More than 600 million people worldwide have been infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), resulting in the pandemic of coronavirus disease 2019 (COVID-19). In particular, new waves of COVID-19 caused by emerging SARS-CoV-2 variants pose new health risks to the global population. Nanotechnology has developed excellent solutions to combat the virus pandemic, such as ACE2-based nanodecoys, nanobodies, nanovaccines, and drug nanocarriers. Lessons learned and strategies developed during this battle against SARS-CoV-2 variants may also serve as inspiration for developing nanotechnology-based strategies to combat other global infectious diseases and their variants in the future. The COVID-19 virus has already infected millions of people worldwide. The reason for this concerning situation is that many patients are contagious without showing any apparent symptoms. The government had to impose quarantine measures to prevent the virus’s spread. A triumph of speed and innovation, the first approved vaccines against SARS-CoV-2 have been developed by the German biotechnology company BioNTech, working with Pfizer, and by the American firm Moderna. Only sixty-three days after sequence selection, Moderna initiated a Phase I clinical trial for a lipid nanoparticle (LNP)-based mRNA vaccine (mRNA-1273). According to materials physicist Richard Jones, nanomedicine has entered its golden age.SARS-CoV-2 is a 28-kilobase single-stranded positive RNA virus that undergoes two single-letter mutations per month , a relatThe SARS-CoV-2 virus infects host cells by binding to the ACE2 receptor expressed on their surface . MutatioAs a fundamental unit of biology, cells are capable of performing a wide range of functions, including interacting with the environment through membrane proteins. Biomimetic synthetic strategies are used to create biofunctionalized liposome-like nanovesicles (NVs) that can artificially display a variety of peptide ligands and targeting proteins . This apA study has shown that nanodecoys produced from human lung spheroid cells (LSCs) highly expressing ACE2 neutralize SARS-CoV-2 and protect the host from infection . The LSCA recent study found that circulating ACE2-expressing EVs isolated directly from the plasma of patients with COVID-19 effectively inhibited SARS-CoV-2 infection in vitro . EVs areACE2 receptor-modified decoy NPs have also been studied as a potential strategy against SARS-CoV-2. Recent studies have shown that soluble ACE2-related inhibitors, such as recombinant human ACE2, can partially block infection ,30, but Several ACE2-based nanodecoys have entered clinical trials ,35 and hMonoclonal antibodies (mAbs) that target the S protein of SARS-CoV-2 have been widely utilized during the current COVID-19 pandemic . HoweverIn contrast to conventional immunoglobulin G (IgG) antibodies that contain a heavy chain variable domain and a light chain variable domain, camelids can produce only one variable domain of a heavy chain of heavy-chain antibodies (VHH). In the absence of an effector domain, this single variable domain is referred to as a single-domain antibody, VHH, or nanobody. It has higher affinity and specificity than conventional antibodies . Unlike Using a humanized synthetic VHH library, researchers successfully screened neutralizing nanobodies against SARS-CoV-2 in May 2020 . ThroughUsing next-generation sequencing combined with mass spectrometry, Shi Yi’s group discovered over 8000 high-affinity anti-SARS-CoV-2 nanobodies in alpacas ; Nb21 haIn recent months, the Omicron variant has spread throughout the world. This variant has more than 30 mutations in the S protein and 15 in the S-RBD protein. The mutations in the variant present a challenge to vaccine and antibody protection because it differs from other COVID-19 variants with no more than three mutations in the S-RBD protein. Recent research has demonstrated that two nanobodies (n3113v and n3130v) can neutralize the Omicron variant by binding to highly conserved regions on the RBD . The twoRecently, researchers reported the isolation and characterization of a novel group of nanobodies from immunized alpacas . These nDue to their small molecular weight and stable physical and chemical properties, nanobodies can be very effective and rapidly delivered to the respiratory tract, alveolar, and other foci of COVID-19 infection by inhalation. The nanobodies were found to be effective in inhibiting SARS-CoV-2 infection in both mild and severe mouse models, confirming their effectiveness and potential for clinical use. The study of nanobodies has some inherent limitations. Due to the differences in the immune response between alpacas and humans, the antibody responses and the epitopes recognized by the nanobodies may not be an accurate reflection of those in humans. Additionally, nanobody protection experiments were conducted in mice and hamsters, which may not be indicative of protection against SARS-CoV-2 infection in humans. It would be highly desirable to conduct future studies in humans to verify and validate the protection results.Some infectious diseases are associated with uncontrolled inflammation ,59. One Hyperimmune activity has been associated with several subpopulations of the immune system. A continuous positive feedback loop between pro-inflammatory signaling and oxidative stress often causes uncontrolled pro-inflammatory states. A number of challenges arise when it comes to inhibiting the pathological inflammatory response and the cross-talk between oxidative stress and inflammation . HoweverLeukemia inhibitory factor (LIF), secreted by mesenchymal stem cells (MSCs) , can be Despite the potential of mRNA for gene therapy and vaccine development, clinical translation is limited by drug delivery. Since in vivo injection of naked mRNA results in rapid endonuclease-mediated degradation, novel approaches are required to improve the delivery of nucleic acid vaccines. LNPs serve as a viable delivery system for enhancing the efficacy of RNA vaccines and can introduce genes into cells and protect them from degradation in vivo.In recent years, a large body of preclinical data has been generated on mRNA vaccines, and several clinical trials have been conducted in humans. Medical history records the fastest development of mRNA vaccines by Pfizer-BioNTech (BNT162b2), Moderna (mRNA-1273), and CureVac ,78,79. IDespite their high effectiveness against the original SARS-CoV-2 strain, these mRNA vaccines were insufficient against emerging SARS-CoV-2 variants due to mutations in the viral S protein. Therefore, several strategies have been developed to update current mRNA-LNP vaccines or generate new mRNA-LNP vaccines to increase neutralizing antibodies that bind to the mutated S protein and neutralize SARS-CoV-2 variants. Since decreased vaccine-induced immunity is one of the primary reasons for reduced vaccine efficacy against SARS-CoV-2 variants, boosting vaccine-induced immunity through booster doses of vaccines is the most straightforward and effective way to address this problem. Consequently, the Food and Drug Administration approved a booster dose of the mRNA vaccine from Pfizer or Modena for adults. Recent studies have shown that administering a third booster dose of Pfizer’s BNT162b2 or Moderna’s mRNA-1273 vaccine to solid organ transplant recipients significantly improved the immunogenicity of SARS-CoV-2 vaccines ,87. AnotThe storage temperature for mRNA vaccines must be extremely low, which limits their widespread use . To addrIn addition to nanodecoys and nucleic acid vaccines, protein-NP vaccines are also being investigated against SARS-CoV-2 variants. There are four major structural proteins encoded by SARS-CoV-2: S, membranes, envelopes, and nucleocapsids . The S pThere will always be a step or two behind the evolving virus when the COVID-19 vaccines are updated. Scientists hope to develop a vaccine that can be broadly protective against future SARS-CoV-2 variants and even other coronaviruses associated with it. A quadrivalent mosaic NP vaccine displaying S proteins from a prototype SARS-CoV-2 and three different variants was designed to address this issue . The mosOn 13 July 2022, Novavax’s novel coronavirus recombinant protein vaccine, NVX-CoV2373, received an Emergency Use Authorization from the FDA. The process of creating the vaccine begins with the identification of the antigen S that can stimulate an immune response against the virus . This anA virus-like particle (VLP) is a nanostructure that is self-assembled and incorporates essential viral structural proteins . VLP hasSARS-CoV-2 caused the current pandemic, and emerging SARS-CoV-2 variants resulting from persistent mutations in the S protein of SARS-CoV-2 exacerbated and prolonged the pandemic. Targeting mutant S proteins of SARS-CoV-2 variants through nanotechnology-based strategies holds great promise for combating SARS-CoV-2 variants. This latest variant of Omicron still infects host cells via the ACE2 receptor despite having more mutations than other variants. The development of ACE2-based nanodecoys is considered a promising strategy for targeting variant S proteins since all variants have a high binding affinity to the ACE2 receptor, regardless of their persistent mutations. Nanobodies offer another way to target mutant S proteins, especially when vaccine-elicited neutralizing antibodies are insufficient due to impaired immune responses. Although many monomeric antibodies that neutralize SARS-CoV-2 cannot neutralize emerging SARS-CoV-2 variants, multivalent displays of these antibodies on nanoplatforms can significantly promote neutralizing activity. The use of vaccines to induce a specific immune response is another effective way to target mutant S proteins and inhibit virus infection. A wide variety of vaccines have been developed using various technologies, some of which have shown high protective efficacy and have been deployed worldwide. However, the protective efficacy of these vaccines has declined when faced with emerging SARS-CoV-2 variants. The development and application of nanotechnology have provided many solutions for enhancing vaccine efficiency, promoting therapeutic drug delivery, and protecting individuals from SARS-CoV-2 variants. It is believed that the progress and innovation of nanotechnology will provide many ways to accelerate the end of the epidemic.


