P14 CD8+ Teff (CFSE-negative) were co-cultured with CFSE-labeled CD28WTCD8+ or CD28KOCD8+ T cells and the effects of activated CD28WTCD8+ and CD28KOCD8+ T cells on the ability of CD8+ Teff cells to kill tumor were assessed (Fig. 1a). The gene discussed is CD8A; the disease is neoplasm.