A Helminth-Derived Immune Potentiator for Biodefense

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DESCRIPTION (provided by applicant): With the ultimate goal of developing a safe and effective human immune potentiator against pathogens that may be used as bioweapons, we will characterize the immune mechanisms initiated in mice by a strongly immunostimulant protein cloned from the human parasite, Onchocerca volvulus. In our proof-of-principle studies, the LPS-free recombinant O. volvulus activation-associated protein-1 (rOv-ASP-1) acted as a powerful adjuvant for antibody responses in mice vaccinated with: 1) ovalbumin; 2) a peptide from the spike region of the SARS-CoV; 3) an HIV-1 polypeptide. Antibody titers to the antigens augmented by the protein exceeded those adjuvanted by optimal doses of alum or Ribi adjuvants and mice tolerated the protein well. Cellular responses in mice receiving ovalbumin with the parasite protein were predominantly Th1-type. The protein also stimulated high levels of pro-inflammatory cytokine (IFN-gamma, TNF-alpha and GM-CSF) and IL-10 secretion from naive human leukocytes in vitro. rOv-ASP-1 binds to > 94% of human of human B cells and monocytes, 29% of NK cells and 14.5% of CD8+ T cells. To maximize the possible therapeutic applications of the adjuvant protein, it is now important to first establish in detail the humoral and cellular responses it initiates against well-defined, coadministered pathogen antigens. To achieve this we propose two specific aims. Firstly, to define the types of humoral and cellular responses initiated by the rOv-ASP-1 protein adjuvant in mice immunized with human pathogen antigens known to be targets of protective immunity. Specifically, we will use recombinant SARS-CoV receptor binding domain which stimulates potent neutralizing antibodies in mice when combined with Freund's adjuvant and recombinant TUL4 antigen of Francisella tularensis, a proven target of cell-mediated immunity in immunized mice. Secondly, to perform structure-function studies on subunits of rOv- ASP-1, based on what we know about the molecular structure of the protein (including a putative chemokine-like domain), with the goal of identifying possible active sites with optimal adjuvanticity. Based on the preliminary data, we hypothesize that rOv-ASP-1 will be able to stimulate both antibody and Th1/CD8+ T cell responses relevant to protection against SARS-CoV and F. tularensis. Furthermore, studying the bioactivities of rationally-selected subunits of rOv-ASP-1 will help determine the mode of action of the protein and aid in the design of a molecule with optimal adjuvanticity and/or defined ability to elicit particular effector pathways.