Incidence Of Hla Loss In A Global Multicentric Cohort Of Post-Transplantation Relapses: Results From The Hlaloss Collaborative Study

Introduction. Genomic loss of an HLA haplotype encoding incompatible alleles (“HLA loss”) has been described in previous single-center studies as a mechanism by which leukemic cells evade the graft-versus-leukemia effect mediated by alloreactive donor T cells and outgrow into a clinically evident relapse. HLA loss accounts for up to 30% of relapses after HLA-haploidentical transplants (Crucitti, Leukemia 2015), but the actual frequency and clinical relevance of this phenomenon in unrelated donor HSCTs, including cord blood transplants, are largely unknown. Here we present the first global collaborative study to investigate the incidence of HLA loss across different transplant settings.