Cotransplantation of allogeneic islets with allogeneic testicular cell aggregates allows long-term graft survival without systemic immunosuppression.

We prepared single-cell suspensions of Lewis rat ¿RT1(1/l)¿ testicular cells and cultured these in vitro for 48 h under conditions that promoted the formation of cellular aggregates. In the absence of systemic immunosuppression, the transplantation of a sufficient quantity of these aggregates (containing 11 x 10(6) cells, (75% Sertoli cells), together with 2,000 purified Lewis rat islets, reversed the diabetic state for >95 days in 100% (5/5) of the chemically diabetic Wistar-Furth ¿RT1(u/u)¿ recipients. Similar grafts consisting of islets alone or islets plus 50% fewer testicular cell aggregates survived for only 10 days. Functioning composite allografts harvested from normoglycemic animals at approximately 100 days showed healthy beta-cells in close association with Fas ligand-expressing Sertoli cells. Because no gene therapy protocol is required, the transplantation of composite grafts consisting of purified human allogeneic islets plus human allogeneic testicular cell aggregates can be applied in clinical islet transplantation as soon as it has been proven in a large animal model.