INDUCTION OF DONOR-SPECIFIC TOLERANCE TO RAT CARDIAC AND SMALL-BOWEL ALLOGRAFTS BY INTRATHYMIC INOCULATION OF DONOR T-CELLS

We have shown that donor-specific unresponsiveness to cardiac and islet allografts can be induced by intrathymic (IT) inoculation of uv-B-irradiated spleen cells or resting T-cells in the Lewis-to-ACI rat combination. To examine if tolerance to cardiac and small intestinal allografts can be induced in adult animals, we employed intrathymic inoculation of resting donor T-cells combined with sublethal total body irradiation of 200 rads on Day -7 relative to organ transplant and consistently induced permanent donor- specific cardiac allograft survival (>300 days) and small bowel transplant (SBT) survival (>100 days) in the Lewis-to-ACI rat combination. Similarly, IT inoculation of T-cells on Day -7 combined with 1 ml ALS on Days -7 and 0 relative to SBT resulted in indefinite donor-specific graft survival (>100 days) in all recipients without any evidence of graft-versus-host disease (GVHD) in the high responder of Wistar-Furth (WF)-to-Lewis rat combination. In contrast, WF SBT was promptly rejected in recipients pretreated with intravenous administration of donor T-cells and ALS, thus confirming the privileged position of the thymus in the induction of tolerance. The long- term unresponsive ACI recipients challenged 150 days after cardiac transplant with a second-set graft specifically and permanently (>120 days) accepted the second-set SBT without rejecting the primary cardiac grafts and without developing GVHD. Third-party grafts were rejected in a normal fashion. In vitro cell-mediated lymphocytotoxicity assay showed that T-cells obtained from the long-term unresponsive animals had no detectable cytotoxic activity to donor target cells compared to cells obtained from naive rats. Clonal anergy or deletion of precursor cytotoxic T-cells may be the explanation of our findings. This new strategy of thymic reeducation in adult animals is potentially useful in the induction of specific tolerance and in the prevention of GVHD in SBT. © 1993 Academic Press. All rights reserved.