Implementation of biotechnology for the creation or a plant-based vaccine against SARS-CoV-2!

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Implementation of biotechnology for the creation or a plant-based vaccine against SARS-CoV-2!

The biotechnology of plant-based vaccines Today, genetic engineer plants are a consolidated platform for the manufacture of biopharmaceutical products. Plants have been used ​the past three decades for this purpose and have been of great help in the pharmaceutical and medical industries.

Until now, a diverse group of biopharmaceuticals have been functionally produced in plant systems including antibodies, vaccines, growth factors, and cytosines. ​There is a recombinant enzyme produced in carrot cells that has already been approved by the FDA for the treatment of Gaucher disease as a great example in the advancement of plant-based vaccines.

Current of plant-based vaccines Currently, there are candidates for plant vaccines that are in the process of clinical trials, including candidates for swine influenza, rabies and hepatitis B. The candidates of greatest interest at the moment are the flu vaccines developed by the company French biopharmaceutical Medicago Inc. that rel on the use of a non-replicative vector carrying viral regulatory sequences to mediate transient hemagglutinin (HA) expression in N. benthamiana. In conclusion, these vaccines have been considered safe and their immunogenic properties and have been positively demonstrated by in vitro tests with human and mouse cells. Voluntary tests revealed adequate immunogenicity without serious adverse effects. So they reflect a great safety and quality of the therapeutic action of clinical trials.

The relationship between low-cost vaccines and plant-based vaccines The ultimate goal for the development of low-cost vaccines could be achieved by generating oral formulations that do not require purification and that are composed of lyophilized biomass encapsulated in gelatin pills or tablets. Under this approach, the goal is to trigger specific immune responses through the intestine-associated lymphoid tissues (GALT). For this purpose, edible plants that lack toxic metabolites should be used. Perhaps the main disadvantage of this technology is the long time required to generate transformed lines of edible crops that efficiently express the antigen of interest (for example, transgenic lines of rice or corn or transplastomic lines). In terms of costs, avoiding the requirements for sterile devices and trained personnel represents substantial savings. The fact that plant-based vaccine formulations do not require antigen purification will undoubtedly be the main factor that will make them low-cost alternatives, which is necessary to provide broad vaccination coverage in developing countries. and low income.

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Possibilities for developing plant-based anti-COVID-19 vaccines: 1. Virus-like particles (VLP) A prominent approach to vaccine design is based on the use of virus-like particles (VLPs), which are macromolecular complexes that look like viruses, but lack their genome. In this way, VLPs mimic the native structure of viruses, but are not infectious.

This avoids the disadvantages of vaccines formulated with attenuated or inactivated viruses that include reactogenicity and reversion to pathogenic forms. A large number of reports of VLP production can be found in the literature including cases of influenza virus, human papillomavirus, human immunodeficiency virus, foot and mouth disease virus, Norwalk virus , the Rift Valley fever virus and the hepatitis B virus.

There is a history that the enveloped virus VLPs have been successfully expressed in plants through the expression of the HA protein, it can be anticipated that the SARS-CoV-2 VLPs could be assembled through the expression of the S protein. that nuclear expression targeting the trans-Golgi secretion pathway is proposed to produce a protein undergoing the glycosylation and secretion machinery that could make VLP production possible. Therefore, adoption of these works would be valuable during the development of COVID-19 plant-based vaccines.

In addition to VLPs that resemble the SARS-CoV-2 virus, another possible approach is to adopt the SARS-CoV-2 epitopes and express them in chimeric VLPs. In this way, a VLP from an unrelated virus can serve as the scaffold for presenting target SARS-CoV-2 epitopes. For this purpose, the central protein of hepatitis B has been applied as a framework to show unrelated antigens of some pathogens.

The glycosylation patterns of the proteins that make up VLP can affect their immunological and protective capacity. Interestingly, glycoengineering strategies have been successfully implemented for plants, allowing diversification of their application as hosts for the production of biopharmaceuticals. This is a relevant aspect considering that plants lack the ability to perform glycosylation, which is a characteristic of mammalian systems​. ​In some cases, such as the production of antibodies, these differences in glycosylation may be associated with adverse effects that include the generation of immunogenic activity, which may eventually lead to the blocking of antibodies against the therapeutic antibody. However, in the case of vaccines, these differences could add more immunogenic potential and improve the efficacy of the vaccine.

