NK-cell education is shaped by donor HLA genotype after unrelated allogeneic hematopoietic stem cell transplantation

The rules governing natural killer (NK)–cell education in the allogeneic environment created by unrelated hematopoietic stem-cell transplantation (HSCT) are still largely elusive, especially in an unrelated donor setting. NK-cell inhibitory receptors for self-human leukocyte antigen (HLA) play a central role in the acquisition or maintenance of NK-cell functional competence. Therefore, the responsiveness of different NK-cell subsets was assessed as a function of their expression or absence of expression of self-HLA–specific inhibitory receptors, in a large cohort (n = 60) of unrelated HSCT recipients. A fully effective NK-cell education process was achieved within the first year after allogeneic HSCT and lasted for at least 3 years thereafter. In addition, HLA-mismatched HSCT led to a stable education pattern that was determined by the donor's HLA ligands. These data suggest that the NK cell's education partner could be of hematopoietic rather than extrahematopoietic origin. This donor-ligand–driven NK-cell education model would suggest a sustained graft-versus-leukemia effect after HLA-mismatched HSCT.