Background: The most favorable protocol for transplantation is inducing unresponsiveness before operation by means of nondangerous modalities. This would permit discontinuance of long-term use of immunosuppressants. In this study we developed a potential protocol for inducing unresponsiveness to islet allografts by preoperative donor spleen cell inoculation (DSI) and a single injection of FK 506.
Methods: BALB/c (H-2d) and C57BL/6 (H-2b) mice were used as islet donors and recipients, respectively. The streptozocin-induced diabetic mice that had been given DSI at a dose of 1 x 10(7) or 1 x 10(4) and a single injection of FK 506 (10 mg/kg intramuscularly) at different schedules (on day 1, 3, 5, or 7 relative to DSI on day 0) were subjected to islet allografting on day 10.
Results: All islet recipients returned to normoglycemia within a few days with no toxic effect of FK 506 treatment. DSI at a dose of 1 x 10(7) alone led to shortening of the mean survival time to 10.1 +/- 4.1 days, as compared with 13.5 +/- 6.3 days for the untreated animals. In contrast, marked prolongation of graft survival was induced when FK 506 was given on day 3 (> 84 +/- 27.3 days, p < 0.0001) or on day 5 after DSI (> 50.9 +/- 46.0 days, p < 0.05). Five of seven allografts given FK 506 on day 3 and three of seven allografts given FK 506 on day 5 survived indefinitely. Other time schedules of DSI and FK 506 treatment (on day 1 or 7 after DSI) or FK 506 treatment alone had no significant effect on mean survival time. With the same protocol, third-party islet allografts (C3H) were immediately rejected (10.6 +/- 2.6 days).
Conclusions: Prolongation of islet allograft survival was induced by certain doses of DSI and preoperative FK 506 treatment. This modality prevents an adverse effect of FK 506 on grafted islets and can induce unresponsiveness to islet allografts, offering a protocol for successful clinical islet transplantation.