Plasmid cassette-transfer vectors pBHuCϰ and pBHuCy1 have been designed which enable the construction of recombinant baculoviruses directing the co-expression of complete immunoglobulin in insect cells. We describe the application of these vectors for the expression of a human/mouse chimeric monoclonal antibody of potential immunosuppressive clinical value derived from a mouse anti-human CD29 monoclonal antibody (Mu-K20). The chimeric K20 light and heavy chains produced in sf9 insect cells were correctly processed and assembled into a normal immunoglobulin which is secreted into the culture medium of infected cells. The chimeric mAb Ch-K20-sf9 reproduces in vitro the functional properties of the parental mouse K20, including affinity and inhibition of lymphocyte proliferation. These results demonstrate that the baculovirus/insect cell expression system is suitable for the expression of fully active monoclonal antibodies of therapeutic value. Our generic cassette approach makes this system a very flexible and convenient one for the rapid production of either chimeric, humanized or human mAb with heavy and light chains of any isotype.