Cancer immunotherapy has emerged as a novel anti-tumor treatment. Despite significant breakthroughs, cancer immunotherapy remains focused on several types of tumors that are sensitive to the immune system. Therefore, effective strategies to expand its indications and improve its efficacy become key factors for the further development of cancer immunotherapy. In recent decades, the anticancer activities of natural products are reported to have this effect on cancer immunotherapy. And the mechanism is largely attributed to the remodeling of the tumor immunosuppressive microenvironment. The compelling data highlight that natural products offer an alternative method option to improve immune function in the tumor microenvironment (TME). Currently, more attention is being paid to the discovery of new potential modulators of tumor immunotherapy from natural products. In this review, we describe current advances in employing natural products and natural small-molecule drugs targeting immune cells to avoid tumor immune escape, which may bring some insight for guiding tumor treatment. The immune system is a sophisticated integrated network consisted of various immune cells, organs, and soluble mediators that developed to protect the biosome against outside assault which threatens the integrity of biosome . The immCancer immunotherapy is defined that regulates immunological response through activating the organism’s immune defense system to suppress and prevent tumor growth . Now, a Natural products used to treat human diseases can date back over 3000 years and contain several active components found in medicinal plants. Furthermore, mangy natural products were verified and documented in several publications in ancient China. Numerous studies currently have demonstrated that natural products play an important role in the development of new anti-cancer drugs and lead compounds due to their wide range of sources, low cost, structural diversity, diverse biological activities and low adverse effects , 11. SevIn general, the immune cells that have an effect on tumors can be divided into two types: tumor-promoting and tumor-antagonizing immune cells. These two types of cells play various roles at different stages of tumor progression , 19. TheMonocytes/macrophages are derived from bone marrow stem cells, which can enter the bloodstream and be distributed in various organ tissues after developing into monocytes.In the process of participating in innate immunity, monocytes/macrophages can identify pathogen-associated molecular patterns (PAMP) and play an important role in innate immunity. On the other hand, monocytes/macrophages also can mediate and promote inflammatory responses and implement immunity killing, and antigen presentation , 21. Tumvia altering the interaction of macrophages and fat cells. It has been proposed that doing so may improve insulin resistance and the metabolic syndrome  cells are a subtype of T cells with immunomodulatory functions that are closely related to the pathological processes of a variety of human tumors . When thKaempferol enhanced Treg cell immunosuppressive activity by inhibiting the activity of proto-oncogene serine/threonine kinase (PIM1) . The comEffector T cells include CD8+ cytotoxic T cells (CTLs) and effector CD4+ T cells. In the “activated” state, CTL can induce target cancer cells killing through granule cytokinesis and Fas ligand (FasL)-mediated apoptosis . CD4+ T in vitro and in vivo tests, demonstrating a dose-dependent mechanism  have investigated the effect of QS-21 as an immune adjuvant in cancer vaccines designed . Curcumivia ICD  effects. The pathway of ICD-induced tumour cell death relies on damage-associated molecular patterns (DAMPs) such as heat shock proteins (HSPs), high mobility group box 1 (HMGB1) and calreticulin (CRT), making tumour cells a “therapeutic vaccine” that can induce anti-tumour immunity . Capsaicvia ICD .in vivo and in vitro. Unlike traditional chemoimmunotherapy in tumor, natural products display many advantages, such as wide sources, less toxic and side effects, as well as diverse immunomodulatory activities, suggesting that natural products have an attractive prospect in the research of novel tumor immunotherapy. The combination of natural products and chemotherapeutic drugs may exert stronger therapeutic effect than chemotherapeutic drugs alone in tumors, which has synergistic and reducing toxic and side effects.Given the multi-pharmacological activity and chemical diversity, natural products have been described as a non-substitutable source of clinical therapeutics for human tumors. Natural products can mediate multiple immune responses and reduce the tumor escape. They enhance the interaction of immune cells while decreasing the expression of pro-inflammatory cytokines. Previous studies have shown that natural products can exert anticancer activity through immune regulation Although natural products have made encouraging appear promising and progress in various studies as modulators of tumor immunotherapy. For natural products to be better used in cancer immunotherapy, a number of issues still need to be addressed. First of all, natural products will face the problem of individual patient differences, TME differences, tumor heterogeneity. Secondly, a deeper and more comprehensive exploration of the signalling pathways of the immune system relevant to tumor immunotherapy is needed to help select more effective natural products. Thirdly, most natural products have a wide range of pharmacological effects, but their targets and molecular mechanisms relevant to tumour immunity have not been fully elucidated.Above all, the emerging role of natural products in tumor immunotherapy still has greater potential and deserves attention. Future research can screen natural products for targeted antitumor immune drugs using advanced technologies, such as metabolomics, single-cell sequencing, novel drug delivery technologies, and computer-aided design techniques.X-QJ conceptualized the ideas. X-QJ, NL, W-JF, Z-HL, and J-LH performed the literature search, drafted the original manuscript, and drew the figures. Z-SL revised the manuscript. All the authors approved the final version of the manuscript.This work was financially supported by General Program of the National Natural Science Foundation of China Joint project (NO. U21A20348), National Natural Science Foundation of China General Project (No.81970633), Heilongjiang Provincial Higher Education Institutions Basic Research Business Expenses (2021KYYWF0046).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.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


Abdominal pain, including visceral pain, is prevalent in functional gastrointestinal (GI) disorders (FGIDs), affecting the overall quality of a patient’s life. Neural circuits in the brain encode, store, and transfer pain information across brain regions. Ascending pain signals actively shape brain dynamics; in turn, the descending system responds to the pain through neuronal inhibition. Pain processing mechanisms in patients are currently mainly studied with neuroimaging techniques; however, these techniques have a relatively poor temporal resolution. A high temporal resolution method is warranted to decode the dynamics of the pain processing mechanisms. Here, we reviewed crucial brain regions that exhibited pain-modulatory effects in an ascending and descending manner. Moreover, we discussed a uniquely well-suited method, namely extracellular electrophysiology, that captures natural language from the brain with high spatiotemporal resolution. This approach allows parallel recording of large populations of neurons in interconnected brain areas and permits the monitoring of neuronal firing patterns and comparative characterization of the brain oscillations. In addition, we discussed the contribution of these oscillations to pain states. In summary, using innovative, state-of-the-art methods, the large-scale recordings of multiple neurons will guide us to better understanding of pain mechanisms in FGIDs. Pain is an unpleasant experience containing sensory and emotional components. The unpleasant percept that dominates the affective dimension of pain is coupled with the motivational drive and guides us to escape from potentially harmful events associated with actual or potential tissue damage. The experience of pain is evoked by noxious stimuli or through adverse emotional events and memories. The brain receives nociceptive signals and integrates sensory, cognitive, and emotional information to respond appropriately. Pain has two distinct types, acute and chronic pain, and is very common in patients with functional gastrointestinal (GI) disorders (FGIDs). FGIDs are a group of GI conditions characterized by abdominal pain or discomfort, stool irregularities, bloating, and other somatic, visceral, and psychiatric comorbidities. FGIDs account for 40–50% of all new referrals to GI clinics ,2. DespiFGIDs are considered a bio-psycho-social disorder of gut-brain interaction with unclear etiology. Despite differences in etiology, gut-brain communication is essential for understanding the pathophysiology of visceral pain in FGID ,4,5. HowIn the clinical setting, pain  processing is mainly studied using hemodynamic brain imaging techniques such as functional magnetic resonance imaging (fMRI) and positron emission tomography (PET), and neuro-electrical techniques, including electroencephalography (EEG), and magnetoencephalography (MEG). These studies have shown that changes in brain structure and function are correlated with persistent pain. In IBS patients, the brain regions associated with attention, including the anterior cingulate cortex (ACC), medial PFC (mPFC), and thalamus, are more active than healthy controls and may underlie symptom-related anxiety and visceral hypersensitivity . Both maRats and mice are the most commonly used animal models for studying visceral hypersensitivity (VH) in FGIDs. Multiple rodent models of visceral pain have been described. However, a few have been well-established, including intracolonic