The optimal approach to COVID-19 surveillance in congregate populations remains unclear. Our study at the US Naval Academy in Annapolis, Maryland, USA, assessed the concordance of antibody prevalence in longitudinally collected dried blood spots and saliva in a setting of frequent PCR-based testing. Our findings highlight the utility of salivary-based surveillance. Congregate populations, including those in university and military settings, are at high risk for SARS-CoV-2 transmission because of crowding, frequent physical contact, and environmental contamination  SARS-CoV-2 mRNA vaccine in March 2021 (first dose) and April 2021 (second dose); >96% of all midshipmen had documented receipt of 2 doses.The Observational Seroepidemiologic Study of COVID-19 at the USNA (TOSCANA) study enrolled male and female midshipmen to estimate the SARS-CoV-2 attack rate and assess the concordance of seroprevalence between blood and saliva. All midshipmen at USNA  reside in a single dormitory. During the time of the study, nonpharmaceutical interventions included mask wearing, weekly PCR-based surveillance, and isolation of cases . PharmacWe initiated the process of recruiting, enrolling, and acquiring consent of participants at the start of the academic year. After providing consent, participants completed the baseline questionnaire regarding demographic information, risk factors for acute respiratory infection, and previous infections or exposures to SARS-CoV-2. Paired self-collected saliva and dried blood spots were collected at enrollment  and follow-up visits in December 2020 (V2), February 2021 , and April–May 2021 (V4)  Table.https://www.neoteryx.com) and tested them for SARS-CoV-2 reactive IgG by using an in-house multiplex microsphere-based immunoassay. The antigenic targets were a prefusion-stabilized SARS-CoV-2 spike glycoprotein ectodomain trimer and a nucleocapsid protein; we detected antigen-specific IgG levels by using a Bio-Plex 200 HTF multiplexing systems  and reported results as median fluorescence intensity (MFI).Methods for dried blood spot (DBS) collection and testing has been described previously  and tested them as previously described  screening; we also tested 100% of in-season varsity athletes each week. We excluded from weekly testing all participants who had confirmed positive SARS-CoV-2 infection during the preceding 90 days. We tested nasopharyngeal swab samples by using SARS-CoV-2 RT-PCR and made results accessible through electronic medical records.We compared seroconversion rates with cumulative frequencies of molecularly confirmed infections. We calculated correlation coefficients for spike IgG and nucleocapsid IgG MFI in saliva and DBS. We used the Cohen kappa coefficient (κ) to measure concordance of saliva with DBS nucleocapsid IgG and spike IgG positivity and to measure concordance of PCR tests with seroconversions.This study was approved by the Uniformed Services University Institutional Review Board under protocol IDCRP-129. All participants provided written informed consent.In August 2020, a total of 104 midshipmen enrolled in the study; 64.4% were men, 92.3% were white, 8 (7.7%) reported COVID-19 exposure, and 11 (10.6%) reporting a COVID-19 diagnosis before arrival at USNA. At baseline, 17 (16%) participants showed evidence of SARS-CoV-2 infection based on spike IgG values in DBS.Among the participants who were serologically negative for SARS-CoV-2 at enrollment, 18 seroconversions were detected in saliva, 19 were detected in DBS, and 19 were detected by PCR by the end of follow-up ; howeverBy V4, 100% of remaining participants were spike IgG seropositive, and 49.1% of remaining participants with both DBS and saliva seroconverted to nucleocapsid IgG as evaluated by DBS . Among pSpike IgG MFI in saliva and DBS were significantly correlated at all 3 timepoints ; high spThis study, conducted among a population of midshipmen at USNA in the first year of the COVID-19 pandemic, employed blood and saliva collection at multiple visits to evaluate the validity of salivary antibody surveillance. We observed concordance between DBS and saliva for the detection of spike and nucleocapsid IgG, and both biospecimen types were similar to RT-PCR for detection of cases. We noted that all vaccinees mounted a spike IgG response in DBS by V4, consistent with the known immunogenicity of these vaccines, but only 49.1% vaccinees had detectable nucleocapsid IgG at V4, indicating a substantive SARS-CoV-2 infection attack rate in the first half of 2021.This assessment of SARS-CoV-2 detection in a congregate setting can help inform approaches for detection of SARS-CoV-2 in populations before and after vaccination. Prior evidence shows that PCR testing is an efficient method of infection control in congregate communities if administered regularly but that asymptomatic cases may still be undetected (In summary, this assessment supports using saliva testing as a less invasive, more feasible surveillance method for monitoring changes in disease prevalence and susceptibility in large populations. Future directions include validation of alternative antibody targets, in both serum and saliva, which can discriminate antibody prevalence in the context of preexisting vaccination and postinfection hybrid immunity.Additional information about evaluating SARS-CoV-2 saliva and dried blood spot surveillance strategies in a congregate population.


The limitations of autologous bone grafts necessitate the development of advanced biomimetic biomaterials for efficient cranial defect restoration. The cranial bones are typical flat bones with sandwich structures, consisting of a diploe in the middle region and 2 outer compact tables. In this study, we originally developed 2 types of flat-bone-mimetic β-tricalcium phosphate bioceramic scaffolds (Gyr-Comp and Gyr-Tub) by high-precision vat-photopolymerization-based 3-dimensional printing. Both scaffolds had 2 outer layers and an inner layer with gyroid pores mimicking the diploe structure. The outer layers of Gyr-Comp scaffolds simulated the low porosity of outer tables, while those of Gyr-Tub scaffolds mimicked the tubular pore structure in the tables of flat bones. The Gyr-Comp and Gyr-Tub scaffolds possessed higher compressive strength and noticeably promoted in vitro cell proliferation, osteogenic differentiation, and angiogenic activities compared with conventional scaffolds with cross-hatch structures. After implantation into rabbit cranial defects for 12 weeks, Gyr-Tub achieved the best repairing effects by accelerating the generation of bone tissues and blood vessels. This work provides an advanced strategy to prepare biomimetic biomaterials that fit the structural and functional needs of efficacious bone regeneration. The cranial bone in the human body performs very important functions, such as protecting the brain and enabling the passage of the cranial nerves that are essential to physiological functioning ,2. CritiBiomaterials mimicking the composition and microstructure of natural bone are widely acknowledged to be ideal for bone defect regeneration –11. MimiThe cranial bones are typical flat bones, which are generally thin and broad with a flattened or curved surface. A flat bone presents a sandwich structure . As showInspired by the composition and structural features of cranial bones, for the first time, we designed and fabricated 2 flat-bone-mimetic β-TCP bioceramic scaffolds, namely, Gyr-Comp scaffolds and Gyr-Tub scaffolds. Both scaffolds had gyroid pore structures in the inner layers. The Gyr-Comp scaffolds had 2 compact outer layers, which were designed according to the low-porosity feature of the outer tables of flat bones. The Gyr-Tub scaffolds had tubular pore structures in the 2 outer layers, which were designed to mimic the tube-like Haversian canals and Volkmann canals in the outer tables. The biomimetic architecture of bioceramic scaffolds was realized utilizing VPP-based 3D printing. We expected that the biomimetic scaffolds would facilitate angiogenesis and osteogenesis of cranial defects Fig. . The por3(PO4)2 was identified in the biomimetic bioceramic scaffolds by the use of x-ray diffraction 2 to α- Ca3(PO4)2 at 1,200 °C [We originally designed 2 kinds of flat-bone-mimetic structures, Gyr-Comp and Gyr-Tub  is a vital marker of early-stage osteogenic differentiation . ALP actA live/dead assay showed that many viable cells attached to the scaffolds, and the number of viable cells increased over time Fig. . The quaRabbit cranial defect models were developed to investigate the effect of flat-bone-mimetic bioceramic scaffolds on the bone regeneration of cranial defects Fig. . At 6 anHistological examinations by hematoxylin and eosin (HE) staining and Masson’s staining were conducted to further verify the effects of flat-bone-mimetic scaffolds on repairing cranial defects Fig. . As showImmunohistochemical staining of von Willebrand factor (vWF) and CD31 was conducted to assess the angiogenesis of scaffolds in vivo Fig. . vWF is The results of in vivo investigations, including μ-CT scanning and HE, Masson’s, and immunohistochemical staining, showed that the Cross-hatch scaffolds were more effective in osteogenesis and angiogenesis in the early stage of implantation (6 wk), while Gyr-Tub outperformed Cross-hatch scaffolds in the generation of bone tissues and blood vessels in the later stage of implantation (12 wk). Gyr-Comp showed the weakest osteogenesis and angiogenesis capacities throughout the implantation period. The results of in vivo osteogenesis and angiogenesis were not consistent with those of the in vitro study. Compared with the conventional Cross-hatch scaffolds, the flat-bone-mimetic scaffolds (Gyr-Tub and Gyr-Comp) showed more favorable in vitro osteogenic and angiogenic performances, which were demonstrated by promoting rBMSC proliferation and osteogenic differentiation, as well as HUVEC proliferation and angiogenesis. Compared with Gyr-Comp scaffolds, Gyr-Tub showed a similar level of angiogenic potential but better in vitro osteogenic performance. In the cell experiments, the cells were seeded onto the surface of the scaffold. The in vitro cell response mainly hinges on the pore topology of scaffolds, due to their same composition and similar porosity. The tubular pores featured concave surfaces, which have been proven to be more favorable for the generation of bone tissues and blood vessels, in contrast with pores with flat or convex surfaces ,24,52–55In this study, to develop an alternative to autologous bone grafts for cranial defect reconstruction, 2 flat-bone-mimetic β-TCP bioceramic scaffolds (Gyr-Comp and Gyr-Tub) were designed and fabricated by VPP-based 3D printing. Gyr-Comp had 2 compact outer layers and a diploe-like inner layer with a gyroid pore structure. The Gyr-Tub consisted of 2 outer layers with tubular pores and a diploe-like inner layer. The anisotropic flat-bone-mimetic scaffolds differed in compressive strength along different directions. Compared with the conventional Cross-hatch scaffolds, the flat-bone-mimetic scaffolds possessed higher compressive strength and energy absorption capacity, and the Gyr-Comp scaffolds had the highest values. Gyr-Tub promoted in vitro cell proliferation, osteogenesis, and angiogenesis. Gyr-Comp presented high in vitro angiogenic activities. In the early stage of implantation (6 wk), the bone regeneration of rabbit cranial defects implanted with biomimetic scaffolds was inferior to that of defects implanted with Cross-hatch scaffolds, due to the higher permeability of Cross-hatch scaffolds. With the extension of implantation time (12 wk), Gyr-Tub outperformed Cross-hatch in the repairing effects of cranial defects, reflected by profoundly enhanced osteogenesis and angiogenesis. The Gyr-Comp scaffolds were the least effective implants for repairing cranial defects, because the presence of compact layers suppressed blood vessel ingrowth and decreased permeability. This study provides a novel concept for developing biomimetic bone regenerative materials, and Gyr-Tub scaffolds with favorable mechanical properties and excellent osteogenic and angiogenic capacities have high prospects for treating cranial bone defects in clinical applications.The detailed experimental procedures are presented in the Supplementary Materials. All animal experiments were approved by the Laboratory Animal Ethics Committee of Guangzhou Huateng Biomedical Technology, approval number: HTSW220418.


