Production of IgM monoclonal antibodies in DG44 cells

Two-bicistronic vectors for the production of recombinant IgM monoclonal antibodies in the DG44 DHFR-negative cell line have been designed. We used tandem vectors, in which one bicistronic unit encoded the immunoglobulin light chain and DHFR and the other encoded the heavy chain and EGFP. The construct structure presumes that green cells surviving selection would be capable of producing both immunoglobulin chains. We found that the agglutinating IgM antibodies could be secreted in the absence of J-peptide. It was shown that the germinal leader peptide plays a key role in the expression of the genes for the light and heavy chains. A comparison of the chromatin regulatory elements demonstrated that construct-flanking 2xHS4 insulators stabilized the biosynthesis of the recombinant antibodies, whereas the 5′-MARLyz matrix attachment region proved to be less efficient. The strategy for obtaining a DG44-based producer cell line should include the following consecutive steps: selection on the medium without nucleoside → amplification of the inserted gene → cloning of transfectants → selection of high-productive clones. An attempt to clone before amplification and to amplify individual clones failed to result in effective producers. Cloning on a medium without selection pressure allows a more adequate assessment of the stability of the antibody production.