Integrative transcriptomic and single-cell protein characterization of colorectal carcinoma delineates distinct tumor immune microenvironments associated with overall survival.

PURPOSE: Colorectal carcinoma (CRC) is a heterogeneous group of tumors with varying therapeutic response and prognosis, and evidence suggests the tumor immune microenvironment (TIME) plays a pivotal role. Using advanced molecular and spatial biology technologies, we aimed to evaluate the TIME in patients with CRC to determine whether specific characteristics of immune composition correlated with prognosis.

METHODS: We identified primary and metastatic tumor samples from 31 consented patients, which were profiled with whole-exome sequencing and bulk RNA-seq. Immune cell deconvolution followed by gene set enrichment analysis and unsupervised clustering was performed. A subset of tumors underwent in situ analysis of the TIME spatial composition at single-cell resolution through Imaging Mass Cytometry.

RESULTS: Gene set enrichment analysis revealed two distinct groups of advanced CRC, one with an immune activated phenotype and the other with a suppressed immune microenvironment. The activated TIME phenotype contained increased Th1 cells, activated dendritic cells, tertiary lymphoid structures, and higher counts of CD8 + T cells whereas the inactive or suppressed TIME contained increased macrophages enriched for immunosuppressive M2 macrophages. Our findings were further supported by RNA-seq data analysis from the TCGA CRC database, in which the ratio of inactivated to activated dendritic cells within the CRC TIME correlated with a lower overall survival probability (HR 1.66, p = 0.007).

CONCLUSION: We identified distinct immunologic tumor microenvironments in colorectal cancer. Cancers harboring an activated TIME are associated with improved survival. Identifying key molecular drivers of the CRC TIME may offer opportunities to improve patient survival.