Helicobacter pylori infection influences the therapeutic response to and the drivers of malignant changes in chronic gastritis. The successful use of transplanted mesenchymal stem cells (MSCs) for gastric ulcer healing has raised interest in studying their effects on tumor neovascularization and in potential antiangiogenic therapies that could use mesenchymal stem cell secretion into extracellular vesicles—such as exosomes—in GC cells. The use of MSCs isolated from bone marrow in order to achieve angiogenic modulation in the tumor microenvironment could exploit the inherent migration of MSCs into GC tissues. Bone marrow-derived MSCs naturally present in the stomach have been reported to carry a malignancy risk, but their effect in GC is still being researched. The pro- and antiangiogenic effects of MSCs derived from various sources complement their role in immune regulation and tissue regeneration and provide further understanding into the heterogeneous biology of GC, the aberrant morphology of tumor vasculature and the mechanisms of resistance to antiangiogenic drugs.Individualized gastric cancer (GC) treatment aims at providing targeted therapies that translate the latest research into improved management strategies. Extracellular vesicle microRNAs have been proposed as biomarkers for GC prognosis.  Gastric cancer (GC) is highly heterogeneous and its molecular classification is based on the location, histology and immunohistochemical evaluation of human epidermal growth factor receptor 2 (HER2) expression and the replication error (RER) phenotype of tumors and their molecular and genetic profiles. Blood markers proposed for the detection of patients at risk of GC or those likely to benefit from specific treatments include pepsinogen I, ghrelin and various microRNAs . DNA metMiRNAs are widespread in mesenchymal stem cells (MSCs). The exosomes secreted by MSCs (MSC-exos) isolated from bone marrow (BM), adipose tissue (AD), dental pulp (DP), umbilical cords (UCs), amniotic fluid (AF) or the placenta could be used as miRNA delivery systems in malignancies .MSC-exos have either a pro- or antiangiogenic effect on tumors through various mechanisms: the ERK1/2 pathway, AKT (protein kinase B)/eNOS pathway or miRNA transport . Exome sDeregulated angiogenesis promotes gastric tumor growth through the expansion of capillaries that provide nutrients and oxygen to the tumor microenvironment. Tumor growth is supported by the transition from an avascular dormant phase to a vascular expanding one. The leaky tumor endothelial cells of the tumor microenvironment increase the interstitial pressure and interact with various growth factors. Some of these growth factors  are angiogenesis mediators found in hypoxic, acidic areas, created by fast proliferating cancer cells due to their high dividing rate ,10,11. GThe goal of genome-guided personalized therapy in gastric cancer has required a study of the relationship between MSC-exos and angiogenesis. A literature search was performed on Pubmed/Medline, Google Scholar and Embase with the keywords “ AND  AND (gastric cancer OR stomach neoplasm)”.Anti-angiogenic agents—such as apatinib, ramucirumab and bevacizumab—have been so far used in GC treatment, but the results have not been as expected . MSCs suThe gastric epithelium renews itself incessantly with the help of adult stem cells, derived either from the base or the neck of antral glands or from the isthmus. Similarly to the gut epithelium, two gastric stem cell populations with a different plasticity, longevity and cycling rate have been hypothesized . MSCs plHelicobacter felis-infected mice [Helicobacter pylori infection increases MSC proliferation and migration and activates the PI3K-AKT signaling pathway, due to the reduction of glutamine and the metabolite alpha-ketoglutarate (α-kg), produced by the gamma-glutamyltransferase enzyme secreted by Helicobacter pylori—as shown by an in vivo study on nude mice [The presence of MSC-like cells has been confirmed in human GC tissues and they share similar characteristics to BM-MSCs , but havted mice . Helicobude mice . BM-MSCsude mice . BM-MSCsude mice . MSC-like cells are also found in adjacent non-cancerous gastric tissues, sharing the same fibroblast-like appearance as normal BM-MSCs and being different in respect to their gene profiles . GC-MSCs have a higher inflammatory response, with increased levels of IL-6, MCP-1 and VEGF . GC-MSCsThe effect of GC-MSCs on GC progression, migration and angiogenesis is superior to those of adjacent non-cancerous tissue-derived MSCs (GCN-MSCs) and BM-MSCs in vitro. A list of the pro-angiogenic effects of GC-MSCs is provided in GC-MSCs have the highest levels of the pro-angiogenic factors VEGF, MIP-2, transforming growth factor TGF-β1, IL-6, and—especially—IL-8, showing the ability of GC-MSCs to enhance GC angiogenesis—mostly by secreting the inflammatory cytokine IL-8. GC cells cultured with GC-MSCs achieve a highly branched structure, suggesting an increased capacity to form tube-like structures . MSC-derGC angiogenesis is stimulated by IL-8 cytokines secreted by GC-MSCs and by the interaction of GC-MSCs with neutrophils that produce pro-angiogenic factors . IL-8 haThe miRNAs expressed in GC tissue are not unique to a specific cell type, as tumor stroma contains various mesenchymal cell types. MiRNAs packaged into GC-MSC-exos are delivered to GC cells and mediate GC progression. GC-MSCs promote GC progression by transporting these exosomal miRNAs to GC cells. Aberrant miRNA expression found in miR-214, miR-221 and miR-222 was found to be significantly higher in GC-MSCs and in GC tissues as compared to non-GC-MSCs and non-GC tissues. These increased miRNAs help GC-MSCs to promote lymph node metastasis, venous invasion and tumor node metastasis (TNM) staging in vitro and in vivo. GC-MSCs alter miR-221 expression in GC cells by delivering exosomal miRNAs to target cells ,31.MiR-15b-3p packed into exosomes (exo-miR-15b-3p) secreted by BGC-823 cells is increased in GC cells, tissues and serum and promote the malignant transformation of normal gastric mucosa epithelium cells GES-1 by regulating the dynein light chain Tctex-type 1 (DYNLT1)/Caspase-3/Caspase-9 signaling pathway, with decreased expression of the DYNLT1 gene .biomediGC cells release EVs in abundance. GC-EVs—which are classified in increasing order according to their size as exosomes, microvesicles and apoptotic bodies—are rich in non coding RNAs, which circulate in the circulation, saliva and urine. Conflicting data on the pro- vs. anti-angiogenic/tumoral effects of MSC-EVs in GC development are explained by the methodologic heterogeneity in EV collection, with EVs obtained from serum-deprived MSCs promoting tumor growth and EVs harvested from MSCs cultured with serum having tumor-suppressive roles. Moreover, MSC preconditioning with tumor cells and the timing of EV administration at varying GC stages can also differently influence study outcomes .GC cell-derived exosomes (GC-exos) promote tumor angiogenesis by activating endothelial cells and by transforming pericytes, fibroblasts and MSCs into myofibroblasts .GC exos are loaded with various cargos with the purpose of modulating angiogenesis. MiRNAs inhibit the expression of angiogenesis-related genes, but in cancer cells miRNAs are downregulated and their activity is inhibited by increased expression of other non-coding RNAs: circular RNAs (circRNAs) and long non-coding RNAs (lncRNAs). CircRNAs stimulate VEGF-A expression via the sequestration of miRNAs that directly target the 3′-untranslated region (3′-UTR) of VEGF-A, because MiRNAs downregulate VEGF-A expression in endothelial cells . HUVEC tExo-miRNAs mirror the pathological changes found in the source GC cells and can be used as biomarkers of GC metastasis spreading via the hematogenous route. Exo-miRNAs have an increased expression of MiR-379-5p and miR-410-3p in serum samples of metastatic patients after stage II/III GC surgery, being able to predict metastasis before imaging confirmation .Exosomes contain miRNAs that carry angiogenic molecules from tumor cells to various close or distant neovasculature related cells. Pro-angiogenic exosomes are involved in endothelial cell reprogramming by inducing the expression of angiogenic genes .GC exos carrying hepatocyte growth factor small interfering RNA (HGF siRNA) have been shown to inhibit tumor growth and angiogenesis in nude mice in vivo; human embryonic kidney 293T cells were used as exosome donors. The HGF protein is upregulated and is associated with poor prognosis in GC. By silencing HGF in SGC-7901 cells with siRNA, tumor angiogenesis was also suppressed and VEGF expression was also downregulated. HUVECs co-cultured with these exosome-pretreated SGC-7901 cells exhibited less vascular ring formation . As a HGGC exos were also loaded with the multifunctional Y-box binding protein 1 (YB-1), an element of inactive messenger RNAs that is overexpressed in the vascular endothelial cells of GC tissues and is either oncogenic or tumor-suppressive. In GC, YB-1 overexpression is associated with advanced cancer stages and increased angiogenesis. In vitro angiogenesis studies on HUVECs and SGC-7901 GC cells have shown that YB-1-overexpresseing GC exos promote increased neovasculature and tube formation as compared to negative controls and phosphate buffered saline; a lentivirus vector transfered the YBX1gene sequence into the HUVECs, leading to angiogenic effects. Pro-angiogenic factors such as VEGF, angiopoietin-1, MMP-9 and IL-8 are upregulated in HUVECs treated with YB-1-overexpressing GC exos .Transplantation of human MSCs overexpressing GRP78 accelerates angiogenesis by intercellular communication. GC exos containing glucose-regulated protein 78 (GRP78) have been shown to promote angiogenesis in an in vitro study on human AGS cells. HUEhT-1 cells, an immortalized HUVEC line, were incubated with overexpressed GRP78 exos and the tube formation assay showed increased angiogenesis mediated by AKT phosphorylation .Vascular stress caused by radiation or anti-angiogenic drugs increases tumor ischemia, leading to high MSC-exo recruitment . CD9 andex vivo study on HGC-27 cells that underwent epithelial-to-mesenchymal transition through the AKT pathway [MSC-exos increased human gastric carcinoma cell line HGC-27 numbers by 2–3-fold and the number of invading cells by 8-fold in an  pathway . Chemoth pathway . MSC-exo pathway . In gast pathway .MSC-exos have been tested as a therapeutic vehicle for the selective delivery of genes into the tumor endothelium and