Dual Ligand Insertion in gB and gD of Oncolytic Herpes Simplex Viruses for Retargeting to a Producer Vero Cell Line and to Cancer Cells

Oncolytic viruses gain cancer specificity in several ways. Like the majority of viruses, they grow better in cancer cells which are defective in mounting the host response to viruses. Often they are attenuated by deletion or mutation of virulence genes which counteract the host response, or are naturally occurring oncolytic mutants. In contrast, retargeted viruses are not attenuated or deleted; their cancer-specificity rests on a modified, specific tropism for cancer receptors. For herpes simplex virus (HSV)-based oncolytics, the detargeting-retargeting strategies employed so far were based on genetic modifications of gD. Recently, we showed that even gH or gB can serve as retargeting tools. To enable the growth of retargeted HSVs in cells that can be used for clinical grade virus production, a double retargeting strategy has been developed. Here we show that several sites in the N-terminus of gB are suitable to harbour the 20 aa long GCN4 peptide, which readdresses HSV tropism to Vero cells expressing the artificial GCN4 receptor, and thus enables virus cultivation in the producer non-cancer Vero-GCN4R cell line. The gB modifications can be combined with a minimal detargeting modification in gD, consisting in the deletion of two residues, aa 30 and 38, and replacement of aa 38 with the scFv to HER2, for retargeting to the cancer receptor. The panel of recombinants was analysed comparatively in terms of virus growth, cell-to-cell spread, cytotoxicity,in vivoanti-tumor efficacy to define the best double retargeting strategy.IMPORTANCEThere is increasing interest in oncolytic viruses, following FDA and EMA approval of HSV OncovexGM-CSF, and, mainly, because they greatly boost the immune response to the tumor and can be combined with immunotherapeutic agents, particularly checkpoint inhibitors. A strategy to gain cancer specificity and avoid virus attenuation is to retarget the virus tropism to cancer-specific receptors of choice. Cultivation of fully retargeted viruses is challenging, since they require cells that express the cancer receptor. We devised a strategy for their cultivation in producer non-cancer Vero cell derivative. Here, we developed a double retargeting strategy, based on insertion of one ligand in gB for retargeting to Vero cell derivative, and of anti-HER2 ligand in gD for cancer retargeting. These modifications were combined with a minimally-destructive detargeting strategy. Current and accompanying study teach the clinical-grade cultivation of retargeted oncolytic HSVs, and promote their translation to the clinic