnception .α therapy did not result in increased adverse pregnancy outcomes, but it was worse, compared to pregnancies before inflammatory bowel disease diagnosis [Schnitzler et al. recorded the pregnancy results of 212 women in 2011 with inflammatory bowel disease under infliximab and adalimumab treatment. Forty-two pregnancies exposed directly to anti-TNF agents  were compared to 23 pregnancies before inflammatory bowel disease diagnosis, 78 pregnancies before starting infliximab, 53 pregnancies treated with infliximab, and 56 pregnancies of healthy women. Thirty-two of 42 pregnancies resulted in live fetuses. Seven premature deliveries occurred, 6 children with low weight, and one stillbirth. One boy weighed 1630 g delivered in 33rd week and died of necrotic colitis 13 days later. Eight miscarriages were observed and one trisomy 18 on a 37-year-old pregnant woman was terminated. The authors stated that direct exposure to anti-TNFMahadevan et al. published another study considering the placental transfer of anti-TNF agents with IBD in 2013. 31 pregnant women were treated with infliximab (11), adalimumab (10), and certolizumab pegol (10). The median level of infliximab and adalimumab was measured 160% and 153% in the cord compared to that of the mother. In contrast the median ratio of cord to maternal certolizumab pegol level was 3.9%. Even though the authors concluded that certolizumab pegol has a very low placental transfer, no statistically important result could be derived since there were no birth defects or serious adverse outcomes related to biological agents used in any of the gestations .n = 254), miscarriages , induced abortion (n = 32), and stillbirth . The authors stated lack of harmful effects of certolizumab pegol exposure during gestation; however more experimentation is needed to confirm such a claim [The Journal of Rheumatology published a MEB Clowse et al.'s study in 2015 of maternal exposure to certolizumab pegol on the 1st trimester; a third out of them continued the drug into the second and/or third trimesters, in 339 pregnancies, and paternal exposure in 33 pregnancies (372 known outcomes out of 625 pregnancies since September 2014). In maternal exposure pregnancy the outcome was categorized into live births  presented a study of 38 pregnant women out of whom 24 were exposed to anti-TNF agents at conception/1st trimester, 11 were exposed prior to conception, and 3 followed paternal exposure. Of the 38 pregnancies, one infant exposed to adalimumab at conception/1st trimester was diagnosed with congenital diaphragmatic hernia and obstructive megaureter and one fetus exposed to etanercept 4 weeks before conception was diagnosed with trisomy 16. Study results suggested that anti-TNF agents could be safe when administered during conception/I trimester .n = 24), biologic agents combined with thiopurine (n = 10), thiopurine only (n = 7), or neither biological agents nor thiopurine exposure (n = 31). Out of these patients 23 were treated with infliximab, 1 with adalimumab, and 10 with both infliximab and thiopurines. Between the groups no differences concerning low birth weight, premature birth, birth weight, or congenital abnormalities were observed. A statistically significant difference however was observed in spontaneous abortion rates to those exposed to anti-TNF agent group [In 2016 also, the Korean Association for the Study of Intestinal Diseases published a cross-sectional study by Komoto et al., of the outcomes of exposure to biological agents and thiopurines in pregnant women. Disease, age, duration of disease, smoking, and drinking were characteristics taken into consideration. The patients were divided in 4 groups according to use of biologic agents only  inhibitors during the first part of pregnancy should be considered. Etanercept and certolizumab may be considered for use throughout pregnancy due to the low rate of transplacental passage,” but the need of a better understanding of anti-TNF use with more studies is necessary since the majority take place in the 1st trimester [Parallel to the above, the European League Against Rheumatism (EULAR) constantly research the use of anti-TNF agents. According to EULAR “continuation of tumor necrosis factor-rimester .Even though certolizumab pegol and golimumab are drugs which have been released in recent years, certolizumab is an anti-TNF agent specific for humans; thus there are not enough information since there are no studies on laboratory animals. Also golimumab lack on recorded data of use on human pregnancies. At present, clinical evidence for both golimumab and certolizumab pegol mentioned before does not indicate connection with increased rates of congenital malformations and even certolizumab is considered safe throughout the entire pregnancy period. Due to limited results on golimumab, alternative medications should be considered for treatment during pregnancy , 33.In the last years the use of biologic therapies has rapidly expanded. They promote an “ally” to disease-modifying