Heterologous expression of the C-terminal antigenic domain of the malaria vaccine candidate Pfs48/45 in the green algae Chlamydomonas reinhardtii

Abstract

Malaria is a widespread and infectious disease that is a leading cause of death in many parts of the world. Eradication of malaria has been a major world health goal for decades, but one that still remains elusive. Other diseases have been eradicated using vaccination, but traditional vaccination methods have thus far been unsuccessful for malaria. Infection by Plasmodium species, the causative agent of malaria, is currently treated with drug-based therapies, but an increase in drug resistance has led to the need for new methods of treatment. A promising strategy for malaria treatment is to combine transmission blocking vaccines (TBVs) that prevent spread of disease with drug-based therapies to treat infected individuals. TBVs can be developed against surface protein antigens that are expressed during parasite reproduction in the mosquito. When the mosquito ingests blood from a vaccinated individual harboring the Plasmodium parasite, the antibodies generated by vaccination prevent completion of the parasites life-cycle. Animal studies have shown that immunization with Pfs48/45 results in the production of malaria transmission blocking antibodies; however, the development of this vaccine candidate has been hindered by poor expression in both prokaryotic and eukaryotic hosts. Recently, the chloroplast of Chlamydomonas reinhardtii has been used to express complex recombinant proteins. In this study, we show that the C-terminal antigenic region of the Pfs48/45 antigen can be expressed in the chloroplast of the green algae C. reinhardtii and that this recombinant protein has a conformation recognized by known transmission blocking antibodies. Production of this protein in algae has the potential to scale to the very large volumes required to meet the needs of millions at risk for contracting malaria.

Strategies & recent development of transmission-blocking vaccines against Plasmodium falciparum

“…Various TBV candidates have been successfully produced in plant system707172 with high recovery and desired immunogenicity (Table IV). Algae are also a promising system for the production of TBV that are orally delivered to avoid expensive purification and injectible delivery737475. These results sustain the feasibility of expressing TBV antigens in the plant based system.…”

“…Currently, many efforts for the development of transmission blocking malaria vaccine are focused on the production of TBV in plant-based expression system with a good safety profile, which are capable of inducing a strong immune response to reduce the malaria transmission717374. Completed clinical trials with Pfs25 formulations have been found immunogenic but shown some safety outcome issues like local and systemic adverse events8182.…”

Expression and membrane-targeting of an active plant cytochrome P450 in the chloroplast of the green alga Chlamydomonas reinhardtii

“…A fully functional human IgG1 monoclonal antibody against anthrax protective antigen 83 was expressed from two separate genes and assembled into a fully active antibody (Tran et al, 2009). In addition, immunotoxins for cancer therapeutics as well as vaccine candidates against malaria or foot-and-mouth-disease virus have been produced in the chloroplast Jones et al, 2013). However, most of the recombinant proteins produced, have been soluble proteins, and furthermore have generally been proteins that can be considered 'benign' in that they have no effect on chloroplast metabolism.…”

Steps toward a globally available malaria vaccine

“…3 This surface protein plays a role in the male/female gamete interaction within the mosquito midgut. It is a member of a family of surface proteins that contain a 6-cysteine conserved domain structure and is believed to work in conjunction with a second member of this family of surface proteins, Pfs230, to allow for reproduction.…”