184 Development of the broadly neutralizing human antibody m9 for anti-HIV prophylactics
ScFv m9 is a human antibody fragment that exhibits potent and broad anti-HIV activity. Identified by using phage display, scFv-m9 targets a highly conserved CD4-induced (CD4i) epitope on gp120 and potently neutralizes Groups M (clades A-G) and N HIV-1 in PBMC/primary isolate-based and cell line/pseudovirus-based assays most likely by interfering with envelope engagement to the coreceptor. This monoclonal antibody fragment neutralized more than 80% of the tested primary isolates and showed superior potency and breadth to b12, 2F5, 4E10, and 2G12. In addition, scFv-m9 lacks reactivity to self antigens such as cardiolipin that plagued the development of 2F5 and 4E10. While effective as a scFv or a Fab, the potency of m9-IgG is significantly less suggesting that the target CD4i epitope has a size restriction. To exploit scFv m9 or Fab m9 as clinical products, we must extend their pharmacokinetic half-life in-vivo. Binding to albumin via albumin binding peptides has been used as a strategy to dramatically improve the pharmacokinetics of antibody fragments without significant increase in their size. We have engineered two variants of scFv m9, called m9hc and m9sa, in which two albumin binding peptides independently were fused to the C-terminus of the scFv m9. The new constructs have been expressed in E-coli and tested for binding to gp120-CD4 complex and for neutralization of HIV-1. Albumin binding peptide scFv m9 variants preserved the binding and neutralizing properties of the original scFv m9. If pharmacokinetic characteristics of m9sa and m9hc constructs are appropriate for once a day injection, these human antibody fragments will be developed as clinical candidates for anti-HIV prophylactics in incidences of accidental exposure, mother-to-child transmission; or salvage treatment therapy.© 2009 Lippincott Williams & Wilkins, Inc.