NK cells are innate immune cells implicated in ALS; whether NK cells impact ALS in a sex-and age-specific manner was investigated. In mice, NK cells were depleted in male and female SOD1 G93A ALS mice, survival and neuroinflammation were assessed, and data were stratified by sex. NK cell depletion extended survival in female but not male ALS mice with sex-specific effects on spinal cord microglia. In humans, NK cell numbers, NK cell subpopulations, and NK cell surface markers were examined in prospectively collected blood from ALS and control subjects; longitudinal changes in these metrics were correlated to Revised ALS Functional Rating Scale (ALSFRS-R) slope and stratified by sex and age. Expression of NK cell trafficking and cytotoxicity markers were elevated in ALS subjects, and changes in CXCR3+ NK cells and seven trafficking and cytotoxicity markers (CD11a, CD11b, CD38, CX3CR1, NKG2D, NKp30, NKp46) correlated with disease progression. Age impacted the associations between ALSFRS-R and markers NKG2D and NKp46, while sex impacted the NKp30 association. Collectively, these findings suggest that NK cells contribute to ALS progression in a sex-and age-specific manner and demonstrate that age and sex are critical variables when designing and assessing ALS immunotherapy.

Amyotrophic lateral sclerosis (ALS) is a fatal and incurable neurodegenerative disease with few therapeutic options. However, the immune system, including natural killer (NK) cells, is linked to ALS progression and may constitute a viable therapeutic ALS target. Tofacitinib is an FDA-approved immunomodulating small molecule which suppresses immune cell function by blocking proinflammatory cytokine signaling. This includes the cytokine IL-15 which is the primary cytokine associated with NK cell function and proliferation. However, the impact of tofacitinib on NK activation and cytotoxicity has not been thoroughly investigated, particularly in ALS. We therefore tested the ability of tofacitinib to suppress cytotoxicity and cytokine production in an NK cell line and in primary NK cells derived from control and ALS participants. We also investigated whether tofacitinib protected ALS neurons from NK cell cytotoxicity. Finally, we conducted a comprehensive pharmacokinetic study of tofacitinib in mice and tested the feasibility of administration formulated in chow. Success was assessed through the impact of tofacitinib on peripheral NK cell levels in mice. We found tofacitinib suppressed IL-15-induced activation as measured by STAT1 phosphorylation, cytotoxicity, pro-inflammatory gene expression, and pro-inflammatory cytokine secretion in both an NK cell line and primary NK cells. Furthermore, tofacitinib protected ALS neurons from NK cell-mediated cytotoxicity. In mice, we found tofacitinib bioavailability was 37% in both male and female mice; using these data we formulated mouse containing low and high doses of tofacitinib and found that the drug suppressed peripheral NK cell levels in a dose-dependent manner. These results demonstrate that tofacitinib can suppress NK cell function and may be a viable therapeutic strategy for ALS.