Broadly reactive antibodies against a gp120 V3 loop multi-epitope polypeptide neutralize different isolates of human immunodeficiency virus type 1 (HIV-1)

Efficient CD8+ T cell response to the HIV-env V3 loop epitope from multiple virus isolates by a DNA prime/vaccinia virus boost (rWR and rMVA strains) immunization regime and enhancement by the cytokine IFN-γ

The cytotoxic T-lymphocyte response (CTL) has been shown to be determinant in the clearance of many viral infections and hence, vaccine candidates against AIDS are designed to enhance this arm of the immune system. In this study, we have analyzed the antigen specific immune responses triggered in mice by different combinations of vaccine vehicles expressing the multiepitope polypeptide TAB13. This chimeric protein contains the V3 region of the gp120 from eight different HIV-1 isolates and was efficiently expressed by a DNA vector (DNA-TAB), and also by vaccinia virus recombinants (rVV) based either on the attenuated modified vaccinia virus Ankara (MVA-TAB) or Western Reserve (VV-TAB) strains. Inoculation of a DNA-TAB vector in priming followed by a booster with VV-TAB or MVA-TAB induces a humoral immune response against TAB13 protein and efficiently enhanced the CD8+ T cell response against V3 epitopes from HIV-1 isolates LR150, MN, and IIIB in comparison with animals immunized with two doses of DNA-TAB. A protocol that incorporates a DNA vector expressing IFN-gamma (DNA-IFN-gamma) with DNA-TAB in the priming, followed by a booster with MVA-TAB, triggered the highest values of specific CD8+ T cell response. By examining the cytokine pattern, the immune response induced by these vaccination approaches was predominantly of Th-1 type. These findings establish safe strategies for the enhanced generation of T cell mediated immunity to HIV-1 that can benefit in the design of an effective vaccine against AIDS.

Induction of a strong HIV-specific CD8+ T cell response in mice using a fowlpox virus vector expressing an HIV-1 multi-CTL-epitope polypeptide

Recombinant avipoxvirus vectors are attractive candidates for use in vaccination strategies for infections such as human immunodeficiency virus type 1 (HIV-1), where induction of a CD8+ T cell response is thought to be an important component of protective immunity. Here, we report the expression of a multiepitope polypeptide (TAB9) composed of the central 15 amino acids of the V3 loop from six different isolates of HIV-1 in a fowlpox virus (FWPV) vector, and the use of this vector (FPTAB9LZ) to induce strong HIV-specific CD8+ T cell responses in mice. In animals immunized twice intravenously with FPTAB9LZ, almost 2% of the CD8+ T cells in the spleen were shown to produce IFN-gamma in response to stimulation with HIV-1 peptides 1 week after the second immunization. The most dominant response was to the HIV-1 IIIB peptide. A strong HIV-specific response was also induced by intraperitoneal immunization of mice with FPTAB9LZ, whilst subcutaneous immunization elicited a weaker response. Intraperitoneal immunization with FPTAB9LZ was also shown to provide protection against challenge with a recombinant vaccinia virus expressing antigens, including those in TAB9. These results confirm the potential of FWPV vectors for use in HIV vaccination strategies.

Enhanced CD8+ T cell immune response against a V3 loop multi-epitope polypeptide (TAB13) of HIV-1 Env after priming with purified fusion protein and booster with modified vaccinia virus Ankara (MVA-TAB) recombinant: a comparison of humoral and cellular immune responses with the vaccinia virus Western Reserve (WR) vector