administration of different active compounds or experimental infection with biological agents. Here we briefly discuss some popular methods used to induce VH in rats and mice.Infusing chemical substances such as acetic acid (AA) into the descending colon and rectum is commonly used to establish VH. The VH in adulthood can be induced by intrarectal infusion of 0.2 mL of 0.5% AA solution in saline in 10 days old pups; the animals develop VH in response to colorectal distension (CRD) in adulthood . Adult r−1 increased colonic motility, visceral perception, and induced anxiety-like behavior [Corticotropin-releasing factor (CRF) is a crucial regulator of the hypothalamic–pituitary–adrenal (HPA) axis. It is involved in stress response in the brain–gut axis and is considered an essential mediator of visceral hypersensitivity. Previous studies reported that microinjection of CRF into the cerebral ventricle or the central nucleus of the amygdala (CeA) with a dose of 0.1–10 μgkgbehavior ,27. Thesbehavior . Moreovebehavior , suggestStress in early life, including childhood negligence, and physical or sexual abuse, could have detrimental impacts on individuals. Previous evidence suggests that early life stressors like neonatal maternal separation increase the risk of developing IBS in adulthood ,31. The Water avoidance stress (WAS) is a non-invasive technique to induce visceral hypersensitivity in rodents. The most conventional approach to constructing this experimental model is to place animals on a dry platform surrounded by water in a plexiglass tank. The animal is placed on the platform for only 1 h (acute stressor) or 1 h daily for 10 consecutive days (chronic stressor). Some studies demonstrated that a single exposure to WAS induced visceral hypersensitivity , while oCitrobacter rodentium (C. Rodentium) caused transient visceral hypersensitivity in mice and persisted for about 2–3 weeks [Trichinella spiralis  infection is commonly used to produce long-term colonic hypersensitivity in rats and mice. In response to CRD, these animals demonstrated increased EMG and AWR scores in rats [Chronic and persistent IBS symptoms could develop after the remission of acute intestinal infection, known as post-infectious irritable bowel syndrome. Biological agents such as bacteria or parasites can destroy the balance of intestinal microecology and effectively induce visceral hypersensitivity in rats and mice. Bacterial infection with –3 weeks . Trichin in rats  and mice in rats , respectSeveral rat models of FD have been mentioned previously; however, we will discuss a few of the most popular animal models. Oral gavage of 0.2 mL of 0.1% iodoacetamide in 2% sucrose to male neonatal pups on PN10-16 can induce FD-like responses to gastric balloon distension in adulthood . AdminisAlthough it is challenging to completely mimic visceral pain in animal models, these models provide an opportunity to investigate the visceral pain mechanism in conjunction with the brain–gut axis.It is worth comparing the differences among different animal models; however, the data is limited to the best of our knowledge as all animal models share the standard mechanisms for inducing VH, although some differences still exist. Herein, we very concisely summarized these observations in Studies ranging from humans to animals, including neuroimaging, functional, anatomical, and biochemical, suggest the involvement of different brain nuclei in pain processing associated with FGIDs. This section will discuss key brain regions involved in nociception.To better understand pain perception and develop novel therapies for chronic pain disorders, it is important to exploit the neuronal circuitry associated with pain processing. Research from human and animal studies has emerged to show that the anterior cingulate cortex (ACC) is a critical brain region necessary for processing the emotional aspects of pain ,50. The Synaptic plasticity, such as long-term potentiation (LTP) and long-term depression (LTD), provides the neural basis for learning and memory ,67. Chro→BLA pathway is responsible for regulating both the sensory and aversive components of pain, the activation of the MD→BLA pathway only contributes to the aversive-affective component of pain [The amygdala , a limbi of pain .Several lines of evidence suggest the role of the amygdala in modulating visceral pain. Chemical activation of the CeA enhanced visceromotor responses to CRD in rats and caused the sensitization of spinal neurons . In respThe midbrain periaqueductal gray PAG;  plays a Based on anatomical and functional observations, the PAG has been subdivided into dorsomedial (dmPAG), dorsolateral (dlPAG), lateral (lPAG), and ventrolateral (vlPAG) columns ,106,107.The brain nucleus locus coeruleus (LC) is located in the dorsolateral pons and is a significant source of norepinephrine (NE) in the brain . RetrogrAcupuncture, electrical stimulation at ST 36 acupoint, has been widely used for treating VH in an animal model of FD ,152 and In the previous sections, we already summarized that chronic pain reorganizes the structural and functional connections in both cortical and subcortical structures, including the mPFC ,84, thalA previous study suggested that the limbic forebrain structures, including the hippocampus, are responsible for modulating the aversive component of pain . ElectroConverging evidence shows that to understand the pathophysiological basis of pain in FGIDs, it is necessary to precisely decode how the information is processed between the brain–gut axis and across different brain regions. Various methods have been applied to study the pain processing mechanism in the brain; however, the currently available techniques have yet to gain widespread clinical use. Neuroimaging techniques, such as fMRI and PET, measuring indirect neuronal activity, have been widely used to study pain processing. Although these methods have contributed significantly to understanding the pain mechanism, these techniques have a relatively poor temporal resolution. Consequently, a high temporal resolution method, such as electrophysiology , that caHere we summarized previous findings  that useEnglish databases, including PubMed (PM), and Web of Science core collection (WS), were searched for published articles without restricting the year of publication. The following keywords were used in the searching process: (1) visceral pain and extracellular recording in animals ; (2) visceral pain and electrophysiological recordings in functional gastrointestinal disease , and (3) Electrophysiological recordings in functional gastrointestinal disease . Moreover, 18 articles were found in the citation search processing.Inclusion and Exclusion criteria: Based on the focus of our review, we aimed to include studies that performed extracellular recordings from the brain in animal models of FGIDs. The following exclusion criteria were established: (1) studies conducted in human patients; (2) studies involving brain imaging techniques such as fMRI and PET; (3) non-empirical studies, such as editorial letters, conference proceedings, and literature reviews; (4) articles not written in English, or (5) studies performing intracellular recordings.Selection process: From all search methods, 195 articles were identified. After removing duplicates, the titles and abstracts were retrieved and screened for eligibility according to the exclusion criteria. The number of reports was adjusted to 162, the full texts of the 34 articles were reviewed, and 9 papers matched the requirements and were included for reporting . ExtraceDifferent brain regions are interconnected and must communicate to provide the basis for integrating information critical for learning, memory formation, perception, and the behavior of organisms. Cell assembly theory  suggestsBrain oscillations are transient and emerge in bursts or packets. The principal approach to studying these oscillations from LFPs involves decomposing these signals into magnitude and phase information for each frequency and characterizing their changes over time . This approach is commonly used for hunting oscillation bursts in neural data and is known as time-frequency analysis ,212. TheCommunication between selective brain structures is a crucial component of the neural processing underlying cognition ,216. Ele→S1) pathway encodes sensory–discriminative attribution of nociception. The medial (MD→ACC) pain system contributes to the motivational–affective component of pain arising from deep somatic and visceral structures. In chronic pain states, both pain pathways are known to be disrupted. Human and animal studies suggest that disruption of brain oscillatory activity is associated with neurological and GI disorders. However, the precise mechanisms underlying the disturbances of the rhythm coherence in FGIDs still need to be better understood.Increasing evidence strongly indicates that the crosstalk between the gut and brain is important for understanding visceral pain pathophysiology in FGIDs. However, the mechanisms by which these regions communicate are still in their early infancy. The brain receives noxious pain stimuli through anatomically and functionally distinct medial and lateral pain pathways. The lateral (lateral thalamusThe role of theta oscillations in cognition is widely accepted, and emerging evidence suggests pain specific ongoing activity in the theta band. Therefore, theta oscillation dynamics can serve as a basis for decoding pain sensation. Future works in this field are beneficial for identifying the oscillatory basis of pain perception in FGIDs and provide a deeper understanding of the nociceptive systems in these disorders. Electrophysiological methods such as large-scale neuronal population recordings could be suitable for studying pain mechanisms because of their relatively low cost, high temporal resolution, and ease of use compared to other neuroimaging techniques. In clinical practice, this also offers exciting prospects for investigating pathological mechanisms of visceral pain in FGIDs, thus promoting the development of a rational therapeutic strategy.


