Dynamic establishment and maintenance of the human intestinal B cell population and repertoire following transplantation in a pediatric-dominated cohort.

Introduction: It is unknown how intestinal B cell populations and B cell receptor (BCR) repertoires are established and maintained over time in humans. Following intestinal transplantation (ITx), surveillance ileal mucosal biopsies provide a unique opportunity to map the dynamic establishment of recipient gut lymphocyte populations in immunosuppressed conditions. Methods: Using polychromatic flow cytometry that includes HLA allele group-specific antibodies distinguishing donor from recipient cells along with high throughput BCR sequencing, we tracked the establishment of recipient B cell populations and BCR repertoire in the allograft mucosa of ITx recipients. Results: We confirm the early presence of naïve donor B cells in the circulation (donor age range: 1-14 years, median: 3 years) and, for the first time, document the establishment of recipient B cell populations, including B resident memory cells, in the intestinal allograft mucosa (recipient age range at the time of transplant: 1-44 years, median: 3 years). Recipient B cell repopulation of the allograft was most rapid in infant (<1 year old)-derived allografts and, unlike T cell repopulation, did not correlate with rejection rates. While recipient memory B cell populations were increased in graft mucosa compared to circulation, naïve recipient B cells remained detectable in the graft mucosa for years. Comparisons of peripheral and intra-mucosal B cell repertoires in the absence of rejection (recipient age range at the time of transplant: 1-9 years, median: 2 years) revealed increased BCR mutation rates and clonal expansion in graft mucosa compared to circulating B cells, but these parameters did not increase markedly after the first year post-transplant. Furthermore, clonal mixing between the allograft mucosa and the circulation was significantly greater in ITx recipients, even years after transplantation, than in deceased adult donors. In available pan-scope biopsies from pediatric recipients, we observed higher percentages of naïve recipient B cells in colon allograft compared to small bowel allograft and increased BCR overlap between native colon vs colon allograft compared to that between native colon vs ileum allograft in most cases, suggesting differential clonal distribution in large intestine vs small intestine. Discussion: Collectively, our data demonstrate intestinal mucosal B cell repertoire establishment from a circulating pool, a process that continues for years without evidence of stabilization of the mucosal B cell repertoire in pediatric ITx patients.

Sodium tanshinone IIA sulfonate protects vascular relaxation in ApoE-knockout mice by inhibiting the SYK-NLRP3 inflammasome-MMP2/9 pathway.

BACKGROUND: Hyperlipidemia damages vascular wall and serves as a foundation for diseases such as atherosclerosis, hypertension and stiffness. The NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome is implicated in vascular dysfunction associated with hyperlipidemia-induced vascular injury. Sodium tanshinone IIA sulfonate (STS), a well-established cardiovascular protective drug with recognized anti-inflammatory, antioxidant, and vasodilatory properties, is yet to be thoroughly investigated for its impact on vascular relaxant imbalance induced by hyperlipidemia. METHODS: In this study, we treated ApoE-knockout (ApoE-/-) mouse with STS and assessed the activation of the NLRP3 inflammasome, expression of MMP2/9, integrity of elastic fibers, and vascular constriction and relaxation. RESULTS: Our findings reveal that STS intervention effectively preserves elastic fibers, significantly restores aortic relaxation function in ApoE-/- mice, and reduces their excessive constriction. Furthermore, STS inhibits the phosphorylation of spleen tyrosine kinase (SYK), suppresses NLRP3 inflammasome activation, and reduces MMP2/9 expression. CONCLUSIONS: These results demonstrate that STS protects vascular relaxation against hyperlipidemia-induced damage through modulation of the SYK-NLRP3 inflammasome-MMP2/9 pathway. This research provides novel insights into the mechanisms underlying vascular relaxation impairment in a hyperlipidemic environment and uncovers a unique mechanism by which STS preserves vascular relaxation, offering valuable foundational research evidence for its clinical application in promoting vascular health.

FGF21 overexpression alleviates VSMC senescence in diabetic mice by modulating the SYK-NLRP3 inflammasome-PPARγ-catalase pathway.

