UCLA

Epigenetic regulation, changes in gene expression without alterations to the genetic material, has brought to light another layer of regulatory mechanisms that control immune effector processes in response to immune threats such as viral infection, cancer, and autoimmunity. Elucidating epigenetic regulators driving immune cell differentiation and modulation of effector processes are critical to our understanding of endogenous immune responses. Our studies aim to delineate mechanisms driven by an X-linked epigenetic regulator, UTX, in regulation of natural killer (NK) and T cells, two cell types important in the innate and adaptive arms of our immune system.Viral infection outcomes are sex-biased, with males generally more susceptible than females. Paradoxically, the numbers of anti-viral NK cells are increased in males. We demonstrate that while numbers of NK cells are increased in male mice, they display decreased effector function compared to females in mice and humans. These differences were not solely dependent on gonadal hormones, since they persisted in gonadectomized mice. Kdm6a (UTX), an epigenetic regulator which escapes X inactivation, was lower in male NK cells, while NK cell-intrinsic UTX deficiency in female mice increased NK cell numbers and reduced effector responses. Furthermore, mice with NK cell-intrinsic UTX deficiency showed increased lethality to mouse cytomegalovirus (MCMV). Integrative multi-omics analysis revealed a critical role for UTX in regulating chromatin accessibility and gene expression critical for NK cell homeostasis and effector function. Collectively, these data implicate UTX as a critical molecular determinant of sex differences in NK cells. Low oxygen levels, or hypoxia, has been associated with immune defects in multiple contexts. Hypoxia is associated with higher levels of H3K27me3 in CD4+ T cells. T cell-specific deletion of the histone demethylase is sufficient to recapitulate multiple features of hypoxia, including increased H3K27me3 accumulation and decreased production of IFN-γ+ CD4+ T cells in response to IL-12 cytokine stimulation. T cell specific UTX deletion has functional consequences, as mice are more susceptible to colon cancer and is not responsive to IFN-γ-dependent checkpoint therapy with anti-PD-1 treatment. However, mice with loss of UTX in T cells protected from colitis in which IFN-γ production has been tied with pathogenesis. Concomitant RNA and H3K27me3 CUT&Tag sequencing demonstrate an important role for UTX in removing repressive H3K27me3 marks to promote upregulation of IL12/STAT4 pathway genes including Il12rb, Tbx21, and Ifng. Together, these data demonstrate that UTX functions through its demethylase activity to promote Th1 cell differentiation and suggest that hypoxia’s HIF-independent effects on Th1 effector function may be mediated through UTX.