Unit: Virology and Cellular Immunology - URA CNRS 1930

Director: Hovanessian, Ara

Innate and adaptive immunity are essential for the control of HIV infection. The innate immunity has two functions. Firstly by giving a direct resistance to viral and microbial pathogens through the action of cytokine/lymphokines and chemokines, and secondly by determining the initiation and type of adaptive immune responses. In this respect, our projects involve on one hand the triggering the innate antiviral response by alpha IFNs and on the other hand by eliciting broadly neutralizing antibody production specific for the transmembrane envelope glycoprotein of HIV.

Control of HIV infection by triggering the innate antiviral respons (A. Hovanessian, I. Marié, Helene Collandre, A. Caullaud).

Among the cytokines, type I interferons, IFN-alpha and IFN-beta, play an essential role in the innate immunity since besides their antiviral action, they augment antiviral functions of effector cells and mediate activation and differentiation of dendritic cells.

In the context of control of viral infections, the family of alpha interferons represents one of the most important cytokine for the natural defense mechanism in an organism, and also for the development of an efficient innate immunity against virus infections. A family of 13 structurally related genes encodes IFN-alpha, whereas a single gene encodes IFN-beta. The IFN-alpha gene expression during virus infections could be divided into two distinct phases. The first phase involves induction of IFN-beta and IFN-alpha-4 through activation of pre-existing transcription factor IRF-3 resulting in the induction of another transcription factor IRF7. The second phase involves phosphorylation of IRF7 that becomes translocated into the nucleus to result the induction of the remaining members of the IFN-alpha gene family. Accordingly, IRF7 ensures a maximum antiviral response to stop virus replication in infected cells and prevent infection in healthy cells. By studying the phosphorylation sites in IRF7 necessary for induction of the IFN-alpha gene promoters, we generated a series of IRF7 mutants that are constitutively active. Consequently, such mutants of IRF7 represent efficient candidates for the induction of IFN-alpha in view of reconstitution of the innate immune response during virus infections. The expressions of IRF7, either wild type or mutated, could increase the production of IFN during a viral infection and thus be used as an experimental approach to control the viral propagation. This will be investigated first by using HIV as a model virus, since our previous results have shown that HIV is sensitive to the antiviral action of IFN-alpha and furthermore IFN-alpha is the type of interferon produced during in vitro infection of primary T-lymphocytes by HIV. The use of the mutant constructs of IRF7 might be of further importance, in case HIV has evolved a mechanism that might inhibit IRF7 phosphorylation.

A synthetic B-cell epitope HIV-vaccine candidate based on the caveolin-binding motif in gp41 (A . Hovanessian, B. Krust, E. Said, J. Svab).

A successful vaccine preparation for HIV should have components to stimulate T-cell responses and elicit neutralizing antibodies. Currently more than 20 HIV vaccines designed to stimulate T-cell responses are in clinical trials, whereas no vaccine that is capable of stimulating the production of broadly neutralizing antibodies has yet been evaluated. Thus the design of a vaccine capable of stimulating neutralizing antibodies that inhibit primary HIV isolates is considered currently to be one of the highest priorities in the HIV vaccine research.

Caveolin-1 is a major protein constituent of caveolae, a type of plasma membrane lipid rafts. We identified a conventional but distinct caveolin-binding motif in the ectodomain of the transmembrane envelope glycoprotein (TM gp) of HIV. This motif starting few amino acids upstream of the C-terminal heptad repeat sequence in the TM gp is highly conserved among various HIV-1 and HIV-2 isolates. In view of this, we designed several synthetic 15-25 amino acid peptides containing this distinct caveolin-binding motif. When injected to rabbits, these peptides consistently elicited the production of neutralizing antibodies that inhibited HIV-1 and HIV-2 infection of primary CD4+ T lymphocytes by various T lymphocyte and macrophage-tropic viral isolates and as well as by primary HIV-1 isolates. As a consequence of amino acid sequence variability of HIV, previous attempts to generate neutralizing antibodies have resulted in specific antibody responses that target only a very narrow range of HIV-1 variants. In this respect, the caveolin binding domain in the HIV TM gp, named as the CBD epitope, represents an efficient peptide vaccine candidate because of its capacity in eliciting broadly neutralizing antibodies against HIV, and because of its unique property to contain a distinct caveolin-binding motif conserved among all HIV-1 and HIV-2 isolates.

Our current projects therefore are designed for the development of a candidate epitope vaccine suitable for HIV-1 and HIV-2 infection. The various projects include studies on the amino acid composition of the peptide eliciting high titer and broadly neutralizing antibodies, the mechanism of action of the neutralizing antibodies, the role of caveolin-1 in HIV infection, the preparation of neutralizing mouse and human monoclonal antibodies against the caveolin-binding motif, the efficacy of this epitope vaccine in the macaque experimental model and finally other vaccine strategies based on the caveolin-binding motif of HIV.

Keywords: HIV, HIV entry, vaccine, neutralizing antibodies, interferon, IRF7

Activity Reports 2003 - Institut Pasteur

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