The humoral and cytotoxic T-lymphocyte (CTL) responses have been shown to be determinant in the clearance of many viral infections and because of those characteristics, vaccine candidates against AIDS are designed to enhance both arms of the immune system. While a protocol of immunization able to confer protection in humans against HIV will have to await the results of current clinical trials, it remains important to identify protocols of immunization in animals that achieve significant levels of humoral and cellular immune responses to HIV. In this study we have carried out a comparative analysis of the immune responses elicited in mice immunized with recombinants based on the modified vaccinia virus Ankara strain (rMVA) versus the Western Reserve strain (WR) of vaccinia virus (rVV), both expressing a V3 loop multi-epitopic protein from eight different HIV isolates (TAB13). We found that during priming, rMVA elicited a two- to three-fold higher specific CD8+ T cell response than rVV. Similar enhancement was observed during priming with purified protein TAB13 followed by a booster with rMVA. The epitopes LR150, MN and IIIB, located at the ends and in the middle of the chimeric protein, were able to induce a specific CD8+ T cell response, both after priming or prime/booster with the recombinant viruses but not after prime/booster with TAB13. By examining the cytokine pattern, the immune response triggered by these vectors was of Th-1 type. Humoral immune responses were higher in animals immunized with TAB13/TAB13 or TAB13/rVV than in animals immunized with TAB13/rMVA. These findings demonstrate that during priming or in a prime/booster immunizations, rMVA is superior to rVV in the ability to enhance specific cellular responses to an HIV-1 protein, and that both humoral and cellular immune responses to theV3 loop epitope of HIV-1 Env can be obtained by priming with TAB13 followed by a booster with viral vectors.

Impact of epitope permutations in the antibody response of mice to a multi-epitope polypeptide of the V3 loop of human immunodeficiency virus type 1

Our group have produced in Escherichia coli and evaluated the immunogenicity of different multi-epitope polypeptides (MEPs) bearing one copy of V3 loop sequential B cell epitopes from several isolates of human immunodeficiency virus type 1 (HIV-1) gp120. One of these MEPs called TAB9 comprises the 15 central amino acids of the V3 loop from isolates LR150, JY1, RF, MN, BRVA and IIIB in this order. Antibodies against all V3 regions were elicited after immunization of rabbits, macaques and humans with TAB9. In contrast, mice immunized with this protein only developed antibodies against epitopes JY1, LR150 and MN in that order (JY1>LR150>MN>>>RF, BRVA, IIIB) resembling an immunodominant gradient from the N-terminus to the C-terminal portion of this construction. To assess what role the location of the V3 epitopes in TAB9 could play, we constructed the protein TAB16, by altering the position of V3 epitopes in TAB9 primary structure and compared the pattern of antibodies elicited by both MEPs in H-2(d) Balb/c mice. The MEP TAB16 elicited antibody titers comparable to that of the sera from mice immunized with TAB9. There were no statistical differences in antibody titers between both groups (P>0.05). JY1, LR150 and MN V3 epitopes were again immunodominant in mice immunized with TAB16 fusion protein. The highest antibody titers detected in both groups among V3 epitopes corresponded to JY1, now located at the C-terminus of the permuted chimera. Antibodies against V3 epitopes RF, BRVA and IIIB were again not detected. Additionally, the MN V3 epitope showed to be significantly more immunogenic in its new orientation in TAB16, possibly as a result of a higher degree of accessibility in the surface of the protein. The results of the present investigation strongly suggest that the sequential order or the intramolecular position of V3 epitopes inside the primary structure of TAB9 and TAB16 MEPs does not interfere with the global immunogenicity or with the hierarchy of immunodominance of these regions.

Study of different coupling agents in the conjugation of a V3-based synthetic MAP to carrier proteins

The conjugation of synthetic peptides to carrier proteins is a widely used method for immunological studies. Different coupling agents have been described to form the conjugate with carrier proteins. In this paper, we demonstrate that the antibody response toward V3-based synthetic MAPs derived from HIV-1, JY1 isolate, conjugated to two different carrier proteins using either m-maleimidobenzoyl-N-hydroxysuccinimide ester (MBS) or beta-maleimidopropionic acid N-hydroxysuccinimide ester (MPS), or succinic anhydride (SA) show different behaviors. An excellent anti-JY1 response without a strong response to the coupling agent is observed in the case of succinic anhydride spacer. In contrast, MBS produces total abrogation of the antibody response with a high response toward the coupling agent.

