CHIMERIC ANTIBODIES WITH ANTI-DEXTRAN-DERIVED COMPLEMENTARITY-DETERMINING REGIONS AND ANTI-P-AZOPHENYLARSONATE-DERIVED FRAMEWORK REGIONS

The framework regions of antibodies fold into a conserved beta-sheet s tructure that acts as scaffolding for the antigen-contacting complemen tarity-determining regions (CDR). To test the structural equivalence o f the frameworks between two antibodies with widely different combinin g sites, we created chimeric H and L chains by grafting the CDR of an alpha(1-->6)dextran specific antibody onto the framework of a p-azophe nylarsonate (Ars) specific antibody through oligonucleotide-directed m utagenesis of the anti-Ars variable region genes. Antibodies consistin g of various chain combinations of the chimeric, anti-dextran, and ant i-Ars derived H and L chains were generated in transfectomas and teste d for binding to dextran and Ars. Of the newly created chimeric and/or hybrid antibodies, an antibody with the chimeric H chain and the anti -dextran L chain bound to dextran with the same association constant a s the parental anti-dextran antibody, and like the anti-dextran antibo dy was shown by immunochemical mapping to have a site complementary to six glucose residues. None of the other new variable region combinati ons, including the all-chimeric combination, showed binding to either dextran or Ars. These results indicate that the H chain but not the L chain anti-dextran and anti-Ars frameworks are functionally equivalent . Attempts to confer dextran binding on the H and L chain chimeric ant ibody, by mutagenizing selected framework residues, were unsuccessful. This study demonstrates the important role of the frameworks in the p recise alignment of the CDR for Ag binding.