Given that production of IFN-γ, one of the most critical cytokines for antitumour immunity3, 5, 7, was defective in tumour-specific CD4+ T cells in aged mice, we next examined whether IL-6-induced impairment of Th1 differentiation indeed contributed to the age-associated dysfunction in antitumour responses of CD4+ T cells. This evidence concerns the gene CD4 and neoplasm.