Ruiz-Garcia R, et al. - Heterozygous gain-of-function mutations in PI3K110 lead to lymphadenopathy, lymphoid hyperplasia, Epstein-Barr virus (EBV) and cytomegalovirus (CMV) viremia, and sinopulmonary infections. Researchers, herein, looked at the functional and phenotypic effect of PI3K110δ mutations on NK cell subsets and cytotoxic function in view of the known role of NK cell function in the control of EBV and CMV. In this study, PI3K110δ mutation-induced novel NK cell functional deficiency was described, which was a likely contributor to the severe viremia observed in these patients. Data reported that NK cell function was partially restored by rapamycin treatment.