antirheumatic drugs (DMARDs) for the treatment of autoimmune and rheumatologic diseases and are considered a big innovation due to the good efficacy and safety profiles (as studies have proven so far), as well as to the better understanding of the initial targets of altered immune regulation and activity in various diseases.Today, more and more documented case series and reports, registries, and other multicenter cohort studies have been published considering the safety of biological drug use during gestation, gathering important information, and data regarding their use as first-line medical treatments and also the safety for the mother and the fetus during and after gestation. It is now certain that anti-TNF agents can cross the placenta (in the late second and third trimester) raising concerns about fetal growth. By far some of the biological factors have been investigated more while others have been used less in clinical research. Nevertheless, until now research seems promising for the future of these therapies. To date, there is no evidence that anti-TNF agents are associated with teratogenicity, increased pregnancy loss, or embryo toxicity. Even though no firm conclusions can yet be gathered and it is firmly believed that more studies are required to reach safe conclusions, the results are more and more reassuring about the safety of this medications. As human knowledge is limited, therapists should start considering some of these drugs as a therapy of choice more often, balancing the potential risks associating it against DMARDS and steroids, especially when increasingly more data support no increased risk of adverse outcome , 24, 31


PRDM14 ensures hypomethylation in mouse ESCs and PGCs through two distinct layers, transcriptional repression of the DNA methyltransferases Dnmt3a/b/l and active demethylation by recruitment of TET proteins. However, the function of PRDM14 remains unclear in other species including humans. Hence, here we focus on the unique characteristics of mouse PRDM14 in the epigenetic regulation of pluripotent cells and primordial germ cells. In addition, we discuss the expression regulation and function of PRDM14 in other species compared with those in mice.PR-domain containing protein 14 (PRDM14) is a site-specific DNA-binding protein and is required for establishment of pluripotency in embryonic stem cells (ESCs) and primordial germ cells (PGCs) in mice. DNA methylation status is regulated by the balance between  Prdm14 is transiently expressed in the inner cell mass (ICM) of the blastocyst, followed by rapid downregulation in the epiblast at the post-implantation stage in mice  -thymine DNA glycosylase (TDG)-base excision repair (BER) pathway in ESCs with serum containing LIF  retain metastable pluripotency in serum containing leukemia inhibitory factor (LIF), whereas the transfer of culture conditions from serum plus LIF to the presence of two pharmacological inhibitors for ERK and GSK3β, called 2i plus LIF, leads to ground-state pluripotency associated with pronounced reduction in genome-wide DNA demethylation Figure  Ying et. The res Figures , 2A  and Cbfa2t2 KO ESCs, revealed that CBFA2T2 was involved in both transcriptional activation and repression via PRDM14 in mESCs  of the blastocyst, similar to the phenotype of CARM1 overexpression. Several studies have reported the functional correlation between PRDM14 and its binding partners; however, the direct functional interaction of PRDM14 with its binding partners in transcriptional regulation has not been investigated.PRDM14 has multiple functions in transcriptional regulation, e.g., DNA demethylation and transcriptional activation and repression, depending on the target genes. Biochemical studies have identified CBFA2T2, NODE complex, and BRG1 complex as PRDM14-containing complexes in mESCs Figure . PRDM14 Esrrb, Tcl1, and Klf4 is lower in hESCs and EpiSCs than in mESCs  differentiated from mESCs induces the conversion of EpiLCs into mESCs through activation of pluripotent markers and the repression of differentiation markers  is sustained through bFGF and ACTIVIN signaling. Epiblast stem cells (EpiSCs) derived from epiblast cells at the post-implantation stage of mouse embryos can be expanded and maintained through bFGF and ACTIVIN signaling , which is a fossorial rodent, develops flat embryonic discs, as observed in non-rodent mammals , reptiles (gecko), and humans is necessary to uncover the evolutionarily conserved and diverse function of PRDM14 in pluripotent cells and primordial germ cells in deuterostomes.Findings regarding the role of The author confirms being the sole contributor of this work and approved it for publication.The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Dear Editor,Aedes aegypti and potentially Ae. albopictus as urban vectors, a recent article1 suggests that Culex quinquefasciatus may serve as a ZIKV vector in Recife, Brazil, a region that has experienced a high incidence of infection. Accurately identifying the vector of a pathogen enables public