ABH-antigens and A-and B-glycosyltransferase activity were examined in four patients who received an ABO-incompatible bone marrow transplant from HLA-matched donors. ABO phenotype and ABO genotype were analyzed using flow cytometry and polymerase chain reaction with sequence specific reaction, respectively. On day 14 after bone marrow transplantation (BMT), the ABO genotype of erythroid burst-forming units was converted into the ABO genotype of the donors in all of the recipients. Afterward,

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... phenotype of red blood cells. (RBC) in all recipients completely changed to that of the donors. Rh, P, Diego, Kidd, Duffy and MNSs phenotypes were also changed into the donor's phenotypes. However, in one patient the Lewis blood type did not change into the donor's phenotype. Similarly, using an elution method, ABH antigens of the recipients were detected in RBC in all of the recipients after BMT. In two recipients, the serum glycosyltransferase activities of the recipients were only detected after BMT. These findings indicate that ABH antigens may be released from non-blood cells and adsorbed by RBC, although the possibility of ABO chimeras or unknown mechanisms is not ruled out. Further studies are needed to determine the nature of ABH antigens eluted from RBC of recipients receiving an ABO-incompatible bone marrow transplant.