Chan YLT, et al. - In this current study, researchers investigated very early natural killer (NK) cell reconstitution in patients following T cell-depleted allogeneic stem cell transplantation (allo-SCT) and found that clinical outcome was crucially determined by robust reconstitution of immunoregulatory NK cells by day 14 after allo-SCT. This indicated that development of the T cell-mediated alloreactive immune response may be suppressed by NK cells via IL-10 production.