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Text Box: IL-4 GENE MODIFICATION INDUCES THE EXPRESSION OF CELLULAR SURFACE MOLECULES IN HL-60 LI CR, FU JR Children’s Hospital of Shenzhen, Shenzhen 518026, China Objective: To further explore the mechanism enhancing killing activities of tumor cell-specific cytotoxical T lymphocyte (CTL) by IL-4 gene modification. Methods: IL-4 gene was introduced into HL-60 cells using retroviral vector PL-IL-4-SN. Wild and IL-4 gene- modificed tumor cells were used to induce CTL responses, and cellular surface molecules were evaluated using flow cytometry. Results: The killing activities of tumor cell-specific CTL in IL-4 gene-modified groups were increased from 11.8% to 77.2%, which was about sevenfold higher than CTL killing activities induced by wild HL-60 cells (p<0.01). High levels of expression of MHC class Ⅱantigens as well as the costimulatory molecules B7-1 and adherent molecules ICAM-1 were found in IL-4 gene-transferred tumor cells. The expression of MHC class I was not affected by IL-4 gene modification .The expression of cellular surface molecules induced by IL-4 gene-modified tumor vaccines were completely abrogated through using anti-IL-4 McAb. A significant increase of IL-2 secretions was detected during induction of CTL responses when IL-4 gene-modified tumor cells were used as stimulatory cells. IL-2 secretion and CTL responses were inhibited using anti-IL-4 or anti-surface molecule McAb. Conclusion: IL-4 gene modification might enhance tumor cell-specific CTL killing activities through induction of the expression of cellular surface molecules and facilitation of IL-2 secretion.