Diabetes accelerates vascular senescence, which is the basis for atherosclerosis and stiffness. The activation of the NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome and oxidative stress are closely associated with progressive senescence in vascular smooth muscle cells (VSMCs). The vascular protective effect of FGF21 has gradually gained increasing attention, but its role in diabetes-induced vascular senescence needs further investigation. In this study, diabetic mice and primary VSMCs are transfected with an FGF21 activation plasmid and treated with a peroxisome proliferator-activated receptor γ (PPARγ) agonist (rosiglitazone), an NLRP3 inhibitor (MCC950), and a spleen tyrosine kinase (SYK)-specific inhibitor, R406, to detect senescence-associated markers. We find that FGF21 overexpression significantly restores the level of catalase (CAT), vascular relaxation, inhibits the intensity of ROSgreen fluorescence and p21 immunofluorescence, and reduces the area of SA-ß-gal staining and collagen deposition in the aortas of diabetic mice. FGF21 overexpression restores CAT, inhibits the expression of p21, and limits the area of SA-ß-gal staining in VSMCs under high glucose conditions. Mechanistically, FGF21 inhibits SYK phosphorylation, the production of the NLRP3 dimer, the expression of NLRP3, and the colocalization of NLRP3 with PYCARD (ASC), as well as NLRP3 with caspase-1, to reverse the cleavage of PPARγ, preserve CAT levels, suppress ROSgreen density, and reduce the expression of p21 in VSMCs under high glucose conditions. Our results suggest that FGF21 alleviates vascular senescence by regulating the SYK-NLRP3 inflammasome-PPARγ-catalase pathway in diabetic mice.

Immune cell profiling in intestinal transplantation.

Since the first published case study of human intestinal transplantation in 1967, there have been significant studies of intestinal transplant immunology in both animal models and humans. An improved understanding of the profiles of different immune cell subsets is critical for understanding their contributions to graft outcomes. While different studies have focused on the contribution of one or a few subsets to intestinal transplant, no study has integrated these data for a comprehensive overview of immune dynamics after intestinal transplant. Here, we provide a systematic review of the literature on different immune subsets and discuss their roles in intestinal transplant outcomes on multiple levels, focusing on chimerism and graft immune reconstitution, clonal alloreactivity, and cell phenotype. In Sections 1, 2 and 3, we lay out a shared framework for understanding intestinal transplant, focusing on the mechanisms of rejection or tolerance in the context of mucosal immunology and illustrate the unique role of the bidirectional graft-versus-host (GvH) and host-versus-graft (HvG) alloresponse. In Sections 4, 5 and 6, we further expand upon these concepts as we discuss the contribution of different cell subsets to intestinal transplant. An improved understanding of intestinal transplantation immunology will bring us closer to maximizing the potential of this important treatment.

Inhibition of YAP/TAZ pathway contributes to the cytotoxicity of silibinin in MCF-7 and MDA-MB-231 human breast cancer cells.

Breast cancer is one of the most common cancers threatening women's health. Our previous study found that silibinin induced the death of MCF-7 and MDA-MB-231 human breast cancer cells. We noticed that silibinin-induced cell damage was accompanied by morphological changes, including the increased cell aspect ratio (cell length/width) and decreased cell area. Besides, the cytoskeleton is also destroyed in cells treated with silibinin. YAP/TAZ, a mechanical signal sensor interacted with extracellular pressure, cell adhesion area and cytoskeleton, is also closely associated with cell survival, proliferation and migration. Thus, the involvement of YAP/TAZ in the cytotoxicity of silibinin in breast cancer cells has attracted our interests. Excitingly, we find that silibinin inhibits the nuclear translocation of YAP/TAZ in MCF-7 and MDA-MB-231 cells, and reduces the mRNA expressions of YAP/TAZ target genes, ACVR1, MnSOD and ANKRD. More importantly, expression of YAP1 gene is negatively correlated with the survival of the patients with breast cancers. Molecular docking analysis reveals high probabilities for binding of silibinin to the proteins in the YAP pathways. DARTS and CETSA results confirm the binding abilities of silibinin to YAP and LATS. Inhibiting YAP pathway either by addition of verteporfin, an inhibitor of YAP/TAZ-TEAD, or by transfection of si-RNAs targeting YAP or TAZ further enhances silibinin-induced cell damage. While enhancing YAP activity by silencing LATS1/2 or overexpressing YAPS127/397A, an active form of YAP, attenuates silibinin-induced cell damage. These findings demonstrate that inhibition of the YAP/TAZ pathway contributes to cytotoxicity of silibinin in breast cancers, shedding lights on YAP/TAZ-targeted cancer therapies.

