Adenovirus Gene Transfer Vectors Inhibit Growth of Lymphatic Tumor Metastases Independent of a Therapeutic Transgene

Abstract

Adenovirus (Ad) gene transfer vectors traffic to regional lymph nodes (RLNs) after footpad injections in mice, resulting in localized production of interferon γ (IFN-γ). With this background, we evaluated the hypothesis that Ad vector administration may inhibit RLN tumor metastasis independent of the transgene in the expression cassette. Tumors of MM48, a cell line with a propensity toward lymphogenous metastasis, were established in the footpads of syngeneic C3H mice, and E1^-E3^- Ad vectors encoding no transgene (AdNull) or encoding an irrelevant transgene (AdCD;Escherichia coli cytosine deaminase with no 5-fluorocytosine administration) were administered (10¹⁰ particles) in a peritumoral location. Both vectors suppressed the growth of tumor in the regional (popliteal) lymph node. This effect was localized to the regional, but not distant, lymph nodes (p < 0.05). Heat inactivation of the vector or decreasing the dose of the vector to 10⁹ particles did not suppress RLN growth of the tumor when compared with 10¹⁰ particles of active AdNull (p < 0.05 and p < 0.01, respectively). The ability of an E1^-E4^- vector expressing β-galactosidase (AdRSVβgal.11) to suppress RLN tumor growth showed that the E4 region of the Ad vector was not responsible for the effect. Blocking either IFN-γ or natural killer (NK) cells with systemic antibody treatment in immunocompetent mice allowed rapid growth of RLN metastases despite Ad vector administration, and Ad vector injection into the footpads of tumor-free mice induced the accumulation of NK cells in the RLN. These data demonstrate that, in a metastatic murine tumor model, a low dose (10¹⁰ particles) of replication-deficient Ad vectors inhibits RLN metastases independent of a therapeutic transgene, an effect that is mediated, at least in part, by IFN-γ and NK cells.