microenvironment. Anti-angiogenic gene therapy strategies have used retroviral vector producers, naked DNA, adenoviral vectors and genetically engineered MSCs as angiogenesis-inhibiting gene delivery vehicles. By being naturally involved in injury repair, MSCs have the potential to differentiate into various tissues and to home in on damaged tissues. Side effects are most likely to occur when the MSCs migrate to other tissues than those needed. MSC homing efficiency has been attempted through the direct administration of MSCs into GC tissues—even if this does not guarantee the best outcomes . GeneticMSCs have also been used for gastric ulcer treatment in various animal experiments. On the third day following local injection of AD-MSCs in rats, angiogenesis was confirmed in the sutured gastric perforation—with increased levels of VEGF, cyclo-oxygenase-2 (COX-2) and TGF-β1 . Due to Helicobacter pylori infection, transplantation of BM-MSCs—which may be involved in either gastric mucosa repair or cancer—was used for inducing GC. In a cell line characterized by rapid proliferation, scirrhous gastric cancer (SGC)—which was subcutaneously engrafted together with BM-MSCs into nude mice—BM-MSCs significantly increased GC neovascularization, especially after Helicobacter pylori exposure; this was shown by the increased expression of CD31—a platelet-endothelial cell adhesion molecule used as a marker of angiogenesis—and the neuron-glial antigen 2 (NG2) proteoglycan, which stimulates tumor vascularization by mediating pericyte endothelial cell interactions. BM-MSCs pretreated with Helicobacter pylori contribute to tube formation and migration in HUVECs co-cultured with SGC cells in vitro. BM-MSC transplantation to Helicobacter pylori-infected GC tissues leads to overexpression of THBS4, a gene that encodes the proangiogenic thrombospondin-4 protein. Integrin α2, an adhesion receptor that responds to changes in the extracellular matrix and adjacent cells, acts as a receptor for THBS4 during endothelial cell migration. Integrin α2 shows increased levels and a proangiogenic effect in HUVECs treated with recombinant Thbs4 (rTHBS4). The THBS4/integrin α2 axis facilitates tube formation in HUVECs by activating the PI3K/AKT signaling pathway [In an in vivo mouse model of  pathway . These rBy injecting MSCs into the peripheral circulation of mice or rats with GC, therapeutic genes could be carried to the GC microenvironment to produce toxins that damage proliferative cells. Tumor growth may also be suppressed by inhibiting the growth of vascular endothelial cells. The differentiating potential of MSCs can be used in the tumor vasculature for developing endothelial features. BM-derived endothelial cell precursors have the advantage of being obtained from the patient themselves, posing no compatibility issues . GastricHuman BM-MSC-exos promoted angiogenesis in co-implanted tumors induced by human SGC-7901 GC cells in an in vivo study performed in mice. The increased microvascular density and the overexpression of VEGF and the chemokine receptor CXCR4 were caused by the activation of the ERK1/2 and p38 mitogen-activated protein kinase (MAPK) pathways .BM-MSCs loaded with miRNAs transduced by lentiviral vectors have been used to form exosomes which have been co-cultured with gastric cells. MiR-1228 is negatively associated with GC survival. Decreased levels of miR-1228 have been found in patients with stage III and IV GC. BM-MSC-exos carrying miR-1228 and MMP-14 have been co-cultured with SGC-7901 and MGC-823 GC cells, confirming that miR-1228 is a tumor suppressor that targets and downregulates MMP-14—a protein coding gene involved in metastasis .The angiogenic features of GC impact the response to chemotherapy, as tumor vascular endothelial cells are more resistant than normal vascular endothelial cells to cytotoxic agents. Ramucirumab—a monoclonal antibody—and apatinib, a tyrosine kinase inhibitor, both target VEGFR2 and have been used for gastric tumor environment reprogramming. The use of various angiogenesis inhibitors may exacerbate the pro-tumor effects of tumor-associated stromal cells ; this maMSCs seem to have the benefit of acting not only as a carrier of anti-angiogenic agents, but also as an angiogenesis modifier in their own right. So far, gastric tumors have provided solid evidence that MSCs exert pro-angiogenic activity, but the use of MSCs and MSC-exos as carriers for anti-angiogenic genes such as NK4 and TNFSF14, or anti-angiogenic miRNAs such as MiR-205-5p and miR-1228, may yield clinically useful results. The cancer cell stem niche in the gastric tumor microenvironment is supported by BM-MSCs through the upregulation of the Wnt and TGF-β signaling pathways. The diagnostic value of miRNAs in GC-MSCs is supported by the higher levels of miR-214, miR-221 and miR-222 in GC-MSCs, which may help differentiate between GC tissues and nonmalignant gastric tissues. GC-MSCs could be also used as a GC biomarker via the secretion of pro-angiogenic factors such as IL-8, given that the elevated serum levels of IL-15 derived from GC-MSCs have already been suggested as a predictor of gastric malignancy . Future Increased tumor vessel density and proangiogenic factor levels indicate poor prognosis in various GC cell lines. Exosomes packaged with diverse cargos upregulate the expression of these growth factors in most studies on GC angiogenesis. The exosome-mediated interactions between MSCs and tumor cells may activate or inhibit angiogenesis signaling pathways and can be used either as tumor biomarkers or for developing antiangiogenic treatment strategies.


Retraction Note: BMC Complement Med Ther 19, 318 (2019)10.1186/s12906-019-2718-yThe Editor has retracted this article because the DAPI, TUNEL and Merged images in Fig. 6 do not appear to correspond with each other. In addition, the authors have not been able to provide original western blotting data that match the images shown in this article. The Editor therefore no longer has confidence in the results and conclusions presented. Zi-ming Zhao and Yuan-liang Liu disagree with this retraction. Wei Liu, Hua-feng Pan and Li-zhu Lin have not responded to correspondence from the Editor about this retraction.


These tools enable detectionof chemistry across many length scales for fundamental biologicaldiscovery to devices for translational diagnostic applications inmedicine and the environment.Perhaps nowherein chemistry illustrates the proverb “seeing is believing”like the fields of sensing and imaging. From the invisible gases thatmake up the air we breathe, to the nanoscopic and microscopic moleculesof life that make up the central dogma of DNA to RNA to proteins,to the metal ions and metabolites that shape cell behavior from firingof action potentials of neurons or triggering cell growth and deathpathways in cancer and infectious diseases, sensors can make the invisiblevisible and help us understand and better our daily lives. In KL-Z) is sufficientfor the prediction of fluorogenicity.1 Adye with a low KL-Z spends most of thetime in its closed nonfluorescent form thereby greatly improving cellpermeability but exhibits significant enhancements in absorption andfluorescence upon binding with a target of interest, characteristicswhich make an ideal dye for super-resolution imaging. After determiningthe KL-Z of a large palette of rhodamine-baseddyes, focusing on Janelia Fluor (JF) derivatives, they went on todevelop JF526, which serves as a highly versatile dye thatcan be easily modified with an array of self-labeling tags  or other targeting groups that enhance localizationwithin the cell.1 Moving into the near-IRwavelength segment of the electromagnetic spectrum, a collaborationbetween the Bewesdorf and Schepartz laboratories introduced a photostableand near-IR-emitting dye, Yale676sb, for use in SMLM.2 Their work highlights a methodical approach tofluorophore design, where they improved upon the previous gold-standardSMLM dye, hydroxy-methyl Si-rhodamine (HMSiR), introduced by Urano.3 A panel of indoline, julolidine, and tetrahydroquinolineSiR derivatives exhibits red-shifted excitation/emission profilesand enhanced quantum yields due to restriction of twisted intramolecularcharge transfer processes. Further improvements to the photophysicaland spirocyclization equilibrium properties of the dyes were madevia modification of the heterocyclic amines with electron-withdrawingalkyl fluorine substituents. They then went on to demonstrate theutility of the tetrahydroquinoline SiR derivative, Yale676sb, in tandem with HMSiR for the two-color, live-cell SMLM imagingof both the endoplasmic reticulum and mitochondrial membrane simultaneously.2Synthetic, small-moleculeprobe platforms continue to underpin a significant amount of biologicaldiscoveries using chemical sensors. Ample opportunities exist forinnovation using archetypical small molecule fluorophores , etc.) to improve localization, enableratiometric imaging, and enhance photophysical and molecular characteristicsfor implementation in super-resolution imaging technologies, suchas stimulated emission depletion (STED) imaging and single moleculelocalization microscopy (SMLM). A key parameter in creating suitablerhodamine-based dyes for super-resolution imaging is to control theequilibrium between the closed lipophilic nonfluorescent lactone formand the open zwitterionic fluorescent form. Dyes optimal for super-resolutionimaging should exhibit a spirocyclization equilibrium that lies predominatelytoward the lactone form. Along these lines, the Lavis group establishedquantitative design principles which dictate that the lactone-zwitterionequilibrium constant , that are amenable to both STED and SMLM techniques.7 Anchoring the tetrazine scaffold near the SiRcore enabled efficient fluorescence quenching of the free dye withlarge fluorescence enhancements upon inverse electron demand Diels–Alder(DAinv) labeling of alkyne-labeled biomolecules. The utilityof these HDyes was showcased in high-resolution live-cell imagingof both intra- and extracellular targets modified with alkyne tagsvia unnatural amino acid incorporation.In the aforementioned studies, fluorophorelocalization was promoted through conjugation of small-molecule organelletargeting groups to the dye scaffolds or via genetically encoded self-labelingtags. However, biorthogonal chemistries such as copper-catalyzed orstrain promoted azide–alkyne cycloaddition, and Staudingerand tetrazine ligation, among others, remain popular alternativesfor enhancing dye localization.8 The COT group acts as a triplet