Triple combination of oncolytic herpes simplex virus-1 vectors armed with interleukin-12, interleukin-18, or soluble B7-1 results in enhanced antitumor efficacy

Abstract

Conditionally replicating herpes simplex virus-1 (HSV-1) vectors are promising therapeutic agents for cancer. Insertion of therapeutic transgenes into the viral genome should confer desired anti-cancer functions in addition to oncolytic activities. Herein, using bacterial artificial chromosome and two recombinase-mediated recombinations, we simultaneously created four "armed" oncolytic HSV-1, designated vHsv-B7.1-Ig, vHsv-interleukin (IL)-12, vHsv-IL-18, and vHsv-null, which express murine soluble B7.1 (B7.1-Ig), murine IL-12, murine IL-18, and no transgene, respectively. These vHsv vectors possess deletions in the γ34.5 genes and contain the green fluorescent protein gene as a histochemical marker and the immunostimulatory transgene inserted in the deleted ICP6 locus. The vHsv showed similar replicative capabilities in vitro. The in vivo efficacy was tested in A/J mice harboring s.c. tumors of syngeneic and poorly immunogenic Neuro2a neuroblastoma. The triple combination of vHsv-B7.1-Ig, vHsv-IL-12, and vHsv-IL-18 exhibited the highest efficacy among all single vHsv or combinations of two viruses. Combining 1 × 105 plaque-forming units each of the three armed viruses showed stronger antitumor activities than any single armed virus at 3 × 105 plaque-forming units in inoculated tumors as well as in noninoculated remote tumors. Studies using athymic mice indicated that this enhancement of antitumor efficacy was likely mediated by T-cell immune responses. The combined use of multiple oncolytic HSV-1 armed with different immunostimulatory genes may be a useful strategy for cancer therapy. © 2006 American Association for Cancer Research.