Vaccinia virus (VV) has emerged as a promising platform for
oncolytic virotherapy. Many clinical VV candidates, such as the double-deleted VV, vvDD, are engineered with deletions that enhance viral
tumor selectivity based on cellular proliferation rates. An alternative approach is to exploit the dampened
interferon-based innate immune responses of
tumor cells by deleting one of the many VV immunomodulatory genes expressed to dismantle the
antiviral response. We hypothesized that such a VV mutant would be attenuated in non-
tumor cells but retain the ability to effectively propagate in and kill
tumor cells, yielding a
tumor-selective oncolytic VV with significant anti-
tumor potency. In this study, we demonstrated that VVs with a deletion in one of several VV immunomodulatory genes (N1L, K1L, K3L, A46R, or A52R) have similar or improved in vitro replication, spread, and cytotoxicity in colon and
ovarian cancer cells compared to vvDD. These deletion mutants are
tumor selective, and the best performing candidates (ΔK1L, ΔA46R, and ΔA52R VV) are associated with significant improvement in survival, as well as
immunomodulation, within the
tumor environment. Overall, we show that exploiting the diminished
antiviral responses in
tumors serves as an effective strategy for generating
tumor-selective and potent oncolytic VVs, with important implications in future oncolytic virus (OV) design.