Evaluation of Blood Group Conversion Following ABO-Incompatible Hematopoietic Stem Cell Transplantation (HCT)

Title: Evaluation of blood group conversion following ABO-incompatible Hematopoietic Stem Cell Transplantation (HCT).

Background:

While there have been a number of reports concerning the influence of AB0 incompatibility on hematopoietic transplantation (HCT) outcomes, data evaluating post-HCT blood group conversions following ABO incompatible transplants remains extremely limited.

Methods:

We performed a single centre retrospective analysis of 97 patients undergoing major or minor or bidirectional ABO-mismatched bone marrow (BM), peripheral blood (PB), and cord blood (CB) hematopoietic stem cell transplantation (HCT) between January2005 – April 2014, in whom engraftment had occurred and blood group data was available. The aim of the study was to analyse the red cell ABO phenotype (forward grouping) and levels of anti-A/B antibodies (reverse grouping) in these patients following the ABO-mismatched transplants.

Results:

97 patients transplanted between January 2004 and April 2014 were included in the analysis. There were 40 (41%) matched sibling, 32 (33%) matched unrelated and 25 (26%) CB transplants. Indications for HSCT included both haematological malignancies (n=87) and benign conditions (n=10). Of these donor recipient pairs, there were 44 (45%) minor, 39 (40%) major and 14 (15%) bidirectional ABO mismatches. All patients had achieved full donor type chimerism at the time of analysis.

Analysis of post –HCT blood group conversion was performed in each of the three groups. Amongst the major mismatch patients (n=39), all had conversion of RBC phenotype to donor ABO phenotype and loss of their host derived anti-donor ABO antibodies. Interestingly, in the minor mismatch patients who were tested (n=44), all the patients had conversion of their RBC phenotype, but 43 out of 44 patients failed to produce recipient directed anti-ABO antibodies. Similarly in the bidirectional mismatch group, all 14 patients converted to donor ABO phenotype, but none produced recipient directed anti-ABO antibodies.

Conclusion:

In one of the largest study looking at this issue, our study demonstrated the lack of a development of recipient directed anti A/B antibodies despite complete donor chimerism in the majority (1 out of 58) of patients undergoing minor or bidirectional ABO-mismatched HSCT. We postulate that this phenomenon may be due to the donor B cell tolerance against host ABO antigen due to the presence of host A and B antigens within other body tissues.