Aspects of allograft rejection, IV: Evaluation of new pharmacologic agents for prevention of allograft rejection

Current thinking on chronic renal allograft rejection: issues, concerns, and recommendations from a 1997 roundtable discussion

Chronic rejection accounts for most renal allograft losses after the first year posttransplantation. On March 24 and 25, 1997, a roundtable of five transplant surgeons, two nephrologists, and one pathologist assembled in Dallas, Texas, to review critical issues surrounding chronic renal allograft rejection. This article summarizes the presentations and relevant discussions of this meeting regarding the cause of chronic rejection, clinical diagnoses, risk factors, future prospects for intervention strategies, and general recommendations for the transplant community. Growing evidence indicates that chronic rejection is the aggregate sum of irreversible immunologic and nonimmunologic injuries to the renal graft over time. A history of acute rejection episodes and inadequate immunosuppression, likely attributable to inconsistent cyclosporine exposure or poor patient compliance, are among the most recognizable immunologic risk factors for chronic rejection. Donor organ quality, delayed graft function, and other donor and recipient variables leading to reduced nephron mass are nonimmunologic factors that contribute to the progressive deterioration of renal graft function. Clinical management of renal transplant recipients should incorporate both immunologic- and nonimmunologic-based intervention strategies aimed at minimizing risk factors to thwart the progression of chronic rejection and improve long-term allograft and patient survival.

New immunosuppressive drugs in organ transplantation

An examination of the mechanisms by which four new immunosuppressive drugs--rapamycin, mizoribine, mycophenolate mofetil, and 15-deoxyspergualin--exert their effects reveals three major categories. Rapamycin binds to an intracellular immunophilin. The resulting drug-immunophilin complex inhibits the action of cytokines, thus blocking the activation and proliferation of T cells. Mizoribine and mycophenolate mofetil are antimetabolites that inhibit a key enzyme in the de novo purine biosynthetic pathway. As a result, the proliferation of T cells and B cells is inhibited selectively compared with that of nonlymphoid cells because the salvage pathway is unavailable to lymphocytes. Finally, 15-deoxyspergualin has a unique mechanism of action, which includes suppressive effects on macrophage function, the induction of cytolytic T cells, B-cell reactivity, and antibody responses. The demonstrated synergism among certain immunosuppressants allows reduction in the dose of each agent to minimize the individual toxicities. As more of these new agents become available, it is likely that azathioprine will be replaced, and it may be possible to eliminate the need for long-term maintenance steroid therapy.