Current updates and research on plant-based vaccines for coronavirus disease 2019

Plants as Biofactories for Therapeutic Proteins and Antiviral Compounds to Combat COVID-19

The outbreak of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) had a profound impact on the world's health and economy. Although the end of the pandemic may come in 2023, it is generally believed that the virus will not be completely eradicated. Most likely, the disease will become an endemicity. The rapid development of vaccines of different types (mRNA, subunit protein, inactivated virus, etc.) and some other antiviral drugs (Remdesivir, Olumiant, Paxlovid, etc.) has provided effectiveness in reducing COVID-19's impact worldwide. However, the circulating SARS-CoV-2 virus has been constantly mutating with the emergence of multiple variants, which makes control of COVID-19 difficult. There is still a pressing need for developing more effective antiviral drugs to fight against the disease. Plants have provided a promising production platform for both bioactive chemical compounds (small molecules) and recombinant therapeutics (big molecules). Plants naturally produce a diverse range of bioactive compounds as secondary metabolites, such as alkaloids, terpenoids/terpenes and polyphenols, which are a rich source of countless antiviral compounds. Plants can also be genetically engineered to produce valuable recombinant therapeutics. This molecular farming in plants has an unprecedented opportunity for developing vaccines, antibodies, and other biologics for pandemic diseases because of its potential advantages, such as low cost, safety, and high production volume. This review summarizes the latest advancements in plant-derived drugs used to combat COVID-19 and discusses the prospects and challenges of the plant-based production platform for antiviral agents.

Tobacco-Based Vaccines, Hopes, and Concerns: A Systematic Review

Emerging infectious diseases have vigorously devastated the global economy and health sector; cost-effective plant-based vaccines (PBV) can be the potential solution to withstand the current health economic crisis. The prominent role of tobacco as an efficient expression system for PBV has been well-established for decades, through this review we highlight the importance of tobacco-based vaccines (TBV) against evolving infectious diseases in humans. Studies focusing on the use of TBV for human infectious diseases were searched in PubMed, Google Scholar, and science direct from 1995 to 2021 using the keywords Tobacco-based vaccines OR transgenic tobacco OR Nicotiana benthamiana vaccines AND Infectious diseases or communicable diseases. We carried out a critical review of the articles and studies that fulfilled the eligibility criteria and were included in this review. Of 976 studies identified, only 63 studies fulfilling the eligibility criteria were included, which focused on either the in vitro, in vivo, or clinical studies on TBV for human infectious diseases. Around 43 in vitro studies of 23 different infectious pathogens expressed in tobacco-based systems were identified and 23 in vivo analysis studies were recognized to check the immunogenicity of vaccine candidates while only 10 of these were subjected to clinical trials. Viral infectious pathogens were studied more than bacterial pathogens. From our review, it was evident that TBV can be an effective health strategy to combat the emerging viral infectious diseases which are very difficult to manage with the current health facilities. The timely administration of cost-effective TBV can prevent the outburst of viral infections, thereby can protect the global healthcare system to a greater extent.

Modern vaccine strategies for emerging zoonotic viruses

INTRODUCTION

The significant increase in the emergence of notable zoonotic viruses in the previous decades has become a serious concern to global public health. Ninety-nine percent of infectious diseases have originated from zoonotic viruses with immense potential for dissemination, infecting the susceptible population completely lacking herd immunity.

AREAS COVERED

Zoonotic viruses appear in the last two decades as a major health threat either newly evolved or previously present with elevated prevalence in the last few years are selected to explain their current prophylactic measures. In this review, modern generation vaccines including viral vector vaccines, mRNA vaccines, DNA vaccines, synthetic vaccines, virus-like particles, and plant-based vaccines are discussed with their benefits and challenges. Moreover, the traditional vaccines and their efficacy are also compared with the latest vaccines.

EXPERT OPINION

The emergence and reemergence of viruses that constantly mutate themselves have greatly increased the chance of transmission and immune escape mechanisms in humans. Therefore, the only possible solution to prevent viral infection is the use of vaccines with improved safety profile and efficacy, which becomes the basis of modern generation vaccines.

