Intratumoral, genetically engineered HSV-1 that selectively replicates in tumor cells due to virulence gene deletions, causing direct oncolysis and local spread; releases tumor antigens to activate dendritic cells and cytotoxic T cells; delivers a transgene encoding a recombinant bispecific antibody to further enhance antitumor immunity and counter local immunosuppression. Evaluated primarily in head and neck squamous cell carcinoma.