Rejection of intestinal allotransplants is driven by memory T helper type 17 immunity and responds to infliximab

Regulatory T Cell and T Helper 17 Cell Imbalance in Patients with Unexplained Infertility

Purpose

Female infertility is a global health concern. The aim of this study was to investigate the relationship between regulatory T (Treg) cells and helper T cells 17 (Th17) in peripheral blood and unexplained infertility (UI). In addition, we explored potential valuable diagnostic biomarkers for patients with UI and ascertained whether Treg and Th17 cells are associated with primary and secondary UI.

Patients and Methods

The patients underwent standard fertility evaluation test, including blood tests, ultrasound examination, fallopian tube tests, ovulation assessment, and male partner's semen analysis. According to the inclusion and exclusion criteria, this study enrolled 37 patients with UI (30 with primary UI and 7 with secondary UI) and 26 age-matched healthy volunteers as the control group. Flow cytometry was used to detect the frequency of Treg and Th17 cells. The area under the receiver operating characteristic curve (AUC) with a 95% confidence interval (CI) was used to assess the diagnostic performance. An AUC > 0.800 indicated good diagnostic performance.

Results

The percentage of Treg decreased significantly, whereas the percentage and absolute count of Th17 cells increased. Moreover, the Th17/Treg ratio in patients with UI increased significantly. As a diagnostic biomarker for UI, the Th17/Treg ratio exhibited remarkable diagnostic performance (AUC: 0.813 (95% CI = 0.709-0.917)). However, the percentages and absolute counts of Treg and Th17 cells in the peripheral blood of women with primary and secondary UI, as well as their Th17/Treg ratios, did not differ significantly.

Conclusion

The distribution of Treg and Th17 cells is imbalanced in patients with UI. Therefore, the Th17/Treg ratio may be a promising indicator of UI. However, there were no significant differences in the distribution of Treg and Th17 cells between women with primary and secondary UI.

New insights in immunomodulation for intestinal transplantation

Tolerance is the Holy Grail of solid organ transplantation (SOT) and remains its primary challenge since its inception. In this topic, the seminal contributions of Thomas Starzl at Pittsburgh University outlined foundational principles of graft acceptance and tolerance, with chimerism emerging as a pivotal factor. Immunologically, intestinal transplantation (ITx) poses a unique hurdle due to the inherent characteristics and functions of the small bowel, resulting in increased immunogenicity. This necessitates heavy immunosuppression (IS) while IS drugs side effects cause significant morbidity. In addition, current IS therapies fall short of inducing clinical tolerance and their discontinuation has been proven unattainable in most cases. This underscores the unfulfilled need for immunological modulation to safely reduce IS-related burdens. To address this challenge, the Leuven Immunomodulatory Protocol (LIP), introduced in 2000, incorporates various pro-tolerogenic interventions in both the donor to the recipient, with the aim of facilitating graft acceptance and improving outcome. This review seeks to provide an overview of the current understanding of tolerance in ITx and outline recent advances in this domain.

Biologicals in the prevention and treatment of intestinal graft rejection: The state of the art: Biologicals in Intestinal Transplantation

Intestinal transplantation is the standard treatment for patients with intestinal failure with severe complications due to parenteral nutrition; however, rejection leads to graft failure in approximately half of both adult and pediatric recipients within 5 years of transplantation. Although intensive immunosuppressive therapy is used in an attempt to reduce this risk, commonly used treatment strategies are generally practice- and/or expert-based, as head-to-head comparisons are lacking. In this ever-developing field, biologicals designed to prevent or treat rejection are used increasingly, with both infliximab and vedolizumab showing potential in the treatment of acute cellular rejection in individual cases and in relatively small patient cohorts. To help advance progress in clinical care, we review the current use of biologicals in intestinal transplantation, and we provide future perspectives to guide this progress.

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.