Plant Molecular Pharming and Plant-Derived Compounds towards Generation of Vaccines and Therapeutics against Coronaviruses

The current century has witnessed infections of pandemic proportions caused by Coronaviruses (CoV) including severe acute respiratory syndrome-related CoV (SARS-CoV), Middle East respiratory syndrome-related CoV (MERS-CoV) and the recently identified SARS-CoV2. Significantly, the SARS-CoV2 outbreak, declared a pandemic in early 2020, has wreaked devastation and imposed intense pressure on medical establishments world-wide in a short time period by spreading at a rapid pace, resulting in high morbidity and mortality. Therefore, there is a compelling need to combat and contain the CoV infections. The current review addresses the unique features of the molecular virology of major Coronaviruses that may be tractable towards antiviral targeting and design of novel preventative and therapeutic intervention strategies. Plant-derived vaccines, in particular oral vaccines, afford safer, effectual and low-cost avenues to develop antivirals and fast response vaccines, requiring minimal infrastructure and trained personnel for vaccine administration in developing countries. This review article discusses recent developments in the generation of plant-based vaccines, therapeutic/drug molecules, monoclonal antibodies and phytochemicals to preclude and combat infections caused by SARS-CoV, MERS-CoV and SARS-CoV-2 viruses. Efficacious plant-derived antivirals could contribute significantly to combating emerging and re-emerging pathogenic CoV infections and help stem the tide of any future pandemics.

Role of Diet and Nutrients in SARS-CoV-2 Infection: Incidence on Oxidative Stress, Inflammatory Status and Viral Production

Coronavirus illness (COVID-19) is an infectious pathology generated by intense severe respiratory syndrome coronavirus 2 (SARS-CoV-2). This infectious disease has emerged in 2019. The COVID-19-associated pandemic has considerably affected the way of life and the economy in the world. It is consequently crucial to find solutions allowing remedying or alleviating the effects of this infectious disease. Natural products have been in perpetual application from immemorial time given that they are attested to be efficient towards several illnesses without major side effects. Various studies have shown that plant extracts or purified molecules have a promising inhibiting impact towards coronavirus. In addition, it is substantial to understand the characteristics, susceptibility and impact of diet on patients infected with COVID-19. In this review, we recapitulate the influence of extracts or pure molecules from medicinal plants on COVID-19. We approach the possibilities of plant treatment/co-treatment and feeding applied to COVID-19. We also show coronavirus susceptibility and complications associated with nutrient deficiencies and then discuss the major food groups efficient on COVID-19 pathogenesis. Then, we covered emerging technologies using plant-based SARS-CoV-2 vaccine. We conclude by giving nutrient and plants curative therapy recommendations which are of potential interest in the COVID-19 infection and could pave the way for pharmacological treatments or co-treatments of COVID-19.

A Review of Virus-Like Particle-Based SARS-CoV-2 Vaccines in Clinical Trial Phases

The Coronavirus disease 2019 (COVID-19) pandemic has affected more than 269 million worldwide, with more than five million deaths as of early December 2021. The main concerns in this pandemic include the asymptomatic nature of COVID-19, leading to the infection of many healthy people, the infectious nature of the pathogen, and its high spreading rate. The disease features have highlighted the importance of controlling this pandemic via vaccines. There has been a worldwide race to produce better, more protective, and efficacious vaccines. Simultaneously, different new variants of the virus are emerging. Therefore, there is a concern about the efficacy of the vaccines against new variants. The platform used for COVID-19 vaccine development needs to be flexible enough to enable the manufacturer to react suitably to new virus variants. We performed a comprehensive search in the online databases of PubMed, Scopus, Google Scholar, clinicaltrials.gov, WHO, ICTRP, and Cochrane until December 10th, 2021. There are 331 candidate vaccines in clinical development, with 194 in the preclinical stage and 137 in different clinical phases. Eleven platforms have been used for the development of COVID-19 vaccines, including inactivated/live attenuated virus, protein subunit, virus-like particle (VLP), non-replicating/replicating viral vectors (VVnr or VVr), VVr or VVnr plus antigen-presenting cell, bacterial antigen-spore expression vector, DNA, and RNA. The VLP-based vaccine platform is a safe, highly immunogenic, and flexible platform for developing vaccines. This review focuses on VLP-based vaccine platforms and explicitly discusses the six VLP-based COVID-19 vaccines in clinical trial phases.

