CD4 and neoplasm: Interestingly, T cells expressing FoxP3, a marker usually associated with a regulatory T cell phenotype (Treg) with inhibitory function on CD4+ T cells (41, 42), were more abundant in GL261-CIITA tumors compared to GL261 parental tumor (FoxP3: 618 cells/mm2 in GL261-CIITA; 29 cells/mm2 in GL261) (Figure 2).