CD44 and neoplasm: In more detail, at first cells were incubated with the fixable viability dye (APC-eFluor780) to allow for the detection and exclusion of dead cells, and then the staining for surface antigens was performed by using the following antibodies: CD4 (Brilliant Violet 785) for cell lineage identification, CD44 (Brilliant Violet 510) as activation marker, OX40 (Brilliant Violet 605), a member of TNF-receptor superfamily highly expressed in tumor Tregs and CD71 (Brilliant Violet 421), the transferrin receptor.