Metastatic cancer is a multifaceted complex disease. It is mainly characterized by a strong invasive potential, metastasis, resistance to therapy, and poor clinical prognosis. Although the use of immune checkpoint inhibitors (ICI) has substantially improved cancer treatment and therapy, there are many significant challenges to be addressed. In this review, we provide an overview of the mechanisms used by metastatic or disseminating tumor cells (DTCs) in order to understand cancer progression to metastasis, and establish new strategies for novel therapeutic interventions.The tumor microenvironment plays a key role in the progression of lung tumorigenesis, progression, and metastasis. Recent data reveal that disseminated tumor cells (DTCs) appear to play a key role in the development and progression of lung neoplasiaby driving immune system dysfunction and established immunosuppression, which is vital for evading the host immune response. As a consequence, in this review we will discuss the role and function of DTCs in immune cell signaling routes which trigger drug resistance and immunosuppression. We will also discuss the metabolic biology of DTCs, their dormancy, and their plasticity, which are critical for metastasis and drive lung tumor progression. Furthermore, we will consider the crosstalk between DTCs and myeloid cells in tumor-related immunosuppression. Specifically, we will investigate the molecular immune-related mechanisms in the tumor microenvironment that lead to decreased drug sensitivity and tumor relapse, along with strategies for reversing drug resistance and targeting immunosuppressive tumor networks. Deciphering these molecular mechanisms is essential for preclinical and clinical investigations in order to enhance therapeutic efficacy. Furthermore, a better understanding of these immune cell signaling pathways that drive immune surveillance, immune-driven inflammation, and tumor-related immunosuppression is necessary for future personalized therapeutic approaches. The metastatic spread of tumor cells is a key process for cancer progression. Accumulating evidence reveals that the spread of tumor cells can occur even at the early stages of carcinogenesis ,2. This The mechanism of dissemination alters the phenotypic morphology of tumor cells in order to obtain traits that allow them to leave the primary tumor and spread (metastasize) to distant tissues or organs via blood circulation . These cThe peripheral blood contains numerous sources of tumor-derived material, like circulating tumor DNA (ctDNA), CTCs, and exosomes, which support tumorigenesis. Furthermore, the extracellular matrix (ECM) plays a critical role in the maintenance of the tumorigenic profile of DTCs ,12. ThesBoth the epithelial to mesenchymal transition (EMT) and mesenchymal to epithelial transition (MET) are developmental programs that are activated during embryogenesis and tissue repair . During Integrins are transmembrane proteins that mediate cell adhesion, regulate the cell cycle, and organize the intracellular cytoskeleton . AccumulRecent data reveal that in the early stages of the metastatic cascade, bidirectional communication between malignant cells and the TME is essential for maintaining tissue homeostasis and tumor expansion. Metastatic tumorigenesis is a heterogeneous disease progressing in a multistep process involving aberrant mutated tumor cells, altered phenotype immune cells, and highly polarized stromal cells. As a whole, metastatic colonization is a very ineffective mechanism, where only 0.01% of tumor cells survive to form micro-metastases. During this early phase of metastasis, cytoskeleton rearrangements within tumor cells in cooperation with aberrant differentiation signaling of Notch, WNT, and Hedgehog pathways guide tumor cell invasion. This metastatic cascade occurs via single tumor cells or cell clusters. Recently, the ability of CTCs to form clusters has been linked to increased metastatic potential. In particular, CTC clustering shapes DNA methylation to enable metastasis seeding and the promotion of stemness . These CIn a plethora of tumors, dormant DTCs can reside in distinctive compartments inside the TME which sustain their proliferation and survival from immune surveillance. Dormant or quiescent DTCs may lay dormant for long periods and are characterized by the reversible growth arrest in the G0-G1 phase of the cell cycle. This tumor dormancy is characterized by a balance between tumor cell proliferation and apoptosis . Endowin+/Tie2+ macrophages and induces Wnt-1 upregulation that, in response, downregulates E-cadherin junctions in the HER2+ early cancer cells. The formation of macrophage compartments in the pre-malignant lesions was detected, and they can operate as portals for intravasation [− negative cells, which display an intrinsic capacity to become CSCs in a niche-independent manner and can restore epithelial hierarchies in metastatic tumors [DTCs are mainly characterized by their EMT characteristics. This EMT transition can mediate both the dissemination and possible acquisition of CSC traits and phenotype by tumor cells. Recently, it was shown that the bone microenvironment facilitates breast and prostate cancer cells further metastasizing and establishing multi-organ secondary metastases. This metastasis-promoting effect is driven by epigenetic reprogramming that confers stem cell-like properties to cancer cells . In addivasation . Recent vasation . A recenc tumors . Moreovec tumors .Primary tumors are highly dependent on their residual stromal microenvironment. For DTCs residing at distant organs, their dormant quiescent state is mainly regulated by the local microenvironment. The transition of tumor cells from a dormant state to an activated outgrowth state may be provoked by changes in their local microenvironment. The increased expression of specific factors such as TGF-β/TGF-β2, CXCL12, bone morphogenic protein 7 (BMP7), leukemia inhibitory factor (LIF), and Wnt signaling can break dormancy and promote tumor cell proliferation . DormancAccumulating evidence shows that the interactions of DTCs with the stromal cells of the TME prompt immune system inhibition and immunosuppression . These sA significant factor in tumor cell dissemination is the formation of new blood vessels via angiogenesis in order to support tumor growth and expansion. VEGF is the main coordinator of new blood vessel formation from pre-existing endothelial cells on blood vessels . Tumor cThe advances of modern tumor immunotherapy approaches have revolutionized the field of cancer research. Several small clinical trials targeting DTCs post-treatment are really promising, and second-line chemotherapy regimens such as bisphosphonates  show promising and encouraging results. Furthermore, the advancement of single-cell analysis techniques, mainly single-cell RNA sequencing and immune signaling pathway profiling, is vital for the phenotypic analysis of tumor cell heterogeneity. A better understanding of the crosstalk between DTCs and the tumor immune microenvironment  may alsoMetastatic dissemination is a complex multistep process. An ideal systemic therapy should target the molecular immune-related mechanisms in the tumor microenvironment that lead to decreased drug sensitivity and tumor relapse, and also reverse drug resistance and tumor-induced immunosuppression. Therefore developing specific therapeutic strategies in order to inhibit metastatic colonization will be a promising direction in lung cancer treatment.and will radically enhance therapeutic efficacy


Coronary artery disease (CAD) represents a widespread burden to both individual and public health, steadily rising across the globe. The current guidelines recommend non-invasive anatomical or functional testing prior to invasive procedures. Both coronary computed tomography angiography (cCTA) and stress cardiac magnetic resonance imaging (CMR) are appropriate imaging modalities, which are increasingly used in these patients. Both exhibit excellent safety profiles and high diagnostic accuracy. In the last decade, cCTA image quality has improved, radiation exposure has decreased and functional information such as CT-derived fractional flow reserve or perfusion can complement anatomic evaluation. CMR has become more robust and faster, and advances have been made in functional assessment and tissue characterization allowing for earlier and better risk stratification. This review compares both imaging modalities regarding their strengths and weaknesses in the assessment of CAD and aims to give physicians rationales to select the most appropriate modality for individual patients. Coronary artery disease (CAD) represents a widespread burden to both individual and public health, steadily rising across the globe . Thus, sBoth cCTA and vasodilator stress CMR are robust imaging modalities with reported diagnostic image quality in >97% of cases .However, to compare both in their diagnostic capabilities, comprehension of what both modalities primarily test for is indispensable. In general, cCTA is widely used for the assessment of the anatomical presence of coronary artery disease, whereas stress CMR tests for the functional presence of ischemia.cCTA has the highest sensitivity 97%) of all non-invasive imaging modalities for the detection of anatomically significant CAD, but low specificity for anatomically (78%) or functionally (53%) significant CAD 7% of all. The latter is often due to partial volume or blooming artifacts which can lead to an enlargement of calcified plaques, thus resulting in an overestimation of stenosis severity . ConsequHowever, cCTA allows for the identification of patients in the early stage of CAD having non-obstructive coronary plaques. These patients have long been underrecognized since these plaques typically do not cause reduced blood flow and consequently most non-invasive tests assessing ischemia are inconspicuous. Yet, these patients are at increased risk since the rupture of non-obstructive plaques is the main cause of myocardial infarction ,13. FurtThe identification of additional patients at risk by cCTA improves patient outcome significantly, as shown in the PROMISE, CONFIRM and SCOT-HEART trial ,17,18,19In the SCOT-HEART trial, 4,146 patients with angina and suspected CAD were randomly assigned to standard care or standard care and cCTA . In the The same was observed by a registry study on 33,552 patients with <50% coronary stenoses on a cCTA, in which a new medication with a statin after cCTA was associated with a reduction in myocardial infarctions and all-cause death, directionally proportional to the observed CAD burden . cCTA isApart from coronary stenosis assessment and plaque characterization, cCTA also allows for visualization and quantification of perivascular fat suggestive of coronary inflammation, which is shown to be a negative predictor for cardiac outcome ,25.In summary, cCTA is the diagnostic modality of choice to safely assess the presence of CAD, independently