Search

Memory T cells (T mems) represent a major barrier to allograft tolerance in clinical transplantation. Alloreactive T mems form in response to MHC alloantigen exposure from prior transplant, blood transfusion or pregnancy. Here we investigated the ability to achieve cardiac allograft tolerance in multiparous female non-human primates (NHPs) using IL-6 blockade and mixed chimerism. Eight NHPs (Group A (n=6): male recipients; Group B (n=2): multiparous female recipients) underwent heart and donor bone marrow transplantation with non-myeloablative conditioning including total body and thymic irradiation, ATGAM, aCD154 mAb, cyclosporine, and aIL-6R mAb (tocilizumab, 10 mg/kg IV x7) through day 84 post-transplant (pTx). NHPs were then monitored off immunosuppression. In Group A, 4/6 recipients had >400 days allograft survival pTx; 2 failed from rejection (169, 383 days pTx) [Table]. In Group B, 2/2 failed from rejection by 200 days pTx. Group A had substantially lower CD8+ pre-Tx circulating T mems than Group B [Figure], including the 2 Group A rejectors. Group A had similar magnitude but longer duration of lymphocyte chimerism (median 4.9%, 180 days pTx) than Group B (median 5.3%, 90 days pTx). Mixed chimerism failed to achieve cardiac allograft tolerance in multiparous female NHPs using a protocol successful in males, presumably due to higher pre-transplant host T mem burden. This suggests the need for additional therapy for successful clinical application of this tolerance protocol in specific patient populations. [ABSTRACT FROM AUTHOR]

Mixed hematopoietic chimerism can achieve tolerance of kidney but not heart allografts in non-human primates (NHPs). Inhibiting IL-6 signaling has been shown to dampen inflammation and promote regulatory T cells (T regs) and can be achieved by blocking the cytokine (aIL-6 mAb) or its receptor (aIL-6R mAb). We investigated whether adding aIL-6 or aIL-6R mAb therapy to a mixed chimerism protocol could achieve heart allograft tolerance in NHPs. Twelve MHC-mismatched NHPs underwent simultaneous heart and donor bone marrow transplantation with non-myeloablative conditioning including total body and thymic irradiation, ATGAM, aCD154 mAb, and cyclosporine until day 28 post-transplant (pTx). Group A (n=2) received no aIL-6R/ aIL-6 mAb therapy, Group B (n=6) received aIL-6R mAb (tocilizumab, 10 mg/kg IV x7) through day 84 pTx and Group C (n=4) received aIL-6 mAb (clazakizumab, 50 mg/kg IV x1 then 10 mg/kg SC x6) through day 84 pTx. NHPs were then monitored off immunosuppression for graft function and histologic evidence of rejection. Group A recipients (2/2) had allograft failure due to rejection within 130 days pTx [Table]. In Group B, 4/6 recipients experienced allograft survival >400 days pTx; two failed due to rejection (days 169, 383 pTx). Among Group C recipients, 3/4 are ongoing with functioning heart allografts (days 280, 203, and 168 pTx); one was euthanized for CMV infection. Recipients in Group B had greater magnitude and duration of lymphocyte chimerism (median 4.9%, 180 days pTx) than those in Groups A (median 2.5%, 32 days pTx) or C (median 2.6%, 51 days pTx). There was no difference in peripheral T reg expansion among groups (p>0.05). Blocking IL-6 signaling in a mixed chimerism NHP model induced long-term immunosuppression-free cardiac allograft survival. Further investigation will determine the potential benefit of aIL-6 therapy in avoiding rebound alloimmune responses from accumulation of serum IL-6 following cessation of aIL-6R therapy. [ABSTRACT FROM AUTHOR]

After transplantation of allogeneic tissues and organs, recognition by recipient T cells of donor MHC molecules initiates the pro-inflammatory adaptive immune response leading to allograft rejection. T cell allorecognition has long been known to be mediated via two distinct pathways: the direct pathway in which T cells recognize intact allogeneic MHC molecules displayed on donor cells and the indirect pathway whereby T cells recognize donor MHC peptides processed and presented by recipient antigen-presenting cells (APCs). It is believed that direct allorecognition is the driving force behind early acute allograft rejection while indirect allorecognition is involved in chronic allograft rejection, a progressive condition characterized by graft vasculopathy and tissue fibrosis. Recently, we and others have reported that after transplantation of allogeneic skin and organs, donor MHC molecules are transferred from donor cells to the host's APCs via trogocytosis or extracellular vesicles. Recipient APCs having captured donor MHC molecules can either present them to T cells in their intact form on their surface (semi-direct pathway) or the form of peptides bound to self-MHC molecules (indirect pathway). The present article provides an overview of recent studies evaluating the role of intercellular exchange of MHC molecules in T cell alloimmunity and its contribution to allograft rejection and tolerance., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

