Expression of Hepatitis B Surface Antigen in Human Cells by a Recombinant BK Virus DNA Vector

1 Institute of Microbiology, University of Ferrara, Via L. Borsari 46, I-44100 Ferrara, 2 Institute of Biochemical and Evolutionary Genetics, National Research Council, Via Abbiategrasso 187, I-27100 Pavia, Italy and 3 The Wistar Institute of Anatomy and Biology, 3601 Spruce Street, Philadelphia, Pennsylvania 19104, U.S.A. The construction of the first stable human cell lines that express and secrete authentic hepatitis B virus surface antigen (HBsAg), using a BK virus (BKV) episomal plasmid vector, is described. The amount of HBsAg produced by BKV vectors (up to 600 ng/10 7 cells) was comparable to other eukaryotic vector systems. The level of HBsAg expression remained the same regardless of the orientation of the HBsAg gene, substitution of the HBsAg gene promoter with the mouse metallothionein I gene promoter or the tissue origin of the human cell lines used to establish stable cellular transformants. Northern blot analysis also indicated synthesis of normal HBsAg transcripts. Surprisingly, however, the vectors were maintained at far lower than expected copy number (one to five copies/cell). Reasons for this are discussed. Keywords: hepatitis B virus, HB surface antigen, eukaryotic episomal vector Received 8 June 1987; accepted 7 October 1987.