Decreased effect of immunosuppression on immunocompetence in African--Americans after kidney and liver transplantation.

Several studies indicate that the poorer outcomes for African--Americans after transplantation may be due to decreased effectiveness of immunosuppressive agents. Using an in vitro test of immunocompetence (IMC), we measured the effects of immunosuppression on African-American, compared with Caucasian, kidney or liver transplantation recipients. The IMC result was the highest of three mixed lymphocyte culture responses using validated stimulator cell pools. A total of 293 tests were done in Caucasians and 144 in African--Americans. Overall, the IMC for African--Americans was 38, compared with 19 for Caucasians (p<0.01). This decreased effect of immunosuppression (higher IMC) was the same for liver as for kidney transplant recipients, occurred at the 2--3-yr interval, and was largely in patients of tacrolimus (FK506), with a strong but not significant trend in cyclosporine (CYA) recipients. The two groups were on the same nominal immunosuppression and FK506 and CYA levels were not different. We conclude that African-Americans retain more immune responsiveness on equivalent dose immunosuppression, notable particularly in years 2--3 after transplantation when earlier graft loss occurs in this group.