The purpose of the STAR 2019 Working Group was to build on findings from the initial STAR report to further clarify the expectations, limitations, perceptions, and utility of alloimmune assays that ...are currently in use or in development for risk assessment in the setting of organ transplantation. The goal was to determine the precision and clinical feasibility/utility of such assays in evaluating both memory and primary alloimmune risks. The process included a critical review of biologically driven, state‐of‐the‐art, clinical diagnostics literature by experts in the field and an open public forum in a face‐to‐face meeting to promote broader engagement of the American Society of Transplantation and American Society of Histocompatibility and Immunogenetics membership. This report summarizes the literature review and the workshop discussions. Specifically, it highlights (1) available assays to evaluate the attributes of HLA antibodies and their utility both as clinical diagnostics and as research tools to evaluate the effector mechanisms driving rejection; (2) potential assays to assess the presence of alloimmune T and B cell memory; and (3) progress in the development of HLA molecular mismatch computational scores as a potential prognostic biomarker for primary alloimmunity and its application in research trial design.
This meeting report from an AST‐ASHI expert workgroup provides recommendations on the utility and “clinical‐grade” qualification of assays and biomarkers to evaluate alloimmune risk.
ABSTRACT
The microbiome is increasingly implicated in immune regulation and mortality from sepsis. Mice with identical genetic backgrounds but distinct microbiomes were obtained from different ...vendors and analyzed following cecal ligation and puncture (CLP), β diversity of the microbiome measured from feces demonstrated significant differences between The Jackson Laboratory (Jax; Bar Harbor, ME, USA) and Charles River Laboratories (CR; Wilmington, MA, USA) C57/B6 mice. Jax mice had 7‐d mortality of 90% following CLP, whereas CR mice had a mortality of 53%. Differences in vendor were associated with altered immunophenotype with increased splenic IFN‐γ+CD4+ T cells, effector memory CD4+ T cells, and central memory CD4+ T cells and increased Peyer's patch effector memory CD4+ T cells in septic CR mice. To determine whether differences in the microbiome were responsible for these differences, Jax and CR mice were cohoused for 3 wk, after which they assumed a similar microbiota composition. Cohoused mice had improved survival following CLP compared to Jax mice and had similar survival regardless of their vendor of origin. All differences in immunophenotype between septic Jax and CR mice disappeared following cohousing. These findings suggest that the microbiome plays a crucial role in survival and the host immune response from sepsis and represents a potential target for therapeutic intervention.—Fay, K. T., Klingensmith, N. J., Chen, C.‐W., Zhang, W., Sun, Y., Morrow, K. N., Liang, Z., Burd, E. M., Ford, M. L., Coopersmith, C. M. The gut microbiome alters immunophenotype and survival from sepsis. FASEB J. 33, 11258–11269 (2019). www.fasebj.org
Human leukocyte antigen antibodies are important immunologic mediators of renal allograft loss and are difficult to control. The inability to permanently eliminate donor-specific antibodies (DSA) is ...partly due to an incomplete understanding of the cellular mechanisms driving alloantibody formation, recurrence, and maintenance. Memory T follicular helper (mTfh) cells rapidly interact with memory B cells upon antigen re-exposure for anamnestic humoral responses, but little is known about Tfh memory in transplantation. We hypothesized that alloreactive mTfh cells form after transplantation and play a critical role in DSA formation following alloantigen re-encounter. To test this hypothesis, we utilized murine skin allograft models to identify and characterize Tfh memory and interrogate its ability to mediate alloantibody responses. We identified alloreactive Tfh memory as a mediator of accelerated humoral alloresponses independent of memory B cells and primary germinal center, or DSA, formation. Furthermore, we demonstrate that mTfh-driven alloantibody formation is susceptible to CD28 costimulation blockade. These findings provide novel insight into a pathologic role for memory Tfh in alloantibody responses and strongly support shifting therapeutic focus from the singular targeting of B cell lineage cells and alloantibodies themselves to multimodal strategies that include inhibition of mTfh cells to treat DSA.