The adaptive immune response leading to the rejection of allogeneic transplants is initiated and orchestrated by recipient T cells recognizing donor antigens. T-cell allorecognition is mediated via 3 distinct mechanisms: the direct pathway in which T cells recognize allogeneic major histocompatibility complex (MHC) molecules on donor cells, the indirect pathway through which T cells interact with donor peptides bound with self-MHC molecules on recipient antigen-presenting cells, and the recently described semidirect pathway whereby T cells recognize donor MHC proteins on recipient antigen-presenting cells. In this article, we present a description of each of these allorecognition pathways and discuss their role in acute and chronic rejection of allogeneic transplants., Competing Interests: The authors declare no conflicts of interest., (Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.)

Background: Vascularized composite allografts (VCAs) allow reconstruction of devastating injuries and amputations, yet require lifelong immunosuppression that is associated with significant morbidity. Induction of immune tolerance of VCAs would permit widespread use of these procedures. VCAs are acquired from deceased donors most likely to be fully -MHC-mismatched (in contrast to living-related renal transplant donor-recipient pairs matched at one MHC haplotype). After achieving VCA tolerance in a swine model equivalent to clinical living-related renal transplants (single-haplotype MHC mismatches: e.g., "mother-daughter"/haploidentical), we tested our protocol in MHC class I, class II, and fully-MHC-mismatched pairs. Although class II mismatched swine demonstrated similar results as the haploidentical scenario (stable mixed chimerism and tolerance), our protocol failed to prevent rejection of class I and full mismatch VCAs. Here, we describe a new adapted conditioning protocol that successfully achieved tolerance across MHC class-I-mismatch barriers in swine., Methods: Swine were treated with non-myeloablative total body and thymic irradiation two days prior to infusion of bone marrow cells from an MHC class I-mismatched donor. They also received a short-term treatment with CTLA4-Ig (Belatacept ® ) and anti-IL6R mAb (Tociluzimab ® ) and were transplanted with an osteomyocutaneous VCA from the same donor., Results: Stable mixed chimerism and tolerance of MHC class-I-mismatched VCAs was achieved in 3 recipients. Allograft tolerance was associated with a sustained lack of anti-donor T cell response and a concomitant expansion of double negative CD4 - CD8 - T cells producing IL-10., Conclusions: This study demonstrates the first successful mixed chimerism-induced VCA tolerance in a large animal model across a MHC class-I-mismatch. Future studies aimed at fully-mismatched donor-recipient pairs are under investigation with this protocol., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Lellouch, Andrews, Saviane, Ng, Schol, Goutard, Gama, Rosales, Colvin, Lantieri, Randolph, Benichou and Cetrulo.)

Dynamic profiling of changes in gene expression in response to stressors in specific microenvironments without requiring cellular destruction remains challenging. Current methodologies that seek to interrogate gene expression at a molecular level require sampling of cellular transcriptome and therefore lysis of the cell, preventing serial analysis of cellular transcriptome. To address this area of unmet need, we have recently developed a technology allowing transcriptomic analysis over time without cellular destruction. Our method, TRACE-seq (TRanscriptomic Analysis Captured in Extracellular vesicles using sequencing), is characterized by a cell-type specific transgene expression. It provides data on the transcriptome inside extracellular vesicles that provides an accurate representation of stress-responsive cellular transcriptomic changes. Thus, the transcriptome of cells expressing TRACE can be followed over time without destroying the source cell, which is a powerful tool for many fields of fundamental and translational biology research., Competing Interests: Francois Cherbonneau and Aurore Prunevieille are founders of QUIDDITAS Therapeutics which did not play any role in this study. Dr. Das is a founder of Switch Therapeutics and Long QT Therapeutics, which did not play any role in this study, and has consulted for Amgen., (© 2022 The Author(s).)