Mapping human natural killer cell development in tonsil

Secondary lymphoid tissue, including tonsil, supports human NK cell development, but the spatial organization and tissue niches that drive this differentiation remain undefined. Here, we used single cell analysis of cyclic immunofluorescence to generate a comprehensive atlas of human NK cell development in tonsil. By integrating regional localization, chemokine signaling, cytokine availability, and cell phenotype, we show that NK cell differentiation follows a reproducible spatial trajectory defined by stage-specific cell-cell interactions. CD34+ NK cell progenitors are found in the interfollicular domain in proximity to high endothelial venules, consistent with this route of progenitor entry into tissue. Mature NK cells are primarily found in the T cell-rich parafollicular domain, where they interact with other NK cells and T cell subsets. Local inflammation increases NK cell frequency in tissue through both proliferation of NK progenitors and increased frequency of mature NK cells. Finally, we identify a subset of tonsil stromal cells that support differentiation of NK cells in vitro and proliferation of NK precursors in situ. Together, these findings demonstrate that spatial localization defines human NK cell development and provide an in situ definition of niches that support human NK cell differentiation in tonsil.