COL6A1 and undifferentiated pleomorphic sarcoma: In light of our in vitro findings that ColVI suppresses CD8+ T cell function, we investigated this relationship in vivo by generating control and Col6a1 shRNA–expressing UPS tumors (syngeneic allograft of SKPY42.1 KP cells on a pure C57BL/6 background) in C57BL/6 hosts.