Spatial profiling reveals unique innate inflammation in high-mutation colon cancers

Objectives: The immune microenvironment of high-mutational-burden colon cancers is characterized by enhanced immune surveillance including increased cytotoxic T lymphocytes and expression of immune checkpoints. While much is known about adaptive immunity, the impact of mutational status on innate inflammation is less well studied.

Methods: Forty primary human colorectal cancers and surrounding tissues were collected and determined by genomic sequencing to be microsatellite-instability-high (MSI; n=20) or -low (MSS; n=20). Tissues were subjected to multiplex fluorescent immunohistochemistry and analyzed with the Akoya Polaris and InForm software packages.

Results: MSI tumors had a mean mutation count of 72.7 compared to 1.7 in MSS tumors (p<0.001). Additionally, MSI tumors were more frequently found in the right colon (68% vs 15%; p<0.001) and were of an earlier stage (Stage 1 and 2; 56% vs 0%; p<0.001). Low-mutation tumors had increased infiltration of NK cells (CD56+CD16+) compared to high-mutation tumors, and these tended to be spatially associated with tumor cells (mean intercellular distance = 138.8 vs. 340.6 microns; p<0.0001). This was not seen in surrounding tissues. Low-mutation tumors also had a greater infiltration of myeloid cells, with CD11B+ cells found closer to tumor cells (127.6 vs 247.6 microns; p<0.0001). Macrophages (CD11B+CD16+) were more closely associated with tumor cells than neutrophils (CD11B+CD15+). In surrounding non-neoplastic tissue, an opposite association was noted, with myeloid cells spatially distant from epithelial cells (95.8 vs 75.1 microns; p=0.036). When looking at survival, there was an inverse relationship with myeloid cells surrounding tumors where lower infiltration portended a worse prognosis (r² = 0.139; p=0.0046).

Conclusions: We present the first ever spatial characterization of the innate immune microenvironment of primary colorectal cancers and surrounding normal tissue from MSI and MSS tumors. Infiltration and spatial distribution suggest a unique adaptive immune response in low- vs high-mutation colorectal tumors.