Synthetic peptides derived from the variable regions of an anti-CD4 monoclonal antibody bind to CD4 and inhibit HIV-1 promoter activation in virus-infected cells

The monoclonal antibody (mAb) ST40, specific for the immunoglobulin complem entarity-determining region (CDR) 3-like loop in domain 1 of the CD4 molecu le, inhibits human immunodeficiency virus type 1 (HIV-1) promoter activity and viral transcription in HIV-infected cells. To design synthetic peptides from the ST40 paratope that could mimic these biological properties, a set of 220 overlapping 12-mer peptides frameshifted by one residue, correspond ing to the deduced ST40 amino acid sequence, was synthesized by the Spot me thod and tested for binding to recombinant soluble CD4 antigen. Several pep tides that included in their sequences amino acids from the CDRs of the ant ibody and framework residues flanking the CDRs were found to bind soluble C D4, Eleven paratope-derived peptides (termed CM1-CM11) were synthesized in a cyclic and soluble form. All the synthetic peptides showed CD4 binding ca pacity with affinities ranging from 1.6 to 86.4 nM. Moreover, peptides CM2, CM6, CM7, CM9, and CM11 were able to bind a cyclic peptide corresponding t o the CDR3-like loop in domain 1 of CD4 (amino acids 81-92 of CD4), Peptide CM9 from the light chain variable region of mAb ST40 and, to a lesser exte nt, peptides CM2 and CM11 were able to inhibit HIV-1 promoter long terminal repeat-driven beta-galactosidase gene expression in the HeLa P4 HIV-1 long terminal repeat beta-galactosidase indicator cell line infected with HIV-1 , The binding of mAb ST40 to CD4 was also efficiently displaced by peptides CM2, CM9, and CM11, Our results indicate that the information gained from a systematic exploration of the antigen binding capacity of synthetic pepti des from immunoglobulin variable sequences can lead to the identification o f bioactive paratope-derived peptides of potential pharmacological interest .