of its hemodynamic relevance, and, thus, guide further treatment such as the initiation of preventive medical therapies. cCTA can achieve non-inferior diagnostic accuracy in stable CAD patients without having the periprocedural risks of an invasive coronary angiography . Stress CMR cannot safely exclude the presence of CAD. Its strength lies in the accurate assessment of the hemodynamic relevance of coronary stenosis, i.e., the testing for ischemia. Ischemia, however, is not a bivalent marker, but rather a continuum . CAD witIn summary, CMR is the modality of choice to assess hemodynamic relevance, predict prognosis and for a thorough differential diagnosis in suspected CAD patients. Broad advances have been made in the technical capabilities of contemporary CT scanners. High-end CT detectors with ≥128 slices have become a standard in many academic and non-academic sites in developed countries .source CT when operated with two different energies). An alternative technology is the combination of a single x-ray source rapidly alternating between low and high energies (fast switching) with a single detector that registers information from both energies [While conventional CT utilized a single polychromatic X-ray beam received by a single detector, dual-energy CTs (DECT) show increasing popularity. Depending on the vendor, different techniques are used. One is a second tube and detector unit at a 90° angle  and therefore a reduction in motion artifacts, which is critical in the assessment of a moving structure such as the heart . They caRegarding unenhanced CT such as coronary calcium scoring, the application of a tin filter may decrease the radiation dose in unenhanced scans without negatively affecting subjective image quality . The tinThe most recent step in hardware advances for cCTA is the so-called photon-counting CT. It uses photon-counting detectors that separately register the energy of each photon. These offer a smaller pixel size and do not require the coating of each detection pixel by an optical reflector, which accounts for a 2- to 3-fold higher resolution than conventional CT (approximately 250 µm). In a recent clinical study photon-counting coronary CT led to significantly improved image quality (detectability indexes 2.3-fold to 2.9-fold higher) at a comparable radiation dose in 14 patients who underwent both standard energy-integrating detector dual-layer cCTA and photon-counting CT . These rApart from hardware improvements, computational advances with iterative or model-based reconstruction algorithms have improved image quality and reduced radiation dose ,49,50. Since invasive FFR is the current reference standard to assess the hemodynamic relevance of coronary stenosis, great effort has been directed into implementing a non-invasive cCTA-derived FFR value that can be interpreted similarly to its invasive equivalent ,51. Different techniques have evolved that are either applied in a core lab or on-site. Models based on fluid dynamics are computationally demanding, whereas recent advances in machine learning enabled faster on-site calculation ,52,53. TA number of studies show the discriminatory power of CT-FFR for the prediction of hemodynamic relevance to be superior to cCTA alone when compared to invasive FFR or stress CMR, improving diagnostic accuracy and especially specificity ,54,55,56Another example of cCTA exceeding the limits of pure anatomical testing for CAD is CT perfusion (CTP). The anatomical visualization of coronary arteries by cCTA is followed by vasodilator stress and repeated CT imaging to assess perfusion deficits in patients where cCTA alone was not able to exclude hemodynamically relevant stenosis . CTP mayExtensive advances have also been made in the field of CMR introducing a more robust imaging acquisition, new acquisition sequences, and vast post-processing possibilities. The relatively long acquisition times remain a modality-dependent issue but decreased considerably. For example, acquisition time of cine images was reduced by ~80% through the introduction of compressed sensing . In addiThe introduction of myocardial strain measurements boosted the assessment of myocardial function with superior predictive power than ejection fraction . MyocardImproved resolution achieved by combining undersampling and motion correction has also allowed obtaining sub-millimeter isotropic CMR images. In proof-of-concept studies, the derived coronary lumenography visualizes coronaries at a quality that is sufficient to screen for coronary anomalies and even (to some degree) stenoses ,82.In stress CMR, the introduction of quantitative rather than qualitative perfusion imaging has decreased reader dependency and enabled a faster and simpler analysis . FurtherRisks of both cCTA or stress CMR are linked to the technique itself, the application of contrast agent or necessary stress medication in the course of the exam.CMR is a non-ionizing technique working with a static magnetic field and radiofrequency pulses that may be causative for (reversible) headaches or vertigo . BesidesAcute adverse reactions can occur after both CT and CMR contrast agent application, although slightly more frequently in Iodine-based CT (0.2–0.4%) than Gadolinium-based MRI (0.1–0.18%) contrast agents ,95,96,97Apart from contrast agents, both cCTA and stress CMR usually require specific medication. For cCTA, beta blockers and glyceryl trinitrate (GTN) are used to achieve adequate heart rate control, if necessary, and to dilate coronary arteries prior to the exam . These m2A receptor [For CMR, vasodilator stress CMR with regadenoson, dipyridamole, or adenosine is the current standard for patients with suspected CAD. Of those, regadenoson is best tolerated due to its high specificity to the Areceptor . Common receptor . Patientreceptor . Althougreceptor . As an areceptor . NeverthIn summary, both cCTA and vasodilator stress CMR exhibit excellent safety profiles.Over the last decade, cCTA has evolved from an imaging modality, which was mainly used to exclude significant CAD in patients at a rather low risk, to a valuable method for risk stratification and therapeutic decision making resulting in a significant improvement in patient outcome. Image quality has improved, radiation exposure has decreased, and anatomical information can be complemented by information on the hemodynamic relevance of stenoses. Consequently, it is recommended as a first-line imaging modality in patients with stable chest pain in the current guidelines ,4,108. HHowever, several factors limit the use of cCTA and the most relevant are summarized in Second, although assessment of coronary stents has improved, assessment of in-stent stenosis and their functional assessment with CT-FFR is hampered and in some cases even not possible. In addition, the evaluation of patients with severe and extensive coronary calcifications, coronary artery occlusion  or previous coronary artery bypass graft surgery can be challenging. In CT-FFR negative stenoses, additional factors such as symptom burden, current medication and comorbidities must be considered to decide whether further testing might be necessary. Here, the cCTAs and CT-FFRs blind spot concerning the presence of the coronary microvascular disease has to be mentioned . CTP migCAD evaluation by stress CMR is an important imaging modality in the diagnosis and risk stratification and, thus, is represented in current guidelines ,3,108.Of note, the concept of inducible ischemia is not yet fully understood and is the subject of current discussions ,112. TheIn patients with myocardial scarring, the viability of ischemic regions and therefore the potential benefit of revascularization is important. In these patients, the diagnostic assessment goes beyond stenosis evaluation alone and CMR can provide information on both, ischemia and viability, in a single examination. Its ability to characterize myocardial tissue allows for differential diagnostics in patients with MINOCA as CMR can identify various etiologies such as myocarditis, tako-tsubo syndrome, and thromboembolic myocardial infarction. The visualization/quantification of arrhythmogenic substrate of scar and exact calculation of left-ventricular ejection fraction with CMR is also useful in clinical practice to decide for or against an implantable cardioverter-defibrillator in patients with ischemic and non-ischemic heart disease .Regarding the choice for the appropriate imaging modality aside from the individual patient site-specific conditions should be taken into consideration. Especially, the diagnostic quality of cCTA depends on the scanner model. On a global scale, ≤64 slice CT detectors are still widely used and the possibilities for CTP or CT-FFR are limited in most areas due to technical and reimbursement restrictions . As mentApart from hardware, local staff expertise may also be different as not all sites offer cCTA and CMR. Reimbursement is different in every country and influences waiting times, local expertise, and referral choice . The totThe strength of cCTA evidently lies in the identification of additional at-risk patients, in which preventive approaches  are beneficial. Here, the fact that >50% of all myocardial infarctions are caused by non-obstructive plaques has to be emphasized, so the initiation of preventive treatment is key in influencing patient outcome ,118. HowThe potential to detect early stages of CAD makes cCTA the diagnostic modality of choice for a large proportion of patients with suspected CAD, taking into account that 75% of patients in the SCOT-HEART trial had no obstructive CAD, despite a high prevalence of cardiovascular risk factors . Although this review focuses on CAD patients, cardiac and pulmonary comorbidities also play an important role in the selection of the appropriate modality. While heavy smokers suffering from dyspnea may benefit from a combined assessment of the coronary arteries and the lungs, younger patients with a differential diagnosis of myocarditis or cardiomyopathy may benefit from myocardial tissue characterization offered by a CMR. In general, for CAD evaluation, cCTA is favorable in patients that are younger, have few comorbidities, no known cardiac disease and are currently not taking preventive medication, whereas stress CMR is more appropriate in older patients, in those with known CAD, already taking ASA/statin and in need of regular follow-ups. Of note, both cCTA and stress CMR can be used as a downstream diagnostic testing method in patients with an inconclusive test result of the primarily chosen modality.Thus, it is important to view cCTA and stress CMR as mostly complementary diagnostic modalities, each possessing strengths and limitations but both providing valuable and accurate diagnostic information to guide physicians’ treatment decisions. Physicians should strive for an individual approach in each patient with regard to patient-related factors and patient wishes considering each modality’s strengths and limitations.


