New HIV infections worldwide are occurring at alarming rates. Immunity mediated by cytolytic T lymphocytes (CTLs) and antibodies may protect against infection and limit disease. Listeria monocytogenes is an intracellular microorganism that has been studied as a paradigm for the induction of cell mediated immunity for many years and has been shown to be effective as a vaccine vector for influenza and LCMV infections and for the treatment of model cancers. Listeria may also prove to be a useful vehicle to generate immune responses against HIV. However, Listeria is a pathogen, and we therefore constructed a completely attenuated strain of the organism that nevertheless can induce effective immunity following appropriate immunization conditions. An HIV-1 gag recombinant of this strain induces in mice a strong, long-lasting systemic and mucosal CTL response in spleen, Peyer's patches and mesenteric lymph nodes that can protect against systemic or mucosal challenge by recombinant vaccinia viruses expressing the HIV-1 gag gene. As there is evidence to suggest a protective role of antibodies against HIV infection, we will attempt to modify our hyper-attenuated strain of Listeria so as to produce an anti-HIV antibody response, augmenting its induction of CTLs. We will construct Listeria recombinants that express linear or conformational mimotopes of gpl20/gp4l recently identified by phage display technology to induce neutralizing antibodies in mice. These will be expressed as fusions with a T helper epitope in different contexts at the bacterial surface or in soluble form. Sera and intestinal secretions of immunized mice that contain anti-env antibodies will be tested for their ability to neutralize primary isolates of HIV-1.
