FOXP3 and neoplasm: Studies examining proliferation of intra-tumoral Foxp3+ T cells in brain tumors imply that the majority of proliferating cells are helios+; for example in mouse models of glioblastoma, it has been reported that the majority of tumor-infiltrating Foxp3+ T cells express helios and are highly proliferative, significantly more so than helios−Foxp3+ and Foxp3−CD4+ T cells (79).