Bispecific adapter-mediated retargeting of a receptor-restricted HSV-1 vector to CEA-bearing tumor cells

The safety and efficacy of viral therapies for solid tumors can be enhanced by redirecting the virus infection to tumor-specific cell-surface markers. Successful retargeting of herpes simplex virus type 1 (HSV-1) has been achieved using vectors that carry a modified envelope glycoprotein D (gD) engineered to interact directly with novel receptors. In addition, soluble bridging molecules (adapters) have been used to link gD indirectly to cell-specific receptors. Here, we describe the development of an adapter connecting gD to the common tumor antigen carcinoembryonic antigen (CEA). The adapter consisted of a CEA-specific single-chain antibody fused to the gD-binding region of the gD receptor, herpes virus entry mediator (HVEM). We used this adapter in combination with a vector that is detargeted for recognition of the widely expressed gD receptor nectin-1, but retains an intact binding region for the less common HVEM. We show that the adapter enabled infection of HSV-resistant Chinese hamster ovary (CHO) cells expressing ectopic CEA and nectin-1/CEA-bearing human gastric carcinoma cells that are resistant to the vector alone. We observed cell-to-cell spread following adapter-mediated infection in vitro and reduced tumor growth in vivo, indicating that this method of vector retargeting may provide a novel strategy for tumor-specific delivery of tumoricidal HSV.