Host-versus-commensal immune responses participate in the rejection of colonized solid organ transplants

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.

Advancing mouse models for transplantation research

Mouse models have been instrumental in understanding mechanisms of transplant rejection and tolerance, but cross-study reproducibility and translation of experimental findings into effective clinical therapies are issues of concern. The Mouse Models in Transplantation symposium gathered scientists and physician-scientists involved in basic and clinical research in transplantation to discuss the strengths and limitations of mouse transplant models and strategies to enhance their utility. Participants recognized that increased procedure standardization, including the use of prespecified, defined endpoints, and statistical power analyses, would benefit the field. They also discussed the generation of new models that incorporate environmental and genetic variables affecting clinical outcomes as potentially important. If implemented, these strategies are expected to improve the reproducibility of mouse studies and increase their translation to clinical trials and, ideally, new Food and Drug Administration-approved drugs.

Modulating microbiome-immune axis in the deployment-related chronic diseases of Veterans: report of an expert meeting

The present report summarizes the United States Department of Veterans Affairs (VA) field-based meeting titled "Modulating microbiome-immune axis in the deployment-related chronic diseases of Veterans." Our Veteran patient population experiences a high incidence of service-related chronic physical and mental health problems, such as infection, irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), various forms of hematological and non-hematological malignancies, neurologic conditions, end-stage organ failure, requiring transplantation, and posttraumatic stress disorder (PTSD). We report the views of a group of scientists who focus on the current state of scientific knowledge elucidating the mechanisms underlying the aforementioned disorders, novel therapeutic targets, and development of new approaches for clinical intervention. In conclusion, we dovetailed on four research areas of interest: 1) microbiome interaction with immune cells after hematopoietic cell and/or solid organ transplantation, graft-versus-host disease (GVHD) and graft rejection, 2) intestinal inflammation and its modification in IBD and cancer, 3) microbiome-neuron-immunity interplay in mental and physical health, and 4) microbiome-micronutrient-immune interactions during homeostasis and infectious diseases. At this VA field-based meeting, we proposed to explore a multi-disciplinary, multi-institutional, collaborative strategy to initiate a roadmap, specifically focusing on host microbiome-immune interactions among those with service-related chronic diseases to potentially identify novel and translatable therapeutic targets.

Microbiota-dependent and -independent effects of obesity on transplant rejection and hyperglycemia

Obesity is associated with dysbiosis and a state of chronic inflammation that contributes to the pathogenesis of metabolic diseases, including diabetes. We have previously shown that obese mice develop glucose intolerance, increased alloreactivity, and accelerated transplant rejection. In the present study, we investigated the influence of the microbiota on diet-induced obesity (DIO)-associated transplant rejection and hyperglycemia. Antibiotic treatment prolonged graft survival and reduced fasting glycemia in high-fat diet (HFD)-fed specific-pathogen-free (SPF) mice, supporting a role for the microbiota in promoting accelerated graft rejection and hyperglycemia induced by DIO. Further supporting a microbiota-dependent effect, fecal microbiota transfer from DIO SPF mice into germ-free mice also accelerated graft rejection when compared with lean mice-fecal microbiota transfer. Notably, HFD could be also detrimental to the graft independently from microbiota, obesity, and hyperglycemia. Thus, whereas HFD-associated hyperglycemia was exclusively microbiota-dependent, HFD affected transplant outcomes via both microbiota-dependent and -independent mechanisms. Importantly, hyperglycemia in DIO SPF mice could be reduced by the addition of the gut commensal Alistipes onderdonkii, which alleviated both HFD-induced inflammation and glucose intolerance. Thus, microbial dysbiosis can be manipulated via antibiotics or select probiotics to counter some of the pathogenic effects of obesity in transplantation.

Microbiome influencers of checkpoint blockade-associated toxicity

Immunotherapy has greatly improved cancer outcomes, yet variability in response and off-target tissue damage can occur with these treatments, including immune checkpoint inhibitors (ICIs). Multiple lines of evidence indicate the host microbiome influences ICI response and risk of immune-related adverse events (irAEs). As the microbiome is modifiable, these advances indicate the potential to manipulate microbiome components to increase ICI success. We discuss microbiome features associated with ICI response, with focus on bacterial taxa and potential immune mechanisms involved in irAEs, and the overall goal of driving novel approaches to manipulate the microbiome to improve ICI efficacy while avoiding irAE risk.

The Effect of the Gut Microbiota on Transplanted Kidney Function

The intestinal microflora is extremely important, not only in the processes of absorption, digestion and biosynthesis of vitamins, but also in shaping the immune and cognitive functions of the human body. Several studies demonstrate a correlation between microbiota composition and such events as graft rejection, kidney interstitial fibrosis, urinary tract infections, and diarrhoea or graft tolerance. Some of those changes might be directly linked with pathologies such as colonization with pathogenic bacterial strains. Gut microbiota composition also plays an important role in metabolic complications and viral infections after transplantation. From the other side, gut microbiota might induce graft tolerance by promotion of T and B regulatory cells. Graft tolerance induction is still an extremely important issue regarding transplantology and might allow the reduction or even avoidance of immunosuppressive treatment. Although there is a rising evidence of the pivotal role of gut microbiota in aspects of kidney transplantation there is still a lack of knowledge on the direct mechanisms of microbiota action. Furthermore, some of those negative effects could be reversed by probiotics of faecal microbiota trapoinsplantation. While diabetes and hypertension as well as BKV and CMV viremia are common and important complications of transplantation, both worsening the graft function and causing systemic injuries, it opens up potential clinical treatment options. As has been also suggested in the current review, some bacterial subsets exhibit protective properties. However, currently, there is a lack of evidence on pro- and prebiotic supplementation in kidney transplant patients. In the current review, we describe the effect of the microbiota on the transplanted kidney in renal transplant recipients.

Methods to Study TLRs in Transplantation

Toll-like receptors (TLRs) are key regulators of immune responses, including alloimmune responses. In this chapter, we present protocols to study whether and/or how TLRs can contribute to solid-organ transplant rejection. We describe methods to reduce heterogeneity in microbiome variations between animals before beginning experiments to limit confounding factors, protocols using TLR agonists to prevent anti-CD154/donor splenocyte transfer-mediated tolerance, and recipes to heat-kill microbes or use hosts genetically deficient in TLR-dependent pathways to distinguish between TLR-dependent and live bacteria-dependent effects.