COL1A1 and cancer: However, like fibroblasts (and unlike PDAC cancer cells) (60), Col6a1-sufficient and -deficient UPS cells secreted both Col1a1 and Col1a2 (Supplemental Figure 11E), demonstrating that differential ColI trimer composition likely does not underlie the divergent effects of CAF-derived versus UPS cell–derived matrix on CD8+ T cell function.