CD4 and neoplasm: To determine whether naive CD4+ T cells can develop into Tregs in the tumor microenvironment13, we co-cultured naive CD4+ T cells, isolated from the PB of breast cancer patients, with autologous plasmacytoid DCs (pDCs), isolated from the blood or breast cancer tissues in normal culture medium or medium that was supplemented with 30% conditioned medium (CM) from autologous cancer tissue slices (Figure 3A and 3B).