The use of HAdV5 as a gene transfer vector for FLS has been limited due to their non-permissiveness to HAdV5 as they do not express CAR, the cellular receptor of HAdV5 on their surface. To overcome this hurdle, we design an efficient gene delivery strategy using a dual vector system by complexing HAdV5 to a baculovirus vector carrying CAR molecules on its envelope (BVCAR; Fig. 1a,b)14. The BVCARHAdV5 complex binds to the cell surface via the baculoviral envelope glycoprotein Gp64 (Fig. 1a,b), and is internalized by endocytosis, even in cells lacking CAR, such as FLS14. BVCAR serves as a transporter to bring the HAd5V vector into the target cells. Transduction of human and rat FLS with HAdV5-GFP alone, at a vector dose of 20 vector particles per cell (vp/cell), gave <2% of GFP-positive cells (Fig. 1c, d; grey bars), whereas more than 50% GFP-positive cells were obtained with the BVCARHAdV5-GFP complex at the same vector dose (Fig. 1c,d; grey bars). To mimic the inflammatory conditions in arthritic joints, FLSs were pre-treated with proinflammatory cytokines (TNFα, IL-17) before transduction with BVCARHAdV5-GFP. This resulted in almost 70% GFP-positive cells (Fig. 1c,d; black bars).Fig. 1Vector duo and transduction of human and rat synoviocytes. a The BVCARHAdV5 binary complex can be visualize by electron microscopy. The HAdV5 vector with a icosahedral shape, is bound to BVCAR, a rod-shaped baculovirus which has incorporated the CAR glycoproteins in its envelope. Scale bar, 100 nm. b The schematic representation shows the BVCARHAdV5 binary complex, with HAdV5 bound to BVCAR via the CAR glycoprotein at the baculoviral membrane. The baculoviral envelope glycoproteins Gp64 are localized at the head of the baculoviral particle. c Human and d rat fibroblast-like synoviocytes (FLS) non-treated (grey bars) or pre-treated (black bars) with the proinflammatory cytokines were transduced with HAdV5-GFP alone, or with the BVCARHAdV5-GFP complex. The figures represent the percentage of GFP-positive FLS cells analysed by flow cytometry. The average of three independent experiments, each in triplicates are shown. Statistical analysis using one-way ANOVA test, ***P < 0.001, **P < 0.01, *P < 0.05