Evaluation of Immunocompetence and Biomarkers of Tolerance in Chimeric and Immunosuppression-free Kidney Allograft Recipients

Background. Thirty-seven patients have received a living-donor kidney transplant in a phase 2 study designed to induce tolerance with facilitated allogeneic hematopoietic stem cell transplant. The study protocol is based on tolerogenic CD8+/T-cell receptor− facilitating cells (FCR001; also including hematopoietic stem cells and αβ-T-cell receptor+ T cells) and low-dose, nonmyeloablative conditioning. Persistent chimerism allowing full immunosuppression (IS) withdrawal was achieved in 26 patients (time off IS 36–123 mo). Methods. We evaluated biomarkers of tolerance through urinary cell mRNA profiling and immunocompetence to respond to vaccination in these patients. We also assessed kidney function and metabolic parameters compared with standard-of-care patients on IS. Results. Persistently chimeric patients retained chimerism after removal of IS and remained rejection free without donor HLA–specific antibody development. The presence of donor chimerism at >50% correlated with a signature of tolerance in urinary cell mRNA profiles, with a uniquely elevated increase in the ratio of cytotoxic T lymphocyte–associated protein 4 to granzyme B mRNA. Tolerance was associated with protection from recurrence of immune-mediated causes of kidney disease. Tolerant participants were safely vaccinated, developed protective immune responses, and did not lose chimerism after vaccination. When compared with kidney transplant recipients treated with standard IS, tolerant participants showed stable kidney function and reduced medication use for hypertension and hyperlipidemia. Conclusions. These results suggest that elimination of IS has distinct advantages in living-donor kidney allograft recipients.