A phase I clinical trial of a multi-epitope polypeptide TAB9 combined with Montanide ISA 720 adjuvant in non-HIV-1 infected human volunteers
Introduction
Since the number of HIV infections is still growing in developing countries, there is an increasing need for an effective vaccine. Because the correlates of immunity have not been clearly defined there is a controversy about what type of immune response should be induced by candidate AIDS vaccines. Antibodies are the only component of the adaptive immune system that are able to block infection by free virus particles, and have been an essential element in the protection conferred by other viral vaccines such as measles, rubella, polio, influenza and hepatitis B. Previous experiments conducted in different animal models support the notion that neutralising antibodies can also play a role in protection against HIV infection [1], [2], [3], [4]. Based on these considerations the majority of the vaccine candidates evaluated so far have been designed to elicit neutralising antibody [5]. The principal criticism against these candidates has been the type-restricted nature of the neutralising antibodies and their failure to neutralise primary HIV-1 isolates. [6], [7], [8]
Some vaccine formulations, based on the V3 loop of gp120, have been evaluated in phase I clinical trials. These candidates comprise synthetic peptides from the V3 loop either coupled to a protein carrier [9], [10] or in a Multi-Antigenic Peptide format [11], [12]. The minimalistic approach of using exclusively the V3 region in a vaccine preparation has several potential advantages over the recombinant gp120 based strategies that have already been evaluated in phase II trials and are currently undergoing efficacy trials. First, the inclusion in a single preparation of epitopes from many HIV-1 isolates as a way to confront viral variation, which is one of the most formidable obstacles for vaccine development. Second, the exclusion from the immunogen of gp120 amino acid sequences known to be homologous to human proteins, notably MHCII antigens, that could elicit potentially harmful auto-antibodies in human recipients. Third, the elimination of epitopes that are not targets for neutralising antibodies could minimize the presence of “infection enhancing” antibodies in the vaccine's serum, although the role of these kinds of antibodies in HIV-1 infection in vivo is presently unknown. However, among the drawbacks of the peptide approach are the low immunogenicity of peptides and the loss of conformation dependent epitopes that could be important in eliciting a protective response.
An alternative strategy to the use of V3 synthetic peptides is the construction of multi-epitope polypeptides (MEPs). These are chimeric recombinant proteins expressing the V3 loop of gp120 from several HIV-1 isolates. The V3 coding regions are joined by short spacer sequences of five amino acids, and the gene is fused to a stabilising sequence to achieve high expression levels in Escherichia coli. These proteins were able to elicit neutralising antibodies in mice and rabbits against HIV-1 laboratory strains using Freund's Complete Adjuvant [13], [14].
The MEP TAB9 contains the V3 region from HIV-1 isolates LR150, JY1, RF, MN, BRVA and IIIB, fused to the amino terminal part of the Neisseria meningitidis P64K protein. In a previous study, it was shown to be as immunogenic in rabbits as MEP TAB4, which displays the same V3 regions but the stabilising sequence from human IL2 [15].
The effect of several adjuvant formulations on the antibody response against TAB9 has also been assessed. Oil in water emulsions were the most potent stimulators of this response [16]. One of the adjuvants that were able to induce a potent antibody response in rabbits, mice and macaques [17] was Montanide ISA720 (M-ISA720, SEPPIC, Paris), which has been recommended by the manufacturer for clinical trials in humans.
The immunogenicity of TAB9 in M-ISA720 has been evaluated before in mice, rabbits and cynomolgus monkeys [16], [17] where it was able to develop widely reactive antibodies able to recognize a range of V3 peptides and neutralize several HIV-1 laboratory isolates. In the present work we assessed the reactogenicity and immunogenicity of TAB9 formulated in M-ISA720 in HIV seronegative volunteers.
Section snippets
TAB9 vaccine candidate
TAB9 is a MEP containing one copy of the central region of the V3 loop for each of the following isolates: LR150 (SRGIRIGPGRAILAT) ; JY1 (RQSTPIGLGQALYTT); RF (RKSITKGPGRVIYAT); MN (RKRIHIGPGRAFYTT); BRVA (RKRITMGPGRVYYTT) and IIIB (SIRIQRGPGRAFVTI) in this order, fused to the amino terminal 47 amino acids from P64K protein of N. meningitidis [15]. Montanide ISA720 (M-ISA720, SEPPIC, Paris) is an oil adjuvant composed of a natural metabolizable oil and a highly refined emulsifier from the
Subjects
Twenty-four subjects with a median age of 27.4 yr were enrolled. All of them had normal values for the laboratory parameters studied. Twenty-three of them received three immunisations. One subject from the high dose group received only two injections, the first in the deltoid muscle, the second in the anterolateral thigh, and did not receive the third dose due to a large local reaction after the second dose. A fourth dose, originally planned, was not offered to any subject due to the increasing
Discussion
Several vaccine candidates based on recombinant gp120 [20], [21], [22], [23], [24], [25], [26] or synthetic peptides from the V3 loop [9], [10], [11], [12] have already been evaluated in phase I clinical trials. The vaccine candidate evaluated here is also focused on the V3 loop of HIV-1 gp120, but instead of synthetic peptides it uses a chimeric recombinant protein exhibiting the V3 loop from six HIV-1 isolates. This protein, named TAB9, has been evaluated in several animal models including
Acknowledgements
We are greatly indebted to all the volunteers that made this clinical trial possible. We thank SEPPIC for the adjuvant Montanide ISA720 used in this study, the Departments of Process Developing, Formulation and Quality Control of CIGB for the production and control of the experimental batches of the vaccine candidate, and the Department of Peptide Synthesis of CIGB for supplying the synthetic peptides used in the study. We are also obliged to Dr. Harvey Holmes and the MRC AIDS Reagent Project,
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