Mechanistic insights from inflammasome structures.

Inflammasomes are supramolecular complexes that form in the cytosol in response to pathogen-associated and damage-associated stimuli, as well as other danger signals that perturb cellular homoeostasis, resulting in host defence responses in the form of cytokine release and programmed cell death (pyroptosis). Inflammasome activity is closely associated with numerous human disorders, including rare genetic syndromes of autoinflammation, cardiovascular diseases, neurodegeneration and cancer. In recent years, a range of inflammasome components and their functions have been discovered, contributing to our knowledge of the overall machinery. Here, we review the latest advances in inflammasome biology from the perspective of structural and mechanistic studies. We focus on the most well-studied components of the canonical inflammasome - NAIP-NLRC4, NLRP3, NLRP1, CARD8 and caspase-1 - as well as caspase-4, caspase-5 and caspase-11 of the noncanonical inflammasome, and the inflammasome effectors GSDMD and NINJ1. These structural studies reveal important insights into how inflammasomes are assembled and regulated, and how they elicit the release of IL-1 family cytokines and induce membrane rupture in pyroptosis.

Dynamic establishment of recipient resident memory T cell repertoire after human intestinal transplantation.

BACKGROUND: Understanding formation of the human tissue resident memory T cell (TRM) repertoire requires longitudinal access to human non-lymphoid tissues. METHODS: By applying flow cytometry and next generation sequencing to serial blood, lymphoid tissue, and gut samples from 16 intestinal transplantation (ITx) patients, we assessed the origin, distribution, and specificity of human TRMs at phenotypic and clonal levels. FINDINGS: Donor age ≥1 year and blood T cell macrochimerism (peak level ≥4%) were associated with delayed establishment of stable recipient TRM repertoires in the transplanted ileum. T cell receptor (TCR) overlap between paired gut and blood repertoires from ITx patients was significantly greater than that in healthy controls, demonstrating increased gut-blood crosstalk after ITx. Crosstalk with the circulating pool remained high for years of follow-up. TCR sequences identifiable in pre-Tx recipient gut but not those in lymphoid tissues alone were more likely to populate post-Tx ileal allografts. Clones detected in both pre-Tx gut and lymphoid tissue had distinct transcriptional profiles from those identifiable in only one tissue. Recipient T cells were distributed widely throughout the gut, including allograft and native colon, which had substantial repertoire overlap. Both alloreactive and microbe-reactive recipient T cells persisted in transplanted ileum, contributing to the TRM repertoire. INTERPRETATION: Our studies reveal human intestinal TRM repertoire establishment from the circulation, preferentially involving lymphoid tissue counterparts of recipient intestinal T cell clones, including TRMs. We have described the temporal and spatial dynamics of this active crosstalk between the circulating pool and the intestinal TRM pool. FUNDING: This study was funded by the National Institute of Allergy and Infectious Diseases (NIAID) P01 grant AI106697.

Changes in physicochemical properties and formation process of colloidal nanoparticles (CNPs) during the lamb soup stewing.

