The antitumor activity of B. longum 420 is WT1-specific because the cytotoxic activity of CD8+ T cells on WT1 peptide-pulsed RMAS cells increased in the B. longum 420 group, implying that CD8+ T cells collected from mice in the B. longum 420 group recognize WT1 peptide and are capable of lysing WT1-expressing tumor cells. The gene discussed is WT1; the disease is neoplasm.