T-Cell suicide gene therapy for organ transplantation: induction of long-lasting tolerance to allogeneic heart without generalized immunosuppression.

Standard immunosuppressive drugs used for allogeneic organ transplantation do not specifically target alloreactive T cells and must be given for the lifetime of the patient, resulting in significant morbidity and mortality. We aimed to induce experimental immune tolerance to vascularized heart allograft using a suicide gene allowing selective elimination of dividing T cells expressing Herpes simplex virus type 1 thymidine kinase upon ganciclovir administration. We show that without ganciclovir, transgenic mice selectively expressing thymidine kinase in T cells rejected a vascularized cardiac allograft in 7 days. In contrast, allograft was definitively accepted after a 7-day course of ganciclovir initiated at the time of allotransplantation. Interestingly, T cells from both rejecting and tolerant mice proliferated in response to donor or third-party allogeneic stimulation. This state of tolerance was challenged through a second vascularized cardiac allotransplantation. Third-party allografts were rejected while those syngeneic to the first allograft were accepted without any additional treatment. These results show that short-term pharmacogenetic immunosuppression can induce long-lasting, robust, and specific tolerance to solid vascularized allograft without generalized continuous immunosuppression.