Persistence of recipient human leucocyte antigen (HLA) antibodies and production of donor HLA antibodies following reduced intensity allogeneic haematopoietic stem cell transplantation.

The effects of reduced intensity conditioning (RIC) on human leucocyte antigen (HLA)-alloimmunization and platelet transfusion refractoriness (PTR) following allogeneic haematopoietic stem cell transplantation (Allo-HSCT) are unknown. We studied HLA-alloantibodies in a cohort of 16 patients (eight HLA-alloimmunized with pre-transplant histories of PTR and eight non-alloimmunized controls) undergoing Allo-HSCT using fludarabine/cyclophosphamide-based RIC. Pre- and post-transplant serum samples were analysed for HLA-antibodies and compared to myeloid, T-cell and bone marrow plasma cell chimaerism. Among alloimmunized patients, the duration that HLA-antibodies persisted post-transplant correlated strongly with pre-transplant HLA-antibody mean fluorescence intensity (MFI) and PRA levels (Spearman's rank correlation = 0·954 (P = 0·0048) and 0·865 (P = 0·0083) respectively). Pre-transplant MFI >10,000 was associated with post-transplant HLA antibody persistence >100 d (P = 0·029). HLA-antibodies persisted ≥100 d in 3/8 patients despite recipient chimaerism being undetectable in all lympho-haematopoietic lineages including plasma cells. Post-transplant de-novo HLA-antibodies developed in three control patients with two developing PTR; the donors for two of these patients demonstrated pre-existing HLA-antibodies of equivalent specificity to those in the patient, confirming donor origin. These data show HLA-antibodies may persist for prolonged periods following RIC. Further study is needed to determine the incidence of post-transplant PTR as a consequence of donor-derived HLA alloimmunization before recommendations on donor HLA-antibody screening can be made.