Multimeric humanized varicella-zoster virus antibody fragments to gH neutralize virus while monomeric fragments do not

Murine monoclonal antibody 206 (MAb mu206) binds to gH, the varicella-zoste r virus (VZV) fusogen, neutralizing the virus in vitro in the absence of co mplement and inhibiting cell-to-cell spread and egress of VZV in cultured c ells. We have humanized this antibody to generate MAb hu206 by complementar ity determining region grafting. MAb hu206 retained binding and in vitro ne utralizing activity, as well as cross-reactivity with ten different VZV str ains. Single-chain antibody fragments (scAb) derived from MAb hu206 were pr oduced in Escherichia coil. These scAb retained the binding properties of t he whole antibody. However, monomeric scAb exhibited markedly reduced neutr alizing activity compared to the bivalent parental MAb hu206. Shortening th e peptide linker joining the V-H to the V-K domain from 14 to 5 or even O r esidues encouraged multimerization and increased neutralizing efficacy. The fact that Fab fragments enzymatically generated from whole MAb hu206 lost their neutralizing potency lent support to the proposal that valency is imp ortant for VZV neutralization at this epitope.