The rAAV-Ova vector, a kind gift of Roland W. Herzog, was described previously (Wang et al., 2005) . The cDNA encoding mouse PD-L1 (CD274) or PD-L2 (CD273) were cloned using standard molecular biology procedures and introduced in the SSV9-CAG plasmidic backbone after digestion with EcoRI. The resulting expression cassette, flanked by AAV serotype 2 inverted terminal repeats (ITRs), contains the CAG promoter combining the cytomegalovirus early enhancer and the chicken β-actin promoter, a chicken β-actin intron, and a rabbit β-globin polyadenylation signal. rAAV2/1 and rAAV2/8 vectors were generated using a standard helper-virus free three-plasmid transient transfection method and pseudotyped with either AAV1 or AAV8 capsid proteins. Vectors were purified by two cesium chloride gradient centrifugations and dialyzed against PBS as described (Salvetti et al., 1998) . Genome titers of vector preparations were assayed by Dot-blot hybridization using a probe to detect the CAG or CMV promoter.