Significance of Rh Mismatch in Allogeneic Hematopoietic Progenitor Cell Transplants

The Rh D antigen is one of the most immunogenic red blood cell antigens know.  Despite this, it is not considered in matching schemes for hematopoietic progenitor cell (HPC) transplants.  The frequency of anti-D after Rh mismatched allogeneic HPC transplants is reportedly low.  The objective of this study was to retrospectively study Rh mismatched HPC transplants and examine both allogeneic anti-D formation as well as transplant outcome measures.  From January 1999 to April 2011, 104 consecutive adult Rh mismatched HPC transplants were performed at our institution and were available for review.  We compared transplants with Rh+ recipients with Rh- donors (R+/D-, n=60) to those with Rh- recipients and Rh+ donors (R-/D+, n+44).  There was no difference in underlying diagnoses, graft source, dose of HPC, degree of HLA matching, conditioning, or type of graft versus host disease (GVHD) prophylaxis.  The median follow-up was 655.5 days (range 14 – 4264 days).  Only 2 patients formed anti-D during the follow-up period, and both were in the R+/D- group of transplants.  One was never exposed to Rh-positive blood products.  The second patient was exposed to multiple Rh-positive apheresis platelet products prior to antibody formation.  Ten patients formed other red cell alloantibodies with no statistical difference between groups.  The most common antibody formed was anti-E.  The overall use of rbc’s and platelets post transplant was similar in both groups, although the use of Rh-positive rbc’s was more common in the R+/D- group pre-transplant, and the R-/D+ group post-transplant.  A low incidence of chronic GVHD was seen in both groups (82% of R+/D- transplants had no  chronic GVHD, 64% of R-/D+ transplants had no chronic GVHD, p=0.045).  No difference in platelet and neutrophil engraftment was demonstrated.