Colloidal nanoparticles (CNPs), as carriers of nutrients, naturally exist in food or form during cooking. In this study, the colloidal properties, structures, rheological properties, and chemical composition location of CNPs were analyzed during 15 min to 5 h lamb soup stewing. With the increasing stewing time, the particle size and absolute value of the zeta potential of CNPs increased, indicating that CNPs became more stable. As the stewing time increased, the blue-shifted Fourier transform infrared spectroscopy absorption peaks and the red-shifted fluorescence spectroscopy absorption peaks certificated the structural changes in CNPs. And α-helix and ß-turn content decreased, while ß-sheet and random coil content increased in processing, potentially resulting in the opening CNPs structures. In addition, our findings revealed that proteins were encapsulated within the lipids in the inner part, while carbohydrates were dispersed in the outermost layers of the CNPs with a phospholipid bilayer.

Plasticity of intragraft alloreactive T cell clones in human gut correlates with transplant outcomes.

The site of transition between tissue-resident memory (TRM) and circulating phenotypes of T cells is unknown. We integrated clonotype, alloreactivity, and gene expression profiles of graft-repopulating recipient T cells in the intestinal mucosa at the single-cell level after human intestinal transplantation. Host-versus-graft (HvG)-reactive T cells were mainly distributed to TRM, effector T (Teff)/TRM, and T follicular helper compartments. RNA velocity analysis demonstrated a trajectory from TRM to Teff/TRM clusters in association with rejection. By integrating pre- and post-transplantation (Tx) mixed lymphocyte reaction-determined alloreactive repertoires, we observed that pre-existing HvG-reactive T cells that demonstrated tolerance in the circulation were dominated by TRM profiles in quiescent allografts. Putative de novo HvG-reactive clones showed a transcriptional profile skewed to cytotoxic effectors in rejecting grafts. Inferred protein regulon network analysis revealed upstream regulators that accounted for the effector and tolerant T cell states. We demonstrate Teff/TRM interchangeability for individual T cell clones with known (allo)recognition in the human gut, providing novel insight into TRM biology.

Dynamic establishment and maintenance of the human intestinal B cell population and repertoire following transplantation.

It is unknown how intestinal B cell populations and B cell receptor (BCR) repertoires are established and maintained over time in humans. Following intestinal transplantation (ITx), surveillance ileal mucosal biopsies provide a unique opportunity to map the dynamic establishment of gut lymphocyte populations. Using polychromatic flow cytometry that includes HLA allele group-specific mAbs distinguishing donor from recipient cells along with high throughput BCR sequencing, we tracked the establishment of recipient B cell populations and BCR repertoire in the allograft mucosa of ITx recipients. We confirm the early presence of naïve donor B cells in the circulation and, for the first time, document the establishment of recipient B cell populations, including B resident memory cells, in the intestinal allograft mucosa. Recipient B cell repopulation of the allograft was most rapid in infant (<1 year old)-derived allografts and, unlike T cell repopulation, did not correlate with rejection rates. While recipient memory B cell populations were increased in graft mucosa compared to circulation, naïve recipient B cells remained detectable in the graft mucosa for years. Comparisons of peripheral and intra-mucosal B cell repertoires in the absence of rejection revealed increased BCR mutation rates and clonal expansion in graft mucosa compared to circulating B cells, but these parameters did not increase markedly after the first year post-transplant. Furthermore, clonal mixing between the allograft mucosa and the circulation was significantly greater in ITx recipients, even years after transplantation, than in healthy control adults. Collectively, our data demonstrate intestinal mucosal B cell repertoire establishment from a circulating pool, a process that continues for years without evidence of establishment of a stable mucosal B cell repertoire.

The prospect of universal coronavirus immunity: characterization of reciprocal and non-reciprocal T cell responses against SARS-CoV2 and common human coronaviruses.

