Haemolysis after T‐cell depleted bone marrow transplantation involving minor ABO incompatibility

9 recipients of T-cell depleted allogeneic bone marrows (8 group A, 1 group AB) from group 0 donors were monitored after transplantation. Free anti-A/B was demonstrable in 8 of the 9 recipients 10-19 d post-transplant, 5 patients developed a positive direct anti-globulin test and 7 showed a rise in bilirubin. The presence of antibody was generally unrelated to the infusion of incompatible plasma, although 2 patients who also received anti-CMV immunoglobulin subsequently shown to contain high titre IgG anti-A/B were more severely affected, sustaining a fall in Hb of up to 2 g/d. These observations suggest that, after T-cell depleted bone marrow transplantation, immunocompetent B lymphocytes of donor origin are transferred, secrete antibody in the recipient, and may be responsible for self-limiting haemolytic episodes.