Biochemical and biological characterization of a dodecameric CD4-Ig fusion protein: implications for therapeutic and vaccine strategies

Drug toxicities associated with HAART lend urgency to the development of new anti-HIV therapies. Inhibition of viral replication at the entry stage of the viral life cycle is an attractive strategy because it prevents de novo infection. Soluble CD4 (sCD4), the first drug in this class, failed to suppress viral replication in vivo. At least three factors contributed to this failure: sCD4 demonstrated poor neutralizing activity against most primary isolates of HIV in vitro; it demonstrated an intrinsic capacity to enhance viral replication at low concentrations; and it exhibited a relatively short half-life in vivo. Many anti-gp120 monoclonal antibodies, including neutralizing monoclonal antibodies also enhance viral replication at suboptimal concentrations. Advances in our understanding of the events leading up to viral entry suggest strategies by which this activity can be diminished. We hypothesized that by constructing a sCD4-based molecule that is large, binds multiple gp120s simultaneously, and is highly avid toward gp120, we could remove its capacity to enhance viral entry. Here we describe the construction of a polymeric CD4-IgG1 fusion protein. The hydrodynamic radius of this molecule is approximately 12 nm. It can bind at least 10 gp120 subunits with binding kinetics that suggest a highly avid interaction toward virion-associated envelope. This protein does not enhance viral replication at suboptimal concentrations. These observations may aid in the design of new therapeutics and vaccines.