T cell immunity plays a central role in clinical outcomes of Coronavirus Infectious Disease 2019 (COVID-19) and T cell-focused vaccination or cellular immunotherapy might provide enhanced protection for some immunocompromised patients. Pre-existing T cell memory recognizing SARS-CoV-2 antigens antedating COVID-19 infection or vaccination, may have developed as an imprint of prior infections with endemic non-SARS human coronaviruses (hCoVs) OC43, HKU1, 229E, NL63, pathogens of "common cold". In turn, SARS-CoV-2-primed T cells may recognize emerging variants or other hCoV viruses and modulate the course of subsequent hCoV infections. Cross-immunity between hCoVs and SARS-CoV-2 has not been well characterized. Here, we systematically investigated T cell responses against the immunodominant SARS-CoV-2 spike, nucleocapsid and membrane proteins and corresponding antigens from α- and ß-hCoVs among vaccinated, convalescent, and unexposed subjects. Broad T cell immunity against all tested SARS-CoV-2 antigens emerged in COVID-19 survivors. In convalescent and in vaccinated individuals, SARS-CoV-2 spike-specific T cells reliably recognized most SARS-CoV-2 variants, however cross-reactivity against the omicron variant was reduced by approximately 47%. Responses against spike, nucleocapsid and membrane antigens from endemic hCoVs were significantly more extensive in COVID-19 survivors than in unexposed subjects and displayed cross-reactivity between α- and ß-hCoVs. In some, non-SARS hCoV-specific T cells demonstrated a prominent non-reciprocal cross-reactivity with SARS-CoV-2 antigens, whereas a distinct anti-SARS-CoV-2 immunological repertoire emerged post-COVID-19, with relatively limited cross-recognition of non-SARS hCoVs. Based on this cross-reactivity pattern, we established a strategy for in-vitro expansion of universal anti-hCoV T cells for adoptive immunotherapy. Overall, these results have implications for the future design of universal vaccines and cell-based immune therapies against SARS- and non-SARS-CoVs.

Efficacy of an isoxazole-3-carboxamide analog of pleconaril in mouse models of Enterovirus-D68 and Coxsackie B5.

Enteroviruses (EV) cause a number of life-threatening infectious diseases. EV-D68 is known to cause respiratory illness in children that can lead to acute flaccid myelitis. Coxsackievirus B5 (CVB5) is commonly associated with hand-foot-mouth disease. There is no antiviral treatment available for either. We have developed an isoxazole-3-carboxamide analog of pleconaril (11526092) which displayed potent inhibition of EV-D68 (IC50 58 nM) as well as other enteroviruses including the pleconaril-resistant Coxsackievirus B3-Woodruff (IC50 6-20 nM) and CVB5 (EC50 1 nM). Cryo-electron microscopy structures of EV-D68 in complex with 11526092 and pleconaril demonstrate destabilization of the EV-D68 MO strain VP1 loop, and a strain-dependent effect. A mouse respiratory model of EV-D68 infection, showed 3-log decreased viremia, favorable cytokine response, as well as statistically significant 1-log reduction in lung titer reduction at day 5 after treatment with 11526092. An acute flaccid myelitis neurological infection model did not show efficacy. 11526092 was tested in a mouse model of CVB5 infection and showed a 4-log TCID50 reduction in the pancreas. In summary, 11526092 represents a potent in vitro inhibitor of EV with in vivo efficacy in EV-D68 and CVB5 animal models suggesting it is worthy of further evaluation as a potential broad-spectrum antiviral therapeutic against EV.

Chimerism and phenotypic analysis of intraepithelial and lamina propria T cells isolated from human ileal biopsies after intestinal transplantation.

Understanding immune cell dynamics after intestinal transplantation has provided new insights into human lymphocyte biology. However, isolating and characterizing such cells can be challenging. Here, we provide a protocol to isolate intraepithelial and lamina propria lymphocytes from human ileal biopsies. We describe techniques for flow cytometric analysis and determination of multilineage chimerism and T lymphocyte phenotypes. This protocol can be modified to isolate and analyze lymphocytes from other tissues. For complete details on the use and execution of this protocol, please refer to Fu et al. (2019)1 and Fu et al. (2021).2.

Structural Mechanisms of NLRP3 Inflammasome Assembly and Activation.

