LAUSR

The relevance of donor‐specific human leukocyte antigen (HLA) antibodies in HLA‐mismatched haematopoietic cell transplant (HCT) is known, but the importance of HLA antibodies in HLA‐matched HCT is unclear. We hypothesized that HLA antibodies detected before HCT would cause platelet transfusion refractoriness during HCT and investigated this in a multi‐centre study. Pre‐HCT samples from 45 paediatric patients with sickle cell disease (SCD) undergoing HLA‐matched HCT were tested for HLA class I antibodies. The number of platelet transfusions received before day +45 was compared between those with and without antibodies. Thirteen of 45 (29%) patients had a positive HLA class I antibody screen, and these patients received significantly more platelet transfusions than patients without antibodies (median 19 vs. 7·5, P = 0·028). This platelet transfusion association remained significant when controlling for conditioning regimen. Among alloimmunized patients, there was no association between the panel‐reactive antibody and the number of platelet transfusions. Patients with HLA class I antibodies also had a higher incidence of acute graft‐versus‐host disease (GVHD): 6/13 (46%) vs. 3/32 (9%), P = 0·011. Pre‐HCT HLA class I alloimmunization is associated with increased platelet transfusion support and acute GVHD in paediatric HLA‐matched HCT for SCD. Further studies are needed to investigate the pathobiology of this association.