Regulatory B Cells in Solid Organ Transplantation: From Immune Monitoring to Immunotherapy

Regulatory B cells (Breg) modulate the immune response in diverse disease settings including transplantation. Despite the lack of a specific phenotypic marker or transcription factor, their significance in transplantation is underscored by their ability to prolong experimental allograft survival, the possibility for their clinical use as immune monitoring tools, and the exciting prospect for them to form the basis for cell therapy. Interleukin (IL)-10 expression remains the most widely used marker for Breg. Several Breg subsets with distinct phenotypes that express this "signature Breg cytokine" have been described in mice and humans. Although T-cell immunoglobulin and mucin family-1 is the most inclusive and functional marker that accounts for murine Breg with disparate mechanisms of action, the significance of T-cell immunoglobulin and mucin family-1 as a marker for Breg in humans still needs to be explored. Although the primary focus of this review is the role of Breg in clinical transplantation, the net modulatory effect of B cells on the immune response and clinical outcomes is the result of the balancing functions of both Breg and effector B cells. Supporting this notion, B-cell IL-10/tumor necrosis factor α ratio is shown to predict immunologic reactivity and clinical outcomes in kidney and liver transplantation. Assessment of Breg:B effector balance using their IL-10/tumor necrosis factor α ratio may identify patients that require more immunosuppression and provide mechanistic insights into potential therapies. In summary, current advances in our understanding of murine and human Breg will pave way for future definitive clinical studies aiming to test them for immune monitoring and as therapeutic targets.

Updates in induction immunosuppression regimens for intestinal transplantation

Intestinal allografts are the most immunologically complex and carry the highest risk of rejection among solid organ transplantation, necessitating complex immunosuppressive management. We evaluated the latest information regarding induction immunosuppression, with an emphasis on established, novel, and emergent therapies. We also reviewed classic and novel induction immunosuppression strategies for highly sensitized recipients. Comparable progress has been made in intestinal transplantation clinical outcomes since the implementation of induction strategies. This review shows a clear diversity of induction protocols can be observed across different centers. The field of intestinal transplantation is still in its early stages, which is further complicated by the limited number of institutions capable of intestinal transplantation and their geographical variation, which further hinders the development of adequately powered studies in comparison to other organs. As the implementation of institution-specific induction protocols becomes more refined and results are disseminated, future research efforts should be directed towards the development of efficacious induction strategies.

Suppressor T helper type 17 cell responses in intestinal transplant recipients with allograft rejection

BACKGROUND

Intestinal transplant (ITx) rejection is associated with memory T helper type 17 cell (Th17) infiltration of grafted tissues. Modulation of Th17 effector cell response is facilitated by T regulatory (Treg) cells, but a phenotypic characterization of this process is lacking in the context of allograft rejection.

METHODS

Flow cytometry was performed to examine the expression of surface receptors, cytokines, and transcription factors in Th17 and Treg cells in ITx control (n = 34) and rejection patients (n = 23). To elucidate key pathways guiding the rejection biology, we utilized RNA sequencing (RNAseq) and assessed epigenetic stability through pyrosequencing of the Treg-specific demethylated region (TSDR).

RESULTS

We found that intestinal allograft rejection is characterized by Treg cellular infiltrates, which are polarized toward Th17-type chemokine receptor, ROR-γt transcription factor expression, and cytokine production. These Treg cell subsets have maintained epigenetic stability, as defined by FoxP3-TSDR methylation status, but displayed upregulation of functional Treg and purinergic signaling genes by RNAseq analysis such as CD39, in keeping with suppressor Th17 properties.

CONCLUSION

We show that ITx rejection is associated with increased polarized cells that express a Th17-like phenotype concurrent with regulatory purinergic markers.

History of clinical intestinal transplantation

The intestines have been considered the "forbidden organ" for years, and intestinal failure became the last organ failure recognized as such in the medical field. The impossibility of providing adequate nutritional support, turned these patients into recipients of just palliative comfort. In the 1960's, parenteral nutrition appeared as the most reasonable replacement therapy, but the initial success obtained with clinical kidney, heart, liver, lung and pancreas transplantation served as background to explore intestinal transplantation. The first clinical report of an isolated intestinal transplant was done by Richard Lillihei in 1967; in 1983, Thomas Starzl, performed the first multi visceral transplant, and in 1990, David Grant performed the first combined liver-intestinal transplant in an adult recipient in Canada. Since then, advances in immunosuppressive therapies and surgical innovations have allowed not only a continuous increase in indications, but also a worldwide application of all procedures, bringing clinical intestinal transplantation to reality. In this historical account, the most important contributions have been summarized, thus describing the steady progress, expansion and novelties developed over the last 56 years, since the first attempt. Clinical intestinal transplantation remains a complex and evolving field; ongoing research and technological advancements will continue shaping its future.