As an important sensor in the innate immune system, NLRP3 detects exogenous pathogenic invasions and endogenous cellular damage and responds by forming the NLRP3 inflammasome, a supramolecular complex that activates caspase-1. The three major components of the NLRP3 inflammasome are NLRP3, which captures the danger signals and recruits downstream molecules; caspase-1, which elicits maturation of the cytokines IL-1ß and IL-18 and processing of gasdermin D to mediate cytokine release and pyroptosis; and ASC (apoptosis-associated speck-like protein containing a caspase recruitment domain), which functions as a bridge connecting NLRP3 and caspase-1. In this article, we review the structural information that has been obtained on the NLRP3 inflammasome and its components or subcomplexes, with special focus on the inactive NLRP3 cage, the active NLRP3-NEK7 (NIMA-related kinase 7)-ASC inflammasome disk, and the PYD-PYD and CARD-CARD homotypic filamentous scaffolds of the inflammasome. We further implicate structure-derived mechanisms for the assembly and activation of the NLRP3 inflammasome.

The prospect of universal coronavirus immunity: a characterization of reciprocal and non-reciprocal T cell responses against SARS-CoV2 and common human coronaviruses.

T cell immunity plays a central role in clinical outcomes of Coronavirus Infectious Disease 2019 (COVID-19). Therefore, T cell-focused vaccination or cellular immunotherapy might provide enhanced protection for immunocompromised patients. Pre-existing T cell memory recognizing SARS-CoV2 antigens antedating COVID-19 infection or vaccination, may have developed as an imprint of prior infections with endemic non-SARS human coronaviruses (hCoVs) OC43, HKU1, 229E, NL63, pathogens of "common cold". In turn, SARS-CoV2-primed T cells may recognize emerging variants or other hCoV viruses and modulate the course of subsequent hCoV infections. Cross-immunity between hCoVs and SARS-CoV2 has not been well characterized. Here, we systematically investigated T cell responses against the immunodominant SARS-CoV2 spike, nucleocapsid and membrane proteins and corresponding antigens from α- and ß-hCoVs among vaccinated, convalescent, and unexposed subjects. Broad T cell immunity against all tested SARS-CoV2 antigens emerged in COVID-19 survivors. In convalescent and in vaccinated individuals, SARS-CoV2 spike-specific T cells reliably recognized most SARS-CoV2 variants, however cross-reactivity against the omicron variant was reduced by approximately 50%. Responses against spike, nucleocapsid and membrane antigens from endemic hCoVs were more extensive in COVID-19 survivors than in unexposed subjects and displayed cross-reactivity between α- and ß-hCoVs. In some, non-SARS hCoVspecific T cells demonstrated a prominent non-reciprocal cross-reactivity with SARS-CoV2 antigens, whereas a distinct anti-SARS-CoV2 immunological repertoire emerged post-COVID-19, with relatively limited cross-recognition of non-SARS hCoVs. Based on this cross-reactivity pattern, we established a strategy for in-vitro expansion of universal anti-hCoV T cells for adoptive immunotherapy. Overall, these results have implications for the future design of universal vaccines and cell-based immune therapies against SARS- and non-SARS-CoVs.

Defects in Long-Term APC Repopulation Ability of Adult Human Bone Marrow Hematopoietic Stem Cells (HSCs) Compared with Fetal Liver HSCs.

Immunodeficient mice reconstituted with immune systems from patients, or personalized immune (PI) mice, are powerful tools for understanding human disease. Compared with immunodeficient mice transplanted with human fetal thymus tissue and fetal liver-derived CD34+ cells administered i.v. (Hu/Hu mice), PI mice, which are transplanted with human fetal thymus and adult bone marrow (aBM) CD34+ cells, demonstrate reduced levels of human reconstitution. We characterized APC and APC progenitor repopulation in human immune system mice and detected significant reductions in blood, bone marrow (BM), and splenic APC populations in PI compared with Hu/Hu mice. APC progenitors and hematopoietic stem cells (HSCs) were less abundant in aBM CD34+ cells compared with fetal liver-derived CD34+ cell preparations, and this reduction in APC progenitors was reflected in the BM of PI compared with Hu/Hu mice 14-20 wk posttransplant. The number of HSCs increased in PI mice compared with the originally infused BM cells and maintained functional repopulation potential, because BM from some PI mice 28 wk posttransplant generated human myeloid and lymphoid cells in secondary recipients. Moreover, long-term PI mouse BM contained functional T cell progenitors, evidenced by thymopoiesis in thymic organ cultures. Injection of aBM cells directly into the BM cavity, transgenic expression of hematopoietic cytokines, and coinfusion of human BM-derived mesenchymal stem cells synergized to enhance long-term B cell and monocyte levels in PI mice. These improvements allow a sustained time frame of 18-22 wk where APCs and T cells are present and greater flexibility for modeling immune disease pathogenesis and immunotherapies in PI mice.

