Abstract
In this issue of Blood, Umino and colleagues1 reveal the intricate immune interactions that contribute to chronic graft-versus-host disease (cGVHD) after allogeneic hematopoietic cell transplantation (HCT) by identifying drivers of antibody production, specifically, the importance of distinct HLA class II alleles in minor histocompatibility antigen (mHA)-driven alloimmunity by H-Y antigens in sex-mismatched HCT.