Current Advances in Graft-versus-host Disease After Intestinal Transplantation

Graft-versus-host disease (GvHD) remains a potentially fatal complication following intestinal transplant (ITx). Over the past decade, advances in the understanding of the pathophysiology of this complex immunological phenomenon have led to the reassessment of the host systemic immune response and have created a gateway for novel preventive and therapeutic strategies. Although sufficient evidence dictates the use of corticosteroids as a first-line option, the treatment for refractory disease remains contentious and lacks a standardized therapeutic approach. Timely diagnosis remains crucial, and the advent of chimerism detection and immunological biomarkers have transformed the identification, prognostication, and potential for survival after GvHD in ITx. The objectives of the following review aim to discuss the clinical and diagnostic features, pathophysiology, advances in immune biomarkers, as well as therapeutic opportunities in the prevention and treatment of GvHD in ITx.

The Entangled World of Memory T Cells and Implications in Transplantation

Memory T cells that are specific for alloantigen can arise from a variety of stimuli, ranging from direct allogeneic sensitization from prior transplantation, blood transfusion, or pregnancy to the elicitation of pathogen-specific T cells that are cross-reactive with alloantigen. Regardless of the mechanism by which they arise, alloreactive memory T cells possess key metabolic, phenotypic, and functional properties that render them distinct from naive T cells. These properties affect the immune response to transplantation in 2 important ways: first, they can alter the speed, location, and effector mechanisms with which alloreactive T cells mediate allograft rejection, and second, they can alter T-cell susceptibility to immunosuppression. In this review, we discuss recent developments in understanding these properties of memory T cells and their implications for transplantation.

Opportunities for High-plex Spatial Transcriptomics in Solid Organ Transplantation

The last 5 y have seen the development and widespread adoption of high-plex spatial transcriptomic technology. This technique detects and quantifies mRNA transcripts in situ, meaning that transcriptomic signatures can be sampled from specific cells, structures, lesions, or anatomical regions while conserving the physical relationships that exist within complex tissues. These methods now frequently implement next-generation sequencing, enabling the simultaneous measurement of many targets, up to and including the whole mRNA transcriptome. To date, spatial transcriptomics has been foremost used in the fields of neuroscience and oncology, but there is potential for its use in transplantation sciences. Transplantation has a clear dependence on biopsies for diagnosis, monitoring, and research. Transplant patients represent a unique cohort with multiple organs of interest, clinical courses, demographics, and immunosuppressive regimens. Obtaining high complexity data on the disease processes underlying rejection, tolerance, infection, malignancy, and injury could identify new opportunities for therapeutic intervention and biomarker identification. In this review, we discuss currently available spatial transcriptomic technologies and how they can be applied to transplantation.

Small bowel transplant - novel indications and recent progress

INTRODUCTION

Advances in the management of intestinal failure have led to a reduction in the number of intestinal transplants. The number of bowel transplants has been mainly stable even though a slight increase has been observed in the last 5 years.

AREAS COVERED

Standard indication includes patients with a reasonable life expectancy. Recent progress can be deduced by the increased number of intestine transplants in adults: this is due to the continuous improvement of 1-year graft survival worldwide (without differences in 3- and 5-year) associated with better abdominal wall closure techniques. This review aims to provide an update on new indications and changes in trends of pediatric and adult intestine transplantation. This analysis, which stretches through the past 5 years, is based on a collection of related manuscripts from PubMed.

EXPERT COMMENTARY

Intestinal transplants should be solely intended for a group of individuals for whom indications for transplantation are clear and both medical and surgical rehabilitations have failed. Nevertheless, many protocols developed over the years have not yet solved the key question represented by the over-immunosuppression. Novel indications and recent progress in the bowel transplant field, minimal yet consistent, represent a pathway to be followed.

