Intraperitoneal administration of a recombinant VSV variant targeted to Her2/neu-expressing tumours, followed by systemic CTLA-4 blockade one day later, elicited a potent anti-tumour CD4+ and CD8+ T cell response in immunocompetent mice bearing Her2/neu-positive D2F2/E2 murine mammary tumours. The gene discussed is CTLA4; the disease is neoplasm.