The protective effect of cytomegalovirus (CMV) reactivation on post-transplant relapse is in part driven by adaptive natural killer (NK) cell responses, according to a study of 647 patients who received allogeneic hematopoietic cell transplant (HCT). Researchers found:

• Compared to CMV seronegative recipients, patients who had reactivated CMV had lower leukemia relapse (26% vs 35%) and superior disease-free survival (55% vs 46%) 1 year after reduced intensity conditioning (RIC).

• This protective effect was independent of age and graft-versus-host disease and was not seen in patients who received myeloablative regimens.

• Analysis of reconstituting NK cells showed that CMV reactivation is associated with both higher frequencies and greater numbers of CD56^dimCD57⁺NKG2C⁺ NK cells, particularly after RIC.

• Expansion of these cells at 6 months post-transplant independently trended toward lower 2-year relapse risk.

Citation: Cichocki F, Cooley S, Davis Z, et al. CD56dimCD57+NKG2C+ NK cell expansion is associated with reduced leukemia relapse after reduced intensity HCT. [Published online ahead of print September 29, 2015]. Leukemia. doi: 10.1038/leu.2015.260.