Alloimmunity in pancreas transplantation

Simultaneous combined transplantation: Intricacies in immunosuppression management

Simultaneous combined transplantation (SCT), i.e. the transplantation of two solid organs within the same procedure, can be required when the patients develop more than one end-stage organ failure. The development of SCT over the last 20 years could only be possible thanks to progress in the surgical techniques and in the perioperative management of patients in an ageing population. Performing such major transplant surgeries from the same donor, in a short amount of time, and in critical pathophysiological conditions, is often considered to be counterbalanced by the immune benefits expected from these interventions. However, SCT includes a wide array of different transplant combinations, with each time a different immunological constellation. Recent research offers new insights into the immune mechanisms involved in these different settings. Progress in the understanding of these immunological intricacies help to address the optimal induction and maintenance immunosuppressive treatment strategies. In this review, we summarize the different immunological benefits according to the type of SCT performed. We also incorporate the main outcomes according to the immunological risk at transplantation, and the deleterious impact of preformed or de novo donor-specific antibodies (DSA) in the different types of SCT. Finally, we propose comprehensive and evidence-based induction and maintenance immunosuppression strategies guided by the type of SCT.

Indications, Techniques, and Barriers for Pancreas Transplant Biopsy: A Consensus Perspective From a Survey of US Centers

BACKGROUND

Pancreas transplant biopsy practices for the diagnosis of rejection or other pathologies are not well described.

METHODS

We conducted a survey of staff at US pancreas transplant programs (March 22, 2022, to August 22, 2022) to assess current program practices and perceptions about the utility and challenges in the performance and interpretation of pancreas allograft biopsies.

RESULTS

Respondents represented 65% (76/117) of active adult pancreas transplant programs, capturing 66% of recent pancreas transplant volume in the United States. Participants were most often nephrologists (52%), followed by surgeons (46%), and other staff (4%). Pancreas allograft biopsies were performed mostly by interventional radiologists (74%), followed by surgeons (11%), nephrologists (8%), and gastroenterologists (1%). Limitations in the radiologist's or biopsy performer's comfort level or expertise to safely perform a biopsy, or to obtain sufficient/adequate samples were the two most common challenges with pancreas transplant biopsies. Pancreas transplant biopsies were read by local pathologists at a majority (86%) of centers. Challenges reported with pancreas biopsy interpretation included poor reliability, lack of reporting of C4d staining, lack of reporting of rejection grading, and inconclusive interpretation of the biopsy. Staff at a third of responding programs (34%) stated that they rarely or never perform pancreas allograft biopsies and treat presumed rejection empirically.

CONCLUSIONS

This national survey identified significant variation in clinical practices related to pancreas allograft biopsies and potential barriers to pancreas transplant utilization across the United States. Consideration of strategies to improve program experience with percutaneous pancreas biopsy and to support optimal management of pancreas allograft rejection informed by histology is warranted.

Banff 2022 pancreas transplantation multidisciplinary report: Refinement of guidelines for T cell-mediated rejection, antibody-mediated rejection and islet pathology. Assessment of duodenal cuff biopsies and noninvasive diagnostic methods

The Banff pancreas working schema for diagnosis and grading of rejection is widely used for treatment guidance and risk stratification in centers that perform pancreas allograft biopsies. Since the last update, various studies have provided additional insight regarding the application of the schema and enhanced our understanding of additional clinicopathologic entities. This update aims to clarify terminology and lesion description for T cell-mediated and antibody-mediated allograft rejections, in both active and chronic forms. In addition, morphologic and immunohistochemical tools are described to help distinguish rejection from nonrejection pathologies. For the first time, a clinicopathologic approach to islet pathology in the early and late posttransplant periods is discussed. This update also includes a discussion and recommendations on the utilization of endoscopic duodenal donor cuff biopsies as surrogates for pancreas biopsies in various clinical settings. Finally, an analysis and recommendations on the use of donor-derived cell-free DNA for monitoring pancreas graft recipients are provided. This multidisciplinary effort assesses the current role of pancreas allograft biopsies and offers practical guidelines that can be helpful to pancreas transplant practitioners as well as experienced pathologists and pathologists in training.

Impacts of cryopreservation on phenotype and functionality of mononuclear cells in peripheral blood and ascites

Background

Mononuclear cells in peripheral blood and ascites are important clinical resources commonly used in translational and basic research. However, the impact of different cryopreservation durations and extra freeze-thaw cycles on the number and function of mononuclear cells is unknown.

