Construction of adenoviral and retroviral vectors coexpressing the genes encoding the hepatitis B surface antigen and B7-1 protein

Abstract

Recombinant retroviral (re-Rv) and adenoviral (re-Ad) vectors for delivery of two foreign genes were constructed, using the internal ribosomal entry site (IRES) of encephalomyocarditis virus (EMCV) which mediates initiation of cap-independent translation. The first gene encoded the hepatitis B surface antigen (HBsAg) and the second encoded human or murine B7-1 molecule, a cell surface protein which is a costimulator for T cell activation. The EMCV IRES sequence was placed between the first and second coding sequences to form a dicistronic DNA fragment. In Rv vectors, the dicistronic fragment was inserted between the 5′ long terminal repeat (LTR) and an internal promoter for the neomycin ( neo) gene, so that the transcription initiated from the 5′ LTR would generate a dicistronic mRNA for the HBsAg and B7-1 molecules. For Ad vectors, the dicistronic fragment was inserted between a cytomegalovirus promoter and a polyA signal to form a transcription cassette. This transcription cassette was inserted into the early region 1 of Ad5 genome to form a replication-defective re-Ad vector, or into early region 3 to form replication-competent vectors. Human cell line A549 infected with the re-Rv vectors or with the re-Ad vectors synthesized and secreted HBsAg at comparable levels, while the B7-1 molecules were detected at the surface of the infected cells, indicating both foreign genes carried by the Rv and Ad vectors were expressed efficiently.