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Multiepitopic vaccines

Another approach that deserves attention is the development of multi-epitopic vaccines, which offer the opportunity to achieve a rational vaccine design by selecting epitopes that potentially induce robust and protective immune responses. At the same time, this approach will rule out those related to non-protective responses or even those that induce antibody-dependent disease improvement. In this way, a highly effective and safe vaccine can be obtained. Of special interest are reports showing that protein S-specific epitopes improve disease in a pathogen challenge, highlighting the relevance of resorting to rational vaccine design to ensure not only immunoprotection, but also safety.

In the case of multi-epitope vaccines against infectious agents, several reports have focused on selecting the most promising epitopes of T cells, B cells and T cells that 2

could allow the rational design of a vaccine that induces robust protective responses, at the same time as damage is avoided non-relevant responses A key factor that adds importance to the development of multi-epitopic vaccines against viral disease is genetic variability. In fact, it has been suggested that the SARS-CoV-2 virus evolved into two main types, L and S. The L type (​∼​70%) predominates over the S type (​∼​30%), and the latter is proposed as La ancestral version. Type L is more aggressive than type S. The selected epitopes are the targets to which adaptive immune responses must be induced, but lack the complexity required to trigger robust immune responses.

Therefore, a carrier is required to increase the complexity of the antigen and, through adjuvant effects, enhance the potency of the induced immune response, making it appropriately polarized.

Since plant systems have been successfully adopted for the production of multi-epitope proteins, the generation of such vaccines against COVID-19 is considered highly viable. In addition to expressing chimeric proteins, expression of multiple antigens can be accomplished by transplastomic technologies (operon-like expression).

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Immune complexes

The production of immune complexes (ICs) in plants is another approach that makes the agents highly immunogenic. Integrated circuits consist of antigens complexed with antibodies that recognize them, constituting macromolecular entities that are efficiently captured and processed by antigen presenting cells. This results in the induction of robust humoral and cell mediated immune responses. Taking advantage of the machinery of plant cells for protein synthesis and processing, they have been exploited as factories of antibodies and IC. 4. Elastin-like polypeptide fusions Antigen purification is an activity that many hours of work and economic cost. An alternative to purification is based on the fusion of elastin-like polypeptides (ELP) that have a unique property called reversible phase transition, which allows the protein of interest to precipitate by changing the temperature. This approach is an alternative to expensive / complex affinity chromatography that has been applied to develop candidate plant-based vaccines with relevant findings. Therefore, these precedents suggest that ELP technology is a possible approach to explore for the production of antigens against the SARS-CoV-2 virus.

Common steps for the aforementioned antigen design will comprise determining antigen yields and antigenic activity, evaluating immunogenic activity in test animals under different routes of administration, and validating the safety and stability of the vaccine.

Conclusions The new pandemic has placed great demands on the pharmaceutical and biological and biotechnological materials industries to try to develop new treatments as quickly as possible to treat SARS-CoV-2, which currently has not been highly effective​. So a plant-based vaccine is a viable approach to quickly respond to this need. Current expression technologies offer relevant pathways for the development of anti-COVID-19 vaccines.

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The great challenge for the development of COVID-19 plant-based vaccines will be, as is typical of all vaccines, to prove their efficacy in large clinical trials to validate their safety while meeting the requirements of regulatory agencies. The fact that there are precedents for plant-based biopharmaceuticals approved for human use and plant-based influenza vaccines in clinical trials (with promising safety and efficacy) is encouraging. Therefore, some vaccines of plant origin could have great potential to be created.

All scientific information credits go to the authors of the scientific article creation!

Scientific information reference: Rosales, S. e. (2020). What Does Plant-Based Vaccine Technology Offer to the Fight against COVID-19? MDPI Open Access Journals. link: ​https://www.mdpi.com/2076-393X/8/2/183/htm

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