Chloroplast-Derived Therapeutic and Prophylactic Vaccines

Abstract

Despite the development of advanced vaccine technology, as many as 15 million deaths occur annually as a result of inadequate prophylactic or therapeutic treatments against infectious diseases (World Health Organization 2008 ). The emphasis on profi tability by the pharmaceutical industry has led to development of high-cost vaccines targeting diseases with high profi t margins, resulting in an annual death toll for developing countries that is largely preventable. Daniell and co-investigators published the fi rst expression of a vaccine antigen, cholera toxin subunit B, through transgenic tobacco chloroplasts in 2001. The polyploidy nature of the chloroplast genome enables engineering of a high copy number of target gene, while the translational machinery of the plastid directs the synthesis of bioactive proteins with proper folding, disulfi de bond formation, and lipidation. Furthermore, gene integration is site-specifi c, expression is polycistronic, and natural gene containment occurs due to the maternal inheritance of the chloroplast genome. The chloroplast transformation technology (CTT) has been used to express proteins of bacterial, viral, protozoan, and recently mammalian origins that may be subsequently utilized in immunization strategies to produce protective or therapeutic immunity. Such chloroplast-derived vaccines represent an inexpensive and effective means of producing antigen-subunit vaccines. Furthermore, transformation of edible crops such as lettuce could generate stable orally-deliverable vaccine antigens through inexpensive fi eld production and agricultural drying techniques. This platform could therefore obviate cold-chain logistics and the requirement of sterile injectables, drastically reducing downstream production costs of such biopharmaceuticals. With these proof-of-concept studies, focus within CTT is shifting towards establishing a viable platform for human immunization by demonstrating

Steps toward a globally available malaria vaccine

“…It could also be useful to identify proteases in the chloroplast and create additional mutations in these to help prevent the degradation of recombinant vaccine proteins. 6 …”

“…6,7 Algae and plant expression systems offer a unique opportunity to produce therapeutic proteins, particularly vaccines, as oral therapeutics. The production of an oral vaccine for malaria in C. reinhardtii could significantly reduce the production cost, as purification is a major component of recombinant vaccine costs, and because unpurified proteins should have better protein stability and significantly easier distribution and administration.…”

“…The production of an oral vaccine for malaria in C. reinhardtii could significantly reduce the production cost, as purification is a major component of recombinant vaccine costs, and because unpurified proteins should have better protein stability and significantly easier distribution and administration. 6 Ideally, an algae protein expression platform would not only be capable of expressing an edible vaccine for malaria but would be safe enough to be grown by people living in regions with high rates of Plasmodium infection.…”

Production of dengue virus envelope protein domain III-based antigens in tobacco chloroplasts using inducible and constitutive expression systems

“…Maternal inheritance of chloroplasts in most plant species prevents the transgene spread via pollen (Ruf et al 2007;Svab and Maliga 2007) and the presence of up to 10,000 copies of plastid DNA in photosynthetic cells (Bendich 1987) is beneficial to obtain high recombinant protein expression levels (Bock and Warzecha 2010;Koop et al 2007;Maliga and Bock 2011). Furthermore, the possibility of multi-gene engineering in a single transformation event (Lu et al 2013) and the ability of the plastid translation machinery to produce recombinant proteins with proper folding, disulfide bond formation and lipidation (New et al 2012) makes chloroplasts an attractive expression platform for recombinant proteins (Clarke and Daniell 2011;Clarke and Zhang 2013;Bellucci et al 2015). …”

Production of recombinant thanatin in watery rice seeds that lack an accumulation of storage starch and proteins

“…To obtain a sufficient level of product accumulation, several strategies could be used, including taking advantage of suitable promoters, codon optimization for expression of the target gene, adaptation of the untranslated sequences involved in mRNA stability, coordination of subcellular localization, and choosing a host plant suitable for production of the desired materials (Obembe et al, 2011;Twyman et al, 2003). Furthermore, systems that enable high levels of expression of the desired gene have been developed, such as chloroplast transformation and transient production using a plant virus vector system carrying an appropriate gene (New et al, 2012;Wang, 2012). 4 These expression systems often lead to high productivity compared with conventional methods (Chebolu and Daniell 2009;Pogue et al, 2010).…”