Update on immunosuppressive strategies in intestinal transplantation

Durable mixed chimerism may permit subsequent immunosuppression-free intestinal transplantation-A proof-of-principle study

Intestinal transplantation (ITx) is the definitive treatment for intestinal failure but has the highest rejection rate among solid organ transplants, requiring high doses of immunosuppressive medication, which is associated with high rates of infection, graft-versus-host disease, and malignancy. Transplant tolerance would overcome the need for long-term immunosuppression (ISP). Using nonmyeloablative conditioning, our laboratory has developed a novel swine model of hematopoietic stem cell transplantation (HSCT) that produces durable mixed chimerism (MC) and immune tolerance without toxicity. We investigated whether durable MC would promote tolerance of subsequently transplanted donor-matched intestinal allografts without ISP. Using miniature swine with a defined major histocompatibility complex (MHC), we performed HSCT across an MHC-class-I haplotype mismatch. Immunosuppressive therapy was stopped by day 45. MC was evaluated using flow cytometry, and mixed lymphocyte reaction assays were used to evaluate cellular responses. Subsequently, orthotopic ITx was performed without ISP using a donor that was MHC-matched to the HSCT donor. The recipients were observed for 4 weeks and euthanized for tissue collection and mechanistic assays. After HSCT, the recipients developed durable multilineage MC and apparent deletional tolerance. After ITx, recipients showed no clinical or histologic signs of rejection, and chimerism was unchanged. These results demonstrate the potential value of generating durable MC to achieve transplant tolerance.

Trends in the Perioperative Practices for Immunological Assessment and Immunosuppression Strategies for Patients Undergoing Intestinal Transplantation at American Transplant Centers

BACKGROUND

Intestinal transplantation (IT) is a complex procedure that requires nuanced immunosuppressive strategies to optimize patient outcomes. Despite advancements, significant variability remains in immunosuppressive protocols across transplant centers due to a lack of consensus on the optimal approaches for induction, maintenance, and clinical testing. This variability complicates standardization and identification of best practices for IT recipients.

METHODS

A descriptive survey study was conducted to characterize immunosuppressive and testing strategies in IT at major transplant centers in the United States. Ten centers known to have performed over 10 ITs since 2015 were selected from the Scientific Registry of Transplant Recipients database. A 22-question survey was distributed to surgical directors, collecting data on pre-, peri-, and post-transplant immunological testing, desensitization strategies, immunosuppressive regimens, and management of antibody-mediated rejection (AMR) and acute cellular rejection (ACR).

RESULTS

Nine centers (90%) responded. All centers conducted pretransplant human leukocyte antigen (HLA) and donor-specific antibody (DSA) testing, with varying frequencies and methodologies. Desensitization was reported by 44% of centers for isolated IT and by 22% for multivisceral transplants. Induction therapy predominantly involved antithymocyte globulin (89%) and rituximab (44%). Tacrolimus was universally used for maintenance, with varying trough level targets across centers. Post-transplant DSA testing was performed by all centers, and protocol-driven endoscopic bowel biopsies were routine at 67% of centers. AMR was diagnosed at 89% of centers, with plasmapheresis and IVIG being the most common treatments. Variability was noted in desensitization practices and AMR management.

CONCLUSION

This survey highlights considerable consistency in pre- and post-transplant testing and immunosuppressive regimens for IT recipients, while significant variability exists in desensitization strategies and AMR management. Further research is needed to standardize these practices to improve patient outcomes across transplant centers.

Mucosal Mixed Lymphocyte Reaction Assay Using Intestinal Lymphocytes as a Biomarker for Intestinal Transplant Tolerance Development

BACKGROUND

Intestinal transplantation (ITx) has the highest rate of rejection among solid organ grafts. We aimed to study the pathophysiology of rejection after ITx but lacked a tool for assessing cellular responses within the graft. Therefore, we developed a novel mixed lymphocyte reaction (MLR) assay to investigate immune responses in the graft.

