Cytotoxic Granzyme C Expressing ILC1s Contribute to Antitumor Immunity and Neonatal Autoimmunity

Innate lymphocytes are integral components of the cellular immune system that coordinates host defense against a multitude of challenges and can trigger immunopathology when dysregulated. Natural killer (NK) cells and innate lymphoid cells (ILCs) are innate immune effectors postulated to functionally mirror conventional cytotoxic T lymphocytes and helper T cells, respectively. Here, we show that the cytolytic molecule granzyme C was surprisingly expressed in cells with the phenotype of type 1 ILCs (ILC1s) in mouse liver and salivary gland. Cell fate-mapping and transfer studies revealed that granzyme C-expressing innate lymphocytes could be derived from ILC progenitors and did not interconvert with NK cells, ILC2s, or ILC3s. Granzyme C defined a maturation state of ILC1s, which required the transcription factor T-bet and to a lesser extent Eomes specifically in the salivary gland for their maintenance. Furthermore, transforming growth factor-b (TGF-b) signaling promoted maintenance of granzyme C-expressing ILC1s in the salivary gland and in the tumor of a transgenic breast cancer model, and their depletion caused accelerated tumor growth. ILC1s gained granzyme C expression following interleukin-15 (IL-15) stimulation, which enabled perforin-mediated cytotoxicity. Strikingly, constitutive activation of the IL-15-regulated transcription factor Stat5 in granzyme C-fate-mapped ILC1s triggered lethal perforin-dependent autoimmunity in neonatal mice. Thus, granzyme C marks a cytotoxic effector state of ILC1s, broadening their function beyond 'helper-like' lymphocytes. Overall design: ATAC-seq and bulk RNA-seq data sets analyzed in Nixon, et al. 2022. Murine cell populations profiled by ATAC-seq include two populations with an NK cell phenotype (NK1.1+NKp46+CD49a-CD49b+) from the liver and spleen, and two populations with an ILC1 phenotype (NK1.1+NKp46+CD49a+) from the liver and salivary gland (Figures 1 and S1, Tables S1 and S2). Murine cell populations profiled by bulk RNA-seq from the murine liver include S1pr5eGFP+ NK cells as well as three different ILC1 populations: ILC1s with current granzyme C expression (GzmC+GzmcFM+, double-positive [DP]), past but not current granzyme C expression (GzmC-GzmcFM+, fate mapped single-positive [FMSP]), and no history of expression (GzmC-GzmcFM-, double-negative [DN]) (Figures 6, S9, and S10; Tables S3 and S4). Four DP, four FMSP, three DN, and four NK cell samples were processed from a total of six mice.