Leptospirosis Vaccine Development

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Summary/abstract. Leptospirosis is a globally important neglected disease caused by pathogenic Leptospira. It is estimated to cause more than 1 million global cases annually with a 5-20% case-fatality rate, significant morbidity, and important public health consequences. Currently there is no safe and effective vaccine to prevent human leptospirosis. LeptoX, Inc. proposes to develop the first human leptospirosis vaccine. Pathogenic Leptospira are extracellular organisms, but mechanisms by which they exert their pathogenetic effects were unclear until our discovery of the leptospiral Virulence Modifying (VM) proteins’ cytotoxin function, followed by our demonstration of the potential for VM proteins to be the antigen components of a pan- leptospirosis vaccine. Severe human leptospirosis has almost exclusively been reported to be due to strains of L. interrogans. This proposal focuses on a L. interrogans VM protein-based leptospirosis vaccine, although cross species protection may be possible. Recently published animal model data demonstrated that as few as two recombinant VM proteins provide robust cross-serovar protection from disease/death after lethal L. interrogans challenge in mice. These data indicate strong potential for VM proteins as pan-L. interrogans protective antigens. In this Phase I, we will optimize dose, delivery and composition of recombinant E. coli- produced VM proteins in combination with human-compatible adjuvant to determine protective efficacy in the lethal hamster challenge model of leptospirosis. In Aim 1, we will produce recombinant tagless VM protein immunogens, analyze their immunogenicity and, in the standard hamster model, compare their protective efficacy to standard, commercially available bacterin vaccines; contingency experiments will also assess chemically inactivated wild type proteins and proteins purified from inclusion bodies as alternative forms of the VM protein immunogen; structural modeling suggests that VM protein disulfide bond-dependent conformation may not be critical for antigenicity. In Aim 2, we will compare wild type and genetically mutated toxoid-forms of tagless, recombinant E. coli-produced VM proteins in the lethal hamster model. Protective immune responses for both Aims will be assessed by protection from clinical disease and death and by determination of bacterial load and viability in liver and kidney at various time points. Biomarkers of protective immunity (i.e., antibody titers against the prototype vaccine antigens and cross-reactivity among serovars and between different Leptospira species’ VM proteins) will be measured; the putative antibody-mediated protective mechanism of immunity will be tested by passive transfer experiments. At the end of this Phase I project, we will have developed final pan-L. interrogans VM-protein-based vaccine prototypes for further animal testing. Following Phase I, this prototype will be tested in dog clinical trials, which will lead to a first commercial product for these companion animals. Animal vaccine development will lead towards FDA IND submission for a human leptospirosis vaccine, upon which strategic partnerships for leptospirosis vaccine development will be formed.