Single-cell transcriptome analysis reveals tumor immune microenvironment heterogenicity and granulocytes enrichment in colorectal cancer liver metastases

Colorectal cancer (CRC) is among the top 3 leading causes of cancer-related deaths, and tumor malignant progression and metastases contribute to the high mortality of advanced CRC. Immune components in the tumor microenvironment can modulate tumor progression and are attractive therapeutic targets. Recently, intra-tumor mutational diversification of colorectal cancer cells at the single cell level was conducted. However, single cell transcriptome analysis of the microenvironment composition and characteristics in CRC liver metastases has yet to be performed. In this study, samples of liver metastasis cancer tissue and adjacent tissue from CRC patients were examined by single cell RNA sequencing. A total of 12 clusters corresponding to 6 cell types, including cancer cells, T cells, myeloid cells, endothelial cells, fibroblasts and B cells, were identified. Expression clustering of 445 cell cluster deregulated genes (CCDGs) identified 6 gene modules and functional enrichment was conducted to analyse the pathways in cancer cell and T cell populations. Next, the clinical significance of the expression of 93 cell cluster specifically deregulated genes (CCSDGs) in tumor-infiltrating immune cells and the correlation of the expression of these genes with patients' survival rates were investigated with the TCGA dataset. Then, the mechanisms for increased proportion of granulocytes in the cancer sample were explored, and abnormal ferroptosis-mediated granulocyte cell death was proposed. Finally, the Wnt signalling pathway was found to be activated and promote granulocytes migration. This single cell RNA sequencing study may shed light on the tumor microenvironment composition and pave the way for CRC liver metastasis therapy.