NK cells produce high levels of IL-10 early after allogeneic stem cell transplantation and suppress development of acute GVHD.

Natural killer (NK) cells rapidly reconstitute following allogeneic stem cell transplantation (allo-SCT), at the time when alloreactive T cell immunity is being established. We investigated very early NK cell reconstitution in 82 patients following T cell-depleted allo-SCT. NK cell number rapidly increased, exceeding T cell reconstitution such that the NK:T cell ratio was over 40 by day 14. NK cells at day 14 (NK-14) were donor-derived, intensely proliferating and expressed chemokine receptors targeted to lymphoid and peripheral tissue. Spontaneous production of the immunoregulatory cytokine IL-10 was observed in over 70% of cells and transcription of cytokines and growth factors was augmented. NK-14 cell number was inversely correlated with the incidence of grade II-IV acute graft versus host disease (GVHD). These findings reveal that robust reconstitution of immunoregulatory NK cells by day 14 after allo-SCT is an important determinant of the clinical outcome, suggesting that NK cells may suppress the development of the T cell-mediated alloreactive immune response through production of IL-10.