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Abstract Background Noninvasive models to predict the presence of coronary artery disease (CAD) may help reduce the societal burden of CAD. Objectives From a prospective registry of patients referred ...for coronary angiography, the goal of this study was to develop a clinical and biomarker score to predict the presence of significant CAD. Methods In a training cohort of 649 subjects, predictors of ≥70% stenosis in at least 1 major coronary vessel were identified from >200 candidate variables, including 109 biomarkers. The final model was then validated in a separate cohort (n = 278). Results The scoring system consisted of clinical variables (male sex and previous percutaneous coronary intervention) and 4 biomarkers (midkine, adiponectin, apolipoprotein C-I, and kidney injury molecule–1). In the training cohort, elevated scores were predictive of ≥70% stenosis in all subjects (odds ratio OR: 9.74; p < 0.001), men (OR: 7.88; p <0.001), women (OR: 24.8; p < 0.001), and those with no previous CAD (OR: 8.67; p < 0.001). In the validation cohort, the score had an area under the receiver-operating characteristic curve of 0.87 (p < 0.001) for coronary stenosis ≥70%. Higher scores were associated with greater severity of angiographic stenosis. At optimal cutoff, the score had 77% sensitivity, 84% specificity, and a positive predictive value of 90% for ≥70% stenosis. Partitioning the score into 5 levels allowed for identifying or excluding CAD with >90% predictive value in 42% of subjects. An elevated score predicted incident acute myocardial infarction during 3.6 years of follow up (hazard ratio: 2.39; p < 0.001). Conclusions We described a clinical and biomarker score with high accuracy for predicting the presence of anatomically significant CAD. (The CASABLANCA Study: Catheter Sampled Blood Archive in Cardiovascular Diseases; NCT00842868 )
Costimulation blockade targeting the CD28 pathway provides improved long-term renal allograft survival compared to calcineurin inhibitors but may be limited as CTLA-4-Ig (abatacept, belatacept) ...blocks both CD28 costimulation and CTLA-4 coinhibition. Directly targeting CD28 while leaving CTLA-4 intact may provide a mechanistic advantage. Fc-silent non-crosslinking CD28 antagonizing domain antibodies (dAb) are currently in clinical trials for renal transplantation. Given the current standard of care in renal transplantation at most US centers, it is likely that lymphodepletion via thymoglobulin induction therapy could be used in patients treated with CD28 antagonists. Thus, we investigated the impact of T cell depletion (TCD) on T cell phenotype following homeostatic reconstitution in a murine model of skin transplantation treated with anti-CD28dAb.
Skin from BALB/cJ donors was grafted onto C56BL/6 recipients which were treated with or without 0.2mg anti-CD4 and 10μg anti-CD8 one day prior to transplant and with or without 100μg anti-CD28dAb on days 0, 2, 4, 6, and weekly thereafter. Mice were euthanized six weeks post-transplant and lymphoid cells were analyzed by flow cytometry.
Anti-CD28dAb reversed lymphopenia-induced differentiation of memory CD4+ T cells in the spleen and lymph node compared to TCD alone. Mice treated with TCD+anti-CD28dAb exhibited significantly improved skin graft survival compared to anti-CD28dAb alone, which was also improved compared to no treatment. In addition, the expression of CD69 was reduced on CD4+ and CD8+ T cells in the spleen and lymph node from mice that received TCD+anti-CD28dAb compared to TCD alone. While a reduced frequency of CD4+FoxP3+ T cells was observed in anti-CD28dAb treated mice relative to untreated controls, this was balanced by an increased frequency of CD8+Foxp3+ T cells that was observed in the blood and kidney of mice given TCD+anti-CD28dAb compared to TCD alone.
These data demonstrate that CD28 signaling impacts the differentiation of both CD4+ and CD8+ T cells during homeostatic reconstitution following lymphodepletion, resulting in a shift towards fewer activated memory T cells and more CD8+FoxP3+ T cells, a profile that may underpin the observed prolongation in allograft survival.
Xenotransplantation has the potential to alleviate the organ shortage that prevents many patients with end‐stage renal disease from enjoying the benefits of kidney transplantation. Despite ...significant advances in other models, pig‐to‐primate kidney xenotransplantation has met limited success. Preformed anti‐pig antibodies are an important component of the xenogeneic immune response. To address this, we screened a cohort of 34 rhesus macaques for anti‐pig antibody levels. We then selected animals with both low and high titers of anti‐pig antibodies to proceed with kidney transplant from galactose‐α1,3‐galactose knockout/CD55 transgenic pig donors. All animals received T‐cell depletion followed by maintenance therapy with costimulation blockade (either anti‐CD154 mAb or belatacept), mycophenolate mofetil, and steroid. The animal with the high titer of anti‐pig antibody rejected the kidney xenograft within the first week. Low‐titer animals treated with anti‐CD154 antibody, but not belatacept exhibited prolonged kidney xenograft survival (>133 and >126 vs. 14 and 21 days, respectively). Long‐term surviving animals treated with the anti‐CD154‐based regimen continue to have normal kidney function and preserved renal architecture without evidence of rejection on biopsies sampled at day 100. This description of the longest reported survival of pig‐to‐non‐human primate kidney xenotransplantation, now >125 days, provides promise for further study and potential clinical translation.
