A developmental program of early residency promotes the differentiation of divergent uterine NK cell subsets in humans.

Human uterine natural killer cells (uNKs) are a tissue-resident, innate lymphocyte population that have critical roles in supporting pregnancy health. uNKs derive from circulatory cells in the peripheral blood which immigrate into the endometrium and become resident as they reconstitute the uterine lining after menses. How tissue-resident uterine NK cells arise from blood-based precursor cells is unknown. Here, we identify early tissue immigrants, developmental intermediates, and mature effector states in human endometrium. We also uncover a transcriptional program of TGF-β responsive genes that is upregulated in recent tissue immigrants prior to expression of effector molecules. Differences in TGF-β responsiveness of uNK precursors promote differential expression of divergent effector uNK subsets, resulting in either repression or preservation of cytotoxic effector potential. Collectively, these data suggest a molecular mechanism of tissue-resident uNK maturation that links tissue residency with the acquisition of divergent effector functions in human endometrium.