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Transplantation between non-identical humans has been limited by the requirement for chronic immunosuppression (CI). This study demonstrates in a nonhuman primate model that long-term acceptance of incompatible kidney allografts can be achieved without the use of CI. Following incompatible kidney transplantation, rhesus monkey recipients were given a 5-day course of clinical rabbit antithymocyte globulin (RATG). On day 12, unfractionated donor bone marrow (BM) was infused intravenously. Recipients were monitored for T-cell levels and T-cell subset levels with monoclonal antibodies and for responses in one way MLR. Graft survival in untreated control animals was 9.2 +/- 2.8 days. In six animals given RATG only, all died of rejection at a mean 35.8 +/- 5.7 days. Of five animals given RATG and donor BM (mean 2.5 RhLA mismatches, mean MLC 12.7), four are alive at 150 days, 248 days, 342 days, and 401 days (median 248 days). The ATG-BM infused group showed a prolonged imbalance of their OKT4/OKT8 cell ratio and cellular suppression of MLR responsiveness. The long-term survival obtained in these outbred primates is apparently due to a synergistic immunoregulatory effect induced by the RATG and donor BM. The model described is apparently the first report of long-term survival of outbred higher primates without CI and may represent a technique for producing tolerance without CI in the human.

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