Summary:

This proposal aims at demonstrating the safety and immunogenicity in humans of a novel recombinant measles virus (MV) vector for use as an AIDS vaccine. The vector is replication competent in vivo and is derived from a widely used measles vaccine strain (Schwarz), which is known to induce very long lasting immunity. Therefore, this novel vector potentially offers a unique combination of safety and potency. The recombinant HIV MV vectors will express three relatively conserved HIV proteins (Gag, Pol, Nef) from HIV clade B and A strains. A good manufacturing practices (GMP) compatible production process for the recombinant MV vector will be developed and a GMP lot will be produced for two clinical studies. The first study will evaluate the safety profile of the MV vector, while the second study will also assess the immunogenicity in MV-immune volunteers. With these two clinical studies, the project will specifically address potential shedding of the recombinant vector into the environment and the potential negative impact of pre-existing MV immunity. It is expected that at the end of the project sufficient clinical data on the safety and immunogenicity will have been generated to decide on subsequent advanced technical and clinical development of this novel vaccine approach.

Background:

In this project, the consortium partners are proposing the development of recombinant measles virus (MV) technology. The measles vaccine, a live attenuated strain of MV, is one of the most efficient and safest human vaccines available and has been given to billions of children since the Sixties. Vaccination campaigns have been very efficient to control MV outbreaks in developed countries. However, because of inadequate distribution of the vaccine in developing countries, there are still 45 million cases of measles and 800 000 child deaths per year worldwide (CDC, 1999). MV vaccine induces a life-long immunity after a single or two low-dose injections and a persistence of antibodies and CD8-positive cells has been shown for as long as 25 years after vaccination. MV vaccine is easily produced on a large scale in most countries and can be distributed at low cost. The MV genome is very stable and reversion to pathogenicity has never been observed. Moreover, MV replicates exclusively in the cytoplasm, ruling out the possibility of integration in host cell DNA. All these characteristics make live attenuated MV vaccine an attractive candidate vaccine vector and to this end, a reverse genetics system for MV has been established, allowing the production of recombinant MV with additional foreign genetic material. The MV vector has been shown to express stably a variety of genes, or combinations of genes, of a large size over more than twelve passages. This stability is likely because there is little constraint on genome size for pleomorphic viruses with a helical nucleocapsid. Interestingly, because MV infects cells of the immune system, in particular macrophages and dendritic cells, MV vectors deliver their foreign genes directly to the most efficient antigen presenting cells.

Institut Pasteur (partner 2) has developed an MV vector based on the Schwarz strain, the safest and most widely used vaccine strain. The vaccine rescued from the molecular clone was as immunogenic as the parental vaccine in primates and mice susceptible to MV infection. Recently, recombinant MV expressing envelope glycoproteins from HIV-1 was generated and shown to induce strong cellular immunity and neutralising antibodies against MV and the HIV inserts. Interestingly, pre-existing immunity to the vector did not impair the immunogenicity of the recombinant MV in mice and in macaques, leading to the possibility of using this vector in adult populations with pre-existing immunity to MV.

The consortium is proposing to construct recombinant MV vectors that express the HIV-1 clade B and A Gag, Pol, and Nef proteins. These proteins possess highly conserved regions that have been shown to be the target of CD8-positive cells, and thereby constitute a promising antigenic composition for an HIV vaccine. It has been demonstrated that CD8-positive cells from individuals infected with virus strains from different clades are highly cross-reactive with respect to the Gag, Pol, and Nef protein. By assuming a similar cross-reactivity for vaccine-induced immune responses, the proposed project will be based initially on HIV clade B antigens. The choice of clade B antigens will also allow for subsequent combination vaccine regimen using GSK’s clade B adjuvanted protein vaccine. In addition, a corresponding clade A MV vector will be constructed and compared at the pre-clinical level to the clade B construct. This will enable the consortium to choose the most appropriate vector for subsequent development after the demonstration of safety and immunogenicity of the clade B construct in phase I clinical trials.

