Memory T cells: A helpful guard for allogeneic hematopoietic stem cell transplantation without causing graft-versus-host disease.

Graft-versus-host disease (GVHD) is a major complication of allogeneic hematopoietic stem cell transplantation (AHSCT) and the major cause of nonrelapse morbidity and mortality of AHSCT. In AHSCT, donor T cells facilitate hematopoietic stem cell (HSC) engraftment, contribute to anti-infection immunity, and mediate graft-versus-leukemia (GVL) responses. However, activated alloreactive T cells also attack recipient cells in vital organs, leading to GVHD. Different T-cell subsets, including naïve T (TN ) cells, memory T (TM ) cells, and regulatory T (Treg ) cells mediate different forms of GVHD and GVL; TN cells mediate severe GVHD, whereas TM cells do not cause GVHD, but preserve T-cell function including GVL. In addition, metabolic reprogramming controls T-cell differentiation and activation in these disease states. This minireview focuses on the role and the related mechanisms of TM cells in AHSCT, and the potential manipulation of T cells in AHSCT.