Hypoxia is a key component in several neurological diseases. Hypoxia in pathological conditions leads to neuronal loss, glial cell activation as well as blood brain barrier (BBB) disturbance, and disruption. The activation of glial cells (both astrocyte and microglia) produces a complex array of inflammatory cytokines and are the primary focus of neuroinflammation in hypoxia and ischaemia. It is further evident that ‘neuroinflammation’ is not a single stereotyped set of processes, but can differ in several important ways, dependent upon both initiating and subsequent stimuli. Hypoxia-potentiated neuroinflammation, and neuroinflammation occurring under hypoxic conditions, both warrant specific study to determine whether these differ from other forms of neuroinflammation.Chen et al. have surveyed databases of gene and protein interactions for stroke-related targets, and attempted to reconcile these with putative targets of various plant extracts. This approach may prove useful in identifying plant-derived molecules/compounds for further investigation in hypoxic/ischaemic models, and prioritising them, based on likelihood of efficacy. A valuable proof-of-concept advance in techniques for neuroimmunomodulation is demonstrated by Eyford et al., who harness a peptide derivative of melanotransferrin to deliver siRNA across BBB. Using an in vivo stroke model (tMCAO), this ‛nanomule’ was shown to deliver anti-Nox4 siRNA into brain parenchyma, with Nox4 knockdown successfully achieved. Importantly, this intervention resulted in smaller infarct size and improved neurological function in the mice following tMCAO.This Research Topic of Frontiers in Molecular Biosciences collates several reports of neuroimmunomodulation in hypoxia and ischaemia. Neuroinflammation is increasingly recognised as key to the progress of pathological events in ischaemic stroke, with both detrimental and beneficial effects reported . IdentifDisruption of BBB can result in profound neurological functional deficits, and commonly occurs in cerebral ischaemia. Jiao et al. report MCC950, a selective inhibitor of NLRP3 inflammasome, reduces the inflammatory response and improves multiple measures of neurological function in a mouse model of SCI. They discovered that MCC950 blocked NLRP3 inflammasome assembly and alleviated downstream neuroinflammation process, such as NLRP3-ASC and NLRP3-Caspase-1 complexes, as well as the release of pro-inflammatory cytokines TNF-α, IL-1β, and IL-18. We believe that this study might contribute toward the development of new treatments for SCI. Huang et al. found Patchouli Alcohol (PA), a sesquiterpene alcohol found in patchouli, reduced hyperpermeability of the blood-spinal cord barrier by reducing the loss of tight junctions and endothelial cells. They further proved that PA exerts neuroprotective effects in the SCI mice.Two original research articles contribute to find and prove some promising candidates for spinal cord injury (SCI) treatment. In conclusion, this Research Topic explores some recent advances in the field of neuroinflammation in Hypoxia/Ischaemia and extends to development of novel protective methods. Collectively, these articles emphasize the point that hypoxia/ischemia induced CNS injury is associated with increased neuroinflammation and highlight the important role of neuroinflammation and immunity in the development of hypoxia/ischemia-related diseases. We hope that this Research Topic provides readers with a glimpse of some of the exciting research and that it stimulates new ideas and future progress. Given the recent technological developments in neuroscience and immunology, we are convinced that the next decade will see a flurry of activity in this exciting field.


This study aimed to examine the association between early childhood resilience profiles and later school outcomes (academic achievement and school involvement) among children in the U.S. child welfare system. This study compared 827 children aged 3–5 years in three latent profile groups  to their baseline profiles using data from the National Survey of Child and Adolescent Well-Being (NSCAW-II). At the three-year follow-up, children with low emotional and behavioral resilience profiles and children with the multi-domain resilience profile had significantly higher basic reading skills, reading comprehension, and math reasoning compared to children with low scores on the cognitive resilience profile. Furthermore, children with the multi-domain resilience profile had significantly higher levels of emotional school engagement than did those with the low emotional and behavioral resilience profile and considerably higher levels of behavioral school engagement compared to those with the low cognitive resilience profile. The findings highlight the persistent effects of early resilience into the later childhood years. Moreover, our results suggest the need for early identification of and intervention for children with low cognitive or emotional/behavioral resilience during the preschool years to promote academic success and school engagement during the school-age years. Building resilience during early childhood has long-lasting positive effects on an individual’s well-being over the life course. There is a growing body of research on resilience among children who have experienced childhood maltreatment. Recently, an emerging line of research has utilized person-centered approaches  to explore patterns of resilience in populations with a history of childhood trauma and maltreatment. Although recent research has made remarkable headway towards identifying resilience patterns in maltreated children, how these patterns affect later developmental functioning, such as school outcomes, remains unclear and understudied. Examining school outcomes related to early childhood resilience  among child-welfare-involved children as this important developmental period remained overlooked in the maltreatment and resilience profile literature . Using aDespite emerging research exploring distinct configurations of resilience among children with maltreatment histories, including our work of three early childhood resilience profiles, little research has examined how resilience profiles in early childhood are associated with distal outcomes such as school outcomes at a later developmental stage. School context and outcomes are critical to examine as they have important short- and long-term implications for elements of quality of life, including child self-esteem/self-worth, mental and behavioral well-being, and later employment status and job satisfaction during adulthood ,29,30,31To date, most studies have examined resilience profiles as an outcome and have focused on identifying predictors or characteristics associated with resilience profiles ,25,26. CBuilding upon our prior work on early childhood resilience profiles , we examThis secondary data analysis used the data from the National Survey of Child and Adolescent Well-Being , which cSD = 0.82). Just under half of the children (46.1%) were girls; 39.6% were non-Hispanic White, 31.4% were non-Hispanic Black, 24.0% were Hispanic, and 5.0% were other races, including American Indian, Asian, Native Hawaiian/Pacific Islander, and multiple races. Regarding caregivers’ characteristics, 25.8% of primary caregivers had not completed high school, and about 78.1% reported household income below the 200% federal poverty line.Descriptive statistics of all study variables are shown in Resilience was conceptualized as a multidimensional construct and measured using multiple instruments in Wave 1 (baseline). Specifically, cognitive resilience, social resilience, emotional resilience, and behavioral resilience were assessed and operationalized as competence and positive functioning in the domains of cognitive, social, emotional, and behavioral development, respectively, after exposure to adversity ,41. ReceAt the 3-year follow-up, the Woodcock–Johnson III Tests of Achievement  was employed to evaluate children’s academic achievement. Three subscales of WJ-III, the Letter–Word Identification scale, the Passage Comprehension scale, and the Applied Problems scale, were used to capture children’s basic reading skills, reading comprehension, and math reasoning, respectively. For each subscale, the standard sum scores of the items were used, with higher scores representing better achievement/performance.At the 3-year follow-up, children’s school engagement was evaluated using the Drug-Free Schools Outcome Study Questions (DFSCA). This scale has been widely used to measure school engagement among children involved in the child welfare system (α = 0.72). Two aspects of school engagement were assessed based on a study that found the two-factor structure of the scale to fit the data well . SpecifiDemographic variables, including children’s age, sex , and race/ethnicity, were controlled for in the present study. Child race/ethnicity was a categorical variable and was dummy coded into White, Hispanic, and Other, using Black as a reference group. Other information was added as covariates, including child abuse , neglect , poverty , and caregiver’s highest education level .A latent profile analysis (LPA) was previously conducted to examine heterogeneity in resilience among children involved with the child welfare system and revealed three distinct resilience profiles  . Buildinp < 0.001), reading comprehension , and math reasoning , compared to children with the low cognitive resilience profile. Similarly, children with the low emotional and behavioral resilience profile showed significantly higher levels of basic reading skills , reading comprehension , and math reasoning , compared to children with the low cognitive resilience profile. There were no