Pascal Dalbon

HCV core immunodominant region analysis using mouse monoclonal antibodies and human sera: characterization of major epitopes useful for antigen detection.

Monoclonal antibodies (MAbs) were generated by immunizing mice with a truncated recombinant protein corresponding to the immunodominant region (residues 1–120) of hepatitis C virus (HCV) nucleocapsid protein. The specific recognition by either human sera or mouse monoclonal antibodies of overlapping peptides spanning the core region 1–120 as well as the comparison with epitopes described earlier allowed the fine mapping of HCV core. Within the region 1–120, the major antigenic domain could be restricted to the first 45 amino acids. Indeed, the peptide S42G (residues 2–45) allowed the detection of an anti‐HCV core response by all anticore‐positive human sera examined. According to their epitope localization, three groups of mouse MABs could be evidenced that were directed against different regions of core. Group II MAbs recognized a strictly linear epitope (QDVKF, residues 20–24), whereas group I MABs were directed against a conformational epitope mainly located at the amino acid residues (QIVGG, 29–33). The epitope of group III MABs was also conformational (PRGRRQPI, residues 58–65). These three epitopes appeared close but different from the three major human epitopes RKTKRNTN, VYLLPR, and GRTWAQPGYPWPLY (residues 7–17, 34–39, and 73–86, respectively). Group II MAB 7G12A8 and group I MAB 19D9D6 were used in a sandwich ELISA for the capture and the detection, respectively, of viral core antigen in sera of patients with chronic HCV infection. After treatment of sera with triton × 100 in acidic conditions, amounts of viral antigen as low as 20 pg/ml of sera could be detected. J. Med. Virol. 56:300–309, 1998.

Two‐dimensional electrophoresis of prostate‐specific antigen in sera of men with prostate cancer or benign prostate hyperplasia

Prostate‐specific antigen (PSA), the main marker for prostate cancer (PCa), is released from the prostate into the blood stream at nanogram level and may increase in PCa and nonmalignant disease such as benign prostate hyperplasia (BPH). More recently, advantage was taken of PSAs ability to bind to protease inhibitors in serum in order to improve discrimination between PCa and BPH, using the free PSA to total PSA ratio. The understanding of this phenomenon at molecular level, which is still unknown, may promise new improvements in the field of diagnostics. For this purpose, we determined the pattern of PSA forms in PCa and BPH sera, using the high resolving power of two‐dimensional electrophoresis (2‐DE) in conjunction with the high sensitivity of chemiluminescence detection. Serum PSA differs drastically from seminal PSA: apart from complexed forms, serum PSA shows few cleaved forms. Moreover, 2‐DE patterns from PCa are relatively homogeneous, whereas patterns from BPH may in some cases present a higher proportion of cleaved forms and in other cases present slightly more basic spots. We therefore demonstrated, for the first time, that an increase in the free to total PSA ratio in BPH cases may be due to cleaved PSA forms (which are enzymatically inactive and unable to bind inhibitors), or possibly related to basic free PSA, which may represent the zymogen forms.

Differential diagnosis of prostate cancer and benign prostate hyperplasia using two‐dimensional electrophoresis

Prostate specific antigen (PSA) is a protease which is characteristic of the prostate. It is widely used as a serum marker for the early diagnosis of prostate cancer (PCa). Nevertheless, for concentrations between 4 and 10 ng/mL, PSA does not enable PCa to be distinguished from benign diseases, such as benign prostate hyperplasia (BPH). In sera, the use of a ratio between free PSA (PSA uncomplexed with protease inhibitor) and total PSA (free PSA and PSA bound to alpha‐1 anti‐chymotrypsin) enables the “gray zone” to be reduced, but an important proportion of patients are still wrongly classed. Using two‐dimensional electrophoresis, we demonstrated using 52 PCa and 40 BPH well‐documented clinical cases that BPH sera show a significantly greater percentage of low‐molecular‐weight free PSA elements (lwPSA) than PCa sera. In our study, the use of a ratio between lwPSA and standard free PSA enables the correct diagnosis of 100% of PCa and 82.5% of BPH cases as against when 73.1% and 42.5% respectively were correctly diagnozed using the total PSA and the free/total PSA ratio. This important finding may be related to differences in the mechanism secreting PSA from the prostate into the bloodstream. We have shown how a tissue marker may be turned into a powerful tumor marker by events probably unrelated to its expression.

Crystal structure of a hydrophobic immunodominant antigenic site on hepatitis C virus core protein complexed to monoclonal antibody 19D9D6.

The first crystal structure of a complex between a hepatitis C virus (HCV) core protein-derived peptide (residues 13–40) and the Ab fragment of a murine mAb (19D9D6) has been solved, allowing determination of the recognized epitope and elucidation of its conformation. This Ab, raised against the first 120 residues of the core protein, recognizes core particles and strongly competes with anticore human Abs, suggesting that it is highly representative of the human anti-HCV core response. Its epitope lies within the first 45 aa of the protein, the major antigenic segment of core recognized both by murine and human Abs. Surprisingly, the recognized epitope (29–37: QIVGGVYLL) has an unusual preponderance of hydrophobic residues, some of which are buried in a small hydrophobic core in the nuclear magnetic resonance structure of the peptide (2–45) in solution, suggesting that the Ab may induce a structural rearrangement upon recognition. The flexibility may reside entirely within the Ag, since the Fab′-peptide complex structure at 2.34 Å shows that the Ab binding site is hardly perturbed by complexation. Given that the recognized residues are unlikely to be solvent exposed, we are left with the interesting possibility that Ab-core interactions may take place in a nonaqueous environment.

SOLID-PHASE SYNTHESIS OF N, N'-UNSYMMETRICALLY SUBSTITUTED UREAS : APPLICATION TO THE SYNTHESIS OF CARBAZA PEPTIDES

The synthesis of Boc- or Fmoc-monoprotected propylenediamine derivatives is reported starting from N-protected α-amino acids. The introduction of these building blocks on solid support via the formation of a urea moiety leads to a new pseudopeptide family (CαCH2CH2Nα(R)CONHCα). Two carbonylating reagents, i.e N,N′-carbonyldiimidazole and triphosgene, as well as different coupling procedures, have been tested to optimize the Boc and Fmoc solid-phase synthesis of a model peptide incorporating this isosteric replacement.