Comparison of T-cell-depleted BMT and PBPCT with respect to chimerism, graft rejection, and leukemic relapse

Chimerism analysis by DNA-based methods is a valuable diagnostic tool for m onitoring engraftment and leukemic relapse after allogeneic BMT or PBPC tra nsplantation (PBPCT), We investigated the chimerism after T-cell-depleted B MT(n = 32) in comparison with T-cell-depleted PBPCT (n = 39). BM grafts wer e T-cell depleted using the Campath-IgM antibody pins complement, For T-cel l depletion of the PBPC grafts, a selection of CD34(+) cells with or withou t a subsequent CD2/3 depletion was performed. In all patients, the T-cell d ose of the transplant was <10(6)/kg body weight. Between day 13 and day 120 after transplantation, chimerism analysis was done by RFLP or amplified fr agment length polymorphism (PCR-AFLP), with a detection limit of 1%-5% reci pient cells, In the BMT group, 8 of 32 (25%) patients showed a mixed chimer ism, but only one graft rejection and no leukemic relapse occurred after a median follow-up of 41 (3-84) months. All patients with PBPCT revealed a co mplete chimerism of their granulocytes, and 38 of 39 patients showed comple te chimerism of their lymphocytes, Follow-up time in these patients is 7 (2 -21) months, with no graft rejection and two leukemic relapses, G-CSF-mobil ized PBPC are superior to BM cells for full engraftment even after T-cell-d epleted transplantation. The more relevant factor for developing complete c himerism seems to be the quantity and possibly the quality of the stem cell s rather than the residual T-cell load of the graft. However, a mixed chime rism of the lymphocytes early after transplantation does not predict a high er rate of graft rejection or leukemic relapse.