state quencher(TSQ) to reduce both photobleaching of the dye and phototoxicity towardneurons and cardiomyocytes. Notably, this single molecule TSQ tetheringapproach presents an attractive alternative toward nondisruptive membranepotential imaging, which previously relied on the exogenous additionof photoprotectant cocktails in millimolar concentrations.Voltage-sensitive fluorescentreporters (VFdyes) are vital for measuring membrane potential in neuronsand cardiomyocytes. However, photobleaching of traditional reportersmakes it challenging to perform prolonged imaging experiments, andphototoxicity results in alterations to neuronal physiology. To bypassthese limitations, Miller and co-workers reported a creative approachwherein they appended a cyclooctatetraene (COT) scaffold to a VFdye.10 Measurementand tracking of amino acid pools in live mammalian cells is one suchexample, as amino acid regulation is pivotal for maintaining cellularhomeostasis. Glass, Lin, and co-workers developed a turn-on fluorescentsensor, NS560, that can visualize 18 of the 20 proteinogenic aminoacid residues in mammalian cell models, with no response observedfor proline and tryptophan.11 NS560 exhibitsunprecedented fluorescence enhancements upon amino acid binding, withan ∼800-fold increase for glutamate. Deploying NS560 in livemammalian cell models, they visualized changes in the localizationof amino acid pools upon pharmacological intervention via fluorescencemicroscopy. Notably, they observed that chloroquine treatment resultsin the accumulation of amino acids in cellular foci, a result thatwas not observed with other autophagy inhibitors. Subsequent chemicalproteomics experiments identified Cathepsin L as the primary chloroquinetarget that led to amino acid accumulation, thus resulting in thediscovery of a new mechanism of action for chloroquine.11 Kim and co-workers exploited a hypoxia-responsiveenamine N-oxide molecular scaffold in both therapeuticand diagnostic applications. The enamine N-oxidemotif plays a dual-function as it can undergo 2e– reduction under hypoxic conditions to release an attached payload while simultaneously generating an electrophilicspecies amenable to modification by nucleophilic amino acid residueson proximal biomolecules.12 By installingthe enamine N-oxide trigger onto an array of distinctsynthetic molecules, the Kim laboratory enabled both in vitro and in vivo cell and tumor imaging and prodrugsof the pan-kinase inhibitor staurosporine.Thedevelopment of small-molecule sensors able to measure biorelevantanalytes or enzyme activity through activity-based sensing strategiesremains an area of intense research interest.13 G-SNAT measuresthe activity of granzyme B (gzmB), a key enzyme involved in the granule-mediatedcytotoxicity mechanism deployed by immune effectors. Cy5 labeled G-SNATproved successful in measuring gzmB activity in CAR T treated lymphomatumor-bearing mice. Moreover, G-SNAT was used in combination withbioluminescence imaging to measure the effectiveness of combinationtherapies, notably anti-PD-1 and anti-CTLA-4, in colorectal tumor-bearingtransgenic mouse models expressing firefly luciferase via multimodalimaging. The longitudinal and multimodal in vivo imagingprovided by the G-SNAT platform revealed insights into immune celltrafficking and tumor infiltration.13Another importantarea of research covered in this virtual issue deals with the creationof sensors that enable the noninvasive surveillance of therapeuticeffectiveness. Rao and colleagues provided an elegant example of thisapproach through their granzyme B sensitive nanoaggregation tracer(G-SNAT) platform, which measures checkpoint blockade and CAR T-celltherapy effectiveness.14 The case is presented for increased attention into the developmentof molecular quantum sensors that combine the modularity and tunabilityof molecular sensors with the incredible sensitivity of quantum sensors.Also highlighted in this virtual issue is a compelling Outlook byFreedman and co-workers, where they examine opportunities for sensingthrough the lens of the quantum world.in vivo imagingof Ras-ERK pathway inhibitor activity in the brain.15 Their strategy addresses long-standing challenges inherentto the measurement of inhibitor activity of drugs targeting the brainand establishes the first example of a bioluminescent readout forRas-Raf-MEK-ERK pathway inhibition.Central to biological probeplatforms is the use of specially tailored biomolecules  typically used to enhance targeting specificityor to catalyze reactions in conjunction with synthetic small moleculeor protein-based reporters that promote a visual response. In oneexample of this approach, Lin, Su, and colleagues engineered the ATP-independentluciferase, NanoLuc, to develop kinase-modulated bioluminescence indicators(KiMBIs) for real-time, noninvasive, 16 They demonstrated the generalizability of their HaloFlipper platformfor measuring membrane tension via live cell fluorescence lifetimeimaging microscopy (FLIM) across a variety of organellar membranes,including those of the mitochondria, endoplasmic reticulum, peroxisomes,endolysosomes, and the Golgi apparatus.Platforms based on geneticallyencoded tags, such as HaloTag, remain a popular approach for controllingfluorophore localization. Along these lines, Straková, López-Andarias,Matile, and co-workers created “HaloFlipper” probesthat consist of twistable dithienothiophene groups on one end anda chloroalkane tail on the opposite end that serves as a HaloTag substratefor targeting membranes of interest (MOI).+), remain challenging to track via fluorescence microscopy.Lithium remains the drug of choice for treating bipolar disorder (BD),but its mechanism of action is poorly understood, and many patientsdo not respond to this therapeutic intervention. Lu and co-workerscreated a novel Li+-specific DNAzyme fluorescent sensorthrough an in vitro selection process.17 The DNAzyme exhibits >100-fold selectivityof Li+ over other biorelevant metal ions and sensitivitythat enables measurement of Li+ down to 1 mM concentrationsin live cells. This team further applied their sensors to monitorLi+ pools in a human-induced pluripotent stem cell (iPSC)-basedmodel. Interestingly upon Li+ treatment, they observedincreased Li+ accumulation in differentiated neurons derivedfrom BD patients compared with controls from healthy patients, butsimilar trends were not observed in neuronal progenitor cells.Beyond enzyme-basedmethods for targeting or catalytic signal generation, single-strandedcatalytic DNA molecules known as DNAzymes offer an attractive routetoward selective monitoring of transient monovalent metal ions inbiological settings. Group 1 metals, particularly lithium  exon 1 proteins andstudying their aggregation in live cells via ratiometric SRS imaging,they determined the absolute concentrations for mHtt vs non-mHtt proteinswithin aggregates, thereby unearthing a dependence of protein compositionon aggregation size. They also made discoveries which contrasted withprevious reports regarding the structure and aggregation density ofmHtt aggregates, thus highlighting distinct advantages of SRS imagingover fluorescence techniques for obtaining conformational and structuralinformation in vitro.Raman bioimaging is currently undergoinga renaissance given advances made in instrumentation and methodology.The Wei group is among those at the forefront of Raman bioimagingand reported stimulated Raman scattering (SRS) to study polyglutamineprotein aggregates in live cells.20 The platform isbased on loop-mediated isothermal amplification (RT-LAMP) coupledwith semiconductor technology developed in their laboratories whichmeasures pH changes during nucleic acid amplification. The authorswent on to create easy-to-use devices that could be coupled with asmart phone application. To prepare for the emergent global healththreats posed by viral mutations, the Amaro and Freeman laboratoriesutilized a biomimetic approach to create a lateral flow assay fordetecting SARS-CoV-2 and its variants termed GlycoGrip.21 They employed computational approachesto gain mechanistic insight into binding interactions between theSARS-CoV-2 spike protein and glycocalyx components, identifying sixnovel binding sites. These results were used to optimize the GlycoGrip assay which detected SARS-CoV-2 and spike variantsdown to low μg/mL concentrations in human patient saliva samples.The use of glycopolymers found in the glycocalyx enhances antigenbinding as a result of multivalent interactions and can be easilytuned to capture mutated strains, thus affording a highly generalizableand inexpensive assay. Merkx and co-workers developed an elegant strategyfor the detection of SARS-CoV-2 that uses a CRISPR-Cas-9-based splitluciferase complementation strategy.22 Theplatform they developed, named LUNAS (Luminescent Nucleic Acid Sensor),uses reverse transcription-recombinase polymerase amplification (RT-RPA)for the amplification of target nucleic acid. The target nucleic acidis identified by a pair of dCAS9-based probes which mediate the complementationof split NanoLuc luciferase and gives rise to a blue luminescent readout.A calibrator luciferase enables ratiometric reporting, and the platformas a whole was demonstrated to be easy-to-use with a simple, highlysensitive, readout that could be recorded on a digital camera.22The SARS-CoV-2 pandemichas prompted the development of novel sensing platforms that enablerapid and sensitive viral detection. The quick spread of the SARS-CoV-2virus, coupled with the long wait times and technical requirementsof testing using reverse transcription-polymerase chain reaction (RT-PCR)-basedtechniques, necessitates the creation of portable and easy-to-usediagnostic tests. Rodriguez-Manzano and co-workers tackled this challengeby introducing a point-of-care diagnostic test that produces resultsin less than 20 min.23 The FLASH probeacts as a substrate for Hip1, a Mycobacterium tuberculosis (Mtb) protease, and produces a chemiluminescentreadout upon proteolytic cleavage. Notably, FLASH exhibits a limitof detection down to 15,000 cells in human sputum and is highly selectivefor Mtb over other nontuberculous mycobacteria. Additionally,this platform was proficient in differentiating live from dead bacteria,thus enabling FLASH to be leveraged for the measurement of antibiotickilling of Mtb and offering a faster alternativeover traditional approaches for determining drug susceptibility.Bacterial infections such as tuberculosisremain a leading cause of death worldwide, disproportionately affectingunder-resourced