CD28 and neoplasm: Consistently, we conducted in vitro suppression assay by co-culturing WT or Bcl6-deficient tumor infiltrating Treg cells with CFSE-labeled naive CD8 T cells that were followed by anti-CD3 and CD28 stimulation, and the results showed that Bcl6-deficient Treg cells exhibited impaired suppressive function compared with that of WT Treg cells.