L1 capsomeres as a next generation preventive HPV vaccine

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The recent development of prophylactic vaccines protective against "high risk" human papillomaviruses (HPV) is a landmark in medicine. The current vaccine is composed of recombinant virus-like particles (VLPs) of the major capsid protein, L1, including the high risk HPV types 16 and 18. Phase ll/lll clinical trials have shown >95% efficacy of these VLP preparations in preventing HPV 16, 18 infection, and thus hopefully preventing the eventual development of about 70% of cervical cancers associated with these types. Despite this success the VLP vaccines have the adverse attributes of high cost ($360 for the initial three immunizations In the USA) and a requirement for refrigeration {i.e., cold chain). We have previously characterized the immunogenic properties of VLP subunits, pentameric L1 capsomeres, and compared these "subunits" to VLPs in a canine infection model. In this model capsomeres appeared near equivalent to VLPs in inducing protection against infection. Capsomeres are purified after recombinant expression of L1 in E. coli as a GST-fusion protein, at levels suggesting a significant reduction in manufacturing expense. The protein is readily purified, and can be precipitated, resuspended, and stored at room temperature without loss of immunogenicity. In the context of an ongoing NCI RAPID award GST-L1 capsomeres have been proposed as a "next generation" HPV vaccine that might be ideally suited for production and use in underdeveloped countries of the world where cervical cancer is particularly prevalent. We propose to use the GST-L1 protein that has been GMP produced (by Shantha Biotechnica), vialed, and toxicology screened under the auspices of a RAPID award for study in a phase I human trial. In aims 1 and 2 we propose a dose escalation scheme of 15 subjects at each of three dose levels (10, 50, 500 micrograms and placebo), repeated three times, with concomitant analysis of toxicity, development of neutralizing antibodies, cytotoxic T-cell responses, and possible adverse effects of GST antibody development. In the third aim, laboratory studies with clinical specimens and animal experiments will test new adjuvant strategies including Toll-like receptor activation, and evaluate the effects on humoral immunity of antigen spacing and linking by comparing capsomeres, cross-linked capsomeres, and VLPs. Knowledge of L1 capsomere structure and interaction with the innate immune system will be utilized to generate longer-lived and broader immunity with lower and fewer doses. The results of this project will determine whether the GST-LI preparation can proceed to further phase II testing.