The goal of this project is to produce novel synthetic malaria vaccines based on epitopes of the circumsporozoite (CS) protein of Plasmodium falciparum, the causative agent of human malaria. Malaria is one of the major diseases in the developing world, causing 200-500 million new infections and over 1 million deaths each year, primarily in young children in Africa. While there is no approved vaccine, previous work has shown that the CS protein of the sporozoite stage contains a number of candidate vaccine epitopes that are recognized by antibodies and T-cells of protected hosts. These include the conserved antibody epitope of the central repeat region (B) and two T-cell epitopes: T1 which overlaps the N-terminus of the central repeat region and T* which is located near the C-terminus of the protein. In preclinical and clinical studies, immunization with the tri-peptide construct T1BT* elicited antibodies to CS that bound to the native protein on the surface of sporozoites, inhibiting their motility and invasion of host hepatocytes, thus disrupting the parasite life cycle and preventing patent blood stage infection responsible for clinical disease. The successes with various CS vaccine strategies have been somewhat moderated by difficulties in production scale-up, poor immunogenicity, and dose-limiting toxicity of adjuvants. To overcome these issues, an innovative approach will be employed which uses layer-by-layer (LbL) fabrication of artificial biofilms to incorporate the CS epitopes in synthetic nanocapsule vaccines. Current results in multiple model systems show that LbL nanocapsule vaccines elicit potent immune responses following one or two immunizations without adjuvants, avoiding undesirable responses such as the release of inflammatory cytokines. The nanocapsules deliver their antigen payload to dendritic cells via multiple pathways including phagocytosis, leading to presentation of Class II-restricted epitopes and cross-presentation of Class I-restricted epitopes. Immunization with LbL nanocapsules elicits balanced T-cell responses including both IFN and IL-4 ELISPOTs, and effector CTL activity. The immune responses elicited by LbL nanocapsules conspicuously do not include antibody responses to the matrix polypeptides used to produce the biofilm, thereby avoiding the so-called vector or carrier effect that has hampered development of many viral vectored vaccines. In this project, mono- and multivalent LbL nanocapsules containing the T1, B, and/or T* epitopes of P. falciparum CS, or the CTL epitope of P. berghei, will be designed and fabricated. Immunogenicity will be studied in mice by monitoring ELISPOT and in vivo CTL responses to the T-cell epitopes and antibody responses to the B epitope. Efficacy will be studied using transgenic P. berghei (mouse pathogen) expressing a hybrid CS containing the B epitope from P. falciparum CS (PfPb) to measure protective antibodies, or wild-type P. berghei to measure protective CD8+ T-cell responses. This project will yield synthetic nanocapsule vaccine candidates that elicit potent CS-specific immune responses and provide protection from malaria without the use of toxic adjuvants.
This project utilizes an innovative vaccine fabrication technology to produce efficacious vaccines for malaria. These vaccines are made of biofilms of materials safe for human use and are fabricated by synthetic chemistry methods with no animal or cell culture products or by-products. The vaccines are potent, safe, and do not require toxic adjuvants that limit vaccine utility.
|Powell, Thomas J; Tang, Jie; Derome, Mary E et al. (2013) Plasmodium falciparum synthetic LbL microparticle vaccine elicits protective neutralizing antibody and parasite-specific cellular immune responses. Vaccine 31:1898-904|