Human IL-15 cDNA fragment, which contains all codons encoding the human IL-15 mature protein and signal peptide was transducted into the human lung squmouse cancer cells ( PG cells ) and murine lung adenocarcinoma cells ( LA795 cell lines ) . Two IL-15 highly expressed cell clones PG1 and LA795A were used to inoculate the nude mice and the T739 syngeneic mice respectively. PG1 cell express higher level of class I MHC molecule on their surface than PG cells. It was shown that the modified LA795A tumor cells grew slowly in T739 mice and induced high levels of CTL/NK/LAK activity in vivo as well, compared with the case of inoculation with LA795 or LA795neo. No significant difference in the tumor growth was observed in groups of the nude mice inoculated by PG1, PG and PGneo cells respectively, except the gene modified cells could not show the lung metastasis of tumors. The supernatants derived from the LA795A cell culture could promote CTL/NK/LAK activity from the whole splenocytes and the CD4-/CD8-deleted splenic cells in vitro. The results indicated that the IL-15 gene transfected tumor cells play important roles in the process of antitumor or antitumor metastasis.