High level expression of hepatitis B virus surface antigen in stably transfected Drosophila Schneider-2 cells

Two transfer vector systems have been constructed for the generation of Dro sophila melanogaster Schneider-2 (DS-2) cells transfected stably and used t o express the small surface antigen of hepatitis B virus (HBsAg). One syste m is based on the cotransfection of an expression vector for the S gene und er the control of an inducible Drosophila metallothionein (Mtn) promotor an d a resistance plasmid which carries a selectable marker dihydrofolate redu ctase (dhfr) gene under the control of a Drosophila actin 5C distal promote r. The second system is based on the transfection of a single plasmid, whic h includes both expression units. Both vector systems were suitable for the generation of stably transfected DS-2 cell-lines secreting high levels of HBsAg. The quantities of HBsAg expression from polyclonal DS-2 cells correl ated strictly with the concentration of the transfected S gene expression v ector. Clonal cell-lines selected from the most efficient HBsAg producing p olyclonal cell-populations were examined in more detail. All of the transfe cted S genes were found to be integrated and the copy numbers per genome va ried extremely between 10 and 240. Furthermore, the levels of secreted HBsA g varied greatly between different clones and in best they reached up to 7 mu g/ml under serum-free cell culture conditions. Thus, DS-2 cells transfec ted stably provide an alternative source for the production of HBsAg partic les for diagnostic purposes and vaccine development. (C) 1999 Elsevier Scie nce B.V. All rights reserved.