Emerging Concepts of Tissue-resident Memory T Cells in Transplantation.

In this review, we summarize and discuss recent advances in understanding the characteristics of tissue-resident memory T cells (TRMs) in the context of solid organ transplantation (SOT). We first introduce the traditionally understood noncirculating features of TRMs and the key phenotypic markers that define this population, then provide a detailed discussion of emerging concepts on the recirculation and plasticity of TRM in mice and humans. We comment on the potential heterogeneity of transient, temporary resident, and permanent resident T cells and potential interchangeable phenotypes between TRM and effector T cells in nonlymphoid tissues. We review the literature on the distribution of TRM in human nonlymphoid organs and association of clinical outcomes in different types of SOT, including intestine, lung, liver, kidney, and heart. We focus on both tissue-specific and organ-shared features of donor- and recipient-derived TRMs after transplantation whenever applicable. Studies with comprehensive sample collection, including longitudinal and cross-sectional controls, and applied advanced techniques such as multicolor flow cytometry to distinguish donor and recipient TRMs, bulk, and single-cell T-cell receptor sequencing to track clonotypes and define transcriptome profiles, and functional readouts to define alloreactivity and proinflammatory/anti-inflammatory activities are emphasized. We also discuss important findings on the tissue-resident features of regulatory αß T cells and unconventional γδ T cells after transplantation. Understanding of TRM in SOT is a rapidly growing field that urges future studies to address unresolved questions regarding their heterogeneity, plasticity, longevity, alloreactivity, and roles in rejection and tolerance.

T cell repertoire profiling in allografts and native tissues in recipients with COVID-19 after solid organ transplantation: Insight into T cell-mediated allograft protection from viral infection.

Introduction: The effects of the SARS-CoV-2 virus on the body, and why the effects are more severe in certain patients, remain incompletely understood. One population of special interest is transplant recipients because of their immunosuppressed state. Understanding the pathophysiology of graft dysfunction in transplant patients with the COVID-19 viral syndrome is important for prognosticating the risk to the graft as well as understanding how best to prevent and, if necessary, treat graft injury in these patients. Methods: We analyzed multiple types of solid organ transplant recipients (liver, kidney, heart or lung) at our institution who died from SARS-CoV-2 and underwent autopsy (n = 6) or whose grafts were biopsied during active SARS-CoV-2 infection (n = 8). Their serum inflammatory markers were examined together with the histological appearance, viral load, and TCR repertoire of their graft tissue and, for autopsy patients, several native tissues. Results: Histology and clinical lab results revealed a systemic inflammatory pattern that included elevated inflammatory markers and diffuse tissue damage regardless of graft rejection. Virus was detected throughout all tissues, although most abundant in lungs. The TCR repertoire was broadly similar throughout the tissues of each individual, with greater sharing of dominant clones associated with more rapid disease course. There was no difference in viral load or clonal distribution of overall, COVID-associated, or putative SARS-CoV-2-specific TCRs between allograft and native tissue. We further demonstrated that SARSCoV-2-specific TCR sequences in transplant patients lack a donor HLArestricted pattern, regardless of distribution in allograft or native tissues,suggesting that recognition of viral antigens on infiltrating recipient cells can effectively trigger host T cell anti-viral responses in both the host and graft. Discussion: Our findings suggest a systemic immune response to the SARS-CoV-2 virus in solid organ transplant patients that is not associated with rejection and consistent with a largely destructive effect of recipient HLA-restricted T cell clones that affects donor and native organs similarly.