METHODS

Intestinal samples were collected, decontaminated, and processed into single-cell suspensions from 9 swine and 2 patients that underwent ITx. Debris was removed using gradient centrifugation. The cells were plated with corresponding stimulator cells and incubated for 6 d before data acquisition and analysis.

RESULTS

Tolerant animals showed no anti-donor or anti-recipient responses in their graft mucosa but maintained strong anti-third-party responses, even after weaning immunosuppression. An animal with graft-versus-host disease displayed robust anti-recipient and anti-third-party responses but no anti-donor response. The animals with graft rejection maintained anti-donor responses at all timepoints. Finally, some tolerant animals developed "split tolerance," with anti-donor responses in the peripheral blood but donor-specific hyporesponsiveness in the mucosal MLR, which regulatory T cells depletion suggested was attributable to local regulatory tolerance. When applied to human sample, this mucosal MLR reliably demonstrated self-tolerance with normal anti-third-party responsiveness.

CONCLUSIONS

The novel mucosal MLR assay presented herein ± CD25 depletion serves as a useful adjunct for assessing immune responses within the intestinal graft mucosa. This could help elucidate immune responses after ITx in future studies, including our own, and could represent a promising tool for studying ITx tolerance development, guiding immunosuppression strategies, and advancing personalized transplant medicine.

Chimerism-Mediated Tolerance in Intestinal Transplantation

In this review, the authors outlined concepts and strategies to achieve immune tolerance through inducing hematopoietic chimerism after solid organ transplantation and introduced challenges and opportunities in harnessing two-way alloresponses to improve outcomes after intestinal transplantation (ITx). Next, the authors discussed the dynamics and phenotypes of peripheral blood and intestinal graft T-cell subset chimerism and their association with outcomes. The authors also summarized studies on other types of immune cells after ITx and their potential participation in chimerism-mediated tolerance. The authors further discussed strategies and future directions to promote chimerism-associated tolerance after ITx to overcome rejection and minimize immunosuppression.

B-Cell Induction Therapies in Intestinal Transplantation

Despite advancements in short-term outcomes since the inception of intestinal transplant, significant long-term graft failure persists. Early successes are attributed to the utilization of tacrolimus for maintenance therapy, coupled with T-cell modulating induction regimens, which effectively reduce the incidence of acute cellular rejection. However, the challenge of chronic allograft injury remains unresolved. There is increasing evidence indicating a correlation between donor-specific antibodies and the survival of visceral allografts. Strategies aimed at reducing the presence or load of these antibodies may potentially enhance long-term outcomes. Consequently, our focus is now turning toward B-cell induction therapies as a possible solution.

Update on Maintenance Immunosuppression in Intestinal Transplantation

Outcomes in intestinal transplantation remain hampered by higher rates of rejection than any other solid organs. However, maintenance immunosuppression regimens have largely remained unchanged despite advances in therapies for induction and treatment of rejection and graft-versus-host disease. Recently, there have been a small number of new maintenance therapies attempted, and older agents have been used in new ways to achieve better outcomes. The authors herein review the traditional maintenance therapies and their mechanisms and then consider updates in new therapies and new ways of using old therapies for maintenance immunosuppression after intestinal transplantation.

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.

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.

Development of a large animal orthotopic intestinal transplantation model with long-term survival for study of immunologic outcomes

Introduction

Intestinal transplantation (ITx) is the last remaining therapy for patients with intestinal failure once parenteral nutrition is no longer an option, however its use is limited by immunological complications, including high rates of rejection and morbidity associated with immunosuppression, such as infection and malignancy. We aimed to develop a large animal model of ITx with which to study the immune response to ITx and to design and test tolerance induction regimens.

Methods

Learning from prior complications, we developed and progressively improved both surgical methods for the donor and recipient as well as postoperative management strategies. Methods of stoma generation, bowel positioning, vessel preparation, and fluid management were optimized. The immunosuppression strategy mirrored our clinical regimen.