health agencies to implement appropriate control strategies and inform citizens of proper prevention measures. Additionally, establishing the vector for an emerging pathogen paves the way for researchers to advance our understanding of virus–vector interactions and pursue novel methods of control. In contrast, erroneously incriminating a vector could lead to misdirected use of limited government funds, diversion of research efforts and misinforming the public through misdirected media and educational programs.Since Zika virus (ZIKV) emerged in the Americas, major research efforts have been focused on identifying the mosquito species responsible for transmission. While almost all published results support 2Traditional criteria for arthropod vector incrimination include: (i) demonstration of feeding or other effective contact with pathogen’s host; (ii) association in time and space of the vector and the pathogen-infected host; (iii) repeated demonstration of natural infection of the vector and (iv) experimental transmission of the pathogen by the vector.Ae. aegypti, with detection of naturally infected mosquitoes with titers compatible with transmission competence in Mexico  representing <10 infectious units in typical RT-qPCR assays, are incompatible with transmission-competent mosquitoes, which typically have viral titers several orders of magnitude higher11 (see also references reviewed in refs 7 (see also references in ref. et al.1 Thus, the wild-caught Recife mosquito pools likely contained trace amounts of residual, viremic blood in their guts, undetectible by their colorimetric assay, legs or other dislodged appendages from other infected mosquitoes of different species, or were false-positives.For ZIKV transmission in the Americas, criterion 3 has been met only for Cx. quinquefasciatus other than those of Guedes et al.,1 only one other group has shown transmission of ZIKV by colonized mosquitoes, from an unreported generation number maintained since 2014.12 At least 15 other studies have found no transmission competence,14 (see also references reviewed in ref. 7 Even after intrathoracic inoculation, generally the most permissive route for arbovirus infection of mosquitoes, Culex mosquitoes were found to be refractory to disseminated infection (reviewed in refs Cx. quinquefasciatus populations to explain the results of Guedes et al.1 In addition, Cx. quinquefasciatus from Recife challenged in another study with the same BRPE243/2015 ZIKV strain used by Guedes et al.,1 as well as with two other ZIKV strains, were consistently refractory to oral infection.15In laboratory studies of et al.1 should engender caution in interpretation and conclusions reported by media and public health authorities unless they are verified by more robust results including detection of genuinely transmission-competent mosquitoes in nature. Until further data are collected and other groups can replicate the Recife findings, it is important that public education and interventions remain focused on the conclusion supported by the vast majority of studies: Ae. aegypti is the only mosquito species for which we have strong evidence of ZIKV transmission in the Americas.The discrepancy between the negative results from so many published studies and the questionable findings of Guedes This submission represents the views solely of the authors and does not constitute those of the Centers for Disease Control and Prevention or the United States Government.


Frizzled4 and Frizzled6, affect vascular network morphogenesis. Experiments were performed on frizzled4 (Fzd4-/-) and frizzled6 (Fzd6-/-) deleted mice and littermate controls (WT) perfused with a contrast medium after euthanasia and exsanguination. The kidneys were scanned with a high-resolution (16 μm) microCT imaging system, followed by 3D reconstruction of the arterial vasculature. Computational treatment includes decomposition of 3D networks based on Diameter-Defined Strahler Order (DDSO). We have calculated quantitative (i) Global scale parameters, such as the volume of the vasculature and its fractal dimension (ii) Structural parameters depending on the DDSO hierarchical levels such as hierarchical ordering, diameter, length and branching angles of the vessel segments, and (iii) Functional parameters such as estimated resistance to blood flow alongside the vascular tree and average density of terminal arterioles. In normal kidneys, fractal dimension was 2.07±0.11 (n = 7), and was significantly lower in Fzd4-/- , and Fzd6-/-  kidneys. The DDSO number was 5 in WT and Fzd4-/-, and only 4 in Fzd6-/-. Scaling characteristics such as diameter and length of vessel segments were altered in mutants, whereas bifurcation angles were not different from WT. Fzd4 and Fzd6 deletion increased vessel resistance, calculated using the Hagen-Poiseuille equation, for each DDSO, and decreased the density and the homogeneity of the distal vessel segments. Our results show that our methodology is suitable for 3D quantitative characterization of vascular