significant mean differences in academic achievement between children with the multi-domain resilience profile and children with the low emotional and behavioral resilience profile.To address our research question, we examined how the three resilience profiles at baseline—low emotional and behavioral resilience 20%), low cognitive resilience (24%), and multi-domain resilience (56%) [0%, low cp = 0.041) compared to children with the low emotional and behavioral resilience profile. Additionally, children with the multi-domain resilience profile at baseline showed significantly higher levels of behavioral school engagement  compared to children with the low cognitive resilience profile. There were no other significant mean differences in school engagement among the three resilience profiles. The effects of covariates on academic achievement and school engagement distal outcomes are shown in Regarding school engagement, children with the multi-domain resilience profile at baseline showed significantly higher levels of emotional engagement  in early childhood predict future school outcomes, including academic achievement and school engagement, three years later, in children involved with the child welfare system. The study findings provide new insight into the long-term effects of early childhood resilience on later development among children involved with the child welfare system.Our hypothesis that children with the multi-domain resilience profile would have greater academic achievement compared to those with the low cognitive or emotional/behavioral resilience profile was partially supported. Children with the multi-domain resilience profile had greater academic achievement compared to those with the low cognitive resilience profile but did not do any better or worse than those with the low emotional and behavioral resilience profile. Interestingly, not just children with the multi-domain resilience profile, but also children with the low emotional and behavioral resilience profile showed significantly higher levels of basic reading skills, reading comprehension, and math reasoning compared to those who had the low cognitive resilience profile at baseline. In other words, children who showed low cognitive competence during early childhood continued to show those lower skills as they entered school. These findings corroborate the broader literature that documents a link between early cognitive skills and later academic performance among high-risk children, including children in low-income families  and chilOverall, resilience profiles during the preschool years were not a strong predictor of the level of school engagement at the three-year follow-up. It should be noted that there is still some ambiguity about the factor structure of the school engagement measure  used in this study . Some stNonetheless, there were two significant findings for school engagement. First, children with the multi-domain resilience profile showed significantly higher levels of emotional school engagement compared to those with the low emotional and behavioral resilience profile. Our first finding is partially consistent with prior studies that measured emotional school engagement and other areas associated with child internalizing and externalizing behaviors ,59,60. TOur second significant finding related to school engagement revealed that children with the multi-domain resilience profile showed significantly higher levels of behavioral school engagement than those with the low cognitive resilience profile did. This finding is aligned in part with previous literature that has found that language and behavior problems often co-occur  and thatGiven their struggles in academic performance and behavioral engagement, it is somewhat surprising that children with the low cognitive resilience profile did not display significantly lower emotional engagement, especially considering they displayed lower social functioning at baseline. This could be explained by the significant change in demands from preschool to school age . While lLike other empirical studies, this study is not without its limitations. First, the use of a sample comprising children involved with the child welfare system due to child maltreatment may limit the generalizability of the study results. Second, despite the temporal order of measuring resilience at baseline and school outcomes 3 years later, any firm causal inference may not be made, because other, unobserved factors may play a role in the associations between these variables. Third, although it is a strength that we utilized multiple indicators and measures of resilience to identify resilience profiles, our measures of cognitive resilience were heavily focused on language ability and did not assess other aspects of cognitive ability, such as reasoning, remembering, problem solving, or decision making. Future research may benefit from including more comprehensive measures of cognitive resilience.The study’s findings offer important insights into practice and policy development to promote the educational well-being of children with a history of CPS involvement. Considering that our results indicated less optimal school outcomes among children who had low cognitive resilience or low emotional and behavioral resilience during early child-hood, it is important to target these children for early identification and intervention to ensure their academic success and school engagement during the school-age years. For instance, it is crucial to test whether interventions, such as Dialogic Reading , designeWe examined the longitudinal associations between early childhood resilience profiles  and school outcomes  among children involved with the U.S. child welfare system. Overall, the study results indicated the lasting effects of early resilience into the later childhood years, demonstrating the virtuous cycles of resilience. Compared to children with the multi-domain resilience profile, children with the low emotional and behavioral resilience profile had comparable academic achievement and were behaviorally engaged in school but displayed lower emotional engagement. In contrast, children with the low cognitive resilience profiles had poorer academic achievement and were not behaviorally engaged, yet still displayed high levels of emotional engagement. Collectively, our findings may suggest that while academic achievement and behavioral engagement may be closely connected, emotional engagement may depend on other factors outside of how well a child is doing in school or how behaviorally engaged they are. It should be noted that multiple mechanisms that were not examined in the study, such as social ecological strengths and resources available during the preschool years, may have contributed to better school outcomes . Future


Enterococcus species, and is associated with poor transplant outcomes. Graft-versus-host disease (GvHD) is a frequent complication of allogeneic HCT caused by immunologic disparity between donor and host cells and results in tissue damage and inflammation. Microbiota injury is particularly pronounced in allogeneic HCT recipients who go on to develop GvHD. At present, manipulation of the microbiome for example, via dietary interventions, antibiotic stewardship, prebiotics, probiotics, or fecal microbiota transplantation, is widely being explored to prevent or treat gastrointestinal GvHD. This review discusses current insights into the role of the microbiome in GvHD pathogenesis and summarizes interventions to prevent and treat microbiota injury.Many patients with hematological malignancies, such as acute myeloid leukemia, receive an allogeneic hematopoietic cell transplantation (HCT) to cure their underlying condition. Allogeneic HCT recipients are exposed to various elements during the pre-, peri- and post-transplant period that can disrupt intestinal microbiota, including chemo- and radiotherapy, antibiotics, and dietary changes. The dysbiotic post-HCT microbiome is characterized by low fecal microbial diversity, loss of anaerobic commensals, and intestinal domination, particularly by  Patients with steroid-refractory acute GvHD have a dismal prognosis.6 In search of new therapeutic strategies to improve the outcome for allogeneic HCT recipients, the intestinal microbiome has rapidly gained attention over the past decade. This review focuses specifically on the role of the intestinal microbiome in the development of GvHD and speculates on pre-transplant strategies to preserve a healthy microbiome or post-transplant therapies that target the gut flora to prevent or treat GvHD.Allogeneic hematopoietic cell transplantation (HCT) is used as consolidation therapy for many hematologic malignancies with the goal to induce a graft-versus-leukemia or graft-versus-lymphoma (GvL) response via alloreactive donor lymphocytes that eliminate residual tumor cells of the patient. These alloreactive lymphocytes, however, often also target the recipients’ tissues, inducing an inflammatory syndrome known as graft-versus-host disease (GvHD).7 Chronic GvHD is predominantly a sclerosing disease that can virtually affect any organ. Allogeneic HCT recipients routinely receive prophylactic immunosuppression, comprising (a combination of) anti-thymocyte globulin (ATG), post-transplantation cyclophosphamide, calcineurin inhibitors, mycophenolic acid, or methotrexate to prevent GvHD but despite these efforts, acute GvHD develops in 30–50% of the allogeneic HCT recipients.GvHD is classified into acute GvHD that develops early (<100 days) after allogeneic HCT, and late-onset acute or chronic GvHD that are considered late (>100 days) transplant-related complications. Acute GvHD primarily involves the skin, liver, and gastrointestinal tract, where symptoms