Vaccination via Chloroplast Genetics: Affordable Protein Drugs for the Prevention and Treatment of Inherited or Infectious Human Diseases

Abstract

Plastid-made biopharmaceuticals treat major metabolic or genetic disorders, including Alzheimer’s, diabetes, hypertension, hemophilia, and retinopathy. Booster vaccines made in chloroplasts prevent global infectious diseases, such as tuberculosis, malaria, cholera, and polio, and biological threats, such as anthrax and plague. Recent advances in this field include commercial-scale production of human therapeutic proteins in FDA-approved cGMP facilities, development of tags to deliver protein drugs to targeted human cells or tissues, methods to deliver precise doses, and long-term stability of protein drugs at ambient temperature, maintaining their efficacy. Codon optimization utilizing valuable information from sequenced chloroplast genomes enhanced expression of eukaryotic human or viral genes in chloroplasts and offered unique insights into translation in chloroplasts. Support from major biopharmaceutical companies, development of hydroponic production systems, and evaluation by regulatory agencies, including the CDC, FDA, and USDA, augur well for advancing this novel concept to the clinic and revolutionizing affordable healthcare.

Codon Optimization to Enhance Expression Yields Insights into Chloroplast Translation

“…Transcript abundance is attributed to the high copy number of transgenes and the strength of the psbA promoter. Among more than 150 transgenes expressed in chloroplasts, more than 75% utilized psbA regulatory sequences (Jin and Daniell, 2015;Daniell et al, 2016aDaniell et al, , 2016b. In addition, three ribosome-binding regions in the 5ʹ UTR of psbA recruit ribosomes and efficiently form the translational initiation complex (Zou et al, 2003).…”

“…The 5ʹ UTR of psbA also showed the highest translation activity in vitro among 11 5ʹ UTRs investigated (Yukawa et al, 2007). Therefore, among 140 transgenes expressed in chloroplasts, more than 75% use the psbA regulatory sequences (Jin and Daniell, 2015;Daniell et al, 2016aDaniell et al, , 2016b. Most importantly, compatibility between the 5ʹ UTR of psbA and its coding region is important for efficient translation initiation (Nakamura et al, 2016).…”

“…Among more than 115 transgenes expressed via the chloroplast genome, 84 use the psbA regulatory sequence (Jin and Daniell, 2015;Daniell et al, 2016aDaniell et al, , 2016b. A recent study (Nakamura et al, 2016) shows the absence of any detectable translation when codons for the tat coding sequence of HIV-1 were optimized using all 79 tobacco chloroplast mRNAs and regulated by the psbA 5ʹ UTR (Nakamura et al, 2016), but the same sequence was expressed well using the phage T7 GENE10 5ʹ UTR.…”

Expression and functional evaluation of biopharmaceuticals made in plant chloroplasts

“…In contrast, expression of transgenes in plant chloroplast, also known as transplastomic expression, has several advantages including higher yield and more stable level of gene expression via the ability to direct transgene integration to precise sites within the chloroplast genome. Also, maternal inheritance of transgenes eliminates the escape of transgenes via pollen, offering total transgene containment when biopharmaceuticals are made in leaves [3]. Recently significant progress has been made in therapeutic protein production in chloroplasts of edible plant cells.…”

“…Recently significant progress has been made in therapeutic protein production in chloroplasts of edible plant cells. Biopharmaceuticals produced in edible plants eliminate expensive fermentation, purification processes and cold storage/transportation [1,3]. Bioencapsulated protein drugs in freeze-dried plant cells are stable after several years of storage at ambient temperature [4••].…”