networks, and that Fzd4 and Fzd6 genes have a deep patterning effect on arterial vessel morphogenesis that may determine its functional efficiency.Quantitative analysis of the vascular network anatomy is critical for the understanding of the vasculature structure and function. In this study, we have combined microcomputed tomography (microCT) and computational analysis to provide quantitative three-dimensional geometrical and topological characterization of the normal kidney vasculature, and to investigate how 2 core genes of the Wnt/planar cell polarity,  Precise and comprehensive measurements of vascular network anatomy are crucial steps for the analysis of normal and pathologic vascular networks, and is of paramount importance for the understanding of several aspects of the vasculature structure and function . MicrocoFrizzled4 (Fzd4) and Frizzled6 (Fzd6), affect vascular morphogenic events.Since vascular networks are highly organized hierarchical structures, an accurate quantitative description of the vascular pattern requires topological analysis of these networks. In the present study, using vessels’ segmentation, which has never been tackled by conventional investigation methods, we have developed a complex analysis of the kidney vascular tree according to the diameter-defined Strahler taxonomy of the vessel segments, which provides a topological description of the branching structure of the arterial network. This methodology enabled us to extract key quantitative parameters from the 3D images, such as (i) The fractal dimension, which measures the ability of a self-similar structure to fill the three-dimensional space it occupies, (ii) Structural parameters, such as hierarchical ordering and diameter, length and branching angles of the vessel segments, both at the global scale and, depending on the hierarchical levels of the vessel, and (iii) Functional parameters, such as estimated resistance to blood flow alongside the vascular tree and average density of terminal arterioles. In the present study, we have applied this methodological approach combined with 3D microCT imaging to provide a quantitative geometrical and topological characterization of the normal kidney vasculature, and to investigate how 2 core genes of the Wnt/Planar Cell Polarity (PCP), Fzd4 favors the Wnt/PCP pathway and altered the 3D structure of the arterial vasculature of the heart and the kidney  is given by N(Dk)  was normalized with the number of vessel segments, and the average diameter with regard to the DDSO classification  see . The res(Dk) see  and 3, ation see . The restion see . VasculaFzd6-/- phenotype. However, the span of the vessel segment lengths appeared not to be affected by the knockout of the receptors. Moreover, the relative distribution of vessel segment lengths . For intermediate DSSO (2), WT were different from mutants, without difference between mutants. For higher DSSO (3 and 4), no statistical differences were found between samples. It appears that, especially in lower DDSO, there is a higher density of bifurcations, thereby implying a higher level of hierarchy of the vascular networks in WT samples.Vessel segment length is defined as the physical distance between two bifurcation points. Results showing the absolute and relative distribution of vessel segments lengths and the average vessel segment length in individual DDSO are shown in  lengths  showed aThe bifurcation angles at the scale of the whole organ were found to have a similar average value of around 90°, without significant differences between phenotypes, and showed a similar dispersion in all three sub-populations . MoreoveFzd4-/- and Fzd6-/-, we have calculated 2 morphofunctional parameters, the resistance of the vessel segments and its distribution along the vascular tree, on which the blood flow rate depends, and the average shortest distance between the distal arterioles, as a surrogate of the density of pre-capillay microcirculation. Results showing the number of vessel segments and the estimated resistance in a given DDSO, together with the average shortest distance between the terminal segments, are shown in In order to estimate the functional impact of the structural alterations observed in Fzd4-/- and Fzd6-/- was smaller overall. The estimated resistance in individual DDSO was computed by following the Hagen-Poiseuille equation using the number, length and diameter of the vessel segments , without influence on its heterogeneity, whereas what was observed was just the opposite.Fzd4 and Fzd6 deletions not only altered the pattern of the vasculature, but the whole organ, since mutant kidneys were significantly smaller than control ones and, between mutants, Fzd4 and Fzd6 have patterning effects on the kidney vasculature, but how these gene products exert these effects remains an open question, since the deletions of these two PCP genes was not tissue-specific. On the one hand, Wnt/PCP genes such as Fzd4 have been shown to determine the 3D development of the epithelial tubes of the kidney [Fzd4 and Fzd6 may be indirect consequences of the direct developmental role of these genes in renal epithelial cells. On the other hand, recent studies have shown that non-canonical Wnt signaling exerts a direct modeling role in endothelial cells during angiogenesis [Fzd4 and Fzd6 pathways in endothelial cells. Further studies are required to identify the underlying mechanisms of the observed vascular patterning effects of Fzd4 and Fzd6.Hence, our results show that e kidney , so the ogenesis , 52–54, Fzd4 and Fzd6 have deep specific patterning effect on arterial vessel morphogenesis that may determine its functional efficiency.In conclusion, we proposed a methodology based microCT scanning followed by 3D computational segmentation of mouse arterial kidney vasculature that determines quantitative parameters that describe the general pattern of the vasculature, such as overall vessel length and volume and fractal dimension, as well as its scaling characteristics, such as vascular segment numbers, diameters, lengths and angles depending on the vessel hierarchical structure and, additionally, provide indexes of morphofunctional properties. This methodology was found suitable for quantitative comparisons of vascular networks between different conditions. Applying this methodology to genetically modified mice, we have shown that the core PCP genes S1 Appendixp for the parent vessel Strahler order, SOd for the daughter vessel Strahler order, Dn for the mean vessel segment diameter belonging to the n-th order, <nn2> for the average physical distance from each node to its second nearest neighbor, <nn5> for the average physical distance from each node to its fifth nearest neighbor and <nn10> for the average physical distance from each node to its tenth nearest neighbor.The flowchart shows the sequential order in which individual subroutines are arranged in our computational protocol in order to segment out the vascular structure and to reconstruct it. Used abbreviation are SO for the Strahler order, SO(PDF)Click here for additional data file.S2 Appendix(PDF)Click here for additional data file.


Adult neurogenesis (AN) is an ongoing developmental process that generates newborn neurons in the olfactory bulb (OB) and the hippocampus (Hi) throughout life and significantly contributes to brain plasticity. Adult neural stem and progenitor cells (aNSPCs) are relatively limited in number and fate and are spatially restricted to the subventricular zone (SVZ) and the subgranular zone (SGZ). During AN, the distinct roles played by cell cycle proteins extend beyond cell cycle control and constitute key regulatory mechanisms involved in neuronal maturation and survival. Importantly, aberrant cell cycle re-entry (CCE) in post-mitotic neurons has been strongly linked to the abnormal pathophysiology in rodent models of neurodegenerative diseases with potential implications on the etiology and progression of such diseases in humans. Here, we present an overview of AN in the SVZ-OB and olfactory epithelium (OE) in mice and humans followed by a comprehensive update of the distinct roles played by cell cycle proteins including major tumors suppressor genes in various steps during neurogenesis. We also discuss accumulating evidence underlining a strong link between abnormal cell cycle control, olfactory dysfunction and neurodegeneration in the adult and aging brain. We emphasize that: (1) CCE in post-mitotic neurons due to loss of cell cycle suppression and/or age-related insults as well as DNA damage can anticipate the development of neurodegenerative lesions and protein aggregates, (2) the age-related decline in SVZ and OE neurogenesis is associated with compensatory pro-survival mechanisms in the aging OB which are interestingly similar to those detected in Alzheimer's disease and Parkinson's disease in humans, and (3) the OB represents a well suitable model to study the early manifestation of age-related defects that may eventually progress into the formation of neurodegenerative lesions and, possibly, spread to the rest of the brain. Such findings may provide a novel approach to the modeling of neurodegenerative diseases in humans from early detection to progression and treatment as well. Neurogenesis or “the birth of neurons” is the developmental process by which mature and functional neurons are generated in the brain from a pool of neural stem and progenitor cells (NSPCs). Although neurogenesis is primarily an embryonic process, the recent discovery that it persists throughout life in vertebrates including mammals  forced a re-assessment of the adult brain's plasticity and regenerative capacity  in addition to neurons Sox2, Ascl1, Dlx2, Pax6, Tbr2, Prox1 as well as mitogens and growth factors e.g., FGF2, EGF are common regulators of both embryonic and adult neurogenesis and act in a developmentally similar context. Yet, significant differences exist about how these factors control NSPCs properties such as cell fate determination and maintenance at the molecular level  found in the