Chimerism after bone marrow transplantation (BMT) was investigated by flow
cytometry analysis of red blood cells (RBCs) and of reticulocytes using a s
eries of selected monoclonal or polyclonal antibodies directed against ABO,
Rhesus, Kell, Duffy or MNSs antigens. The method allows the routine detect
ion of less than 0.1% of positive cells in artificial mixed field populatio
ns. Blood samples from 135 patients undergoing BMT were investigated around
days 15, 30, 45, 60, 90, 180, and then every 6 months after transplantatio
n. Characteristic patterns showing expression of donor red blood cell antig
ens (expansion markers) and concomitant decrease of recipient specific anti
gens (depletion markers) within days 16-20 were observed for 125 successful
ly engrafted patients. Distinct patterns were obtained in 10 patients. A de
lay in engraftment was evidenced in four patients by the absence of chimeri
sm during the first 6 months without any sign of relapse. Re-appearance of
recipient RBCs and reticulocytes was observed in five patients; it was cons
istent with relapse that was later confirmed by clinical, haematological an
d cytogenetic studies. Finally, a stable and partial chimerism with 20% of
RBCs expressing a marker from the recipient was observed in one patient wit
hout any sign of relapse. The reported investigation demonstrated that flow
cytometry of RBCs and reticulocytes represents a powerful method to effici
ently monitor bone marrow transplanted patients on a long-term basis.