Carrasco, Talia Fernandez

Background The varicella-zoster virus (VZV), belonging to the group of human α-herpesviruses, has yet to be developed as a platform for oncolytic virotherapy, despite indications from clinical case reports suggesting a potential association between VZV infection and cancer remission. Methods Here, we constructed oncolytic VZV candidates based on the vaccine strain vOka and the laboratory strain Ellen. These newly engineered viruses were subsequently assessed for their oncolytic properties in the human MeWo melanoma xenograft model and the mouse B16-F10-nectin1 melanoma syngeneic model. Results In the MeWo xenograft model, both vOka and Ellen exhibited potent antitumor efficacy. However, it was observed that introducing a hyperfusogenic mutation into glycoprotein B led to a reduction in VZV’s effectiveness. Notably, the deletion of ORF8 (encodes viral deoxyuridine triphosphatase) attenuated the replication of VZV both in vitro and in vivo, but it did not compromise VZV’s oncolytic potency. We further armed the VZV Ellen-ΔORF8 vector with a tet-off controlled mouse single-chain IL12 (scIL12) gene cassette. This augmented virus was validated for its oncolytic activity and triggered systemic antitumor immune responses in the immunocompetent B16-F10-nectin1 model. Conclusions These findings highlight the potential of using Ellen-ΔORF8-tet-off-scIL12 as a novel VZV-based oncolytic virotherapy.

Abstract Oncolytic virotherapy aims to activate host antitumor immunity, but the effectiveness of current intratumoral herpes-simplex virus (HSV) based monotherapy is limited. Here, to boost the potency of cancer cell targeting α-herpesviruses derived from HSV or Varicella-Zoster Virus (VZV), we coinjected them with myeloid cell-tropic β-herpesviruses derived from cytomegalovirus (CMV) which can powerfully modulate immune responses. Co-administered CMV was shown to promote intratumoral replication of HSV, increase local release of pro-inflammatory cytokines, inhibit adaptive antiviral immune responses, enhance systemic antitumor responses, and lead to superior control of both injected and contralateral tumors. CMV-encoded myeloid-tropic genes, NK evasins (i.e. the vMHC-I homolog), and the m02-m16 region (involved in downregulating classical MHC-I) were implicated in enhancing antitumor activities. CMV is a promising adjuvant to reshape and enhance the antitumor immune responses following α-herpesvirus therapy.