MICROCHIMERISM LINKED TO CYTOTOXIC T-LYMPHOCYTE FUNCTIONAL UNRESPONSIVENESS (CLONAL ANERGY) IN A TOLERANT RENAL-TRANSPLANT RECIPIENT

A patient was found to be functionally tolerant of a maternal kidney a llograft as evidenced by good graft function 5 years after cessation o f all immunosuppressive drug therapy. Despite normal in vitro prolifer ative and IL-2 responses, patient anti-donor 1 degrees MLR cultures yi elded little donor-specific CTL activity in either bulk or limiting di lution analysis (LDA) cultures. Using polymerase chain reaction, the p atient's PBL and skin were found to contain donor-derived Bw6(+) cells . Removal of Bw6(+) donor cells from the patient PBL with mAb and immu nomagnetic beads before stimulation with donor PBL on day 0 failed to restore donor-specific CTL in either bulk 1 degrees MLR or LDA culture s. Restimulation of 1 degrees cultures with donor stimulator cells plu s exogenous IL-2, however, completely restored anti-donor HLA class I- specific CTL, indicating class I-specific CTL precursors were not clon ally deleted. Fresh patient PBL, as well as donor cell-enriched fracti ons, when added at the initiation of 3 degrees MLR cultures, inhibited the generation of anti-donor CTL, whereas donor cell-depleted fractio ns did not. The inhibition was cell dose-dependent, was specific for t he anti-donor response, and was radioresistant (1200 rad). Thus, the c linical tolerance observed in patients with microchimerism may be due to the presence of veto cells within the circulating donor cell pool.