Toxoplasma gondii Infection Promotes NK Cell Conversion into ILC1s and Heterogeneous ILC1 Populations

Innate lymphoid cells (ILCs) comprise several subsets that were originally classified based on their cytokine production profiles. Natural killer (NK) cells and type 1 ILCs (ILC1s) were initially classified together, but recent data supported their separation into different lineages. Here we describe how infection with the parasite Toxoplasma gondii induces changes to NK1.1+ NKp46+ cells that persist independent of ongoing infection. Notably, there is an expansion of Eomes– CD49a+ cells that superficially resemble ILC1s, but express unique genes, circulate throughout the vasculature, and possess distinct epigenetic marks. Single-cell RNA sequencing confirms T. gondii-induced Eomes– CD49a+ cells are distinct from both conventional NK cells and ILC1s. Furthermore, there is heterogeneity within this population, as both conventional NK cells and ILC1s contribute to their formation. Indeed, downregulation of Eomes within conventional NK cells accounts for most T. gondii-induced Eomes– CD49a+ cells, indicating that NK cells can give rise to cells resembling ILC1s during infection. Overall design: Droplet-based 3' end massively parallel single-cell RNA sequencing was performed by encapsulating sorted live CD45+ tumor infiltrating cells into droplets and libraries were prepared using Chromium Single Cell 3' Reagent Kits v2 according to manufacturer's protocol (10x Genomics). The generated scRNAseq libraries were sequenced using an Illumina HiSeq3000.