Plant Based Vaccinations —The Present &Future of Immunization

Vaccines have been around for over four centuries now. As kids, we have all dreaded the occasional vaccine shot, but vaccines have become a necessary evil now-a-days. The concept first used by Edward Jenner and later applied by Louis Pasteur, has now been developed tremendously and used at a large scale to combat the life threatening diseases that originate every other day.

A biological preparation that provides enhanced and improved immunity towards a particular disease is termed as a vaccine. A typical vaccine preparation contains a weakened, killed or a part of the disease causing microorganism or toxins or one of the surface proteins of the same. This agent instigates an immune response in the body that leads to the recognition of the agent as a foreign agent, after which it is destroyed. The immune system recalls it and easily recognizes and destroys it during any future encounters.

With recent advancements in science and technology, the field of Vaccinology has also progressed. From the development of the vaccine to its administration to the patient; there is a high level of precision, scrutiny, and technology that is being practiced. Vaccines are broadly classified into two groups namely; prophylactic (meaning to prevent future infections) or therapeutic (meaning to tackle an existing disease, such as cancer, etc.).
Various types of vaccines include inactivated, attenuated, toxoid, subunit, conjugate, experimental, valence, and heterotypic. These different types of vaccines are categorized on the basis of the strategies that are used to make them, to reduce the risk of development of certain diseases, and also retaining the ability to induce an immune response in the future. The most recent advancement in this space, due to the recent biotechnological spurge, has been the development of Plant based and Recombinant vaccines.

Conventional Way of Vaccine Production: An Overview
The overall vaccine production involves several steps:
Generation of the Antigen (viral component): Over the years, vaccines have been manufactured using fertilized embryonic eggs and cell cultures (bacterial, yeast, or mammalian).

Using the embryonic egg method requires a time span of about four months to produce one batch of vaccines. It is well established that safety and effectiveness of the vaccines produced by the fertilized embryonic eggs are the two chief advantages that this method offers.

Another manufacturing process involves the cell based vaccines, which uses mammalian cells to culture the virus. Various sources of mammalian cell cultures are used for the vaccine development process.  Bacteria cells grown in bioreactors, these are the devices that use a specific growth medium that provides an optimal environment for the production of the antigen. Recombinant proteins or antigens that can be obtained from the pathogens are further generated using yeast, bacteria or mammalian cell cultures.

Release & Isolation of the Antigen: The next step after the generation of the antigen is extracting it from the cells. Numerous levels of purification and inactivation are required to generate pure recombinant of proteins and antigens.

Addition of Supplementary Constituents: The vaccine is finally formulated by adding stabilizers, adjuvant, and preservatives as desirable. The adjuvant intensifies the immune response of the antigen, while stabilizers increase the shelf life and preservatives enable the use of multi-dose vials.
The above described cell-based processes have various advantages over the fertilized embryonic eggs cultures, such as:

  • It enhances the capability of companies to scale up vaccine production easily, within a short time frame
  • It reduces the possibility of the virus culture mutation during the production process. The virus mutation probability increases when we use the embryonic eggs, and the entire batch can go to waste.
  • Also, people allergic to vaccines manufactured from chicken eggs may suffer from allergies to the vaccines

These positives provide a potential candidate process for development of vaccines. But, culturing of cells requires relatively higher manufacturing costs. This leads to the increase in the costs of the vaccines, which is a disadvantage for the masses. Although the cell based process provides a fourfold higher yield than the embryonic egg, the volumetric increase in the process requires voluminous bioreactors. The capital investment for these is much higher than the investment required for the production of plant based vaccines.

Plants as Bio-factories for Vaccine Production
A significant number of drugs that we use have been derived from plants for centuries, which subsequently led to pharmaceutical industry chemically synthesizing medical compounds. However, the recent development and progress in the field of transgenic plants has led the researchers to pay more and more attention towards plants being looked upon as potential bio-reactors or bio-factories for the production of immunotherapeutic molecules. There are numerous advantages that plant based vaccines provide, the chief one being the reduced cost of production, which eventually leads to low priced vaccines. Transgenic plants provide an excellent and promising expression system for the production of the vaccines. Currently, complex plants like tomato, tobacco, and banana are being modified and used to produce usable vaccines for humans.

Why do we need to use Plant Vaccines? 
There are numerous advantages of Plant based vaccines which sets them apart and makes them more cost effective. Transgenic material is basically a seed or a fruit, or any part of the plant that can be easily stored and transported from one place to another. This cuts down the fear of its degradation or damage. They allow a large amount of bio-mass to be effortlessly produced by cultivation in fields with relatively very few inputs. Several different products can be produced at a time using transgenic plants.
The most important advantage is that the plant system does not harbor human pathogens (such as virions or prions) and, thus, they transmit the target subunit vaccine without any contamination. Moreover, plants can be grown in the field or in a greenhouse comparatively inexpensively, and do not require any expensive equipment like fermenters and bioreactors.

The vaccine components can be produced in the edible parts of the plant, such as grain, fruit or even leaves, cutting down the requirement of the purification process, thus increasing the stability and reducing the degradation of the antigenic protein. Production of the vaccine subunit in the edible parts of the plant has an added advantage, since it is delivered orally rather than intramuscularly, offering a simple and non-invasive means of administration to humans. In addition, the reduced cost of vaccinations and their minimalistic storage requirements are often necessary in developing countries; e.g., sterile syringes are not required.

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