A phase I clinical trial of a multi-epitope polypeptide TAB9 combined with Montanide ISA 720 adjuvant in non-HIV-1 infected human volunteers

A phase I clinical trial was performed to examine the safety and immunogenicity of a multi-epitope polypeptide comprising the central 15 amino acids of the V3 loop from six HIV-1 isolates. This protein called TAB9 was emulsified in Montanide ISA720 (Seppic, Paris) and administered intramuscularly at doses of 0, 0.2 and 1 mg to 24 healthy, HIV-1 seronegative adult males. Three immunisations were given at months 0, 1 and 6 in a randomised, double blind, placebo controlled clinical trial. The placebo was generally well tolerated. However, severe local reactions were observed in TAB9 vaccinated subjects after the second and third inoculations. Seven out of eight volunteers from the lower dose group showed moderate or severe local inflammation, while four out of eight subjects from the higher dose group developed granulomas and sterile abscesses. In general, the reactogenicity depended on the number of inoculations given and the dose of TAB9. Both doses were immunogenic, all immunised volunteers seroconverted and antibodies were broadly reactive against the V3 peptides included in the protein. All vaccine's sera reacted against gp120 in Western blot and 50% of them also neutralised at least one out of five laboratory isolates tested. No differences between doses were found. Anti TAB9 lymphoproliferative responses were observed, being more intense in the high dose group. Due to the strong local reactions that were found in this study, a change in the formulation will be required for further trials with this vaccine candidate in humans.

Virolysis and in vitro neutralization of HIV-1 by humanized monoclonal antibody hNM-01

Antibody humanization by transplanting the complimentarity determining region (CDR) to a human framework aims to reduce the response of the human immune system against a foreign molecule during passive immunization. We transferred the CDR from the murine monoclonal antibody (MAb) NM-01 to a human IgG frame. The humanized NM-01 (hNM-01) recognizes the same epitope on Human Immunodeficiency Virus type 1 (HIV-1) envelope as its murine progenitor, but with greater efficiency, and shows enhanced neutralization of HIV-1. We have shown that this increase in reactivity may be attributed to residue 4 of the humanized kappa chain, where the presence of a methionine residue rather than the murine leucine appears to promote a more advantageous conformation of the antigen-binding site, perhaps via packing interactions with the V(kappa) CDR1. The capacity of humanized NM-01 to neutralize direct clinical isolates was also examined with the expectation that hNM-01 will prove suitable for development as a therapeutic agent. This reshaped antibody reacted with several clinical isolates of HIV-1 tested. Moreover, we proved the ability of this antibody of its activation of complement by flow cytometry and electron microscopy analysis. Although hNM-01 alone was capable of neutralizing HIV-1, the presence of complement enhanced neutralization. The enhancement of complement activation was also observed in hNM-01 than murine progenitor. This finding supports a potential role for antibody-dependent complement-mediated virolysis and more effective neutralization in HIV-1 therapy.

Differential antigenicity of recombinant polyepitope-antigens based on loop- and helix-forming B and T cell epitopes

