Biological and pharmacokinetic properties of a novel immunoglobulin-CD4 fusion protein.

We report a CD4-immunoglobulin fusion protein in which the first two extracellular domains of human CD4 replace the Fc region of the immunoglobulin. When co-expressed with a gene encoding an immunoglobulin light chain, the protein was covalently assembled into a form having an M(r) consistent with that expected for two fusion heavy chains and two immunoglobulin light chains. The antigen specificity of the antibody was retained, however, binding to HIV gp120 was lost. Pharmacokinetic analysis revealed the in vivo half-life of the fusion protein to be 2.4 h in mice.