Early Natural Killer Cell Reconstitution Predicts Overall Survival in T Cell-Replete Allogeneic Hematopoietic Stem Cell Transplantation

- Early robust NK cell immune recovery predicts outcomes after T cell-replete HSCT.
- NK cell count > 150 cells/µL on day 30 is associated with improved OS and less TRM.
- Low NK cell counts are associated with occurrences of bacterial and viral infections.
- Low NK cell counts are associated with increased risk of CMV reactivation.

Early immune reconstitution plays a critical role in clinical outcome after allogeneic hematopoietic stem cell transplantation (HSCT). Natural killer (NK) cells are the first lymphocytes to recover after transplantation and are considered powerful effector cells in HSCT. We aimed to evaluate the clinical impact of early NK cell recovery in T cell-replete transplant recipients. Immune reconstitution was studied in 298 adult patients undergoing HSCT for acute myeloid leukemia, acute lymphoblastic leukemia, and myelodysplastic syndrome from 2005 to 2013. In multivariate analysis NK cell numbers on day 30 (NK30) > 150 cells/µL were independently associated with superior overall survival (hazard ratio, .79; 95% confidence interval, .66 to .95; P = .01). Cumulative incidence analyses showed that patients with NK30 > 150 cells/µL had significantly less transplant-related mortality (TRM), P = .01. Patients with NK30 > 150 cells/µL experienced significantly lower numbers of life-threatening bacterial infections as well as viral infections, including cytomegalovirus. No association was observed in relation to relapse. These results suggest an independent protective effect of high early NK cell reconstitution on TRM that translates into improved overall survival after T cell-replete HSCT.