To investigate a strategy for the design of chimeric antigens based on B cell epitopes (BCEs) we have genetically recombined multiple copies of loop- (L) and helix-forming (H) sequential and protective BCEs of the measles virus hemagglutinin protein (MVH) in a number of high-molecular-weight polyepitope constructs (24.5-45.5 kDa). The BCE cassettes were combined semi-randomly together with a promiscuous T cell epitope (TCE; tt830-844) to yield 13 different permutational constructs. When expressed in mammalian cells, all constructs were detectable by Western blot as distinct bands of predicted molecular weight. Flow cytometry with conformation-specific antibodies revealed the Cys-loop in two [(L(4)T(4))(2) and (L(2)T(2))(4)] and the helix conformation in one [(H(2)T(2))(4)] of the different permutational constructs. The larger constructs, containing 16 epitope cassettes, seemed more likely to express the BCEs in their native conformation than the 8-mers. In the T cell proliferation assay, constructs with a higher copy number of TCEs, such as (L(2)T(2))(4), were more antigenic, as long as tandem repeats were separated by spacers. Since the conformation of even sequential BCEs and the processing of TCEs are both sensitive to their molecular environment it is difficult to predict the antigenic properties of polyepitopes. However, with the permutational approach we have developed several polyepitope constructs [(L(4)T(4))(2), (L(2)T(2))(4), (H(2)T(2))(4)] based on complex sequential BCEs that are antigenic for both T and B cells. Several constructs induced sera that reacted with reporter peptides, demonstrating that the sequential nature of the viral epitopes was conserved in the polyepitopes. Although several sera contained antibodies directed against amino acids critical for neutralization, only one construct induced antibodies that cross-reacted with the virus. Our results show the difficulty of designing chimeric antigens based on B cell epitopes mimicking their antigenic and immunologic properties even when these are sequential in nature.

Immunogenicity comparison of a multi-antigenic peptide bearing V3 sequences of the human immunodeficiency virus type 1 with TAB9 protein in mice

The multiple antigenic peptide system (MAP) has been proposed as a novel and valuable approach for eliciting antibodies for peptides and developing synthetic vaccines. Multi-epitope polypeptides (MEP) have also been developed as an alternative to the recombinant approach for vaccines. The V3 loop from the HIV type 1 (HIV-1) external glycoprotein (gp120) contains the principal neutralization domain (PND). Antibodies against this region neutralize HIV-1 in vitro and in vivo. In this work, a novel presentation of di-epitope MAP was synthesized. A monomeric MAP carrying two identical JY1 V3 sequences as B-cell epitopes and the 830-843 region of tetanus toxoid as a T-helper cell epitope was synthesized. This basic structure was covalently linked to produce a four-JY1-branched homodimer (JY1-MAP4). Additionally, six different monomeric MAPs, bearing four copies of V3 from isolates LR150, JY1, RF, MN, BRVA and IIIB, were synthesized. These monomers were conveniently linked among themselves to produce homodimeric and heterodimeric MAPs of eight V3 branches (V3-MAP8). JY1-MAP8 elicited higher antibody titers in Balb/c mice than JY1-MAP4. The immunogenicity of two different, hexavalent V3-MAP8 mixtures and the MEP TAB9, which tandems the same six V3 sequences in a single molecule, were compared. The antibody response against the mixtures of the heterodimeric MAP showed a wider recognition pattern of the V3 region, while the homodimeric cocktail showed an intermediate pattern. Antibodies elicited by TAB9 recognized only the JY1, LR150 peptides. These results emphasize the influence of V3 epitope presentation upon the characteristics of the antibody response generated.

The multi-epitope polypeptide approach in HIV-1 vaccine development

The application of a preventive HIV vaccine is the only hope for most developing countries to halt the AIDS pandemic. A project aimed to develop a preventive AIDS vaccine is being carried out since 1992 by three Cuban research institutions: Centro de Ingeniería Genética y Biotecnologia de La Habana, Instituto de Medicina Tropical 'Pedro Kouri' and Laboratorio de Investigaciones de SIDA de La Habana. The project includes two main strategies: (a) generation of recombinant multi-epitope polypeptides (MEPs) bearing several copies of the V3 loop from different HIV-1 isolates; and (b) development of immunogens capable of inducing a cytotoxic T cell response (CTL) specific for human immunodeficiency virus type 1 (HIV-1) antigens. This article summarizes the work in the first of these strategies. Based on the sequence of the V3 loop of HIV-1 we constructed a series of MEPs and evaluated their immunogenicity in mice, rabbits and macaques. The MEP TAB9, containing six V3 epitopes from isolates LR10, JY1, RF, MN, BRVA and IIIB, was selected together with the oil adjuvant Montanide ISA720 (SEPPIC, France) to perform a Phase I clinical trial in HIV seronegative Cuban volunteers. The trial was double blinded, randomized, and fulfilled all ethical and regulatory requirements. All TAB9 vaccinated volunteers developed a strong immune response and neutralizing antibodies were observed in the 50% of the subjects. However the second and third inoculations of the vaccine were not well tolerated because transient severe local reactions appeared in some individuals. A new formulation of TAB9 is currently in pre-clinical studies and is expected to enter clinical trials in 1999.