SVZ are type B1 radial glia-like quiescent cells that express a number of glial markers including Glial Fibrillary Acidic Protein (GFAP), Glutamate-Aspartate Transporter (GLAST), and Brain Lipid-Binding Peptide (BLBP). They also display regional specification whereby distinct NSCs located in different compartments along the walls of the LV generate distinct subtypes of OB interneurons  is adult neurogenesis necessary for normal olfactory function or specific olfactory tasks only? (2) What are the cellular/molecular properties that distinguish newborn adult neurons from perinatal mature neurons and thus render their influence on circuit function unique? Using variable genetic and chemical approaches to disrupt AN, several studies have attempted to answer these questions and showed that AN is likely dispensable for normal odor and threshold detection but can still accelerate discrimination learning e.g., during operant associative olfactory tasks and enhance long-term memory   in both rodents and humans is an active site of constitutive neurogenesis throughout life where new neurons are continuously generated in order to replace worn out ones under normal conditions or damaged cells after epithelial injury  as described above. In specific, p53 suppresses neuroblast generation by the negative control of the pro-neural genes NeuroD and Math3 whereas p27Kip1 promotes neuronal commitment by stabilizing the neurogenic transcription factor Ngn2 . Moreover, loss of p53 alone also compromises long-term survival in the same neurons eventually leading to their apoptotic death through p53-independent mechanisms . Consistently, Gil-perotin reported an increase in p53-independent cell death in the SVZ in p53-null mice , glioblastoma-like tumors can form in periventricular locations and are characterized by enhanced NSCs self-renewal, recruitment to the fast-proliferating progenitor population (type C) and impaired differentiation  in adult mice which is consistent with concurrent mutations of these pathways in human HGAs  in two or more tumor suppressors is required for gliomagenesis in the adult brain (still with relatively late onset). Given this and the fact that loss of many of the above genes including Pten  and others  can lead to CCE in mature neurons which is believed to be mechanistically related to the onset of AD and PD pathophysiology and once again, places the OB at the early stages of this process as described below. Third, since aging is the major risk factor of most neurodegenerative diseases and affects all brain regions, alterations in the aged SVZ and/or OE can trigger pro-survival compensatory responses in the OB involving mechanisms that are strikingly similar to those observed in neuronal anomalies of neurodegenerative diseases Figure . We prophit of mitogenic signaling dysregulation induces CCE causing a “mitotic steady state” that is not sufficient to cause cell death. However, this comes at the expense of accumulating more insults whereby a second hit such as of oxidative stress then triggers neuronal degeneration  and subsequent cell death mediated by pro-apoptotic downstream targets including E2F genes and cyclin E1  is abundantly expressed in the adult OB where it is essential in mediating spontaneous neural activity and odor habituation  but not its downstream executioner active-caspase 3 that remains at normal level  expression, the main pro-neural gene required for OSN production (Guillemot et al., Studies have shown age-related changes affecting the cell dynamics and regenerative capacity during OE neurogenesis that parallel those observed following aging in the SVZ-OB. Indeed, advanced age is ultimately associated with dramatic decline in OE neurogenesis overall (up to 90% decrease between 3 and 16 months in rodents, Suzukawa et al., In humans, aging also results in a “neurogenically exhausted” OE that is characterized by a gradual loss of OSNs and GBCs but not quiescent HBCs and supporting sustentacular cells. Moreover, the OE can be replaced by metaplastic respiratory epithelium (Holbrook et al., Kip1, p19Ink4d, p18Ink4c, and p21Cip1 change in a temporal pattern between young and adult stages, which may reflect changes in stem cell quiescence, cell cycle exit and neuronal differentiation with older age (Legrier et al., While several factors contribute to age-associated decrease in olfactory function including OE damage resulting from pathogen infections, reduced expression of specific olfactory receptors and nasal engorgement (Attems et al., In this review, we examined the role played by the cell cycle machinery within each stage of the adult neurogenic SVZ-OB axis (as summarized in Figure Previous studies have discussed the diagnostic implications of this proposition, such as the detection of olfactory deficits in order to anticipate the conversion from MCI to AD (Conti et al., SO and CJ wrote the manuscript. NG participated in writing, edited the manuscript and provided financial support.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.