Versican expression and proteolysis as a biomarker for CD8+ T cell infiltration across cancer types and molecular profiles

Background: Current biomarkers for immune checkpoint inhibitor (ICI) response, including tumor mutation burden (TMB) and microsatellite instability (MSI), do not completely identify responsive patient populations. Versican (VCAN), a matrix proteoglycan found in the tumor microenvironment (TME), and its proteolysis product, versikine (Vkine), can regulate immune infiltration. Here we evaluate VCAN status as a biomarker for CD8+ T cell infiltration across cancer types and molecular profiles. Methods: Patients (n=123) were identified and consented as part of an IRB-approved protocol. Patient characteristics were collected for all patients, and PIK3CA , KRAS , TP53 , BRAF , BRCA1/2 , PTEN , and CDKN2A mutation status were identified in a subset of 45 patients. Cancer samples were collected prior to ICI treatment, and were stained for VCAN, Vkine, and CD8. VCAN and Vkine staining was scored 0-3 based on stromal abundance and intensity. CD8+ tumor infiltrating lymphocytes (TILs) were quantified per high powered field (HPF). Cancers were assigned a VCAN status as previously. Results: Clinical characteristics: 28 Colorectal , 8 Bladder, 44 Lung, 16 Skin, 6 Esophageal, and 21 other pan-cancer patients. Median CD8+ TIL abundance was higher in MSI-high (MSI-H) cancers (11.33) than in microsatellite stable (MSS) cancers (7.67; p=0.05). A weak positive correlation between TMB and CD8+ TIL abundance was observed (spearman's 0.201). A trend of elevated CD8+ TILs/HPF were observed in VCAN proteolytic predominant (VPP, percent of cancers 5%, mean CD8+ TILs/HPF 13) and VCAN/Vkine low (VVL, 37%, 15) cancers relative to VCAN proteolytic weak (VPW, 58%, 10). This relationship was preserved independent of MSI status, though MSI-H cancers had higher CD8+TIL abundance in VPP (MSI-H median CD8+ TILs/HPF 20, MSS 9), VVL (15, 11), and VPW (10, 5, p = 0.02) cancers compared to MSS cancers. VVL and VPW cancers were most prevalent across mutation profiles. Those cancers that are KRAS mutant were more likely to be VVL. A trend towards increased CD8+ TILs/HPF in VVL/VPP cancers relative to VPW cancers was observed generally across the mutation profile. However, CD8+ TILs/HPF were similar across VPP/VVL and VPW for KRAS -mutant cancers. Conclusion: While TMB and MSI-H status correlate moderately with CD8+ T cell infiltration, VCAN status predicts CD8+ TIL abundance across several cancer types and mutation profiles. Further studies to investigate the impact of VCAN proteolysis on immune infiltration and ICI response are necessary to better identify patient populations which could receive benefit from ICIs.