A prime-boost regime that combines Montanide ISA720 and Alhydrogel to induce antibodies against the HIV-1 derived multiepitope polypeptide TAB9

A phase I clinical trial with the HIV-1-derived multi-epitope polypeptide (MEP) TAB9 in the oil adjuvant Montanide ISA720 (M-ISA720) was recently performed. Although severe local reactions were reported after the second and third injections of this vaccine candidate, the first inoculation was well tolerated. In this article we evaluated a prime-boost regime consisting of one inoculation of TAB9 in M-ISA720 followed by a booster with the same antigen in aluminum hydroxide. This combination of adjuvants elicited similar antibody levels in rabbits than the traditional two-dose schedule with M-ISA720. A control group injected three times with TAB9 in aluminum hydroxide developed markedly lower antibody titers. These results showed that although oil adjuvants are better than alum for priming the immune system for antibody production against TAB9, both kinds of adjuvants can be equally effective in booster immunizations. Therefore, by using the more reactogenic oil adjuvant only for priming, we should be able to eliminate the undesirable reactions characteristic of these compounds while achieving equivalent levels of specific antibodies.

The V3 loop based multi-epitope polypeptide TAB9 adjuvated with montanide ISA720 is highly immunogenic in nonhuman primates and induces neutralizing antibodies against five HIV-1 isolates

In a previous work we selected montanide ISA720 (M-ISA720) among different adjuvants for the vaccination with a V3 loop based multi-epitope polypeptide TAB9. In this paper we present the evaluation of the toxicity and immunogenicity of this formulation in non-human primates. TAB9 in M-ISA720 was highly immunogenic in macaques (Macaca fascicularis) inducing antibodies against TAB9 in all animals after one inoculation and a strong anamnestic response after booster injections. Furthermore 97% of the V3 peptides included were recognized by TAB9 sera. No differences between doses of 200 microg and 1 mg of TAB9 in M-ISA720 were observed after four immunizations. Neutralizing antibodies against five HIV-1 isolates were detected in most animals. Animals remain healthy throughout the study and did not show lesions at the inoculation site.

An immunoassay with bovine serum albumin coupled peptides for the improved detection of anti V3 antibodies in HIV-1 positive human sera

The V3 loop of the gp120 envelope glycoprotein contains the principal neutralizing determinant of HIV-1. Many serological studies have been carried out to assess the reactivity of HIV-1 infected individuals against V3 loop synthetic peptides from different HIV-1 subtypes. V3 directed serology has also been used to demonstrate the association between ELISA reactivity and progression to AIDS in HIV patients, and to study the reactivity against the V3 region in sera from vaccinated animals and human volunteers. The advantage of the use of bovine serum albumin (BSA) conjugated V3 peptides over free V3 peptides for ELISA is described. 15 meric V3 peptides representing several HIV-1 isolates were synthesized, chemically coupled to BSA, and used to coat ELISA microplates. Conjugated peptides were compared with free peptides for the detection of anti V3 antibodies in the sera from rabbits immunized with V3 containing chimeric proteins and from HIV-1 infected individuals. No differences in reactivity against free or BSA-peptide were found for most rabbit sera, however human plasma recognized preferentially the BSA conjugated peptides. Although technically more complex, ELISA with BSA coupled V3 peptides is more sensitive and appropriate for serological studies of HIV-1 infected persons.