Natural killer (NK) cells play important roles in innate immunity by lysing tumor and virally infected cells and by producing cytokines including interferon‐γ. While NK cell progenitors have been described in the fetal thymus, NK cell generation from hematopoietic stem cells (HSC) in the bone marrow (BM) occurs throughout life, and in athymic mice and humans. Interleukin (IL)‐15 promotes NK development in vitro and is essential for the generation of normal numbers of NK cells in vivo. By characterizing BM cells expressing IL‐15 receptor components, we found marked heterogeneity within the IL‐2 receptor β chain+ (CD122+) subset, which included cells uniquely committed to the NK lineage. These CD122+ NK cell precursors (NKP) are negative for markers used to identify mature NK cells, including NK1.1, DX5 and members of Ly‐49 family, and fail to demonstrate natural cytotoxicity against susceptible targetcells. In vitro culture of NKP generates mature lytic NK1.1+ cells at high frequencies, while they do not give rise to T, B, myeloid or erythroid cells under appropriate conditions. NKP lack transcripts associated with early B and T cell differentiation (pTα, λ5 and CD3ϵ), but express a group of genes (IL‐15Rα, Id2, GATA‐3 and Ets‐1) and the 2B4 marker, which may define NK cell committment. We propose that NKP represent the earliest adult BM precursor uniquely restricted to the NK cell lineage.

The human ovary orchestrates sex hormone production and undergoes monthly structural changes to release mature oocytes. The outer lining of the ovary (cortex) has a key role in defining fertility in women as it harbors the ovarian reserve. It has been postulated that putative oogonial stem cells exist in the ovarian cortex and that these can be captured by DDX4 antibody isolation. Here, we report single-cell transcriptomes and cell surface antigen profiles of over 24,000 cells from high quality ovarian cortex samples from 21 patients. Our data identify transcriptional profiles of six main cell types; oocytes, granulosa cells, immune cells, endothelial cells, perivascular cells, and stromal cells. Cells captured by DDX4 antibody are perivascular cells, not oogonial stem cells. Our data do not support the existence of germline stem cells in adult human ovaries, thereby reinforcing the dogma of a limited ovarian reserve.

SummaryHuman pluripotent stem cells (PSCs) exist in naive and primed states and provide important models to investigate the earliest stages of human development. Naive cells can be obtained through primed-to-naive resetting, but there are no reliable methods to prospectively isolate unmodified naive cells during this process. Here we report comprehensive profiling of cell surface proteins by flow cytometry in naive and primed human PSCs. Several naive-specific, but not primed-specific, proteins were also expressed by pluripotent cells in the human preimplantation embryo. The upregulation of naive-specific cell surface proteins during primed-to-naive resetting enabled the isolation and characterization of live naive cells and intermediate cell populations. This analysis revealed distinct transcriptional and X chromosome inactivation changes associated with the early and late stages of naive cell formation. Thus, identification of state-specific proteins provides a robust set of molecular markers to define the human PSC state and allows new insights into the molecular events leading to naive cell resetting.