BACULOVIRUS EXPRESSION OF A FUNCTIONAL SINGLE-CHAIN IMMUNOGLOBULIN AND ITS IL-2 FUSION PROTEIN

The baculovirus expression system has been used for the production of a variety of proteins, including antibodies. Two single-gene construct s encoding single-chain immunoglobulins have recently been developed. The antibody employed was monoclonal antibody (MAb) CC49 which reacts with the pancarcinoma antigen, tumor associated glycoprotein, TAG-72. One, single-chain construct designated SCA Delta C(L)C(H)1 (SCIg), con sists of the CC49 sFv covalently joined to the human Fc (gamma 1) thro ugh the hinge region. The other, SCA Delta C(L)C(H)1-IL-2 (SCIg-IL-2), has a human IL-2 molecule attached to the carboxyl end of the SCIg. T hese constructs have been used to test the feasibility of producing bi ologically active antibodies using the baculovirus expression system. Both constructs have been succesfully expressed in insect cells and pu rified. The baculovirus recombinant single-chain antibodies have been designated, bV-SCA Delta C(L)C(H)1 (bV-SCIg) and bV-SCA Delta C(L)C(H) 1-IL-2 (bV-SCIg-IL-2) they have been shown to be secreted in the cultu re supernatant as dimeric molecules of approximately 115 kDa and 140 k Da, respectively. The specificity and antibody dependent cellular cyto lytic activity of the baculovirus recombinant single-chain antibodies were shown to be similar to that of the myeloma derived molecules. Gly cosylation analysis showed that baculovirus derived proteins were N-gl ycosylated, but carried few if any high mannose residues. The biologic al activity of the IL-2 moiety was retained in bV-SCIg-IL-2, as eviden ced by its stimulatory effect on the proliferation of the IL-2 depende nt cell line HT-2. The observation that a significantly shorter time i s required to develop baculovirus recombinant molecules as compared to myeloma derived molecules and that insect cells express single chain MAbs at acceptable levels may have implications for the production of these molecules for clinical use.