Results

As a result of our modifications, results improved from survival less than 1 month to consistent long-term survival with good graft function. We review several techniques that were developed to avoid pitfalls that were encountered, which can be used to optimize outcomes in this model.

Discussion

Achieving long-term survival after swine orthotopic ITx permits immunological analysis and pre-clinical trials in a large animal model of ITx.

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.

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 Long Scientific Journey of Sirolimus (Rapamycin): From the Soil of Easter Island (Rapa Nui) to Applied Research and Clinical Trials on β-Thalassemia and Other Hemoglobinopathies

In this review article, we present the fascinating story of rapamycin (sirolimus), a drug able to induce γ-globin gene expression and increased production of fetal hemoglobin (HbF) in erythroid cells, including primary erythroid precursor cells (ErPCs) isolated from β-thalassemia patients. For this reason, rapamycin is considered of great interest for the treatment of β-thalassemia. In fact, high levels of HbF are known to be highly beneficial for β-thalassemia patients. The story of rapamycin discovery began in 1964, with METEI, the Medical Expedition to Easter Island (Rapa Nui). During this expedition, samples of the soil from different parts of the island were collected and, from this material, an antibiotic-producing microorganism (Streptomyces hygroscopicus) was identified. Rapamycin was extracted from the mycelium with organic solvents, isolated, and demonstrated to be very active as an anti-bacterial and anti-fungal agent. Later, rapamycin was demonstrated to inhibit the in vitro cell growth of tumor cell lines. More importantly, rapamycin was found to be an immunosuppressive agent applicable to prevent kidney rejection after transplantation. More recently, rapamycin was found to be a potent inducer of HbF both in vitro using ErPCs isolated from β-thalassemia patients, in vivo using experimental mice, and in patients treated with this compound. These studies were the basis for proposing clinical trials on β-thalassemia patients.

The First Collective Examination of Immunosuppressive Practices Among American Intestinal Transplant Centers

BACKGROUND

Unlike other solid organs, no standardized treatment algorithms exist for intestinal transplantation (ITx). We established a consortium of American ITx centers to evaluate current practices.

METHODS

All American centers performing ITx during the past 3 y were invited to participate. As a consortium, we generated questions to evaluate and collect data from each institution. The data were compiled and analyzed.

RESULTS

Ten centers participated, performing 211 ITx during the past 3 y (range, 3-46; mean 21.1). Induction regimens varied widely. Thymoglobulin was the most common, used in the plurality of patients (85/211; 40.3%), but there was no consensus regimen. Similarly, regimens for the treatment of acute cellular rejection, antibody-mediated rejection, and graft-versus-host disease varied significantly between centers. We also evaluated differences in maintenance immunosuppression protocols, desensitization regimens, mammalian target of rapamycin use, antimetabolite use, and posttransplantation surveillance practices. Maintenance tacrolimus levels, stoma presence, and scoping frequency were not associated with differences in rejection events. Definitive association between treatments and outcomes, including graft and patient survival, was not the intention of this initial collaboration and is prevented by the lack of patient-level data and the presence of confounders. However, we identified trends regarding rejection episodes after various induction strategies that require further investigation in our subsequent collaborations.

CONCLUSIONS

This initial collaboration reveals the extreme heterogeneity of practices among American ITx centers. Future collaboration will explore patient-level data, stratified by age and transplant type (isolated intestine versus multivisceral), to explore the association between treatment regimens and outcomes.

Intestinal and Multivisceral Transplantation: Complications

Advancements in immunosuppression protocols, surgical techniques, and postoperative care in the last few decades have improved outcomes of intestinal transplant patients. Normal immediate postoperative imaging appearance can simulate pathology. Intestinal transplant recipients are prone for several postoperative complications due to the complex surgical technique, which involves multiple anastomoses, and immunogenic nature of the allograft intestine. Imaging plays a crucial role in detection of several major complications including infectious, immunologic, vascular, gastrointestinal, pancreaticobiliary, genitourinary, and neoplastic complications. The awareness of the posttransplant anatomy and normal imaging appearances helps radiologists anticipate and accurately detect posttransplant complications.