Emerging trends of edible vaccine therapy for combating human diseases especially COVID ‐19: Pros, cons, and future challenges

The researchers are still doing efforts to develop an effective, reliable, and easily accessible vaccine candidate to protect against COVID‐19. As of the August 2020, nearly 30 conventional vaccines have been emerged in clinical trials, and more than 200 vaccines are in various development stages. Nowadays, plants are also considered as a potential source for the production of monoclonal antibodies, vaccines, drugs, immunomodulatory proteins, as well as used as bioreactors or factories for their bulk production. The scientific evidences enlighten that plants are the rich source of oral vaccines, which can be given either by eating the edible parts of plants and/or by oral administration of highly refined proteins. The use of plant‐based edible vaccines is an emerging trend as it possesses minimum or no side effects compared with synthetic vaccines. This review article gives insights into different types of vaccines, the use of edible vaccines, advantages of edible vaccines over conventional vaccines, and mechanism of action of edible vaccines. This review article also focuses on the applications of edible vaccines in wide‐range of human diseases especially against COVID‐19 with emphasis on future perspectives of the use of edible vaccines.

Nanotechnology and COVID-19: quo vadis?

The pandemic COVID-19 has worried everyone due to the high mortality rate and the high number of people hospitalized with severe acute respiratory syndrome caused by SARS-CoV-2. Given the seriousness of this disease, several companies and research institutions have sought alternative treatment and/or prevention methods for COVID-19. Due to its versatility, nanotechnology has allowed the development of protective equipment and vaccines to prevent the disease and reduce the number of severe COVID-19 cases. Thus, this article combined the main works and products developed in a nanotechnological field for COVID-19. We performed a literature search using the keywords "COVID-19," "SARS-CoV-2," "nanoparticles," "nanotechnology," and "liposomes" in the SciELO, Scifinder, PubMed, Sciencedirect, ClinicalTrials, and Nanotechnology Products databases Database. The data survey indicated 48 articles, 62 products, and 32 patents. The use of nanotechnology against COVID-19 has brought benefits in several parameters of this disease, helping develop rapid diagnostic tests that release the result in 10 min, as well as developing vaccines containing genetic material from SARS-CoV-2 (DNA, mRNA, and protein subunits). Nanotechnology is an exceptional ally against COVID-19, contributing to the most diverse areas, helping both prevent, diagnose, and treat COVID-19.

A comprehensive review on COVID-19 vaccines: development, effectiveness, adverse effects, distribution and challenges

The present SARS-CoV-2 induced COVID-19 pandemic is responsible for millions of deaths, illnesses, and economic loss worldwide. There are 21 COVID-19 vaccines from different platforms approved worldwide for emergency use until 13 August 2021. Later, BNT162b2 obtained full approval from the FDA. The efficacy of the leading vaccines such as BNT162b2, mRNA-1273, Gam-Covid-Vac, Ad26.COV2.S, ChAdOx1 nCoV-19, and BBIBP-CorV, against SARS-CoV-2 documented as 95%, 94.1%, 91.6%, 67%, 70.4%, and 78.1%, respectively. Moreover, against the Delta variant of SARS-CoV-2, BNT162b2, ChAdOx1 nCoV-19, and BBV152 showed 88%, 70%, and 65.2% efficacy, respectively. Apart from the common adverse effects such as fever, fatigue, headache, and pain in the injection site, Bell's palsy with BNT162b2, myocarditis and pericarditis with mRNA-1273, and thrombosis with ChAdOx1 nCoV-19 have been reported though seemed not alarming. Furthermore, global production and distribution of vaccines should be ensured in an equal and justifiable way that the immunity and protection against the virus would be optimum and persistent.

Plant-Based Vaccines in Combat against Coronavirus Diseases

Coronavirus (CoV) diseases, including Middle East Respiratory Syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS) have gained in importance worldwide, especially with the current COVID-19 pandemic caused by SARS-CoV-2. Due to the huge global demand, various types of vaccines have been developed, such as more traditional attenuated or inactivated viruses, subunit and VLP-based vaccines, as well as novel DNA and RNA vaccines. Nonetheless, emerging new COVID-19 variants are necessitating continuous research on vaccines, including these produced in plants, either via stable expression in transgenic or transplastomic plants or transient expression using viral vectors or agroinfection. Plant systems provide low cost, high scalability, safety and capacity to produce multimeric or glycosylated proteins. To date, from among CoVs antigens, spike and capsid proteins have been produced in plants, mostly using transient expression systems, at the additional advantage of rapid production. Immunogenicity of plant-produced CoVs proteins was positively evaluated after injection of purified antigens. However, this review indicates that plant-produced CoVs proteins or their carrier-fused immunodominant epitopes can be potentially applied also as mucosal vaccines, either after purification to be administered to particular membranes (nasal, bronchus mucosa) associated with the respiratory system, or as oral vaccines obtained from partly processed plant tissue.

