Single-Cell Transcriptomic Landscape Reveals Tumor Specific Innate Lymphoid Cells Associated With Colorectal Cancer Progression

Innate lymphoid cells (ILCs) are tissue-resident lymphocytes differing from conventional T lymphocytes in having no antigen-specific receptors. ILCs include natural killer (NK) cells, helper-like ILC1s, ILC2s, and ILC3s, and lymphoid tissue-inducer (LTi) cells. Tumor ILCs are frequently found in various cancers, but their roles in cancer immunity and immunotherapy remain largely unclear. We report here the single-cell characterization of blood and gut helper-like ILC subsets in healthy conditions and in colorectal cancer (CRC). The healthy gut contains ILC1s, ILC3s, and ILC3/NKs, but no ILC2s. Additional tumor-specific ILC1 -like and ILC2 subsets were identified in CRC patients. Signaling lymphocytic activation molecule family member 1 (SLAMF1) was found to be selectively expressed on tumor-specific ILCs, and higher levels of SLAMF1(+) ILCs were observed in the blood of CRC patients. The SLAMF1-high group of CRC patients had a significantly higher survival rate than the SLAMF1 -low group, suggesting that SLAMF1 is an anti-tumor biomarker in CRC.