Immunogenicity of the GPGRAFY epitope on synthetic peptides

Mucosal and Systemic Adjuvant Effects of Cholera Toxin and Cry1Ac Protoxin on the Specific Antibody Response to HIV-1 C4/V3 Peptides Are Different and Depend on the Antigen Co-administered

Evidence from several sources support the assertion that cholera toxin (CT) is a potent immunogen and mucosal adjuvant; however there are also reports showing its lack of adjuvanticity against some antigens. Cry1Ac protoxin also exerts adjuvant effects in the antibody responses to proteins and polysaccharides but its adjuvanticity with regard to peptide vaccines had not been tested. To probe whether the adjuvant effects of these proteins varied depending on the antigen co-administered, we evaluated antipeptide antibody responses in serum and mucosal samples (vaginal, intestinal, and pulmonary) of mice that were immunized by intranasal or intraperitoneal routes with one of two distinct hybrid C4/V3 HIV peptides, either alone or with CT or Cry1Ac. The tested HIV 1 peptides differed in two aminoacids, T1SP10MN(A) was modified at the SP10 region by the substitution of the isoleucines 12 and 14 for cysteines and was called modified (m)T1SP10MN(A). Our data indicate that the adjuvant effects of CT and Cry1Ac are different. In addition they vary depending on the antigen co-administered and the number of antigen doses, because after three doses moderate adjuvant effects of CT and Cry1Ac on anti-peptide serum and mucosal antibody responses were observed only against the mT1SP10MN(A). In contrast, to attain significant adjuvant effects against the T1SP10MN, four doses were required. Interestingly we found that modification of the HIV peptide increases its immunogenicity without altering the principal neutralizing determinant (SP10).

Epitope-vaccine strategy against HIV-1: today and tomorrow

Vaccines play important roles in preventing infectious diseases caused by different pathogens. However, some pathogens such as HIV-1 challenge current vaccine strategy. Poor immunogenicity and the high mutation rate of HIV-1 make great difficulties in inducing potent immune responses strong enough to prevent infection via vaccination. Epitope-vaccine, which could intensively enhance predefined epitope-specific immune responses, was suggested as a new strategy against HIV-1 and HIV-1 mutation. Epitope-vaccines afford powerful approaches to elicit potent, broad and complete immune protection against not only primary homologous viral isolates but also heterologous viral mutants. Although most studies are still preliminary now, epitope-vaccine as a novel strategy against the AIDS epidemic has great developmental potential. To trigger T-cell-dependent IgG antibody responses and improve affinities of the epitope-specific antibodies, approaches such as recombinant multi-epitope-vaccination and prime-boosting vaccination were suggested. Cellular immune responses, especially CTL responses, could also be elicited and enhanced in addition to humoral immune responses. Developed epitope-vaccines activating both arms of the immune system would benefit prevention and immunotherapy not only against HIV but also other chronic infections.

Recombinant multi-epitope vaccine induce predefined epitope-specific antibodies against HIV-1

Monoclonal antibody 2F5 recognizing ELDKWA-epitope on HIV-1 gp41 has significant neutralization potency against 90% of the investigated viruses of African, Asia, American and European strains, but antibodies responses to ELDKWA-epitope in HIV-1 infected individuals were very low. Based on the epitope-vaccine strategy suggested by us, a recombinant glutathione S-transferase (GST) fusion protein (GST-MELDKWAGELDKWAGELDKWAVDIGPGRAFYGPGRAFYGPGRAFY) as vaccine antigen containing three repeats of neutralizing epitope ELDKWA on gp41 and GPGRAFY on gp120 was designed and expressed in Escherichia coli. After vaccination course, the recombinant multi-epitope vaccine could induce high levels of predefined multi-epitope-specific antibodies in mice. These antibodies in sera could bind to both neutralizing epitopes on gp41 peptide, V3 loop peptide and recombinant soluble gp41 (aa539-684) in ELISA assay (antisera dilution: 1:1,600-25,600), while normal sera did not. Moreover, these antibodies in sera could recognize the CHO-WT cells which expressed HIV-1 envelope glycoprotein on the cell surfaces, indicating that the predefined epitope-specific antibodies could recognize natural envelope protein of HIV-1 though these antibodies were induced by recombinant multi-epitope-vaccine. These experimental results suggested a possible way to develop recombinant multi-epitope vaccine inducing multi-antiviral activities against HIV-1.

Immunogenicity and specificity of the candidate multi-epitope-vaccines against HIV-1

The failure of some candidate HIV-1 vaccines may result from inducing very weak neutralization activity against representative primary viral isolates. Based on our hypothesis that epitope-vaccine may be a new strategy to induce high levels of neutralizing antibodies against HIV-1, we designed two candidate multi-epitope-vaccines, EP1 [C-G-(ELDKWA-GPGRAFY)2-K] and EP2 (CG-GPGRAFY-G-ELDKWA-G-RILAVERYLKD), containing three neutralizing epitopes (GPGRAFY, ELDKWA and RILAVERYLKD) on HIV-1 envelope protein, and expected them to induce epitope-specific antibodies of predefined epitope-specificity. The two peptides were conjugated to carrier protein bovine serum albumin (BSA) and used for immunization of rabbits. Proteins were purified from the rabbit sera induced by both candidate multi-epitope-vaccines (EP1-BSA and EP2-BSA) through affinity chromatography with epitope-peptide-conjugated sepharose-column, and identified as antibodies in silver-staining and immunoblotting. These antibodies were demonstrated to recognize three neutralizing epitopes on peptides and the recombinant gp41 in ELISA-assay and immunoblotting. These results indicated that both candidate multi-epitope-vaccines could induce high levels of antibodies of predefined epitope-specificity which recognized a few of neutralizing epitopes on peptides and protein, providing experimental evidence for the new strategy to develop an effective neutralizing-antibody-based multi-epitope-vaccine against HIV-1.

Candidate multi-epitope vaccines in aluminium adjuvant induce high levels of antibodies with predefined multi-epitope specificity against HIV-1

Some neutralizing epitopes on HIV-1 envelope proteins were identified to induce antibodies which could effectively inhibit the infection of different strains in vitro. But only very low levels of these antibodies were determined in the HIV-1 infected individuals. To increase the levels of protective antibodies in vivo, we suggested multi-epitope vaccine as a new strategy to induce high level of neutralization antibodies with predefined multi-epitope specificity. A synthesized epitope peptide MP (CG-GPGRAFY-G-ELDKWA-G-RILAVERYLKD) containing three neutralizing epitopes (GPGRAFY, ELDKWA, RILAVERYLKD) was conjugated to carrier protein KLH, and then used for immunization in mouse together with aluminium adjuvant or Freund's adjuvant (FA). The candidate MP-KLH multi-epitope vaccine in aluminium adjuvant could induce antibody response very strongly to the epitope peptide C-(RILAVERYLKD-G)2 and the immunosuppressive peptide (P1) (LQARILAVERYLKDQQL) (antibody titer: 1:51200), strongly to the epitope peptide C-(ELDKWA-G)4 and the C-domain peptide (P2) (1:12800), and moderately to the epitope peptide C-(GPGRAFY)4 and the V3 loop peptide (1:1600). The immunoblotting analysis demonstrated that the antibodies in sera could recognize P1, P2, V3 loop peptides and rsgp41 (aa 539-684). These results are similar with that in the case of PI-BSA in FA, and suggest that the multi-epitope vaccine in aluminium could induce high levels of antibodies of predefined multi-epitope specificity, which provides experimental evidence for the new strategy to develop an effective neutralizing antibody-based multi-epitope vaccine against HIV-1.