Production of functional antibody Fab fragment by recombinant insect cells

The production of an Fab fragment of the catalytic antibody 6D9 in stably transformed lepidopteran insect cells was investigated. On the basis of an expression vector that utilizes the Bombyx mori cytoplasmic actin promoter, from which foreign gene expression is stimulated with the B. mori nucleopolyhedrovirus (BmNPV) IE-1 transactivator and the BmNPV HR3 enhancer, two plasmid vectors were constructed which contain either a neomycin or a blasticidin resistance gene for use as a selectable marker. The genes encoding the heavy chain (Hc; Fd fragment) and light chain (Lc) of the 6D9 Fab fragment were inserted separately into the expression vectors. After cotransfection with the resulting plasmids to introduce the Hc and Lc genes and the two different antibiotic resistance genes, Trichoplusia ni BTI-TN-5B1-4 (High Five) cells were cultured in the presence of G418 and blasticidin. Colonies of cells resistant to the antibiotics were obtained around 2 weeks after cotransfection. Western blotting and enzyme-linked immunosorbent assay (ELISA) of the cell culture supernatant suggested that the resistant cells stably secrete an Fab fragment which retains an antigen-binding activity. High yields of over 300 μg/ml of Fab fragment were achieved in simple batch shake-flask culture of transfected insect cells. These results indicate that recombinant insect cells may offer a novel approach for efficient production of antibody molecules.