Transplantation is the treatment of choice for most causes of end stage renal disease.(1, 2) However, without some modification of the recipient's immune system all allografts succumb to rejection. To prevent this, patients must take immunosuppressive drugs for life, generally a combination of steroids, a calcineurin inhibitor (CNI), such as cyclosporine or tacrolimus, and an antiproliferative agent (azathioprine, mycophenolate mofetil or sirolimus).(3-6) Induction with a brief course of an anti-T lymphocyte antibody preparation (daclizumab, basiliximab, muromonab, alemtuzumab, polyclonal anti-thymocyte globulin) is also used in approximately 70% of U.S. transplant centers.

Dependence on immunosuppression tempers the substantial benefit obtained from transplantation (1-13). The typical regimens are relatively complex and expensive. More importantly, they increase the risk of opportunistic infection and malignancy, and have many non-immune side effects that hamper their tolerability. Specifically, CNIs are nephrotoxic, a side effect of significant concern in renal transplantation. Steroids exacerbate osteoporosis and hyperlipidemia, and cause avascular osteonecrosis. Both classes of agent worsen glucose tolerance and hypertension, and are associated with cosmetic effects causing non-compliance. As such, methods of transplantation that lessen the dependence on chronic immunosuppression stand to reduce the risk and expense of transplantation. They must, however, also prevent rejection. Development of alternate therapies that help to minimize the need for lifelong immunosuppression, or eliminate entirely the need for drugs through the induction of tolerance, are therefore of great interest.

Regulatory CD4+CD25+ T cells (Treg) derived from the thymus and/or peripheral tissues have been demonstrated to broadly control T cell reactivity (14). Importantly, Tregs have been shown to control immune responsiveness to alloantigens and significantly contribute to operational tolerance in transplantation models (15, 16). However, there have been limited efforts to harness the therapeutic potential of directly isolated CD4+CD25+ Treg cells for controlling graft rejection and inducing transplantation tolerance, such as for kidney transplants. In order for CD4+CD25+ Treg cells to be used as a clinical treatment, the following cell properties could be necessary: ex vivo generation of sufficient numbers of cells, migration in vivo to sites of antigenic reactivity, ability to suppress rejection in an alloantigen-specific manner, and survival/expansion after infusion for a critical, but currently unknown, period of time. Our published work and that of other investigators has demonstrated 1) the feasibility of expanding Treg ex vivo, 2) the ability of these cells to downregulate allogeneic immune responses in vitro, and 3) the efficacy of Treg for prevention of allograft rejection in animal models (15,16). We have developed strategies for the ex vivo expansion of naturally occurring human Tregs (nTregs) that allow for the practical employment of this cellular therapy in the clinic. Our central hypothesis is that sufficient human nTreg can be expanded ex vivo and used to both prevent renal transplant rejection and facilitate the reduction and subsequent withdrawal of drug-based immunosuppression. This study will allow for us to define the safety of Treg adoptive cellular transfer (TRACT) in living donor renal transplant recipients that draws upon our extensive preclinical experience with expanded Tregs, as well as our recognized clinical expertise with designing immunosuppressive regimens compatible with this type of therapeutic cell transfer.