Methods

Peripheral blood samples (n = 21) and ascites samples (n = 8) were collected from healthy volunteers and ovarian cancer patients. Mononuclear cells were isolated, frozen, and thawed at 6 and 12 months. The impact of cryopreservation on cell viability, the phenotype, and the activation and proliferation of T cells were analyzed by flow cytometry. Single-cell sequencing was applied to investigate the underlying mechanism.

Results

The cell number and viability of mononuclear cells in peripheral blood and ascites were significantly decreased after cryopreservation. The T lymphocytes, especially CD4+ T cells, were affected the most significantly. By contrast, monocytes, natural killer (NK) cells, natural killer T (NKT) cells, and B cells were more tolerant. Meanwhile, T cell proliferation and IL-2 secretion are significantly affected after long-term cryopreservation. Mechanistically, the cell death induced by elevated reactive oxygen species (ROS) was involved in the reduction of CD4+ T cells after cryopreservation.

Conclusions

Our data indicates that different subtypes of mononuclear cells exhibit different tolerance capacities upon cryopreservation. Thus, our research can provide evidence and support for individuals who are conducting experiments using frozen clinical patient-derived mononuclear cells, for basic research or clinical trials. In addition, extra caution is worthwhile when researchers compare immune cell functionality from peripheral blood or ascites across datasets obtained in different cryopreservation conditions.

BSHI and BTS UK guideline on the detection of alloantibodies in solid organ (and islet) transplantation

Solid organ transplantation represents the best (and in many cases only) treatment option for patients with end-stage organ failure. The effectiveness and functioning life of these transplants has improved each decade due to surgical and clinical advances, and accurate histocompatibility assessment. Patient exposure to alloantigen from another individual is a common occurrence and takes place through pregnancies, blood transfusions or previous transplantation. Such exposure to alloantigen's can lead to the formation of circulating alloreactive antibodies which can be deleterious to solid organ transplant outcome. The purpose of these guidelines is to update to the previous BSHI/BTS guidelines 2016 on the relevance, assessment, and management of alloantibodies within solid organ transplantation.

Draining Lymph Nodes in Human Kidney Pancreas Transplant: Potential Implications in Alloimmunity and Tolerance

BACKGROUND

Draining lymph nodes (DLNs) are implicated in alloimmunity and tolerance regulation. The role of DLNs in human organ transplant is unknown due to the lack of relevant clinical tissues.

METHODS

During a combined kidney and pancreas transplant, the distal vena cava and both right and left common and external iliac vessels were mobilized and exposed. Draining lymph nodes along these vessels were removed sequentially and archived before the pancreas transplant. Similarly, the DLNs along the left iliac vessels were removed and archived before implantation of the kidney allograft.

RESULTS

Among 13 patients undergoing kidney and pancreas transplants, 6 had pre- and postreperfusion DLNs clinically archived. The remaining 7 either had only prereperfusion DLNs archived or none. Clinical archiving of DLNs did not alter operative times or parameters.

CONCLUSION

This study describes an approach for clinical archiving of DLNs obtained within the operative field during combined kidney-pancreas transplant in humans. The availability of relevant DLNs is essential for investigating fundamental initial primary immune responses potentially important in allograft alloimmunity and tolerance.

Donor-specific antibodies in kidney transplantation: the University of Wisconsin experience

PURPOSE OF REVIEW

Antibody-mediated rejection (ABMR) is the leading cause of allograft failure in kidney transplant recipients. This article provides a summary of the clinical research relating to donor-specific antibodies (DSA) and ABMR in kidney transplant recipients at the University of Wisconsin-Madison Transplant Center.

RECENT FINDINGS

Over 40% of the kidney transplant candidates on the UNOS waitlist are sensitized, and both preformed and de novo DSA are associated with increased risk of rejection and graft loss. We have developed graded induction-desensitization treatment and monitoring protocols based on the degree of immunologic risk. We have also implemented standard treatment and surveillance strategies for patients with ABMR. Additional important observations from our studies include high rates of ABMR in patients with positive C4d staining in postreperfusion biopsies and rise in DSA at 1 week after transplant, and increased risk of kidney allograft failure in patients with de novo DSA and ABMR, as well as in patients with HLA-DSA undetectable ABMR. We also found worse outcomes with de novo DSA following simultaneous pancreas--kidney and liver--kidney transplantation. Notably, favorable long-term graft outcomes were observed in patients with DSA who do not present the classic histopathological findings of ABMR.

SUMMARY

In order to improve long-term outcomes for kidney transplant recipients, further research focusing on the pathogenic mechanisms elicited by HLA and non-HLA DSA, and novel therapies targeting these pathways is needed.