Keywords: HIV microbicide, preventive vaccine, therapeutic vaccine
The objective of the proposed project is to establish proof of concept that a trimolecular construct, consisting of MHC antigens combined with microbial HSP70 and extracellular CCR5 peptides can be utilized in microbicidal, preventive and therapeutic immunization. This strategy utilizes a novel microbicidal-immunogenic agent to protect against mucosal SHIV infection in female macaques. The construct blocks HIV-1 or SIV binding CCR5- coreceptors and elicits both extracellular and intracellular anti-HIV-1 or -SIV factors. However, as the trimolecular agent is immunogenic, repeated applications will elicit mucosal, regional and systemic immunity. Furthermore, it elicits innate antiviral responses and targets different stages in the infectious process. The novel strategy of combining a short term microbicide with a longterm preventive vaccine may deal with the serious difficulty of compliance, demanded by repeated application of microbicides before each intercourse.
The rationale for the proposed alloantigen-HSP70-CCR5 microbicidalvaccination project is based on the two natural HIV-1 resistance states, alloimmunity and homozygous CCR5 mutation. There is evidence that among the large number of host antigens expressed by HIV-1 or SIV virions, MHC class I and II and HSP70 are of considerable significance, but have received limited attention. Monoclonal antibodies to HLA-class I or II heavy chains inhibited HIV-1 production in human PBMC. This was caused by direct interaction between the antibodies and the HIV-virion associated HLA-I antigens. Furthermore, allo-immune stimulation may engage up to 10% of T cells, producing cytokines and chemokines, and activating the costimulatory pathway, all of which have a robust effect on the immune response.
The evidence supporting alloimmunity in preventing HIV/SIV infection involves epidemiological studies, alloimmunization studies in human volunteers and xeno- or allo-immunization in macaques. HSP70 is also found within the virion membrane of HIV-1 and functions as a chaperone during intracellular transport. HSP70 expression is significantly increased in lymphocytes from HIV-1 infected subjects. In addition HSP70 elicits innate immune responses, by generating chemokines and cytokines which exert robust adjuvanticity.
These data are consistent with recent findings that HSP70 binds CCR5 directly and that HSP70 inhibits infectivity of primary CD4+ T cells by R5 strains of HIV-1. Preliminary evidence suggest both in vitro and in immunized macaques that HSP70 stimulates upregulation of the innate intracellular APOBEC3G anti-viral factor. This has been demonstrated with human CD4+ T cells, DC and simian mononuclear cells. Furthermore, allostimulation with HLA-class I Dextramers elicits APOBEC3G and CD4+ T cell proliferative responses, emphasizing the dual function of Dextramers.
The second "experimemnt of nature" is the striking resistance to HIV-1 infection in homozygous ?32 CCR5 mutation found in about 1% of Caucasians. These lack cell-surface expression of CCR5, they show increased concentration of 3 CC chemokines, they may develop antibodies to CCR5, and do not suffer from ill-health. An important principle utilised by the proposed strategy is potentiation between alloimmune, CCR5 and HSP70 responses and this takes into account the concept that a combination of cytokines, chemokines, immunomodulatory and costimulatory molecules potentiate multiple steps in eliciting an effective immune response.
The aim of the project is to utilize one cohort of macaques for three HIV-1/SIV preventive modalities in microbicide, preventive and therapeutic immunization. Three common macaque MHC molecules (Mamu A1,A4,A8) will be selected and expressed as novel Dextramer constructs, to inhibit mucosal transmission of SHIV SF162P.4. Alloantigens will be combined with microbial HSP70 and 3 extracellular peptides of CCR5 which inhibit transmission of R5 strains of SIV or HIV. Macaques will be challenged with SHIVSF162P.4 (R5 strain of HIVenv gene construct), after each of 4 applications of the microbicidal agent and test for infectivity. The investigation will include vaginal antibodies, CC chemokine responses, and systemic innate and adaptive immune responses to the microbicidal agent and the challenge virus. Macaques which were not infected will then be evaluated for preventive immunity by challenging with SHIV SF162P.4. Animals that were infected will be utilized for therapeutic immunization 2 months after infection by first treating them with ART and then by IM administration of the microbicidal construct, followed by rechallenge with SHIV SF162P.4.
It is expected that in a proportion of macaques treated with the trimolecular construct, SHIV SF162P.4 infection will be prevented at the mucosal site of viral entry. As the construct is immunogenic, repeated applications will induce immune responses and memory to the vaccine components which may prevent subsequent viral challenge. Thus, the microbicidal agent will also function as a preventive vaccine. The same vaccine will then be used in macaques which were infected after challenge with SF162P.4, as a therapeutic vaccine and it is expected that the vaccine candidate will prevent SHIV SF162P.4 emerging after ART is discontinued.
Developing the trimolecular virucidal agent will empower women to be in control of a preventive measure against HIV infection. This may also have long-term effect in eliciting immune responses and thereby acting as a preventive vaccine. The construct should also be effective as a therapeutic vaccine. Thus, the 3 principle preventive strategies against HIV-1 may be achieved with the same vaccine construct.
Thomas Lehner, MD, FRCPath, F Med Sci
Professor of Basic & Applied Immunology, Mucosal Immunology Unit, Guy’s,
King’s & St. Thomas’ Medical & Dental School, Guy’s Hospital, Guy’s Tower
London SE1 9RT
Phone: 44 207 188 3072
Fax: 44 207 188 4375
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