Transplantation Tolerance through Hematopoietic Chimerism

Negative Vaccination Strategies for Promotion of Transplant Tolerance

Organ transplantation requires the use of immunosuppressive medications that lack antigen specificity, have many adverse side effects, and fail to induce immunological tolerance to the graft. The safe induction of tolerance to allogeneic tissue without compromising host responses to infection or enhancing the risk of malignant disease is a major goal in transplantation. One promising approach to achieve this goal is based on the concept of "negative vaccination." Vaccination (or actively acquired immunity) involves the presentation of both a foreign antigen and immunostimulatory adjuvant to the immune system to induce antigen-specific immunity. By contrast, negative vaccination, in the context of transplantation, involves the delivery of donor antigen before or after transplantation, together with a "negative adjuvant" to selectively inhibit the alloimmune response. This review will explore established and emerging negative vaccination strategies for promotion of organ or pancreatic islet transplant tolerance. These include donor regulatory myeloid cell infusion, which has progressed to early-phase clinical trials, apoptotic donor cell infusion that has advanced to nonhuman primate models, and novel nanoparticle antigen-delivery systems.

Delayed graft rejection in autoimmune islet transplantation via biomaterial immunotherapy

The induction of operational immune tolerance is a major goal in beta-cell replacement strategies for the treatment of type 1 diabetes. Our group previously reported long-term efficacy via biomaterial-mediated programmed death ligand 1 (PD-L1) immunotherapy in islet allografts in nonautoimmune models. In this study, we evaluated autoimmune recurrence and allograft rejection during islet transplantation in spontaneous nonobese diabetic (NOD) mice. Graft survival and metabolic function were significantly prolonged over 60 days in recipients of syngeneic islets receiving the biomaterial-delivered immunotherapy, but not in control animals. The biomaterial-mediated PD-L1 immunotherapy resulted in delayed allograft rejection in diabetic NOD mice compared with controls. Discrimination between responders and nonresponders was attributed to the enriched presence of CD206+ program death 1+ macrophages and exhausted signatures in the cytotoxic T cell compartment in the local graft microenvironment. Notably, draining lymph nodes had similar remodeling in innate and adaptive immune cell populations. This work establishes that our biomaterial platform for PD-L1 delivery can modulate immune responses to transplanted islets in diabetic NOD mice and, thus, can provide a platform for the development of immunologic strategies to curb the allo- and autoimmune processes in beta-cell transplant recipients.

Human kidney-derived hematopoietic stem cells can support long-term multilineage hematopoiesis

Long-term multilineage hematopoietic donor chimerism occurs sporadically in patients who receive a transplanted solid organ enriched in lymphoid tissues such as the intestine or liver. There is currently no evidence for the presence of kidney-resident hematopoietic stem cells in any mammal species. Graft-versus-host-reactive donor T cells promote engraftment of graft-derived hematopoietic stem cells by making space in the bone marrow. Here, we report full (over 99%) multilineage, donor-derived hematopoietic chimerism in a pediatric kidney transplant recipient with syndromic combined immune deficiency that leads to transplant tolerance. Interestingly, we found that the human kidney-derived hematopoietic stem cells took up long-term residence in the recipient's bone marrow and gradually replaced their host counterparts, leading to blood type conversion and full donor chimerism of both lymphoid and myeloid lineages. Thus, our findings highlight the existence of human kidney-derived hematopoietic stem cells with a self-renewal ability able to support multilineage hematopoiesis.