Ruxolitinib partially reverses functional NK cell deficiency in patients with STAT1 gain-of-function mutations

Background: Natural Killer (NK) cells are critical innate effector cells whose development is dependent on the JAK-STAT pathway. NK deficiency can result in severe or refractory viral infections. Patients with Signal Transducer and Activator of Transcription (STAT)1 gain of function (GOF) mutations have increased viral susceptibility. Objective: We sought to investigate NK cell function in STAT1 GOF patients. Methods: NK cell phenotype and function were determined in 16 STAT1 GOF patients. NK cell lines expressing patient mutations were generated with CRISPR-Cas9 mediated gene editing. STAT1 GOF NK cells were treated in vitro with ruxolitinib. Results: Peripheral blood NK cells from of STAT1 GOF patients had impaired terminal maturation. Specifically, patients with STAT1 GOF mutations have immature CD56dim NK cells with decreased expression of CD16, perforin, CD57 and impaired cytolytic function. STAT1 phosphorylation was elevated but STAT5 was aberrantly phosphorylated in response to IL-2 stimulation. Upstream inhibition of STAT signaling with the small molecule JAK1/2 inhibitor ruxolitinib in vitro and in vivo restored perforin expression in CD56dim NK cells and partially restored NK cell cytotoxic function. Conclusions: Properly regulated STAT1 signaling is critical for NK cell maturation and function. Modulation of elevated STAT1 phosphorylation with ruxolitinib is an important option for therapeutic intervention in patients with STAT1 GOF mutations.