CD4 and cancer: The second interaction, called co-stimulation, occurs between B-7 (CD80 or CD86) and CD28 molecules (Figure 4, on the left), and is a prerequisite for the activation of T helper (CD4) cells to generate antitumor effectors (capable of destroying cancer cells, bearing a particular tumor antigen, either alone or by helping cytotoxic CD8 T cells to do so).