Influence of ABO compatibility on haploidentical hematopoietic stem-cell transplant

Introduction: Allogenic hematopoietic stem cell transplantation (HSCT) is the only curative treatment for hematologic malignancies. Nowadays, usually, haploidentical stem cell transplant is performed across the ABO blood group barrier; however, the effect of ABO incompatibility on haploidentical hematopoietic stem-cell transplantation is still uncertain. Methodology: Retrospective analysis of data of patients who underwent haploidentical hematopoietic stem-cell transplantation at our hospital was performed. The patient cohort was classified in to two arms: ABO compatible and ABO-incompatible haploidentical stem cell transplantation. ABO-incompatible was further categorized as major mismatch, minor mismatch and bidirectional mismatch. The average follow-up period was 6 months posttransplant for which the following parameters were studied: (a) engraftment kinetics for white blood cell (WBC) and platelets, (b) graft rejection, (c) overall graft survival, (d) graft-versus-host disease (GVHD), and (e) clinical variation in outcome for patients receiving peripheral blood stem cell/bone marrow harvest (BMH) as the source of stem cells. Results: The median age of recipients for both ABO compatible and ABO incompatible was 24 years and most of them were parent-offspring transplants. A total of 39 patients underwent haploidentical stem cell transplantation during the study period. Our cohort consisted of 23 ABO-compatible patients and 17 ABO incompatible patients. Out of these 17, 6 were major mismatch, 11 were minor mismatch and none were bidirectional mismatch. Of these 39 patients, 82% (32/39) engrafted within the normal expected time frame. The average days to WBC and platelet engraftment in these subgroups were noted to be as follows: Major – 12 and 18 days, compatible – 9 and 17 days, and minor – 10 and 17 days, respectively. Graft failure was observed in 20% (8/39) of patients, of which 4 patients had undergone ABO-compatible transplants while 4 patients had undergone minor ABO incompatible transplants. In this study, we observed that major ABO incompatibility had severe risk of GVHD (17%) compared to compatible (39%) and minor (27%) blood group mismatch. The overall survival rate in 6 months was equal (70%) in both arms. 5/39 patients, i.e., 12% received BMH as the source of stem cells, of these 80% are alive. Conclusion: Haploidentical transplants done in patients with ABO-incompatible donors had outcomes comparable to the ABO-compatible group. The risk of severe GVHD did not increased in the ABO mismatch group. Recipient of BMH had a marginally better graft survival.