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.