typically include skin rash, jaundice, nausea, cramping, and diarrhea.7–9 Chemo(radio)therapy preceding allogeneic HCT  induces tissue damage and inflammation of the intestinal mucosa (mucositis), thereby weakening the intestinal mucosal barrier and increasing the risk of bacterial translocation. Together, this leads to the release of damage-associated molecular patterns (DAMPs) and pathogen-associated molecular patterns (PAMPs) which activate hematopoietic and non-hematopoietic antigen-presenting cells (APCs). These APCs produce inflammatory cytokines and promote the priming and differentiation of donor immune cells. Activated neutrophils and alloreactive lymphocytes, including effector cells that are recruited into the tissues, also release inflammatory cytokines that enhance tissue damage and inflammation. It is assumed that chronic GvHD and the curative GvL response develop along the same pathways.10In the classical view of acute GvHD pathophysiology, alloreactivity, and tissue damage are considered key driving factors .7–9 Chem11 Gut microbiota contributes to a tolerant intestinal mucosal immune system for example, via the degradation of dietary polysaccharides into short-chain fatty acids (SCFA), such as butyrate, propionate, and acetate, which have an immunomodulatory function.12 SCFA stimulates the production of anti-inflammatory interleukin (IL)-10 by regulatory T cells  and IL-22 by both CD4+ T cells and innate lymphoid cells (ILC), which enhance epithelial integrity.13–15 SCFA also promote immunoglobulin A (IgA) secretion by B cells that provides a first line of defense against infiltrating pathogens.16 Furthermore, SCFA and other bacterial metabolites such as polyamines enhance gut barrier function by inducing Goblet cells to produce mucus and by stimulating the production of endothelial cell tight junction proteins.18In steady-state conditions, a diverse collection of anaerobic commensal bacteria prevents the outgrowth of potential pathogens, produces essential nutrients, and orchestrates intestinal homeostasis through reciprocal interactions with the mucosal immune system.19 In 2012, it was reported that microbial diversity is reduced early after allogeneic HCT,20 and that this loss of diversity preceded the development of acute GvHD.21 A larger, prospective study later demonstrated that patients who maintained microbiota diversity had a significantly reduced probability of death due to GvHD or opportunistic infections, which translated into a better overall survival than patients who experienced loss of microbiome diversity.22 This association between low microbial diversity and survival disadvantage, more specifically higher transplantation-related and GvHD-related mortality, was recently confirmed in an international, multicenter study that included over 8000 samples from 1362 unique patients.23 Interestingly, this association was less apparent in patients receiving a lymphocyte-depleted allograft. The presence of alloreactive (donor-derived) adaptive immune cells thus appears to be a major contributor to the mortality associated with microbiota disruption. Indeed, in a murine allogeneic HCT model, it was demonstrated that radiotherapy-induced bacterial translocation leads to the recruitment of neutrophils and then, via the activation of alloreactive T cells, to acute GvHD.24Advances in sequencing technology have allowed rapid and large-scale exploration of the compositional and to some extent functional configuration of the microbial communities in the human gut. This has initiated an impressive number of studies focusing on the relationship between microbiota and human health and led to the awareness that damage to the enteric bacterial population is associated with a variety of immune-mediated diseases, including GvHD.25 Moreover, allogeneic HCT recipients who survive the first 1–2 years after transplantation maintain a life-long increased risk for cardiovascular events and secondary malignancies. Loss of microbiome diversity is associated with a risk of cardiovascular events, malignancies, and poor health in general.26 In a cross-sectional study, it was demonstrated that the microbiome of allogeneic HCT survivors who developed secondary malignancies was more perturbed than long-term survivors without secondary malignancies.27 It is safe to assume that long-term complications in allogeneic HCT survivors are related to microbiome damage encountered early after transplantation, but evidence is lacking thus far.Loss of microbiome diversity may play a role in other aspects complicating transplantation outcomes that were noted in the past but less well understood. For example, obesity is associated with adverse outcome after allogeneic HCT. With the help of a murine HCT model, it was demonstrated that obesity, with its associated lack of microbiome diversity, leads to a pro-inflammatory intestinal milieu and an increased risk for GvHD.29 The post-HCT intestinal microbiome commonly features low diversity, decreased abundance of commensals, and a high frequency of Enterococcus, Streptococcus, or Proteobacteria colonization compared to the microbiome of healthy individuals.23 A number of factors have been linked to early microbiota injury during allogeneic HCT. Allogeneic HCT recipients typically receive multiple rounds of chemotherapy, sometimes combined with total body irradiation (TBI), to reduce tumor burden and eliminate the recipients’ adaptive immune system to prevent graft rejection. The toxicity of both therapies has been implicated in the loss of microbial diversity and modulation of microbiome composition.30–36 This toxicity may act directly on gut microbes, and indirectly for example, through the death of Paneth cells. Paneth cells are secretory cells located at the intestinal crypt base where they produce antimicrobial factors to preserve host-microbial homeostasis.37 Patients with acute GvHD have reduced numbers of intestinal Paneth cells, while rescue of Paneth cells via treatment with glucagon-like-peptide-2 restored microbiome damage in a GvHD mouse model.38Intestinal microbial diversity starts to decrease prior to transplantation, during the phase of remission-induced chemotherapy, and continues to decline in the first days after transplantation .20,28,2939 while remission-induction and conditioning chemotherapy regimens frequently lead to neutropenia. Prophylactic antibiotics are therefore routinely prescribed to prevent systemic infections, and patients receive empiric broad-spectrum antibiotics during episodes of neutropenic fever. In a retrospective study, the early administration of broad-spectrum antibiotics  led to a reduction in the abundance of Clostridiales and was associated with higher transplant-related mortality.40 Furthermore, the use of certain antibiotics was associated with a higher incidence of intestinal colonization and subsequent bloodstream infections by the respective dominating species.41 Antibiotics are, however, not the only drugs that can negatively impact microbiome diversity. Almost any drug can disturb the microbial community, as was demonstrated in two large observational studies in the healthy population of The Netherlands and Belgium.43 Commonly used drugs like anti-emetics, proton pump inhibitors, antidepressants, and opiates were demonstrated to affect the composition of the microbiome at a population level, and are therefore likely to impact the microbiome in allogeneic HCT recipients.Most studied to date, however, is the microbiome-damaging effect of antibiotics, generally considered the culprit (but certainly not the only cause) of microbiome damage in allogeneic HCT recipients. Exposure to antibiotics is high and prolonged in allogeneic HCT recipients. Chemotherapy-induced mucositis of the oral cavity and gastrointestinal tract increases the risk of bacterial translocation,45 After allogeneic HCT, this reciprocal interaction between the immune system and the microbiome comes under significant pressure as reconstitution of the donors’ adaptive immune system after transplantation typically takes months to years. This may significantly delay the recovery of the microbiome. In solid organ transplant recipients, the use of immunosuppressive drugs was the single most important determinant of microbiome damage, that lasted for years after transplantation.46 In allogeneic HCT, the microbiome was demonstrated to affect the recovery of innate and adaptive immunity in general and T cell recovery specifically, reinforcing the reciprocal nature of the interaction between the immune system and the microbiome.48Another important factor that disturbs intestinal homeostasis may be the prolonged immunodeficiency that is characteristic of allogeneic HCT. The microbiome is shaped by microbes encountered from birth onwards and the interaction of these microbes with the developing immune system of the infant.50 The oral intake of allogeneic HCT recipients is frequently diminished due to the loss of appetite, pain, and nausea that is induced by mucositis, and this often requires parenteral feeding to ensure sufficient caloric intake.51 In two small cohorts, parenteral feeding was inferior to enteral nutrition in preserving microbiota diversity and composition.53 Moreover, two retrospective studies showed that parenteral nutrition was associated with a higher incidence of gastro-intestinal GvHD and lower survival rates compared to patients receiving adequate enteral nutrition.55Finally, diet has a major influence on the constituents of the intestinal microbiome.56Collectively, these factors can drastically alter the gut microbiota community and disrupt intestinal homeostasis. The insights obtained from the different studies mentioned above led to a revised model of GvHD