PTPRC and neoplasm: The proportion of T cells infiltrating a tumor can depend upon mouse background strain, as T cells represent 12–21% of total CD45 + cells in syngeneic BALB/c models (CT26, RENCA, and 4T1), but only 4–8% of total CD45 + cells in syngeneic C57BL/6 models (MC38, LL/2, and B16F10)5.