Several studies, preclinical or clinical, have shown that the CTL responses induced by vaccine therapy in patients or in vitro in stimulation cultures are short lived.[24–26] We have also shown in in vitro cultures that the induction of CD8+ CTL responses decline in mixed culture with total PBL whereas CTL responses in culture with purified CD8+ cells remain significantly longer in cultures.[25] Table 1 summarizes the results of in vitro cocultures to induce tumor antigen-specific CTL response using total PBL and purified CD8+ cells. The gene discussed is CD8A; the disease is neoplasm.