areas. Access to sensitive, quick, and affordablediagnostic tests is imperative for mitigating the spread of infection.Bogyo and colleagues developed a fast, luminescent, and affordablesensor of Hip1 (FLASH).24 With the increasing dangersof pollution and climate change, gas sensing is at the forefront ofongoing sensor research in this area. Against this backdrop, Dincăand co-workers designed chemiresistors incorporating 2D MOFs basedon hydrated Cu3(hexaiminobenzene)2 frameworksfor the detection of CO2 under ambient conditions.25 Notably, they were able to detect CO2 down to 400 ppm across a broad range of relative humidity (10–80%),addressing a limitation of traditional devices that exhibit diminishedperformance depending on humidity level. Nitrogen dioxide (NO2) represents another atmospheric pollutant prompting interestin sensor development. Lee and colleagues created the first reversibleNO2 MOF-based hybrid sensors composed of Cu3(HHTP)2 and Fe2O3 nanoparticles.26 These materials exhibit exceptional selectivityand sensitivity toward NO2 detection, which can be reversedvia visible light irradiation, thereby releasing the captured NO2. The expanding roles of MOFs as materials in devices necessitatesthe creation of improved synthetic techniques. Bloch, Rosenthal, andtheir teams reported the rapid syntheses of four iron-based MOFs viathe direct electrochemical oxidation of solubilized Fe2+ under ambient conditions.27 Their methodfor accessing MOFs overcomes challenges associated with indirect electrochemicaltechniques, such as unwanted coreduction of metal ions, and obviatesthe need for high temperatures, pressures, and long reaction timesof traditional synthetic procedures. The high level of control inherentto this methodology enabled patterning of high-quality Fe-MIL-101on carboxy-modified ITO electrodes.The rapid growth of researchinto porous materials such as metal–organic frameworks (MOFs)has spawned a flurry of activity in using such platforms for sensordevelopment.2S) sensors based on single-walled carbon nanotubes (SWCNTs)incorporating platinum POMs as highly oxidizing selectors.28 The POM-based sensors exhibit high selectivityfor H2S at ppb-level detection limits and exceptional stabilitywith only miniscule drops in response noted after two months of storageunder ambient conditions. They went on to demonstrate the ease ofdevice manufacturing via surface modification of a commercially availableKapton substrate, an aromatic polyimide film used in a variety ofhigh-performance coatings. Also highlighted in this issue is anothercontribution from the Swager group in which they created activity-basedsensors for ethylene that function via Wacker oxidation chemistry.29 They created a device composed of a catalyticmixture of palladium-based catalysts within a SWCNT network whichenabled ethylene detection in ambient conditions down to ppb levels,even in the presence of other interferents. Excitingly, they wereable to apply their device for monitoring flower senescence.Polyoxometalates (POMs)represent an important class of compounds with which to formulatechemiresistors. Swager and colleagues reported an exceptional demonstrationof this approach through the development of hydrogen sulfide (H3 nanowires interwoveninto 3D mesoporous superstructures (Pt/Si-WO3 NWIMSs) viamulticomponent coassembly with amphiphilic polymer, polyoxometalate,and platinum precursors.30 These highlystable materials displayed excellent properties for the sensing ofethanol at low temperatures (100 °C) with high sensitivitiesand low limits of detection.Mesoporous metal-oxides offer yet another attractive family of materialsfor sensing, catalysis, and storage applications owing to their highsurface areas. Deng and colleagues introduced a facile synthesis ofPt nanoparticle-decorated Si-doped WO31 Cell membrane function is regulated, in part, by the formationof lipid rafts which are alternating assemblies of proteins and lipidswithin the plasma membrane that can cluster to form ordered domains.Key to their methodology is the fluorescence measurement of phase-separatedgiant plasma membrane vesicles (GPMVs) upon addition of a panel ofsmall molecules over a broad concentration range while at constanttemperature. Using their high-throughput screening methodology, theywere able to validate existing small-molecule lipid raft modulators,while identifying completely new ones such as the protease inhibitortosyl-l-lysyl-chloromethane hydrochloride (TLCK), which increasedlipid raft formation. In the realm of materials characterization,Li, Zhang, and Han describe advances in four-dimensional scanningtransmission electron microscopy (4D-STEM) to reveal atomic levelstructure in materials such as MOFs, hybrid halide perovskites, andsupramolecular crystals, which are sensitive to traditional TEM-basedanalysis.32 Beyond highlighting advantagesand applications of 4D-STEM, they also take a deep dive into datacollection and processing methods which should aid both beginner andnovice practitioners in the field. Finally, the rapid pace of materialsscience research results in the consistent generation of new materials.One such example presented in an Outlook article by Liu, Li, and Yangcovers an emerging type of carbon-based nanomaterial referred to ascarbon dots.33 They provide key insightsinto synthetic methods and highlight distinct differences of carbondots from traditional carbon materials such as activated carbon, carbonfibers, and graphite. Additionally, the authors delve into applicationsand emergent research of carbon dots as sensors, catalysts, solarcells, and biomedical applications, among many others.We also highlight articles in thisspecial issue describing emergent imaging technologies and novel classesof nanomaterials. The Kenworthy group has established a high-throughputscreen and image analysis pipeline that enables the identificationof small molecule modulators of lipid raft formation.To close,we hope you enjoy reading this virtual issue on sensing and imagingas much as we have enjoyed organizing it. We believe it highlightsthe creativity and diversity of both early career and establishedresearchers who are tackling the grandest challenges facing our worldtoday through the development of innovative and impactful new sensingand imaging technologies. Chemistry is central to sensing and imaging!


Since the emergency authorization of SARS-CoV-2 vaccines, the medical literature has been investigating the management of allergic reactions to the vaccines. Anaphylaxis has been reported among a minority of vaccinated individuals, and many trials monitoring the safety profile of the vaccines have identified cases of benign cutaneous reactions. Typical features of delayed benign cutaneous hypersensitivity reactions include localized erythema, pruritus, and rash. However, reports have described rare cases of rash and atopy at sites apart from the injection site following vaccine delivery. We will discuss a unique case of delayed benign cutaneous hypersensitivity presenting in the lower extremity after an upper-extremity administration of an mRNA SARS-CoV-2. Additionally, we describe management strategies to guide clinicians who encounter similar vaccine-induced hypersensitivity reactions. Clinical trials investigating the safety profile of mRNA SARS-CoV-2 vaccines have demonstrated rare cases of anaphylaxis and some cases of delayed cutaneous reactions. Per the Centers for Disease Control and Prevention, the rate of anaphylaxis for the Moderna mRNA SARS-CoV-2 vaccine and the Pfizer mRNA SARS-CoV-2 vaccine were 2.5 cases per million and 11.1 cases per million, respectively [A 63-year-old male with no relevant past medical history presented for evaluation of a rash after receiving the first dose of the Pfizer mRNA vaccine against SARS-CoV-2. Of note, the patient denied a known history of SARS-CoV-2 infection before vaccination. Additionally, he denied a prior history of atopy, including seasonal allergies or drug-related hypersensitivity reactions. He also denied having a history of atopic dermatitis, psoriasis, shingles, or any autoimmune conditions like systemic lupus erythematosus. He received the vaccination in his left deltoid without any acute symptoms. Five days after vaccination, the patient developed a fever that lasted for three days and a pruritic, maculopapular rash on his ankles, which spread to his bilateral lower extremities, and eventually to the upper extremities and face Figure . Oral coThe patient was evaluated in the clinic for guidance on second-dose vaccination. Although his cutaneous allergy symptoms were not localized to the site of injection in his left deltoid, they are still suggestive of delayed T-cell mediated hypersensitivity. All in all, we present a unique and rare manifestation of delayed hypersensitivity against the mRNA SARS-CoV-2 vaccine. Numerous studies have documented delayed cutaneous hypersensitivity reactions after mRNA SARS-CoV-2 vaccination. Although most delayed reactions present with hives, injection-site erythema, pruritus, and induration, erythematous lesions appear less commonly on legs, thighs, and forearms . On averRetrospective case series have demonstrated that these reactions are mostly self-limited without serious adverse effects . SupportIn Moderna’s mRNA SARS-CoV-2 vaccine clinical trial, 244 subjects 0.8%) experienced delayed cutaneous allergic reactions after the first dose, and 68 subjects (0.2%) experienced them after the second dose . However% experieDelayed benign cutaneous hypersensitivity reactions have been reported in several patients receiving mRNA SARS-CoV-2 vaccinations with a median time of onset of seven days. Culprits for these reactions may include, but are not limited to, preservatives, adjuvants, accidental contaminants, and stabilizers. Medical literature suggests that these reactions tend to resolve spontaneously without long-term sequelae. Patients who experience such allergic reactions to the first dose of an mRNA SARS-CoV-2 vaccine may receive subsequent doses or boosters in a setting equipped to manage anaphylaxis, as delayed benign hypersensitivity reactions do not contraindicate patients from receiving further vaccinations or boosters. Individuals with known prior delayed benign hypersensitivity reactions may be pre-medicated with antihistamines for subsequent vaccinations. Additionally, patch testing or delayed intradermal testing may be pursued to ascertain the causative agents implicated in hypersensitivity reactions and to guide further vaccinations, but there is currently no valid testing strategy.


