Cartilage oligomeric matrix protein, cancer-associated fibroblast phenotypes, and versican proteolysis modulate CD8+ T cell infiltration in colorectal cancer

Background: Cytotoxic T cell infiltration in colorectal cancers (CRCs) is critical for immunotherapy response and is regulated by various tumor microenvironment (TME) factors. Cartilage oligomeric matrix protein (COMP), a large pentameric glycoprotein involved in extracellular matrix (ECM) organization and stability, has been implicated in elevated fibrosis and immunomodulation in CRC. Likewise, myofibroblastic and inflammatory cancer-associated fibroblasts (myCAFs and iCAFs) regulate ECM remodeling and immunomodulation in the TME. Versican (VCAN) and its proteolysis product, versikine (Vkine) also impact CD8+ T cell infiltration. Here, we evaluate the impact of COMP on CD8+ Tumor-infiltrating lymphocyte (TIL) abundance alone and in combination with CAF phenotypes and VCAN proteolysis status. Methods: Immunohistochemistry was performed on CRC samples from 243 patients to evaluate COMP, myCAF, alphaSMA, TAGLN, PDPN, ICAM1, CD8, VCAN, and Vkine. CD8+ TILs were quantified per high-power field (HPF). COMP was scored from 0-3 based on staining abundance and intensity in the cancer epithelium, CAFs, immune cells, ECM, and the total stromal compartment. All other stains were scored from 0-3 based on stromal abundance and intensity. alphaSMA and TAGLN scores were averaged to calculate a myCAF score, and PDPN and ICAM1 were averaged to calculate an iCAF score. CAF and VCAN status was assigned as per previous. Results: Abundant COMP was observed in the cancer epithelium (80%), CAFs (77%), immune cells (76%), ECM (36.2%), and stroma overall (64%). High stromal COMP expression is more prevalent in myCAF high cancers (25%) relative to iCAF high (8%) cancers. High stromal COMP expression is more prevalent in VCAN proteolytic weak (VPW, percent of samples 41%) vs VCAN/Vkine low (VVL, 15%) and VCAN proteolytic predominant (VPP, 19%) cancers. CD8+ TIL abundance increased with COMP expression across all compartments. A trend of higher CD8+ TIL abundance in stromal COMP high cancers relative to stromal COMP low cancers for iCAF high was observed (mean CD8+ TILs/HPF in COMP low cancers 8, COMP high cancers 10), while myCAF high cancers were comparable (5, 5). Interestingly, CD8+ TIL abundance was significantly higher in iCAF high cancers with high CAF COMP expression vs low CAF COMP (high CAF COMP mean CD8+ TILs/HPF 12, low CAF COMP 3, p=0.0488), though myCAF high cancers exhibit the opposite trend. CD8+ TIL abundance was also higher in stromal COMP high VPP cancers and VVL cancers vs VPW cancers (mean CD8+ TILs/HPF 19, 8 vs 4, respectively, p=1.398e-05). Conclusion: COMP is abundant in the CRC TME and can vary with other TME features. The presence of COMP correlates with enhanced CD8+ T cell infiltration in the setting of a pro-inflammatory TME, including VPP and iCAF high cancers. Mechanistic studies are needed to evaluate how COMP may enhance T cell infiltration.