Application of wheat germ cell-free protein expression system for novel malaria vaccine candidate discovery

Abstract

Malaria causes about 216 million clinical cases and 0.7 million deaths annually. One promising route to address malaria is vaccination. However, so far, not even a single licensed malaria vaccine has been developed. Even the effectiveness of RTS,S, the world’s most advanced malaria vaccine candidate (MVC) in clinical trials, is less than 50% efficacy against the disease. This backdrop indicates that the search for a truly effective vaccine is far from over and galvanizes us to expand the arsenal of promising MVC antigens to include in a next generation subunit vaccine. In our previous proof of principle studies, we have found that the wheat germ cell-free protein synthesis system (WGCFS) is one of the optimal tools for synthesis of quality malaria proteins and hence the identification of novel MVCs. This review summarizes the initial progresses so far made regarding the identification of novel MVCs using WGCFS.

Keywords::

• antibody profiling
• antigen array
• malaria
• Plasmodium falciparum
• Plasmodium vivax
• post-genome
• recombinant proteins
• reverse vaccinology
• vaccine candidate discovery
• wheat germ cell-free protein synthesis system

Financial & competing interests disclosure

This work was supported in part by MEXT KAKENHI (23117008) and JSPS KAKENHI (23406007), Japan. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the production of this manuscript.

Key issues

• Availability of data on malaria genome, transcriptome and proteome provides a framework to systematically discover novel malaria vaccine candidates (MVCs) through approaches like reverse vaccinology and antibody profiling.

• In reverse vaccinology approach, bioinformatics of protein motifs are used to sift the malaria genome for identifying genes coding for putative cell-surface or secreted proteins that could potentially elicit antibody responses in a human host. The antibodies raised against the recombinant proteins expressed from the bioinformatically selected genes will be assayed for their ability to inhibit invasion of the parasite in vitro and thereby ascertain whether these proteins qualify as MVC antigens.

• In antibody profiling approach, protein arrays comprising hundreds of recombinant parasite proteins are used to profile serum antibodies in symptomatic patients and asymptomatic carriers and identify antigens associated with clinical protection for vaccine development.

• The successful utilization of reverse vaccinology and antibody profiling approaches for identification of novel MVCs depends heavily on the synthesis of large quantities of highly soluble properly folded recombinant parasite proteins without artificial glycosylation that might alter the immunogenicity. We have found that the wheat germ cell-free protein synthesis system (an eukaryotic system), rather than Escherichia coli (a prokaryotic system), is highly suitable to this end.

Notes