Vaccine is defined as anything that can generate a sustained/memory protective immune response for future infection. The vaccine components can be anything, including parts of the pathogens or inactivated whole pathogen, or even host cells packed with pathogen components.

As for the process? Do you mean the vaccine components? DNA vaccines are usually not naked DNA, they are either packed/modified. But DNA vaccines don't usually work. For purified proteins, there is almost always some sort of adjuvant required to stimulate the immune response.

Then there are therapeutic vaccines, which are vaccines that can be used post-infection to push the immune response to generate protection. These are usually targeted for cancer.

The process is called molecular cloning. The gene responsible for the S spike protein when transcribed and translation by the cellular machinery will be inserted into a vector for example plasmid DNA. The plasmid DNA containing the S gene then is used to transfect a competent bacteria such as E Coli. The bacteria will be cultured and a large quantities is harvested. The S protein produced during the growth of the bacteria and its plasmid will be purified from the broth in which the bacteria grow. The product will be further characterized and used as a vaccine candidate

Hi Adaobi,

There are many approaches that can be used to create a vaccine with parts of a virus. I will use the vaccines in development for Covid-19 as examples. Each approach has its advantages/disadvantages that I'd be happy to discuss further:

1. You can inject mRNA encoding a virus surface protein. This is the approach being taking in Moderna's frontrunner vaccine mRNA-1273, which is an mRNA encoding the Covid-19 spike protein. Moderna found that by injecting mRNA in a special lipid composition, the mRNA would be translated to protein, primarily in the liver, and the proteins would allow for seroconversion of antigen neutralizing antibodies (https://www.clinicaltrialsarena.com/comment/modernas-phase-i-covid-19-mrna-vaccine-has-manufacturing-edge-but-many-obstacles-to-confirm-protection-lay-ahead/)

2. A chimeric vaccine can be made which has a surface antigen from the target virus displayed on the surface of another virus, usually one that has been proven to be very safe and fit for purpose. This is the approach being taken with the Oxford University Covid-19 vaccine ChAdOx1 nCoV-19. They display the Covid-19 spike protein on an attenuated adenovirus first isolated from chimpanzees. They have also displayed other virus' surface antigens to make other vaccines (https://www.vaccitech.co.uk/technology/)

3. A subunit vaccine is a fragment of a pathogen, typically a surface protein, that is used to trigger an immune response and stimulate acquired immunity against the pathogen from which it is derived. Generally, the proteins are cloned into mammalian cell vectors and produced in mammalian cells such as HEK-293 (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6728104/). Bacterial endotoxins are highly immunogenic, hence, it is preferable to use mammalian cells for production of subunit vaccines intended for human use. AJ therapeutics and Epivax are developing Covid-19 subunit vaccines (https://www.google.com/amp/s/www.evaluate.com/node/15715/amp).

I hope this helps

Hello Adaobi. I read the previous responses and I agree with most of what has already been said. These viral subunits can be used as vaccines simply because they bear partial resemblance to the really pathogenic form of the virus.

Have you heard about VLPs? Virus-like particles? These are even far more immunogenic than just any viral protein expressed after molecular cloning. I will post a link to a VLP hepatitis B vaccine here. I believe reading it will answer some of your questions.

https://www.mdpi.com/2076-393X/8/2/275/htm

Hi Adaobi

Historically vaccines were only known to be either live attenuated or inactivated (Killed). Both types of vaccines make use of the whole pathogen (including components not important for immune responses) and therefore have their strengths and weaknesses. For instances, the live attenuated vaccines are known to be highly immunogenic because they tend to mimmick natural infection in terms of provoking the immune system. They may however revert back to virulence and therefore, are not very safe especially when used against dangerous pathogens. The inactivated vaccines on the other hand cannot revert back to virulence due to their non-replicating nature but are unfortunately poorly immunogenic. This TRADITIONAL VACCINOLOGY has been known for more than 100 years now and the choice of its platforms depends on our preference of either safety or efficacy.

2. With Advances in recombinant DNA technology, attempts have been made to develop vaccines that are both highly effective and incredibly safe in what is currently known as NEXT GENERATION VACCINOLOGY. This form of vaccinology does not use the whole pathogen. Instead, only the components of the pathogen known to be responsible for triggering immune responses are bioinformatically mapped out and engineered into recombinant vaccines.

3. Some of the platforms that are commonly used in next generation vaccinology include

a. Recombinant peptides vaccines: This has been explained by Abdelmalik Ibrahim Khalafalla above

b. Recombinant DNA vaccines: This involves cloning the antigenic portion of the pathogen in a plasmid vector. The recombinant plasmid is then used as vaccine in the chosen host.

c. mRNA vaccines: Genes encoding the antigenic portions of the pathogen are transcribed in vitro and used as vaccines. Please see the comment of Zack Saud above.

c. Viral vectored vaccine; This involves inserting the antigenic component of the pathogen into a virus vector Such as pox virus, adenovirus, Newcastle disease virus etc). The recombinant virus is then used as a vaccine as explained by Zack Saud

d. VLP: This involves in vitro assembly and packaging of a genomeless particle that morphologically resembles the virus against which vaccines are made. See the link shared by Nathaniel Ninyio

So many modifications are currently being made to improve the efficacy and safety of each of these platforms.

Hope this helps

Bashir