Adenovirus-mediated expression of interleukin-12 induces natural killer cell activity and complements adenovirus-directed gp75 treatment of melanoma lung metastases

Based on the knowledge that adenovirus (Ad)-mediated expression of the muri ne gp75 melanoma antigen (Adgp75) will effectively immunize mice against H2 -matched B16 melanoma cells, probably via cell-mediated immune mechanisms, we hypothesized that Ad-mediated delivery of the murine interleukin-12 (IL- 12) complementary DNA heterodimer would have independent therapeutic effect s on tumor growth, and that the combination of the two vectors would work s ynergistically to augment the antitumor response. We evaluated the therapeu tic effect of each vector alone and in combination for efficacy in C57BL/6 mice with preestablished (2 d) B16 melanoma-derived pulmonary metastases, u sing the number of lung metastases as the efficacy parameter. Intraperitone al administration of Adgp75 (10(8) PFU) reduced tumor burden to 45 +/- 7% o f controls (P < 0.01), and AdIL12 administration (10(8) PFU, intraperitonea lly) reduced the number of metastases to 43 +/- 7% of controls (P ( 0.01). The combination of Adgp75 (10(8) PFU, intraperitoneally) and AdIL12 (10(8) PFU, intraperitoneally) provided further protection (15 +/- 3%; P < 0.01 as compared with naive control; P < 0.01 compared with Adgp75 or AdIL12 alone ). Mice receiving AdIL12 showed increased natural killer cell (NK cell) fun ction in an in vitro cytotoxicity assay, with a dose-dependent lysis of YAC -1 cells and, to a lesser extent, lysis of B16 cells. To assess the relativ e contribution of major histocompatibility complex I (MHC I) Dependent and Independent activity in combination therapy with Adgp75 plus AdIL12, we per formed adoptive transfer experiments, using splenocytes from mice receiving Adgp75, AdIL12, or Adgp75 + AdIL12, from among which NK cells had been sel ectively depleted in vitro prior to adoptive transfer. Each group showed si gnificant decreases in tumor burden resembling those with primary treatment . Interestingly, NK-cell depletion from among cells derived from the Adgp75 - and AdIL12-treated mice significantly altered the therapeutic response (P < 0.01 compared with the Adgp75 + AdIL12 group), suggesting a significant role of NK-cell-mediated cytolysis in vivo, although there was still a sign ificantly reduced tumor burden (P < 0.01 compared with that of naive contro ls). Collectively, these data support the concept that the combination of A dIL12 and Adgp75 provides additive effects against pulmonary metastases of B16 melanoma by MHC-independent (NK cell) means as well as MHC-dependent cy totoxic lymphocyte means, suggesting that this therapy may be a useful adju vant in the treatment of metastatic melanoma.