To evaluate if there was immune response to the viral vectors, sera from rats treated for 4 days and 21 days with BVCAR, HAdV5-PUMA or BVCARHAdV5-PUMA, were analysed by ELISA for the presence of antibodies to HAdV5 and BVCAR. The results show that antibodies against both HAdV5 and BVCAR were either absent or not detectable from the day-4 sera (Fig. 8c,d). However, from the day-21 sera, anti-HAdV5 antibodies were detected in 2/4 animals of the HAdV5-PUMA group, and in 3/4 animals of the BVCARHAdV5-PUMA group (Fig. 8c). Low levels of anti-BV antibodies were detected in the sera of 2/4 animals of the BVCARHAdV5-PUMA group (Fig. 8d). Although no viral genomes were detectable in the sera and tissues, the presence of antibodies against the viral vectors in certain individual animals suggested that the immune response observed could be due some vector leakage from the treated joints or induction of Ig by activated B cells inside the synovium15.