TOLERANCE INDUCTION BY PERIOPERATIVE INTRATHYMIC INJECTION IN A RAT "HIGH RESPONDER" COMBINATION:

270 We have recently reported that tolerance was established by intrathymic injection (IT) of donor bone marrow cells at the same time of a BUF(RT1b) to WF(RT1u) heart transplantation to apply for cadaveric organ transplantation. The purpose of this study is to induce tolerance in a rat "high responder", ACI(RT1a) to LEW(RT1l), combination by perioperative IT with use of ALS and FK506. Materials & Methods: Male ACI(RT1a) rats were used as donors, and male LEW(RT1l) rats as recipients. Heterotopic heart transplantation was intraabdominally performed. Intrathymic injectition of 1 × 108 donor BMCs was performed just after heart transplantation. ALS was injected 0.5 ml intraperitoneally each on the day of, and the day after IT, and FK506 was injected intramuscularily. LEW recipients were divided into the following 5 groups. (Table)Tablesummary: Three of 9 ACI grafts prolonged more than 100 days in Group 2 (1 cycle therapy of FK506). The MST in Group 3 was > 100 days. In Group 4, a syngeneic IT protocol of Group 3, all grafts were rejected, within a MST of 47.8 days. In Group 5, received IV injection of IT injection, all grafts were rejected, within a MST of 52.4 days. In MLR and CML assay, tolerant recipients demonstrated hyporesponsiveness against antidonor ACI alloantigens in a donor specific manner. By addition of IL-2, the CTL activity was significantly enhanced. In LDA assay, tolerant rats demonstrated similar fTcp and decreased fThp compared to naive LEW. Immunoregulatory cells did not seemed to be responsible for tolerance mechanism in MLR co-culture and adoptive cell transfer and chimerism was not detected in tolerant rats by FACS. In skin challenge test, tolerant rats had a significantly prolonged donor skin graft survival of 31.7 days as compared to naive LEW rats (9.3 days). Conclusion: Three cycle of FK506 protocol could induce tolerance by IT in a rat "high responder" ACI to LEW combination. Clonal anergy might be responsible for the maintenance of tolerance in this combination. This tolerance mechanism may be due to the decreased IL-2 secretion as well as the decreased CTL activity against antidonor.