EFFECT OF VH AND VL CONSENSUS SEQUENCE-SPECIFIC PRIMERS ON THE BINDING AND NEUTRALIZING POTENTIAL OF A SINGLE-CHAIN FV DIRECTED TOWARDS HUIFN-GAMMA

We have previously reported on the cloning and bacterial expression of a biologically active scFv antibody fragment (scFv-D9D10) derived from the mouse anti-human interferon-gamma (HuIFN-gamma) antibody, D9D10. Since the variable (V) regions were isolated by means of VH and VL consensus sequence-specific PCR primers and cloned in an expression vector relying on primer-incorporated restriction sites, some amino acids (aa) at the N- and C-terminal ends of the cloned V domains were expected to differ from the corresponding ones in the natural D9D10 antibody. Therefore, the naturally occurring sequences of both V domains were isolated by means of traditional cDNA synthesis procedures. In comparison with scFv-D9D10, the ''natural'' V sequences differed in three aa in VH and three in VL. The V domains of scFv-D9D10 were adapted to their natural sequence by means of PCR-directed mutagenesis to yield scFv-D9D10N. Comparison of the binding and neutralizing potentials of both antibody fragments did not reveal differences in either of both activities. In addition, their affinities for HuIFN-gamma were found to be equal. These results show that murine VH and VL consensus-specific primers can yield antibody fragments having functional properties equivalent to those of the natural scFv. Information on the impact of the use of V-specific primers on kinetics of interaction between the recombinant antibody and the corresponding antigen is important for the development of most engineered antibodies or their fragments.