Potent antietumor immunity in mice induced by vaccination with an ovine atadenovirus vector

Identification of adenoviral isolates of nonhuman origin has fostered development of vectors with potential to overcome preexisting immunity in the human population that may affect clinical applications. Ovine adenoviral isolate, OAdV287 (OAdV7), the prototype of the genus Atadenovirus, has been previously characterized as a gene delivery vector although the receptor(s) used for infection remain to be identified. Here, we report the first use of recombinant OAdV7 as a vaccine for inducing an antitumor immune response in a mouse model. Treatment of murine BMDC with OAdV7 vectors expressing ovalbumin (OVA) resulted in upregulation of costimulatory markers and production of IL-12. Splenocytes isolated from immunized mice responded to antigen restimulation in vitro by proliferation and production of IFNγ. In vivo cytotoxicity assays revealed efficient killing of antigenic peptide-pulsed target cells 1 week after immunization, with an average killing efficiency of 75%. In mice inoculated with B16-OVA tumor cells immunization with OAdV7-OVA retarded and essentially prevented tumor growth in prophylactic and therapeutic tumor trials, respectively. Generation of a robust memory response was confirmed on tumor rechallenge in the prophylactic model. Therefore, OAdV7 is a novel vector with potential for further development of tumor vaccines.