Although oral subunit vaccines are highly relevant in the fight against widespread diseases, their high cost, safety and proper immunogenicity are attributes that have yet to be addressed in many cases and thus these limitations should be considered in the development of new oral vaccines. Prominent examples of new platforms proposed to address these limitations are plant cells and microalgae. Schizochytrium sp. constitutes an attractive expression host for vaccine production because of its high biosynthetic capacity, fast growth in low cost culture media, and the availability of processes for industrial scale production. In addition, whole Schizochytrium sp. cells may serve as delivery vectors; especially for oral vaccines since Schizochytrium sp. is safe for oral consumption, produces immunomodulatory compounds, and may provide bioencapsulation to the antigen, thus increasing its bioavailability. Remarkably, Schizochytrium sp. was recently used for the production of a highly immunoprotective influenza vaccine. Moreover, an efficient method for transient expression of antigens based on viral vectors and Schizochytrium sp. as host has been recently developed. In this review, the potential of Schizochytrium sp. in vaccinology is placed in perspective, with emphasis on its use as an attractive oral vaccination vehicle.

Vaccines for human use have conventionally been developed by the production of (1) microbial pathogens in eggs or mammalian cells that are then inactivated, or (2) by the production of pathogen proteins in mammalian and insect cells that are purified for vaccine formulation, as well as, more recently, (3) by using RNA or DNA fragments from pathogens. Another approach for recombinant antigen production in the last three decades has been the use of plants as biofactories. Only have few plant-produced vaccines been evaluated in clinical trials to fight against diseases, of which COVID-19 vaccines are the most recent to be FDA approved. In silico tools have accelerated vaccine design, which, combined with transitory antigen expression in plants, has led to the testing of promising prototypes in pre-clinical and clinical trials. Therefore, this review deals with a description of immunoinformatic tools and plant genetic engineering technologies used for antigen design (virus-like particles (VLP), subunit vaccines, VLP chimeras) and the main strategies for high antigen production levels. These key topics for plant-made vaccine development are discussed and perspectives are provided.

The plant cell is able to produce the VP40 antigen from the Zaire ebolavirus , retaining the antigenicity and the ability to induce immune responses in BALB/c mice. The recent Ebola outbreak evidenced the need for having vaccines approved for human use. Herein we report the expression of the VP40 antigen from the Ebola virus as an initial effort in the development of a plant-made vaccine that could offer the advantages of being cheap and scalable, which is proposed to overcome the rapid need for having vaccines to deal with future outbreaks. Tobacco plants were transformed by stable DNA integration into the nuclear genome using the CaMV35S promoter and a signal peptide to access the endoplasmic reticulum, reaching accumulation levels up to 2.6 µg g FW leaf tissues. The antigenicity of the plant-made VP40 antigen was evidenced by Western blot and an initial immunogenicity assessment in test animals that revealed the induction of immune responses in BALB/c mice following three weekly oral or subcutaneous immunizations at very low doses (125 and 25 ng, respectively) without accessory adjuvants. Therefore, this plant-based vaccination prototype is proposed as an attractive platform for the production of vaccines in the fight against Ebola virus disease outbreaks.

No abstract

No abstract