Predicting CD8+ T-cell infiltration in colorectal cancer using versican proteolysis across molecular profiles.

Abstract

189 Background: The clinical indications for immunotherapies continue to increase across cancer types. In colorectal cancer (CRC), there has been little progress in the use of these therapies outside of mismatch repair deficient cancers (dMMR). However, even in dMMR cancers only a minority actually respond to the FDA-approved anti-PD1 agents. The tumor microenvironment is increasingly implicated in the resistance of cancers to immune-based therapies. Our group has previously described that accumulation of a matrix proteoglycan, versican, correlates with a reduction in CD8+ T-cell infiltration in CRCs, while proteolysis of versican, releasing the bioactive fragment versikine, correlates with increased infiltration. Here we examine the impact of pathogenic mutations on the utility of MMR status and versican proteolysis to predict CD8+ T-cell infiltration. Methods: Matched normal colon and CRC tissues from 122 patients were stained for versican, versikine, MLH1, MSH2, MSH6, PMS2, CNNB1, and CD8. Each was reviewed by a blinded GI surgical pathologist and CD8 quantified as tumor infiltrating lymphocytes (TILs) per high power field (hpf). 107 of the CRC samples were available for sequencing using the Qiagen Comprehensive Cancer Panel examining 160 genes across cancer relevant hotspots. The molecular profile was correlated with the IHC staining. Results: As previously reported, dMMR tumors had higher CD8+ T-cell infiltration. This trend persisted across dMMR genotypes (dMMR vs proficient (p)MMR p = 0.0016). Versican proteolysis correlated with increased CD8+ T cell infiltration in dMMR and pMMR cancers and was present in cancers with/without APC, TP53, and KRAS mutations. Across common mutations, cancers with the versican proteolysis predominant phenotype had more CD8+ T-cell infiltration than those without (APC mutant (mt): 11.82 vs 1.97 CD8+ TILs/hpf, p < 0.001; KRAS mt: 9.39 vs 3.08, p = 0.15; BRAF mt: 25.00 vs 7.50, p = 0.13; TP53 mt: 8.61 vs 1.63, p < 0.001). Conclusions: Across common mutations, versican proteolysis predicts CD8+ T-cell infiltration in both dMMR and pMMR CRC. Further investigation into whether this increase in infiltration will lead to greater immunotherapy response is warranted.