471 In contrast to allograft tolerance, LSFT of XG has few defined parameters and few long term XG to permit detailed studies. We developed a model of cardiac xenograft (CXG) tolerance in the hamster - to rat model using 3 doses of a rabbit - anti-thymocyte globulin splenectomy and 14 days of deoxyspergualin (DSG) at 2.5 mgm/kgm. In 10 animals, 6 or 60% survived past 100 days (mean of 142 days) off immunosuppression and thus had optimal tolerance, while 4 animals rejected their [email protected] mean of 48 +/- 18 days(p<0.05). Tolerant recipients studied at 100 days showed no correlation between T cell parameters (MLC CML or p-CTL) and survival. A significant difference between the two groups was the anti-donor antibody parameters. Both CDC and ADCC antibodies were significantly lower in 100% of LSFT animals (mean of 1:256 vs. 1:2048 in the rejecting animals,p value<0.05) at 14-30 days post transplant. Past 36 days neither CDC nor ADCC antibodies were different between the 2 groups (1:1024 vs. 1:2048, p>0.10). In summary, LSFT of XG is characterized by similar T cell parameters suggesting the T cell was not central to XG rejection or tolerance. LSFT animals in contrast to non-tolerant animal groups had an early block in both CDC and ADCC antibodies up to 30 days indicating a positive correlation of LSFT and early CDC and ADCC block demonstrated to be particularly effective in animals using this immunosuppression treatment. The best correlate of LSFT was a low CDC and ADCC at 1-30 days post-transplant. The low levels of anti-donor antibody had a excellent correlation with a low incidence of long term severe vasculopathy(r=0.86) in the LSFT group. Vasculopathy was an invariable correlate of rejection in animals with early graft loss and conversely was minimal in the LSFT animals. These results indicate a close correlation of anearly (0-30 days) block in anti-donor antibody and long term xenograft survival. Later rises in CDC and ADCC past 30-40 days showed no correlation with either rejection or long term tolerance. Thus, anti-donor antibody patterns critical to graft survival are established early after treatment.