Secretion of the hepatitis B virus surface antigen from mouse cells using an extra-chromosomal eucaryotic vector

Recombinant DNA molecules which contained a subgenomic fragment of the hepatitis B virus (HBV) genome, the pML2 vector and the bovine papillomavirus type 1 (BPV) genome were constructed. The HBV fragment includes the entire transcription unit for the hepatitis B surface antigen (HBsAg). After propagation in Escherichia coli, the recombinant plasmids were cleaved with endonucleases SalI and PvuI to eliminate most of the bacterial sequences before transfection of mouse C127 cells. Foci were observed 10--14 days after transfection. Cells from selected foci were cloned and the supernatants were assayed for the presence of HBsAg. Most of the clones tested were found to secrete HBsAg particles into the growth medium. These particles appear to be similar to the 22 nm particles present in the serum of HBV chronic carriers. SDS-polyacrylamide gel electrophoresis revealed that the particles contain two polypeptides, probably representing the glycosylated and unglycosylated forms of the HBsAg major polypeptide. An analysis of DNA from the transformed clones revealed that they contain multiple extra-chromosomal copies of the recombinant, which, however, had suffered rearrangement.