Transfer of the murine interleukin-12 gene in vivo by a Semliki Forest virus vector induces B16 tumor regression through inhibition of tumor blood vessel formation monitored by Doppler ultrasonography

To elucidate further the potential of a Semliki Forest virus (SN) vector in vivo for gene therapy we constructed a vector, SVF-IL12 to transfer murine IL-12 genes into tumors. A single intratumoral injection of established B1 6 murine melanoma with SFV-IL12 resulted in a significant inhibition of tum or growth, while injection with SFV-LacZ had no effect. This antitumoral ac tivity correlated with an increase of IFN gamma production, MIG and IP-10 m RNA expression, both at the tumor site and at the periphery, In contrast, n o increase in CTL- or NK cell-mediated cytotoxic response could be detected , ruling out the involvement of T and NK cell cytotoxicity. To determine ho w the transfer of IL-12 genes induced tumor regression, the antiangiogenic- activity of SFV-IL12 was investigated using Doppler ultrasonography (DUS). SFV-IL12 inhibited in situ neovascularization within the tumor, without aff ecting the resistance index of pre-existing intratumoral blood flows. In ad dition, histological analysis of SFV-IL12-treated tumors showed massive tum or necrosis induced by SFV-IL12 treatment. These data indicate that SFV-IL1 2 inhibits tumor growth through its antiangiogenic activity, demonstrated f or the first time in vivo by DUS, and suggest that the SFV vector may be a novel valuable tool in tumor gene transfer.