Immunosuppression Protocols in Intestinal and Multivisceral Transplantation-A Literature Review

BACKGROUND

Intestinal transplantation (IT) and multivisceral transplantation (MVT) are curative therapies for patients with intestinal failure and severe complications associated with total parenteral nutrition. High levels of immunosuppression are required to prevent acute cellular rejection (ACR) from the bowel. Studies regarding pre-treatment, induction, and post-transplant therapy have improved graft acceptance, reducing immunosuppression doses and infectious complications. However, the low rate of IT and MVT and the small number of specialized centers have resulted in a limited number of evidence-based immunosuppression protocols. We reviewed immunosuppression in IT and MVT to draw useful conclusions regarding the best protocol strategies for the induction, maintenance, and management of ACR.

METHODS

A review was performed using the PubMed database. Articles on immunosuppression protocols in IT and MVT that addressed graft rejection, infection, or survival, published between 2006 and 2022, were selected.

RESULTS

A total of 690 articles were selected. Two researchers applied the inclusion and exclusion criteria and selected 14 articles independently. For induction, thymoglobulin, alemtuzumab, and basiliximab are the most frequently used immunosuppressants for induction. Classic maintenance therapy consists of a combination of corticosteroids and tacrolimus. Methylprednisolone with an increased tacrolimus dose is used most frequently to manage ACR. Depending on the receptor response, such as thymoglobulin, infliximab, adalimumab, or bortezomib, other immunosuppressants should be considered.

CONCLUSIONS

There have been great advances in IT and TMV immunosuppression. We conclude that the gold standard immunosuppressive protocol is triple therapy, comprising induction with thymoglobulin, maintenance with steroids for a few months, and tacrolimus and mycophenolate therapy. Innovative approaches for treating intestinal rejection episodes with more appropriate drugs, such as infliximab, adalimumab, or bortezomib, are necessary.

Intestinal Transplant Immunology and Intestinal Graft Rejection: From Basic Mechanisms to Potential Biomarkers

Intestinal transplantation (ITx) remains a lifesaving option for patients suffering from irreversible intestinal failure and complications from total parenteral nutrition. Since its inception, it became obvious that intestinal grafts are highly immunogenic, due to their high lymphoid load, the abundance in epithelial cells and constant exposure to external antigens and microbiota. This combination of factors and several redundant effector pathways makes ITx immunobiology unique. To this complex immunologic situation, which leads to the highest rate of rejection among solid organs (>40%), there is added the lack of reliable non-invasive biomarkers, which would allow for frequent, convenient and reliable rejection surveillance. Numerous assays, of which several were previously used in inflammatory bowel disease, have been tested after ITx, but none have shown sufficient sensibility and/or specificity to be used alone for diagnosing acute rejection. Herein, we review and integrate the mechanistic aspects of graft rejection with the current knowledge of ITx immunobiology and summarize the quest for a noninvasive biomarker of rejection.

The Microbiome and Metabolomic Profile of the Transplanted Intestine with Long-Term Function

We analyzed the fecal microbiome by deep sequencing of the 16S ribosomal genes and the metabolomic profiles of 43 intestinal transplant recipients to identify biomarkers of graft function. Stool samples were collected from 23 patients with stable graft function five years or longer after transplant, 15 stable recipients one-year post-transplant and four recipients with refractory rejection and graft loss within one-year post-transplant. Lactobacillus and Streptococcus species were predominant in patients with stable graft function both in the short and long term, with a microbiome profile consistent with the general population. Conversely, Enterococcus species were predominant in patients with refractory rejection as compared to the general population, indicating profound dysbiosis in the context of graft dysfunction. Metabolomic analysis demonstrated significant differences between the three groups, with several metabolites in rejecting recipients clustering as a distinct set. Our study suggests that the bacterial microbiome profile of stable intestinal transplants is similar to the general population, supporting further application of this non-invasive approach to identify biomarkers of intestinal graft function.

