PDCD1 and neoplasm: To specifically deliver immune checkpoint inhibitors to the tumor site, Reul et al. used the above-mentioned Her2/neu-directed AAV vectors [56] to target Her2/neu expressing cells in Balb/c mice for tumor-specific delivery of immune checkpoint inhibitor anti-PD-1 single chain variable fragments (scFv) after intravenous injection and showed reduced off-target expression in the liver.