Aim:

The objective of the project is the demonstration of safety and immunogenicity of a recombinant HIV MV vector in adult HIV-uninfected volunteers. This includes the identification of a suitable dose of recombinant MV, the demonstration of an acceptable reactogenicity profile, and the characterisation of potential virus shedding. Furthermore, the vaccine will have to induce significant levels of HIV-specific CD8-positive cells in volunteers with pre-existing immunity, and ideally also measurable CD4-positive cell and antibody responses.

Expected results:

A mostly sequential development path has been defined. The first stage is the construction and characterisation of recombinant MV expressing HIV clade B Gag, Pol, and Nef proteins. The characterisation includes the evaluation of immunogenicity in mice, established growth characteristics in a production cell line and analysis of genetic stability. Based on these results, a corresponding HIV clade A MV vector will be developed and compared to the clade B vector in a monkey immunogenicity study.

Several parameters that are relevant for the development of a production process that is compatible with GMP manufacture will be assessed. When a suitable HIV clade B MV vector is selected and a process has been established, GMP clinical lot production will be initiated and the resulting material subjected to a formal QC release. The GMP material will also serve for toxicology studies in macaques in order to assess the reactogenicity, toxicity, biodistribution and shedding of the recombinant MV. The analysis of the GMP lots, the data from the toxicology study, and other supportive data will be compiled in a dossier for submission to regulatory authorities.

The early clinical development comprised in this project will address two main issues concerning the recombinant MV vector technology. These issues are the potential in vivo shedding of a genetically modified organism (GMO), and the impact of pre-existing MV immunity. A first phase I dose-escalation study under confinement conditions to assess the safety of the recombinant MV will be initiated upon regulatory approval. In order to minimise the impact of pre-existing immunity, this study will be conducted in volunteers that have only low titer MV antibodies or are completely seronegative. Therefore, MV serological screening of a larger number of volunteers and identification of eligible study participants will be required. Both reactogenicity and virus shedding will be investigated in this first clinical trial. Depending on the results from the study, a larger clinical trial will be initiated in seropositive volunteers with varying antibody titers to expand the safety data and to evaluate the immunogenicity of the vaccine in the face of significant pre-existing immunity. It is anticipated that the results from this second study will provide the necessary safety and immunogenicity information to decide on a potential advanced development of the recombinant MV vectors as candidate HIV vaccines. The choice of the vector (HIV clade A or clade B) will be made, based on the comparative monkey study immunogenicity data and the cross-reactivity data from the second clinical trial.

Coordinator:

Partners:

Nº	Principal Scientific Participants	Official Address	Other Information
2	Frédéric Tangy	Institut Pasteur Unité des virus lents Rue du Dr. Roux 25-28 FR-75724 Paris CEDEX 15 France	Tel: +33 1 45 68 87 73 Fax: +33 1 40 61 31 67 E-mail: ftangy@pasteur.fr
3	Geert Leroux-Roels	Gent Universiteit Centre for Vaccinology Sint Pietersnieuwstraat 25 BE-9000 Gent Belgium	Tel: +32 9 240 3422 Fax: +32 9 240 6311 E-mail: geert.lerouxroels@ugent.be
4	Odile Launay	Centre Cochin-Pasteur d’essais vaccinaux Hôpital Cochin Rue du Faubourg Saint-Jacques 27 FR-75679 Paris CEDEX 14 France	Tel: +33 1 43 25 38 67 Fax: +33 1 40 46 93 08 E-mail: odile.launay@cch.ap-hop-paris.fr
5	David Lewis	St. George’s, University of London Department of Infectious Diseases Cranmer Terrace UK-SW17 ORE London United Kingdom	Tel: +44 20 8725 5826 Fax: +44 20 8725 3487 E-mail: sgjf300@sgul.ac.uk
6	Neil Almond	National Biological Standards Board Division of Retrovirology Blanche Lane, South Mimms UK-EN6 3QG Potters Bar United Kingdom	Tel: +44 1707 641220 Fax: +44 1707 649865 E-mail: nalmond@nibsc.ac.uk