Methyl-Guanine-Methyl-Transferase Transgenic Bone Marrow Transplantation Allows N,N-bis(2-chloroethyl)-Nitrosourea Driven Donor Mixed-Chimerism Without Graft-Versus-Host Disease, and With Donor-Specific Allograft Tolerance

Antigen Specific Regulatory T Cells in Kidney Transplantation and Other Tolerance Settings

Kidney transplantation is the most common solid organ transplant and the best current therapy for end-stage kidney failure. However, with standard immunosuppression, most transplants develop chronic dysfunction or fail, much of which is due to chronic immune injury. Tregs are a subset of T cells involved in limiting immune activation and preventing autoimmune disease. These cells offer the potential to provide tolerance or to allow reduction in immunosuppression in kidney transplants. The importance of Tregs in kidney transplantation has been shown in a number of seminal mouse and animal studies, including those with T cell receptors (TCRs) transgenic Tregs (TCR-Tregs) or Chimeric Antigen Receptor (CAR) Tregs (CAR-Tregs) showing that specificity increases the potency of Treg function. Here we outline the animal and human studies and clinical trials directed at using Tregs in kidney transplantation and other tolerance settings and the various modifications to enhance allo-specific Treg function in vivo and in vitro.

Bone marrow chimerism as a strategy to produce tolerance in solid organ allotransplantation

PURPOSE OF REVIEW

Clinical transplant tolerance has been most successfully achieved combining hematopoietic chimerism with kidney transplantation. This review outlines this strategy in animal models and human transplantation, and possible clinical challenges.

RECENT FINDINGS

Kidney transplant tolerance has been achieved through chimerism in several centers beginning with Massachusetts General Hospital's success with mixed chimerism in human leukocyte antigen (HLA)-mismatched patients and the Stanford group with HLA-matched patients, and the more recent success of the Northwestern protocol achieving full chimerism. This has challenged the original view that stable mixed chimerism is necessary for organ graft tolerance. However, among the HLA-mismatched kidney transplant-tolerant patients, loss of mixed chimerism does not lead to renal-graft rejection, and the development of host Foxp3+ regulatory T cells has been observed. Recent animal models suggest that graft tolerance through bone marrow chimerism occurs through both clonal deletion and regulatory immune cells. Further, Tregs have been shown to improve chimerism in animal models.

SUMMARY

Animal studies continue to suggest ways to improve our current clinical strategies. Advances in chimerism protocols suggest that tolerance may be clinically achievable with relative safety for HLA-mismatched kidney transplants.