Mouse/human chimeric antibodies to a tumor-associated antigen: biologic activity of the four human IgG subclasses.

Variable region genes from mouse monoclonal antibody 17-1A (gamma 2a kappa) with specificity for human gastrointestinal malignancies have been paired with human immunoglobulin constant region genes (for heavy and light chains) to produce mouse/human chimeric immunoglobulin molecules (chIgG) for each of the four human IgG subclasses. Mouse 17-1A and the four chIgG bound similarly to two human colon cancer cell lines and had comparable binding affinities. The chIgG1 and chIgG3 molecules mediated lymphocyte and monocyte antibody-dependent cell-mediated cytotoxicity (ADCC) to colon cancer tumor cell lines comparable to that of the parent murine 17-1A. The chIgG2 and chIgG4 molecules were able to mediate ADCC to colon cancer cell lines but were clearly inferior to the chIgG1 and chIgG3 reagents. None of the chIgG antibodies or the murine 17-1A was able to mediate complement lysis of colon cancer cell lines. These studies demonstrate the ability to produce all four human IgG subclass chimeric molecules which retain biologic activity. We have confirmed the subclass preferences of human lymphocyte and monocyte Fc receptors for human IgG subclasses previously determined by studies with monomeric or aggregated IgG. These data may aid in the selection of chimeric antibodies for in vivo trials.