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.

Prenatal Exposition to Different Immunosuppressive Protocols Results in Vacuolar Degeneration of Hepatocytes

Immunosuppressive drugs are essential for transplant recipients, since they prolong proper function of graft; however, they affect the morphology and function of organs, including liver. One commonly observed alteration in hepatocytes is vacuolar degeneration. Numerous medications are contraindicated in pregnancy and breastfeeding, mostly due to a lack of data concerning their advert effects. The aim of the current study was to compare the effects of prenatal exposition to different protocols of immunosuppressants on vacuolar degeneration in the hepatocytes of livers of rats. Thirty-two livers of rats with usage of digital analysis of the images were examined. Area, perimeter, axis length, eccentricity and circularity regarding vacuolar degeneration were analysed. The most prominent vacuolar degeneration in hepatocytes in the aspects of presence, area and perimeter was observed in rats exposed to tacrolimus, mycophenolate mofetil and glucocorticoids, and cyclosporine A, everolimus with glucocorticoids.This is the first study that demonstrates the results of the influence of multidrug immnunosuppression distributed in utero on the hepatic tissue of offspring.

Induction Versus Maintenance Immunosuppression After Intestinal Transplant: Determining Which Treatment Most Impacts Long-Term Patient And Graft Survival

OBJECTIVES

Immunosuppressive strategies for intestinal transplant have changed over time. However, specific intestinal transplant-oriented protocols and reports on long-term maintenance regimens are scarce. Our objective was to evaluate the impact of 2 different initial immunosuppressive protocols based on thymoglobulin (group A) and basiliximab (anti-interleukin 2 antibody) (group B) and of changes to maintenance immunosuppression over long-term follow-up in intestinal transplant recipients.

MATERIALS AND METHODS

We performed a retrospective analysis of a prospectively established protocol for intestinal transplant immunosuppression, conducted between May 2006 and December 2020. We analyzed 51 intestinal transplant recipients, with 6 patients excluded because of early death or graft loss. Acute cellular rejection frequency and grade, number of acute cellular rejection episodes, time to the first acute cellular rejection episode, response to treatment, number of patients who progressed to chronic allograft rejection, kidney function, infections, incidence of posttransplant lymphoproliferative disorder and graft-versus-host disease, and patient and graft survival were analyzed.

RESULTS

In the study groups, there were 87 acute cellular rejection episodes in 45 patients (33 in group A and 54 in group B). We found degree of acute cellular rejection to be mild in 45 patients, moderate in 18, and severe in 24 (not significant between groups). Our comparison of induction therapy (thymoglobulin [group A] vs interleukin 2 antibody [group B]) did not show any statistical difference during clinical followup. Long-term review showed that all patients were on tacrolimus. Five-year patient and graft survival rates were 62% and 45% for group A and 54% and 46% for group B, respectively (not significant).

CONCLUSIONS

Long-term patient and graft outcomes reflected the use of an individualized follow-up with adjustments and changes in immunosuppressive medications according to the patient's clinical course and complications rather than based on the induction immunosuppressive protocol used.

Pediatric intestinal transplantation

Advancements in donor management, organ preservation and operative techniques, as well as immunosuppressive therapies, have provided children with intestinal failure and its complications a chance not only for enteral autonomy but also long-term survival through intestinal transplantation (ITx). First described in the 1960's, experience has grown in managing these complex patients both pre- and post-transplant. The goals of this review are to provide a brief history of intestinal transplantation and intestinal rehabilitation in pediatric patients, followed by focused discussions of the indications for ITx, induction and maintenance immunosuppression therapies, common post-operative complications, and outcomes/quality of life post-transplant.