pathophysiology, where the importance of the gut microbiota as a mediator of immunologic tolerance and keeper of gut homeostasis was incorporated .56FigurEnterococcus genus, which in the healthy microbiome represents only a very small minority ,57 might be the best-studied pathobiont in relation to acute GvHD. Enterococci in particular, E. faecium and E. faecalis, are a prevalent cause of infection58 and, even more importantly in the context of GvHD, they have emerged as potent stimulators of intestinal inflammation.59 For example, E. faecalis compromises gut barrier integrity,60 induces the production of inflammatory cytokines,61 and causes colitis in IL-10 deficient mice.62 E. faecalis also induced donor T cell activation in a mouse GvHD model, suggesting a direct causal relationship.63 The frequency of intestinal Enterococcus domination is high in allogeneic HCT recipients and peaks at 1 week after HCT.23 In particular, there is a high abundance of E. faecium observed, which correlates with more severe acute GvHD and reduced survival.63 Other commonly dominating genera in allogeneic HCT recipients are Lactobacillus28 and Streptococcus. Streptococcus abundance is associated with induction of pro-inflammatory cytokines64 and has been shown to impair the growth of commensal bacteria in the oral microbiota.65Streptococcus infections are more abundant in allogeneic HCT recipients with GvHD and are associated with higher mortality.66–68With the recognition of the intestinal microbiome as an important factor in GvHD pathogenesis, the question was raised whether gut homeostasis is regulated by the community as a whole, or by certain specific species. A number of studies demonstrated that certain species are in particular associated with worse outcome. The facultative anaerobe Barnesiella69 and Lactobacillus Johnsonii21 suppressed the outgrowth of Enterococcus species and thereby protect microbial homeostasis. A direct association with protection against lethal GvHD in allogeneic HCT recipients has been observed with the presence of Blautia, a genus from the Clostridia class.70 Preservation of Blautia was associated with reconstitution of gut epithelium protective mucosal-associated invariant T (MAIT) cells, which correlated with less acute GvHD and improved survival.72 An earlier study demonstrated that a mixture of 17 rationally selected Clostridia strains induced accumulation of Tregs73 and mitigated GvHD in mice,74 suggesting that this class of bacteria are important mediators in preserving intestinal homeostasis. One of the underlying mechanisms could be SCFA production; several Clostridia species, including Blautia spp., are well-known butyrate producers. A recent study reported that the fecal SCFA concentration is reduced in acute GvHD patients and correlates to the severity of disease.75 The concentration of circulating SCFAs also decreased, specifically in patients that go on to develop chronic GvHD.76 Loss of SCFA-producing bacteria and subsequent reduction of their beneficial metabolites thus appears to be important to limit conditioning or GvHD-mediated damage.74Other species have been attributed to protective and/or anti-inflammatory capacities. For example, Blautia, could be of importance to prevent or treat acute GvHD. Given the many factors that affect the microbiome, there are a number of ways to prevent or treat microbiome damage during allogeneic HCT . Alternative strategies to prevent dysbiosis include compounds that neutralize antibiotic residues once they enter the colon81 and bacteria-specific antibody-antibiotic conjugates.82 These compounds have, however, not been tested in the context of allogeneic HCT. Novel approaches, such as CRISPR-Cas9 phagemids targeting pathogens by producing sequence-specific antimicrobials, are being developed.83The most obvious first step is to limit damage to the intestinal microbiota. Antibiotic stewardship can play an important role in sparing the obligate anaerobe commensal community. In a retrospective study that included 161 allogeneic HCT recipients, it was demonstrated that the use of rifaximin preserved microbiota diversity, even when followed by systemic antibiotics.84 Data obtained from mice and men demonstrate that Enterococcus domination is fed by dietary lactose, suggesting that lactose intake should be limited early after allogeneic HCT to prevent Enterococcus domination and acute GvHD.63 Thus far, reports on specific dietary interventions in allogeneic HCT are lacking but several studies are underway .In healthy individuals, the effect of dietary intake on the microbiome is high and likely depends on the individual microbiome.85 Commercially available probiotics typically contain Lactobacillus and Bifidobacterium strains. In allogeneic HCT mouse models, administration of Lactobacillus rhamnosus GG resulted in less GvHD and increased survival.86 However, these findings were not reproducible in a study including allogeneic HCT recipients.87 In addition, the use of probiotics does raise concern in allogeneic HCT because of the risk of infectious complications.92 More importantly perhaps is the observation that probiotic therapy delayed rather than enhanced recovery of microbiome damage in healthy human volunteers.93 This raises serious questions regarding the efficacy of such therapy in humans.94 A rationally selected consortium of bacterial strains for example, containing Clostridia species, could offer an alternative for the commercial probiotics that are currently available. While further research might be needed to determine the optimal composition, the potential of bacterial consortia has been reported in a number of pre-clinical studies.96When microbiome damage cannot be prevented, ‘health-promoting’ species can be selectively or unselectively reintroduced. Probiotics are viable microorganisms that can be directly introduced in an attempt to restore bacterial diversity.97 and is now applied to treat recurrent Clostridioides difficile infection.98 FMT resulted in restoration of microbiota diversity in patients who had received an allogeneic HCT.100 A few case reports suggested efficacy of FMT in steroid-refractory GvHD.101–103 We performed a prospective, single-arm study including 15 steroid-dependent or steroid-refractory GvHD demonstrating complete remission of GvHD in 10 patients.104 Interestingly, remission was sustained even after cessation of immunosuppressive therapy in 6 out of 10 responders. In this study, the use of antibiotics seemed associated with failure of FMT. Other, larger trials are underway and the results of these trials are expected soon (NCT03359980). Importantly, transfer of pathogens, including multidrug-resistant bacterial strains105 and infectious viruses,106 has been described, emphasizing the importance of careful selection and screening of FMT donors.107Unselective introduction of bacterial species can be achieved by fecal microbiota transplantation (FMT). Donor FMT was first used in 1958 to treat colitis108 and postbiotics are the bacterial components and metabolites that exert beneficial effects on other microbes, the gut epithelium, and the immune system.109 Given the reciprocal effects of pre- and postbiotics on homeostasis and composition of the microbiome, and on health-promoting factors produced by the microbiome, this distinction is somewhat arbitrary however.84A few groups have studied the effects of supplementation of microbiome products in allogeneic HCT recipients.110 Adequate intake of glutamine, fiber, oligosaccharides and resistant starch mixtures decreased diarrhea, mucositis, and bacteremia, and improved survival.111–113 Whether pre- and postbiotic therapy can restore healthy microbial populations, or whether additional support, for example in the form of FMT, is needed remains unanswered.Finally, not the microbial populations themselves but the metabolites they produce could be replenished. Prebiotics are defined as ‘substrates that are selectively utilized by host microorganisms conferring a health benefit’,Efforts of the last couple of years have revealed important associations between the status of the gut microbiota and the prognosis of allogeneic HCT recipients. Outlines of the dysbiotic fecal microbiome in these patients have been drawn and the first careful steps have been taken to apply this knowledge in a clinical, interventional setting. Moving forward, there are several questions that will need to be answered.48 This is in contrast to observations in otherwise healthy individuals, in whom a single insult to the microbiome (e.g. course of antibiotics) induces microbiome damage that is reversible, and warrants further investigation into the causes of the irreversible nature of transplantation-related microbiome damage.93 Possible explanations could be persisting adaptive immunodeficiency or the permanent deletion of specific bacterial, archaeal, or viral species or populations that have a detrimental impact on microbiome homeostasis.45 With this knowledge, randomized controlled trials can be designed to prevent permanent damage to the microbiome. Additionally, we have to gain more insight into the mechanisms by which intestinal microbiota influence transplant-related complications to design more specific and tailor-made interventions.First, a better understanding of the resilience of the microbiome is needed. Recent reports suggest that microbiome damage incurred upon transplantation is not reversible and persists over time.Taken together, better care for the microbiome before and after allogeneic HCT, in addition to early interventions to repair microbiome damage after transplantation may significantly reduce transplantation-related morbidity and mortality, and improve allogeneic HCT outcomes in the short and long run.