The development of a vaccine against P. falciparum has proven to be a difficult bioengineering challenge. Malaria afflicts 500 million people worldwide and annually kills about 3 million people, mostly children. "RTS,S", the most successful malaria vaccine candidate to date, provides only about 40% protective efficacy in humans in clinical and field challenge studies, and it requires formulation with an adjuvant to achieve protective immunogenicity. The application's broad, long-term objective is to develop self-assembling polypeptide nanoparticles (SAPN) as the basis for a P. falciparum malaria vaccine that is potentially more protective than those currently in clinical trials, shows excellent heat stability, and can be delivered without an adjuvant, which is likely to be consistent with formulations suited for delivery without a cold chain. SAPN assemble from linear polypeptide (LP) building blocks. Each LP consists of pentameric and trimeric coiled-coil domains separated by a linker, with epitope antigens displayed internally and on the N- and C- termini. The proposed work aims to identify the best configuration for the display of B cell and T cell epitopes on SAPN for producing the most potent immunogenic and protective immune response. SAPN displaying the P. berghei CSP epitope (analogous to the P. falciparum CSP B-cell epitope in RTS,S) have been shown to stimulate a long lasting protective immune response against a lethal sporozoite challenge in the P. berghei mouse malaria model without the need for an adjuvant. The SAPN particles have been shown themselves to have adjuvant activity. This suggests that the SAPN platform is potentially superior to other protein vaccine technologies used to date as these have all required the addition of extraneous adjuvants to be protective. The SAPN vaccines in our development pipeline will be evaluated for their mechanism of immune enhancement (adjuvanticity);protective efficacy against challenge with a strain of P. berghei (mouse malaria) expressing the CSP transgene from P. falciparum (human malaria);and immunogenic/protective response provided by specific P. falciparum T cell epitopes in human HLA backgrounds using human-HLA transgenic mice.
The Specific Aims are to: (1) Design and produce SAPN in order to determine the optimal density of the immunodominant PfCSP B-cell epitope to stimulate a potent antibody response;(2) Determine the enhancement to the immune response provided by the addition of pan allelic HTL and CTL epitopes to SAPN with the optimized density of immunodominant PfCSP B cell epitope;and (3) Evaluate the safety, reactogenicity and immune response to the lead PfCSP SAPN vaccine candidate in a non-human primate (NHP) model. This R&D plan is expected to advance an innovative vaccine platform and to develop a malaria vaccine based on B cell and T cell epitope antigens from P. falciparum CSP that have already demonstrated successful, though limited, protective efficacy in clinical and field trials as RTS,S in AS02A. Success should qualify the proposed research for further funding for human- use product development and vaccine trials.
A malaria vaccine will be developed based on a new technology, self-assembling peptide nanoparticles, that display malaria parasite immunogens previously shown to elicit protective immunity to malaria. This new vaccine platform holds promise for ultimately producing an inexpensive malaria vaccine for the developing world.
|Murphy, Jittawadee R; Weiss, Walter R; Fryauff, David et al. (2014) Using infective mosquitoes to challenge monkeys with Plasmodium knowlesi in malaria vaccine studies. Malar J 13:215|
|McCoy, Margaret E; Golden, Hannah E; Doll, Tais Apf et al. (2013) Mechanisms of protective immune responses induced by the Plasmodium falciparum circumsporozoite protein-based, self-assembling protein nanoparticle vaccine. Malar J 12:136|
|Guo, Qin; Dasgupta, Debleena; Doll, Tais A P F et al. (2013) Expression, purification and refolding of a self-assembling protein nanoparticle (SAPN) malaria vaccine. Methods 60:242-7|