Epilepsy neuroimaging assessment requires exceptional anatomic detail, physiologic and metabolic information. Magnetic resonance (MR) protocols are often time-consuming necessitating sedation and positron emission tomography (PET)/computed tomography (CT) comes with a significant radiation dose. Hybrid PET/MRI protocols allow for exquisite assessment of brain anatomy and structural abnormalities, in addition to metabolic information in a single, convenient imaging session, which limits radiation dose, sedation time, and sedation events. Brain PET/MRI has proven especially useful for accurate localization of epileptogenic zones in pediatric seizure cases, providing critical additional information and guiding surgical decision making in medically refractory cases. Accurate localization of seizure focus is necessary to limit the extent of the surgical resection, preserve healthy brain tissue, and achieve seizure control. This review provides a systematic overview with illustrative examples demonstrating the applications and diagnostic utility of PET/MRI in pediatric epilepsy. Epilepsy is a common chronic neurologic condition in childhood, affecting 0.5 to 1% of children.18F-fluorodeoxyglucose (FDG) is the most common PET radiotracer used in clinical assessment of epilepsy patients, and in one survey,18F-FDG-PET was shown to provide critical additional information on the localization of epileptogenic zone in 77% of cases and guide surgical decision making in 51% of cases.18F-FDG brain PET. Hypometabolism associated with an underlying structural abnormality, such as malformations of cortical development (MCD), may be greater than the size of the lesion identified by structural imaging and the epileptogenic zone defined by invasive monitoring.18F-FDG-PET is more sensitive than MRI in localizing epileptogenic seizure nidus in both temporal lobe and extra-temporal epilepsy and may successfully identify MCD despite negative MRI.11C-flumazenil (FMZ) radiotracer, which has high affinity for GABAAreceptors.11C-FMZ PET demonstrates interictal decreased binding in the seizure-onset zone and may provide valuable information to complement MRI and FDG-PET in presurgical evaluation.11C (approximately 20 minutes), which limits the use primarily to the research setting and institutions with an on-site cyclotron.11C-alpha-methyl-L-tryptophan (AMT) is a tryptophan analog that traces serotonin metabolism and demonstrates increased interictal activity in the epileptogenic cortex.11C-AMT PET has shown promise in patients with tuberous sclerosis and MCD due to specificity approaching 100% and smaller area of abnormality compared to FDG or FMZ PET.More recently, epileptogenic alterations in the central diazepine receptor system have been used in the localization of epileptogenic foci by utilizing theNeuroinflammation has also been implicated in epileptogenesis. PET radioligands include translocator protein (TSPO) tracers. TSPO is an 18-kDa protein found on the outer mitochondrial membrane of activated microglia and astrocytes, and therefore considered a tissue-specific biomarker of inflammation. The majority of the data supporting TSPO as a potential target for anti-inflammatory treatment in epilepsy are either preclinical or from limited clinical studies, and it is still not clear if TSPO is a more composite measurement of neuroinflammation or if it is specific enough to warrant targeted therapy.15O-H2O PET has not gained widespread popularity given discordance and low diagnostic accuracy between perfusion and metabolic abnormalities in epileptogenic zones.Perfusion imaging for epilepsy usingBrain PET traditionally uses CT for attenuation correction and anatomic correlation. The inherent tissue contrast resolution associated with CT is suboptimal for the evaluation of structural abnormalities related to epilepsy; therefore, necessitating a separately performed brain MRI. Hybrid PET/MRI has become increasingly more common and enables improved accuracy of brain PET and MR image fusion, however, not without some pitfalls. Attenuation correction of brain PET data from PET/MRI uses advanced image-processing techniques and is the most commonly performed with an atlas-based approach, relying on a previously compiled atlas of paired MRI and CT exams to perform a pseudo-CT from the patient's MRI for subsequent attenuation correction, as opposed to utilizing direct information from the patient. Direct attenuation correction can also be performed with MRI using dixon, ultra-short echo, or zero-echo time sequences. In a cohort of children with focal epilepsy, the diagnostic accuracy of PET/MRI was not inferior to PET/CT for seizure focus localization.Hybrid PET/MRI can be obtained with synchronous or sequential systems. A sequential system is based upon patient transportation between PET and MRI scans, which are performed separately. The sequential system is clinically easier to implement because most hospitals own separate PET and MRI scanners. A major drawback is the asynchronous acquisition of the scans, which results in a longer scan and sedation time and misregistration artifacts. A synchronous system is technically more difficult to achieve but preferable in pediatric patientsAdditional advanced neuroimaging modalities such as functional MRI (fMRI), single-photon emission computerized tomography (SPECT), magnetic resonance spectroscopy (MRS), and magnetoencephalography (MEG) may also be utilized in preoperative planning.18F-FDG-PET demonstrated an advantage over MRI alone, with a sensitivity of 87% for FDG-PET versus 77% for MRI alone.18F-FDG-PET can be increased by co-registration of color-coded PET images with MRI, which improves the detection of morphologic abnormalities such as FCD type I, with up to 82% of patients seizure-free after resection guided by PET/MR findings and electrocorticography.18F-FDG-PET detects areas of hypometabolism in 60 to 92% of epilepsy patients with FCD.Focal cortical dysplasia (FCD) is the most common MCD in pediatric medically refractory epilepsy and the most frequent histopathologic diagnosis in children undergoing epilepsy surgery.18F-FDG-PET to obtain lateralizing and localizing information regarding epileptogenic cortex.18F-FDG-PET abnormalities were reported in 84% of cases in a surgical series with patients with temporal lobe epilepsy and negative MRI.In the absence of a focal lesion on MRI and surface EEG without localizing information, children undergoing presurgical evaluation may undergo18F-FDG-PET-positive TLE, with surgical seizure outcomes comparable to MRI-positive patients with mesial temporal sclerosis.Temporal lobe epilepsy (TLE) is the most common medically intractable epilepsy in adults, with mesial temporal sclerosis (MTS) as the underlying cause in approximately 60% of cases. Tumor, MCD, trauma, nonspecific gliosis, and vascular malformations are less frequent etiologies.18F-FDG-PET has proven invaluable in the workup of pediatric patients with refractory epilepsy.Reports demonstrate MCD as a common underlying histopathology in pediatric patients with pure temporal lobe epilepsy, with a predominance of type 1B and 2A focal cortical dysplasia.18F-FDG-PET co-registration can play a valuable role by noninvasively localizing epileptogenic tubers during pre-surgical evaluation.Epilepsy develops in 80 to 90% of tuberous sclerosis patients, in some as early as infancy, and approximately 25 to 50% of TSC patients may develop medically intractable epilepsy.18F-FDG-PET is beneficial in evaluating patients with hemispheric abnormalities, including encephalomalacia, Rasmussen's encephalitis, and diffuse MCD.18F-FDG-PET often demonstrates diffuse hypometabolism affecting the involved hemisphere. However, patients with bilateral18F-FDG-PET abnormalities have unfavorable seizure outcomes following hemispherectomy, emphasizing the benefits of18F-FDG-PET in pre-surgical assessment.18F-FDG PET/MRI is an optimized imaging approach that allows for comprehensive multimodal imaging evaluation with reduction in radiation dose, sedation events, and sedation time.Diagnosis and treatment of pediatric epilepsy are complicated and requires a multidisciplinary and multimodal imaging approach. Accurate localization of a seizure focus is paramount for optimal treatment and favorable outcomes following surgical resection. Hybrid brain


Glucocorticoid-induced TNFR-related protein (GITR) belongs to the TNFR superfamily (TNFRSF) and stimulates both the acquired and innate immunity. GITR is broadly expressed on immune cells, particularly regulatory T cells (Tregs) and natural killer (NK) cells. Given its potential to promote T effector function and impede Treg immune suppression, GITR is an attractive target for cancer immunotherapy. Preclinically, GITR agonists have demonstrated potent anti-tumor efficacy singly and in combination with a variety of agents, including PD-1 blockade. Multiple GITR agonists have been advanced into the clinic, although the experience with these agents has been disappointing. Recent mechanistic insights into the roles of antibody structure, valency, and Fc functionality in mediating anti-tumor efficacy may explain some of the apparent inconsistency or discordance between preclinical data and observed clinical efficacy. The glucocorticoid-induced tumor-necrosis factor receptor related protein  belongs to the TNF superfamily, which comprises 19 ligands and 29 receptors –6. Upon TNFSF ligands are type II membrane proteins comprising a C-terminal TNF homology domain (THD) separated from the cytoplasmic domain by a stalk region of variable length , 8. TNFSTNFRSF members possess a domain that mediates self-assembly of two (or three) receptor molecules creating a single high affinity site for non-covalent binding of TNFSF ligand trimers , 17. FroBecause of the overall and multiple positive effects on T cell responses, GITR has emerged as a promising immunotherapeutic target, similar to other TNFRSF members, including in particular 4-1BB (CD137/TNFRSF9), and OX40 (CD134/TNFRSF4) , 24. SevIn vitro studies demonstrated that GITR stimulation can reduce Treg immunosuppression via two main mechanisms, (1) by protecting Teff from Treg-mediated inhibition [In vivo, agonistic anti-GITR monoclonal Abs (mAbs), such as the anti-mouse GITR DTA-1 and the anti-human GITR MK-4166, were found to transiently increase intratumoral Treg proliferation and activation, although these cells eventually became unstable and were preferentially targeted for elimination [in vivo studies have shown that the anti-tumor activity of GITR agonist Abs is largely dependent on this mechanism of Treg depletion [The rationale for targeting GITR can be separately considered through its effects upon either the Teff or Treg cell compartments , 26. In hibition , and (2)hibition , 33. In mination , 35. In epletion , althougepletion . The extepletion . These mepletion , B16 melepletion , C3 cervepletion . In precepletion , 42–44, epletion .Taken collectively, these preclinical findings in mouse syngeneic models indicate the GITR targeting results in enhanced Teff function, and induces potent anti-tumor efficacy – dependent upon both agonistic GITR signaling and Treg modulation – as neither mechanism singly fully rescues anti-tumor T cell responses , 35, 40.GITR therapeutic targeting requires careful consideration of the complex structural and mechanistic features of GITR:GITRL interactions. Given the observed preclinical efficacy of DTA-1, the initial clinical development of GITR agonists focused on monospecific agonistic mAbs, although more recently bispecific agonistic mAbs, and co-stimulatory GITR ligands have been developed.Nine GITR monospecific agonistic mAbs – AMG-228, ASP1951, BMS-986156, GWN323, INCAGN1876, MK-1248, MK-4166, REGN6569, and TRX518 – have been publicly disclosed, and the structure, isotype, predicted antibody-dependent cellular cytotoxicity (ADCC) and valency of these mAbs are summarized in in vitro and in vivo studies preclinically [TNFRSF receptors such as GITR may also be activated by recombinant forms of their ligands. Fc-GITRL (MEDI1873) is one such example, and comprises 2 trimers of humanized GITRL extracellular domain (ECD) linked to two human IgG1 Fc domains by an isoleucine zipper trimerization domain that enforces ligand trimerization . MEDI187inically . When evinically . Despiteinically .in vitro. In syngeneic mouse tumor models, HERA-GITRL increased antigen-specific CD4+ and CD8+ T cell responses independent of FcγR-binding [To overcome the limitations of antibody based GITR agonists, Apogenix developed a novel hexavalent GITR agonist comprising two trivalent single-chain GITRL-receptor-binding-domain (scGITRL-RBD) units bound to an IgG1-derived silenced Fc-domain that serves as a dimerization scaffold (HERA-GITRL) . Despite-binding . Clinicacis, resulting in enhanced activation, proliferation and memory differentiation of primed antigen-specific GITR+PD-1+ T cells along with consequent anti-tumor activity in syngeneic, genetically engineered and xenograft humanized mouse tumor models [Bispecific Abs targeting a co-stimulatory receptor and either an inhibitory immune receptor or a tumor-associated antigen (TAA) have the potential to localize the agonistic activity to immune cells or the tumor site, respectively. PD-1 and GITR are co-expressed on antigen-experienced T cells and memory T cells , 56. In There is no perfect knowledge which can be entitled ours, that is innate; none but what has been obtained from experience, or derived in some way from our senses.” – William Harvey. Lumleian Lecturer, and author, “De Motu Cordis”.“Overall, the clinical results obtained so far with GITR agonist agents have demonstrated specific immune effects in the expected immune cell populations based on preclinical studies. However, these effects have not produced substantial therapeutic activity in cancer patients. Our maturing understanding of the immune responses to GITR agonism in human cancers have clarified novel issues specific to drug development in this space including Ab structure (monospecific and bispecific mAbs and co-stimulatory GITR ligands), Ab valency, and Fc functionality. This improved understanding of the immune responses to GITR agonism in patients should be kept in consideration for the design of novel rational combinations or treatment regimens in earlier disease settings where immunotherapy is gradually becoming the treatment of choice. Considering the multiple mechanisms by which cancer cells can evade immune surveillance, having agents to modulate multiple immune targets concurrently may facilitate the design of therapeutic strategies that limit the development of resistance. In this direction, the experience with GITR targeting in patients may inform the development of next-generation immunotherapy approaches. Furthermore, these results underscore the mechanistic differences of critical immunotherapeutic pathways between preclinical animal models and humans. This suggests that advancing translational science for transformational impact in patients requires dedicated reverse translational efforts and the use of improved preclinical models.


