RESUMEN
Varicella-zoster virus (VZV), the causative agent of chickenpox and herpes zoster, can be life-threatening in prematurely born children and in children with immune defects or who are under immunosuppressive treatment. Therefore agents for passive immunization, such as VZV-specific immunoglobulin preparations (VZIG) derived from convalescent plasma, are crucial in the prophylaxis of VZV infection. This study describes the isolation of human VZV-neutralizing recombinant antibodies. A human single-chain variable fragment (scFv) phage display library was generated from RNA extracted from peripheral blood lymphocytes of a convalescent varicella patient. Specific phage antibodies were selected against VZV-infected human fibroblasts, and eight unique clones were further expressed as soluble scFv in Escherichia coli. They all showed binding characteristics to varicella antigens with affinities in the K(D) range 0.1-0.2 muM. Two of the scFv antibodies, VZV4 and VZV5, showed dose-dependent in vitro neutralization of VZV. VZV39 also showed a neutralizing effect as scFv, an effect that was increased 4000-fold by conversion into IgG and was further increased by the addition of complement. This is possibly the first time that monovalent scFv antibodies have been shown to neutralize VZV in vitro. This finding will have an impact on the production of new prophylactic antibodies, as such antibody fragments can be cost-effectively produced in E. coli. The antibodies isolated bind both complement-dependent and -independent epitopes for neutralization, thus they may prove useful tools for the study of VZV virulence mechanisms.