Increasing mixed haematopoietic chimaerism after BMT with total depletion of CD4(+) and partial depletion of CD8(+) lymphocytes is associated with a higher incidence of relapse

In this study we analysed the incidence and clinical impact of the persiste nce of host haemopoiesis (mixed chimaerism, MC) after allogeneic BMT in 35 consecutive patients with haematologic malignancies using a total CD4(+) ce ll-depleted graft with an adjusted dose of CD8(+) cells (1 x 10(8)/kg). Chi maerism was assessed by PCR amplification of VNTRs in 30 evaluable patients : 19 non-CML and 11 CML cases which were also evaluated for the BCR-ABL tra nscript by RT-PCR, All but one had complete engraftment with a donor profil e early post-BMT, At the end of the study period, 12 of 30 patients display ed MC (40%), The overall disease-free survival for MC patients was clearly unfavourable when compared to those who exhibited a donor profile (24.7% vs 100%, P = 0.005). However, we found that only two of five patients with MC in the non-CML group relapsed, whereas a clear correlation could be made b etween MC and relapse in CML (seven showed MC, preceding cytogenetic or hae matological relapse in six of them, which displayed a prior BCR-ABL mRNA po sitivity). In addition, a quantitative-PCR approach enabled us to demonstra te that increasing amounts of MC are invariably associated with subsequent relapse, whereas a low stable level of host or complete donor haemopoiesis is consistent with clinical complete remission. Although these results sugg est that the clinical impact of MC may depend on the underlying disease, it is compatible with the concept that the graft-versus-leukaemia effect agai nst CML is mainly exerted by donor CD4(+) lymphocytes, Elimination of this cellular subset may be responsible for the inability of the graft to preven t a progressive increase in the tumor cell burden.