A new vector for the high level expression of chimeric antibodies in myeloma cells

We previously reported the expression of a mouse/human chimeric anti-ganglioside GD3 antibody, KM871 (IgG1,kappa) in mouse myeloma SP2/0 cells under the control of the ecotropic Moloney virus long terminal repeat by the co-transfection of chimeric heavy (H) and light (L) chain vectors (Shitara et al. (1993) Cancer Immunol. Immunother.). To establish an efficient and high level expression system for the chimeric antibody, we did comparative study on vector systems and host cells. An improved expression vector, named 'a tandem vector, pChi641HLGM4' was constructed, in which both of the chimeric H and L chain gene transcription units and a dihydrofolate reductase (dhfr) gene transcription unit were inserted. When two kinds of mouse myeloma cell lines, SP2/0 and P3U1, were used as host cells, frequency of the incidence of antibody-producing transfectants was markedly increased by the use of the tandem vector compared with the use of the mixture of each chimeric H vector and L chain vector. To select out appropriate host cells, transfection frequency and antibody production level were compared among SP2/0, P3U1 and rat myeloma YB2/0 cells by transfection of the tandem vector. YB2/0 cell was shown to have the highest potential in both the transfection frequency and the antibody production. Introduction of the tandem vector into YB2/0 cells and the subsequent amplification with 50-200 nM methotrexate gave rise to several clones that stably secreted 70-100 micrograms/10(6) cells per 24 h of the chimeric antibody. This productivity of the antibody is one of the highest levels which have been achieved by other investigators using transfected myeloma cells. Using this system it took only 2-3 months to establish the transfectant clones which stably produced the chimeric antibody.