# Tumor-infiltrating immature innate lymphoid cells in colorectal cancer are biased toward ILC1/tissue-resident NK cell differentiation

## TL;DR

This study explores immune cell changes in colorectal cancer and peritoneal metastases, finding increased ILC1 and tissue-resident NK cells.

## Contribution

The study identifies immature innate lymphoid cells biased toward ILC1 and tissue-resident NK cell differentiation in CRC and PM.

## Key findings

- CRC and CRC-PM tumors are depleted of ILC3 but enriched for ILC1, trNK, and cNK cells.
- Two immature ILC populations in tumors show a transcriptional bias toward ILC1 and trNK cells.
- nILCs differentiate into ILC1/trNK-like cells when co-cultured with OP9-DL1 cells.

## Abstract

Peritoneal metastases (PM) occur in 10% of patients with colorectal cancer (CRC) and are linked to poor outcomes. Although dysregulated innate lymphoid cells (ILC) have been described in CRC, their function in CRC-PM remains unclear. Here, we analyze tumor samples from CRC and CRC-PM patients using single-cell RNA sequencing (11 patients), flow cytometry (8 patients) and differentiation assays (24 patients). Healthy colon, primary CRC and CRC-PM tumors are infiltrated by heterogeneous populations of ILC3, ILC2, ILC1, tissue resident (tr)NK cells and conventional (c)NK cells. Compared to healthy colons, primary CRC and CRC-PM tumors are depleted of ILC3 but enriched for ILC1, trNK cells and cNK cells. CRC and CRC-PM tumors harbor two immature ILC populations, early NK and naïve (n)ILC, with nILCs being transcriptionally skewed toward ILC1 and trNK cells. Indeed, co-culture of isolated nILCs with OP9-DL1 cells induces intratumoral nILC differentiation into ILC1/trNK-like cells. These findings help understand the immune pathogenesis of CRC and CRC-PM and provide insights for future ILC1 and NK cell-based therapies.

Patients with colorectal cancer (CRC) may develop peritoneal metastases (PM), but information on the immune niche is still lacking. Here, the authors analyze primary tumor and metastasis samples to reveal a skewed innate lymphoid cell balance marked by an increase in ILC1/tissue-resident NK cells.