Consequences of ABO incompatibility in multiple myeloma patients undergoing peripheral blood stem cell transplantation after reduced intensity conditioning.

BACKGROUND: Although the ABO blood group is one of two major antigen systems of relevance for transplantation in humans, there are still conflicting data concerning the influence of ABO-incompatibility on transplant outcome. This study investigated the effect of ABO incompatibility in recipients of haematopoietic progenitor cell transplants from related donors after reduced intensity conditioning (RIC) regimens.
MATERIALS AND METHODS: We retrospectively analysed data from 19 multiple myeloma patients included in a prospective RIC allogeneic haematopoietic progenitor cell transplantation protocol, focusing on engraftment, transfusion requirement, Graft-versus-Host Disease, transplant-related mortality and survival.
RESULTS: Five out of the 19 patients (26%) received an ABO-incompatible transplant, with minor ABO-mismatch in two patients (10%), major ABO-mismatch in one case (5%), and bidirectional incompatibility in two cases. Neutrophil recovery was not significantly different between the ABO-compatible and ABO-incompatible groups (p=0.85). At 30 days after transplantation, 12 of 19 patients tested (63%) had engraftment with all cells of donor origin (100% chimeric), and continued to be fully chimeric on day 100+ evaluations. Patients with major/bidirectional ABO incompatibility required more red blood cell and platelet units after transplantation and were transfused for longer periods of time, as compared with patients with minor or no ABO incompatibility. Transient, mild haemolysis was noted in one patient between days 10 and 30. Graft-versus-Host Disease, disease progression and transplant-related mortality were not affected by ABO matching. DISCUSSION: Although delayed red blood cell engraftment and increased transfusion requirements were documented, in this study ABO incompatibility after the RIC protocol used did not impair the clinical outcome.