The ongoing SARS-CoV-2 pandemic and the influenza epidemics have revived the interest in understanding how these highly contagious enveloped viruses respond to alterations in the physicochemical properties of their microenvironment. By understanding the mechanisms and conditions by which viruses exploit the pH environment of the host cell during endocytosis, we can gain a better understanding of how they respond to pH-regulated anti-viral therapies but also pH-induced changes in extracellular environments. This review provides a detailed explanation of the pH-dependent viral structural changes preceding and initiating viral disassembly during endocytosis for influenza A (IAV) and SARS coronaviruses. Drawing upon extensive literature from the last few decades and latest research, I analyze and compare the circumstances in which IAV and SARS-coronavirus can undertake endocytotic pathways that are pH-dependent. While there are similarities in the pH-regulated patterns leading to fusion, the mechanisms and pH activation differ. In terms of fusion activity, the measured activation pH values for IAV, across all subtypes and species, vary between approximately 5.0 to 6.0, while SARS-coronavirus necessitates a lower pH of 6.0 or less. The main difference between the pH-dependent endocytic pathways is that the SARS-coronavirus, unlike IAV, require the presence of specific pH-sensitive enzymes (cathepsin L) during endosomal transport. Conversely, the conformational changes in the IAV virus under acidic conditions in endosomes occur due to the specific envelope glycoprotein residues and envelope protein ion channels (viroporins) getting protonated by H+ ions. Despite extensive research over several decades, comprehending the pH-triggered conformational alterations of viruses still poses a significant challenge. The precise mechanisms of protonation mechanisms of certain during endosomal transport for both viruses remain incompletely understood. In absence of evidence, further research is needed. During the first two decades of the 21st century, humanity has faced significant difficulties due to the emergence of highly pathogenic and contagious respiratory viruses, including severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV), IAV virus subtype H1N1, and the current severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The substantial levels of illness , increasCompared to the limited knowledge on the pH impact on viral survival in extracellular environments including aerosols and surfaces, inquiry into the impact of pH on respiratory viruses in intracellular environments began decades ago . Both inIn this review, I discuss developments in our understanding of the pH-induced endocytosis mechanisms in IAV and SARS-coronavirus. Drawing upon extensive literature from the last few decades and latest research, this mini-review provides a detailed explanation of the pH-dependent structural changes necessary for viral disassembly and fusion during endocytosis. Using this summary, I recognize the significant differences that result in pH-induced structural changes preceding the viral disassembly and initiating fusion with the host cell. The main aim of this review is to provide a better understanding of how the structural changes of two the highly contagious enveloped respiratory viruses differ in response to intracellular acidic environments.Influenza is a negative-strand RNA virus with eight ribonucleoprotein particles (RNPs) contained within a lipid envelope derived from the host plasma membrane. The IAV viral envelope contains two major glycoproteins proteins, hemagglutinin (HA) and neuraminidase (NA), that project from the lipid membrane as spikes . A thirdThere are several types of viral entries to the cell, also known as endocytic pathways that can be utilized by influenza viruses, including predominantly clathrin-mediated and caveolin-mediated endocytosis . The patEventually, the cleaved pre-fusion neutral pH HA  is attacThe pH dependence of the early stages of HA conformational change is regulated by the histidine residue HR184 of the HA1 and HA2 monomers . The sid+, K+, or Cl– ions regardless of external pH conditions ’s primary role is in the later stages of infection, where it aids in the detachment and spread of the virus to new cells by removing sialic acids from cellular receptors and newly synthesized HA and NA on nascent virions . This prThe M1 protein binds both to the RNP complex and the lipid membrane. The M1–lipid binding is mediated through electrostatic interactions between the positively charged N-terminal domain residues (Arg76 and Arg78) and negatively charged cytoplasmic tails of HA and NA , while tThe positive-stranded RNA genome of SARS-coronavirus encodes three membrane proteins: the spike (S) glycoprotein, responsible for binding the cell-surface receptor to induce virus-host cell fusion ; and theSARS-coronavirus entry into target cells starts with protease-induced preactivation of the S1/S2 cleavage . The proThus, SARS-CoV-2 fusion is essentially independent of pH value as endosomal acid-dependent penetration through cathepsin L occurs only in cells devoid of TMPRSS2  as shownThe M protein is the most abundant structural protein and contains three transmembrane helices, with a short amino-terminal ectodomain and a large carboxy-terminal endodomain . The M pin silico studies and pH imaging . Similar to IAV, SARS-CoV-2 can use mutually exclusive routes to penetrate cells: one fast pH-independent TMPRSS2-mediated plasma route, and one pH-dependent slow clathrin-mediated endocytosis via cathepsin L. The clathrin-mediated endocytosis through cathepsin L occurs only in cells devoid of TMPRSS2. Unlike TMPRSS2, which is active at the cell surface regardless of pH conditions, cathepsin L requires a low-pH environment typical of endolysosomes. Although several studies support the view that TMPRSS2-dependent early entry route is more efficient and results in a more productive infection than the cathepsin L-activated mechanisms for some SARS-coronavirus strains, recent studies indicate that Omicron SARS-CoV-2 variants favor the low-pH endosomal entry route. For fusion activity in SARS-coronavirus, cathepsin Ls have been shown to require reduced pH of at least 6.0 or lower. Although research has verified that the envelope E-protein serves as an ion channel when pH levels decrease, there have been certain inconsistencies observed between various studies and tests. Furthermore, unlike the influenza M1 protein, there has been no evidence of similar pH-sensitive behavior in the SARS-coronavirus M1 protein. However, studies also suggest that cathepsin L is irreversibly inactivated at pH values lower than 4.0, an acidic environment that may occur in matured lysosomes. The pH sensitivity of influenza A and SARS-CoV-2 viral glycoproteins is a potential target for therapeutic interventions and anti-viral drug treatments. So far, there is evidence suggesting that chloroquine, a weak base, inhibits the replication of those influenza A strains whose hemagglutinins require a low pH for their fusion activation . Chloroqeatments . In summThe author confirms being the sole contributor of this work and has approved it for publication.


Late balloon valvuloplasty can be used to treat under-expansion-related transcatheter heart valve (THV) dysfunction. Whether this can be performed following redo-THV implantation is unknown. Herein, we report a case of a 72-year-old male presenting with symptomatic gradient elevation following redo mitral valve-in-valve implantation. The patient was successfully treated with late balloon valvuloplasty with gradient improvement. In conclusion, late valvuloplasty is effective even with several layers of valves. However, larger studies are required to clarify the role of this approach further. Late balloon valvuloplasty with or without bioprosthetic valve fracture has been reported for addressing under-expansion-related transcatheter heart valve (THV) dysfunction, even several months after the index procedure . While tA 72-year-old male with severely reduced ejection fraction (19%) underwent redo-MVIV in 2022 for severely stenotic THV and NYHA III symptoms. He had initially undergone coronary artery bypass graft surgery with mitral valve replacement  in 2004, followed by transapical MVIV  due to the dilated left ventricle. In addition, the failed SAPIEN XT was found severely under-expanded  showed no risk of neo-left ventricular outflow tract (LVOT) obstruction (predicted area of 14.5 cmThe improvement in expansion was associated with a reduction in MG to 6 mmHg (HR 48 bpm) post procedure, and the patient was discharged the following day. During the 2-month follow-up, the patient reported improvement in clinical status (NYHA II). In addition, the transthoracic echocardiogram gradient remained stable at 8 mmHg (HR 55–60 bpm), with no signs of an increased LVOT gradient. The echocardiogram also showed moderate tricuspid regurgitation and elevated pulmonary artery systolic pressure of approximately 60 mmHg, which is stable compared with the pre-redo-MVIV. This case report illustrates several important concepts relative to transcatheter mitral valve replacement.First, redo-MVIV appears feasible in selected patients with acceptable hemodynamic results but might result in significant THV under-expansion if aggressive pre- and/or post-dilatation is not performed. However, it must be noted that the need for redo-MVIV remains relatively rare since MVIV is generally performed on elderly patients who rarely outlive their valves due to comorbidities .Second, late balloon valvuloplasty can be effective despite multiple valve layers and can be used to treat under-expansion-related THV dysfunction. However, this requires long inflations at very high pressure that might be clinically poorly tolerated and with unknown long-term consequences on THV function. Moreover, it is possible that adequate pre-dilatation would facilitate the proper expansion of the redo-THV, similar to that observed in bench studies of redo transcatheter aortic valve replacement (TAVR) .Finally, post-dilatation of several layers of valves may lead to marked flaring of the surgical bioprosthesis posts, which may increase the risk of LVOT obstruction. Indeed, CT simulation for pre-procedural neo-LVOT area prediction depends on assuming a cylindrical geometry projected over the existing bioprosthesis into the LV. If the valve outflow becomes flared post-dilatation, then the resultant valve instead has a conical geometry, with the wider end reducing the true neo-LVOT area compared with that predicted on the CT scan. Similarly, in the aortic VIV TAVR arena, post-dilatation or valve fracture causing under-estimation of coronary obstruction risk has been recently reported . Our casLate balloon valvuloplasty is feasible in selected patients following redo-MVIV. However, further studies are required to assess the effectiveness and implications of high-pressure valvuloplasty following redo-THV implantation.