A probabilistic model of pre-erythrocytic malaria vaccine combination in mice

Optimal control of a two-group malaria transmission model with vaccination

Malaria is a vector-borne disease that poses major health challenges globally, with the highest burden in children less than 5 years old. Prevention and treatment have been the main interventions measures until the recent groundbreaking highly recommended malaria vaccine by WHO for children below five. A two-group malaria model structured by age with vaccination of individuals aged below 5 years old is formulated and theoretically analyzed. The disease-free equilibrium is globally asymptotically stable when the disease-induced death rate in both human groups is zero. Descarte's rule of signs is used to discuss the possible existence of multiple endemic equilibria. By construction, mathematical models inherit the loss of information that could make prediction of model outcomes imprecise. Thus, a global sensitivity analysis of the basic reproduction number and the vaccination class as response functions using Latin-Hypercube Sampling in combination with partial rank correlation coefficient are graphically depicted. As expected, the most sensitive parameters are related to children under 5 years old. Through the application of optimal control theory, the best combination of interventions measures to mitigate the spread of malaria is investigated. Simulations results show that concurrently applying the three intervention measures, namely: personal protection, treatment, and vaccination of childreen under-five is the best strategy for fighting against malaria epidemic in a community, relative to using either single or any dual combination of intervention(s) at a time.

A VLP for validation of the Plasmodium falciparum circumsporozoite protein junctional epitope for vaccine development

Malaria continues to be a pressing global health issue, causing nearly half a million deaths per year. An effective malaria vaccine could radically improve our ability to control and eliminate this pathogen. The most advanced malaria vaccine, RTS,S, confers only 30% protective efficacy under field conditions, and hence the search continues for improved vaccines. New antigens and formulations are always first developed at a pre-clinical level. This paper describes the development of a platform to supplement existing tools of pre-clinical malaria vaccine development, by displaying linear peptides on a virus-like particle (VLP). Peptides from PfCSP, particularly from outside the normal target of neutralizing antibodies, the central NANP repeat region, are screened for evidence of protective efficacy. One peptide, recently identified as a target of potent neutralizing antibodies and lying at the junction between the N-terminal domain and the central repeat region of PfCSP, is found to confer protective efficacy against malaria sporozoite challenge in mice when presented on the Qβ VLP. The platform is also used to explore the effects of increasing numbers of NANP unit repeats, and including a universal CD4⁺ T-cell epitope from tetanus toxin, on immunogenicity and protective efficacy. The VLP-peptide platform is shown to be of use in screening malaria peptides for protective efficacy and answering basic vaccinology questions in a pre-clinical setting.

Discovery of four new B-cell protective epitopes for malaria using Q beta virus-like particle as platform

Malaria remains one of the world’s most urgent global health problems, with almost half a million deaths and hundreds of millions of clinical cases each year. Existing interventions by themselves will not be enough to tackle infection in high-transmission areas. The best new intervention would be an effective vaccine; but the leading P. falciparum and P. vivax vaccine candidates, RTS,S and VMP001, show only modest to low field efficacy. New antigens and improved ways for screening antigens for protective efficacy will be required. This study exploits the potential of Virus-Like Particles (VLP) to enhance immune responses to antigens, the ease of coupling peptides to the Q beta (Qβ) VLP and the existing murine malaria challenge to screen B-cell epitopes for protective efficacy. We screened P. vivax TRAP (PvTRAP) immune sera against individual 20-mer PvTRAP peptides. The most immunogenic peptides associated with protection were loaded onto Qβ VLPs to assess protective efficacy in a malaria sporozoite challenge. A second approach focused on identifying conserved regions within known sporozoite invasion proteins and assessing them as part of the Qβ. Using this VLP as a peptide scaffold, four new protective B-cell epitopes were discovered: three from the disordered region of PvTRAP and one from Thrombospondin-related sporozoite protein (TRSP). Antigenic interference between these and other B-cell epitopes was also explored using the virus-like particle/peptide platform. This approach demonstrates the utility of VLPs to help identifying new B-cell epitopes for inclusion in next-generation malaria vaccines.

Protective efficacy of peptides from Plasmodium vivax circumsporozoite protein

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Short repeat-region peptides from PvCSP on a VLP protect against malaria.

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The AGDR tetramer from PvCSP VK210 can, on a VLP, also protect against malaria.

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Full-length PvCSP is much less protective as a vaccine than truncated PvCSP.

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Region I and II peptides confer no protection against malaria presented on a VLP.

Vivax malaria is a major cause of morbidity and mortality worldwide, with several million clinical cases per year and 2.5 billion at risk of infection. A vaccine is urgently needed but the most advanced malaria vaccine, VMP001, confers only very low levels of protection against vivax malaria challenge in humans. VMP001 is based on the circumsporozoite protein (CSP) of Plasmodium vivax. Here a virus-like particle, Qβ, is used as a platform to generate very high levels of antibody against peptides from PvCSP in mice, in order to answer questions important to further development of P. vivax CSP (PvCSP) vaccines. Minimal peptides from the VK210 and VK247 allelic variants of PvCSP are found to be highly protective as Qβ-peptide vaccines, using transgenic P. berghei parasites expressing the homologous PvCSP allelic variant. A target of neutralising antibodies within the nonamer unit repeat of VK210, AGDR, is found, as a Qβ-peptide vaccine, to provide partial protection against malaria challenge, and enhances protective efficacy when combined with full-length PvCSP vaccination. A truncated form of PvCSP, missing the N-terminal domain, is found to confer much higher levels of protective efficacy than full-length PvCSP. Peptides derived from highly conserved areas of PvCSP, RI and RII, are found not to confer protective efficacy as Qβ-peptide vaccines.