Expression and Characterization of CD4-IgG₂, a Novel Heterotetramer That Neutralizes Primary HIV Type 1 Isolates

Abstract

CD4-IgG2 is a novel fusion protein comprising human IgG2 in which the Fv portions of both heavy and light chains have been replaced by the V1 and V2 domains of human CD4. This tetrameric protein is being developed as an immunoprophylactic agent to reduce the probability of infection following HIV-1 exposure, in settings such as occupational or perinatal exposure to the virus. CD4-IgG2 has been expressed in Chinese hamster ovary cells and is secreted as a fully assembled heterotetramer. The protein binds with nanomolar affinity to purified gp120 from both a laboratory-adapted strain and a primary isolate of HIV-1. Pharmacokinetic studies in rabbits demonstrated that CD4-IgG2 has a plasma terminal half-life greater than 1 day, compared with 15 min for soluble CD4 (sCD4). CD4-IgG2 does not bind to Fc receptors on the surface of U937 monocyte/macrophage cells. Compared to molecules that incorporate the Fc portion of IgG1, CD4-IgG2 has less potential to mediate functions such as antibody-dependent enhancement of infection or transplacental transmission of HIV-1. When tested in a virus-free HIV-1 envelope glycoprotein-mediated cell fusion assay, the tetrameric CD4-IgG2 molecule inhibited syncytium formation more effectively than monomeric sCD4 or a dimeric CD4-gamma 2 fusion protein. This suggests the protein will block cell-to-cell transmission of HIV-1. Moreover, CD4-IgG2 effectively neutralized a panel of laboratory-adapted strains and primary isolates of HIV-1, including strains with different tropisms and isolated from different stages of the disease, at concentrations that should be readily achieved in vivo.

A small molecule HIV-1 inhibitor that targets the HIV-1 envelope and inhibits CD4 receptor binding

“…Although sCD4 demonstrated efficacy against many laboratory strains, it exhibited poor activity against primary isolates (31), which may have contributed to disappointing results in clinical trials (31,32). PRO-542 (a CD4-IgG fusion protein) was shown to be effective in neutralizing many clinical HIV-1 strains in culture (15,33) and is efficacious in the clinics (16,34). However, this recombinant fusion protein requires i.v.…”

Partial Enzymatic Deglycosylation Preserves the Structure of Cleaved Recombinant HIV-1 Envelope Glycoprotein Trimers

“…In the current study, we used monomeric gp120s from the subtype B strain JR-FL. The KNH1144 SOSIP.R6 gp140 protein contains the trimer-stabilizing A501C, T605C, and I559P substitutions and a hexa-arginine (R6) motif at the C terminus of gp120 that increases the efficiency of gp120-gp41 proteolytic cleavage (44,45,53,54). The sequence was also modified to contain epitopes for mAbs 2F5, 4E10, and 2G12 (47).…”

“…mAb b12 was a gift from Dennis Burton (Scripps Research Institute, La Jolla, CA), mAbs 17b, 5.8c, and 1.4e were from James Robinson (Tulane University, New Orleans, LA). The CD4-IgG2 and sCD4 proteins from Progenics Pharmaceuticals have been described elsewhere (53). PGT123 was obtained through the IAVI NAC repository.…”

Closing the door to human immunodeficiency virus

“…It mimics the CD4 receptor and competitively binds to the CD4-binding sites on gp120. PRO-542 exerts potent neutralizing activity against the cell-free HIV-1 infection and cell-to-cell virus transmission in vitro (Allaway et al, 1995). It also protects hu-PBL-SCID mice from HIV-1 challenge (Gauduin et al, 1998).…”