Cytokine gene transfer into mouse tumor cells has been shown to stimulate a strong immune response resulting in the rejection of the transduced tumor when injected in vivo. Therefore, retroviral vectors containing the human interleukin (IL)-2 or IL-4 gene have been constructed to transduce human melanoma cells to explore whether their immunogenicity can be increased both in vitro and in vivo. Our preliminary results indicate that retroviral vectors can efficiently transduce the IL-2 and or IL-4 gene into melanoma clones, inducing production of either cytokine in the range of 0.5-2 ng/ml/10(5) cells in 48-72 h. No modifications of the growth rate, morphology and antigenicity of the transduced tumor cells were found.