Cancer immunotherapy in a neglected population: The current use and future of T-cell-mediated checkpoint inhibitors in organ transplant patients

Although the indications for immune checkpoint inhibitors continue to grow, organ transplant recipients with advanced malignancies have been largely excluded from clinical trials testing the safety and efficacy of these therapies given their need for chronic immunosuppression and the risk of allograft rejection. With the rapid growth of transplant medicine and the increased risk of malignancy associated with chronic immunosuppression, it is critical that we systematically analyze the available data describing immune checkpoint blockade in the organ transplant population. Herein we provide a current and comprehensive review of cases in which immune checkpoint blockade was used on organ transplant recipients. Furthermore, we discuss the differences in efficacy and risk of allograft rejection between CTLA-4 and PD-1 inhibitors and make recommendations based on the limited available clinical data. We also discuss the future of immune checkpoint blockade in this subpopulation and explore the emerging data of promising combination therapies with mTOR, BRAF/MEK, and BTK/ITK inhibitors. Further clinical experience and larger clinical trials involving immune checkpoint inhibitors, whether as monotherapies or combinatorial therapies, will help develop regimens that optimize anti-tumor response and minimize the risk of allograft rejection in organ transplant patients.