Plant-Based Vaccines: Antigen Design, Diversity, and Strategies for High Level Production

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.

Plant-Based COVID-19 Vaccines: Current Status, Design, and Development Strategies of Candidate Vaccines

The prevalence of the coronavirus disease 2019 (COVID-19) pandemic in its second year has led to massive global human and economic losses. The high transmission rate and the emergence of diverse SARS-CoV-2 variants demand rapid and effective approaches to preventing the spread, diagnosing on time, and treating affected people. Several COVID-19 vaccines are being developed using different production systems, including plants, which promises the production of cheap, safe, stable, and effective vaccines. The potential of a plant-based system for rapid production at a commercial scale and for a quick response to an infectious disease outbreak has been demonstrated by the marketing of carrot-cell-produced taliglucerase alfa (Elelyso) for Gaucher disease and tobacco-produced monoclonal antibodies (ZMapp) for the 2014 Ebola outbreak. Currently, two plant-based COVID-19 vaccine candidates, coronavirus virus-like particle (CoVLP) and Kentucky Bioprocessing (KBP)-201, are in clinical trials, and many more are in the preclinical stage. Interim phase 2 clinical trial results have revealed the high safety and efficacy of the CoVLP vaccine, with 10 times more neutralizing antibody responses compared to those present in a convalescent patient's plasma. The clinical trial of the CoVLP vaccine could be concluded by the end of 2021, and the vaccine could be available for public immunization thereafter. This review encapsulates the efforts made in plant-based COVID-19 vaccine development, the strategies and technologies implemented, and the progress accomplished in clinical trials and preclinical studies so far.

Plant-Expressed Receptor Binding Domain of the SARS-CoV-2 Spike Protein Elicits Humoral Immunity in Mice

The current 15-month coronavirus disease-19 (COVID-19) pandemic caused by SARS-CoV-2 has accounted for 3.77 million deaths and enormous worldwide social and economic losses. A high volume of vaccine production is urgently required to eliminate COVID-19. Inexpensive and robust production platforms will improve the distribution of vaccines to resource-limited countries. Plant species offer such platforms, particularly through the production of recombinant proteins to serve as immunogens. To achieve this goal, here we expressed the receptor binding domain (RBD) of the SARS-CoV-2 spike (S) protein in the glycoengineered-tobacco plant Nicotiana benthamiana to provide a candidate subunit vaccine. This recombinant RBD elicited humoral immunity in mice via induction of highly neutralizing antibodies. These findings provide a strong foundation to further advance the development of plant-expressed RBD antigens for use as an effective, safe, and inexpensive SARS-CoV-2 vaccine. Moreover, our study further highlights the utility of plant species for vaccine development.

Potential for Developing Plant-Derived Candidate Vaccines and Biologics against Emerging Coronavirus Infections

The emerging human coronavirus infections in the 21st century remain a major public health crisis causing worldwide impact and challenging the global health care system. The virus is circulating in several zoonotic hosts and continuously evolving, causing occasional outbreaks due to spill-over events occurring between animals and humans. Hence, the development of effective vaccines or therapeutic interventions is the current global priority in order to reduce disease severity, frequent outbreaks, and to prevent future infections. Vaccine development for newly emerging pathogens takes a long time, which hinders rapid immunization programs. The concept of plant-based pharmaceuticals can be readily applied to meet the recombinant protein demand by means of transient expression. Plants are evolved as an expression platform, and they bring a combination of unique interests in terms of rapid scalability, flexibility, and economy for industrial-scale production of effective vaccines, diagnostic reagents, and other biopharmaceuticals. Plants offer safe biologics to fulfill emergency demands, especially during pandemic situations or outbreaks caused by emerging strains. This review highlights the features of a plant expression platform for producing recombinant biopharmaceuticals to combat coronavirus infections with emphasis on COVID-19 vaccine and biologics development.