•T cells are critical for protective immunity but can also induce graft rejection.•T cell differentiation is primarily regulated by intrinsic transcriptional pathways.•New reports suggest that ...context-dependent T cell differentiation programs exist.•Recent advances and implications for transplantation will be discussed.•Specifically, IRF4, Tbet/Eomes and regulation of tissue-resident memory cells (Trm).•Understanding these pathways may aid the development of novel anti-rejection therapies.
While T cells play a critical role in protective immunity against infection, they are also responsible for graft rejection in the setting of transplantation. T cell differentiation is regulated by both intrinsic transcriptional pathways as well as extrinsic factors such as antigen encounter and the cytokine milieu. Herein, we review recent discoveries in the transcriptional regulation of T cell differentiation and their impact on the field of transplantation. Recent studies uncovering context-dependent differentiation programs that differ in the setting of infection or transplantation will also be discussed. Understanding the key transcriptional pathways that underlie T cell responses in transplantation has important clinical implications, including development of novel therapeutic agents to mitigate graft rejection.
Belatacept-based immunosuppression in kidney transplantation confers fewer off-target toxicities than calcineurin inhibitors but comes at a cost of increased incidence and severity of acute ...rejection, potentially due to its deleterious effect on both the number and function of Foxp3+ regulatory T cells (Tregs). TIGIT is a CD28 family coinhibitory receptor expressed on several subsets of immune cells including Tregs. We hypothesized that coinhibition through TIGIT signaling could function to ameliorate costimulation blockade-resistant rejection. The results demonstrate that treatment with an agonistic anti-TIGIT antibody, when combined with costimulation blockade by CTLA-4Ig, can prolong allograft survival in a murine skin graft model compared with CTLA-4Ig alone. Further, this prolongation of graft survival is accompanied by an increase in the frequency and number of graft-infiltrating Tregs and a concomitant reduction in the number of CD8+ T cells in the graft. Through the use of Treg-specific TIGIT conditional knockout animals, we demonstrated that the TIGIT-mediated reduction in the graft-infiltrating CD8+ T cell response is dependent on signaling of TIGIT on Foxp3+ Tregs. Our results highlight both the key functional role of TIGIT on Foxp3+ Tregs under conditions in which CTLA-4 is blocked and the therapeutic potential of TIGIT agonism to optimize costimulation blockade-based immunosuppression.
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Donor‐reactive memory T cells generated via heterologous immunity represent a potent barrier to long‐term graft survival following transplantation because of their increased precursor frequency, ...rapid effector function, altered trafficking patterns, and reduced reliance on costimulation signals for activation. Thus, the identification of pathways that control memory T cell survival and secondary recall potential may provide new opportunities for therapeutic intervention. Here, we discovered that donor‐specific effector/memory CD8+ T cell populations generated via exposure to acute vs latent vs chronic infections contain differential frequencies of CD8+ T cells expressing the inhibitory Fc receptor FcγRIIB. Results indicated that frequencies of FcγRIIB‐expressing CD8+ donor‐reactive memory T cells inversely correlated with allograft rejection. Furthermore, adoptive T cell transfer of Fcgr2b−/− CD8+ T cells resulted in an accumulation of donor‐specific CD8+ memory T cells and enhanced recall responses, indicating that FcγRIIB functions intrinsically to limit T cell CD8+ survival in vivo. Lastly, we show that deletion of FcγRIIB on donor‐specific CD8+ memory T cells precipitated costimulation blockade‐resistant rejection. These data therefore identify a novel cell‐intrinsic inhibitory pathway that functions to limit the risk of memory T cell–mediated rejection following transplantation and suggest that therapeutic manipulation of this pathway could improve outcomes in sensitized patients.
Signaling through the inhibitory FcγRIIB receptor regulates graft‐specific CD8+ memory T cell immunity in a cell‐autonomous manner. See the editorial from Cravedi on page 1967.
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