Immunosuppression Regimens for Intestinal Transplantation in Children

Pediatric intestinal transplant serves as the only definitive treatment for children with irreversible intestinal failure. Successful intestinal transplant hinges upon appropriate management of immunosuppression. The indications for intestinal transplant have changed over time. Immunosuppression regimens can be divided into induction and maintenance phases along with treatment of acute rejection. Intestinal transplant induction now often includes antithymocyte globulin or basiliximab in addition to corticosteroids. Maintenance regimens continue to be dominated by tacrolimus, with additional agents used to either decrease goal tacrolimus levels to limit toxicity or as an adjunct in sensitized patients. Careful monitoring can help to limit serious complications, such as rejection, infection, and malignancy. Future work will aim to decrease variation in practice and identify methods to determine optimal immunosuppression for a particular patient. Furthermore, there is a need for non-invasive monitoring of the intestinal graft and functional assessments of immunosuppression.

Innovations in Immunosuppression for Intestinal Transplantation

It has been 57 years since the first intestinal transplant. An increased incidence of graft rejection has been described compared to other solid organ transplants due to high immunogenicity of the bowel, which in health allows the balance between of dietary antigen with defense against pathogens. Expanding clinical experience, knowledge of gastrointestinal physiology and immunology have progress post-transplant immunosuppressive drug regimens. Current regimes aim to find the window between prevention of rejection and the risk of infection (the leading cause of death) and malignancy. The ultimate aim is to achieve graft tolerance. In this review we discuss advances in mucosal immunology and technologies informing the development of new anti-rejection strategies with the hope of improved survival in the next generation of transplant recipients.

Update on immunosuppressive strategies in intestinal transplantation

PURPOSE OF REVIEW

The intestine is the most immunologically complex solid organ allograft with the greatest risk of both rejection and graft-versus-host disease (GVHD). High levels of immunosuppression are required, further increasing morbidity. Due to low volume of transplants and few centers with experience, there is paucity of evidence-based, standardized, and effective therapeutic regimens. We herein review the most recent data about immunosuppression, focusing on novel and emerging therapies.

RECENT FINDINGS

Recent data are moving the field toward increasing use of basilixumab and consideration of alemtuzumab for induction and inclusion of mammalian target of rapamycin inhibitors and antimetabolites for maintenance. For rejection, we highlight novel roles for tumor necrosis factor-α inhibition, α4β7 integrin inhibition, microbiome modulation, desensitization protocols, and tolerance induction strategies. We also highlight emerging novel therapies for GVHD, especially the promising role of Janus kinase inhibition.

SUMMARY

New insights into immune pathways associated with rejection and GVHD in intestinal allografts have led to an evolution of therapies from broad-based immunosuppression to more targeted strategies that hold promise for reducing morbidity from infection, rejection, and GVHD. These should be the focus of further study to facilitate their widespread use.

CD69+ resident memory T cells are associated with graft-versus-host disease in intestinal transplantation

Graft-versus-host disease (GvHD) is a common, morbid complication after intestinal transplantation (ITx) with poorly understood pathophysiology. Resident memory T cells (T_RM ) are a recently described CD69+ memory T cell subset localizing to peripheral tissue. We observed that T effector memory cells (T_EM ) in the blood increase during GvHD and hypothesized that they derive from donor graft CD69+T_RM migrating into host blood and tissue. To probe this hypothesis, graft and blood lymphocytes from 10 ITx patients with overt GvHD and 34 without were longitudinally analyzed using flow cytometry. As hypothesized, CD4+ and CD8+CD69+T_RM were significantly increased in blood and grafts of GvHD patients, alongside higher cytokine and activation marker expression. The majority of CD69+T_RM were donor derived as determined by multiplex immunostaining. Notably, CD8/PD-1 was significantly elevated in blood prior to transplantation in patients who later had GvHD, and percentages of HLA-DR, CD57, PD-1, and naïve T cells differed significantly between GvHD patients who died vs. those who survived. Overall, we demonstrate that (1) there were significant increases in T_EM at the time of GvHD, possibly of donor derivation; (2) donor T_RM in the graft are a possible source; and (3) potential biomarkers for the development and prognosis of GvHD exist.