Vigneshwar Senthilvel
29th May 2020
When a pathogen enters our body, as a first line of defense, our immune system elicits an immediate, non-specific response known as innate immune response. The purpose of the response is to minimize infection and the amount of spread throughout the body. The second line of defense is called the adaptive/acquired immune response, which is found only in vertebrates. The adaptive immune response is specific to the foreign pathogen which has entered our body. While the innate immune response is immediate, it lasts only for a short period of time. The acquired immune response is delayed, but is highly specific and is long term.
A vaccine is a preparation which contains parts of the pathogen which causes an infectious disease or the pathogen itself in an inactivated or a weakened form. A vaccine is prepared with such precision that when administered, it causes only an immune response and not an infection. Currently there are more than 110 vaccine candidates in development across the globe for the fight against COVID-19.
As SARS- CoV-2 enters our body, a special type of immune cells known as Antigen Presenting Cells (APCs) identifies the virus, engulfs it and presents different portions of the virus(antigens) to T-helper cells. These T-helper cells release cytokines, signaling molecules which activate B-cells. Activated B-cells secrete antibodies specific to the presented antigen. Antibodies are released into the circulation to bind and neutralize any circulating viral particles. The T-helper cells also activate cytotoxic T- cells, which can identify and kill a virus infected cell. By the end of an infection memory B cells and T cells are produced which retain the information of the antigen which has entered our body. These cells remain in circulation for long periods of time giving us extended immunity against a specific pathogen.
29th May 2020
When a pathogen enters our body, as a first line of defense, our immune system elicits an immediate, non-specific response known as innate immune response. The purpose of the response is to minimize infection and the amount of spread throughout the body. The second line of defense is called the adaptive/acquired immune response, which is found only in vertebrates. The adaptive immune response is specific to the foreign pathogen which has entered our body. While the innate immune response is immediate, it lasts only for a short period of time. The acquired immune response is delayed, but is highly specific and is long term.
A vaccine is a preparation which contains parts of the pathogen which causes an infectious disease or the pathogen itself in an inactivated or a weakened form. A vaccine is prepared with such precision that when administered, it causes only an immune response and not an infection. Currently there are more than 110 vaccine candidates in development across the globe for the fight against COVID-19.
Mechanism of infection and adaptive immune response:
As SARS- CoV-2 enters our body, a special type of immune cells known as Antigen Presenting Cells (APCs) identifies the virus, engulfs it and presents different portions of the virus(antigens) to T-helper cells. These T-helper cells release cytokines, signaling molecules which activate B-cells. Activated B-cells secrete antibodies specific to the presented antigen. Antibodies are released into the circulation to bind and neutralize any circulating viral particles. The T-helper cells also activate cytotoxic T- cells, which can identify and kill a virus infected cell. By the end of an infection memory B cells and T cells are produced which retain the information of the antigen which has entered our body. These cells remain in circulation for long periods of time giving us extended immunity against a specific pathogen.
Vaccines and their types:
Vaccines are intended to initiate an immune response similar to a viral infection without causing any damage to the body. It is like creating a rap sheet for the virus which is going to affect our body in the future. By looking at the vaccine, our immune system can get to know beforehand, what to look for when a specific pathogen enters our body.
Vaccine preparations can have different compositions of the virus and are classified mainly into four types:
· Viral vaccines
· Subunit vaccines
· Nucleic acid vaccines
Viral vaccines consist of entire viral particles in a weakened(attenuated) or killed (inactivated) state. They can only cause an immune response and cannot cause the disease. One of the leading candidate SARS-CoV-2 vaccine in preclinical trials, being developed by Codagenix, New York and Serum Institute of India, Pune is an attenuated vaccine. A new subtype of viral vaccine is genetically engineered chimeric vaccines. They contain viral vectors, a weakened form of a known virus, along with a gene which codes for a surface protein of the disease-causing virus.
Subunit vaccines contain only certain components of a virus which can trigger an immune response. They are safe and easy to mass produce, but require additional molecules known as ‘adjuvants’ for creating a stronger immune response.
Nucleic acid vaccines are safer and are relatively new. As the name suggests, they contain nucleic acids such as DNA or RNA from the viral particle which usually codes for a surface protein. This vaccine when delivered inside, can produce the viral surface proteins within our body which in turn initiates an immune response. One of the front runners in nucleic acid vaccines is the lipid nanoparticle encapsulated mRNA vaccine mRNA-1273, in development by Moderna.
Please find the infographic summarizing the different types of vaccines down below.
References:
https://hms.harvard.edu/news/designing-coronavirus-vaccine
Thanh le T, et al. The COVID-19 vaccine development landscape. Nature Reviews Drug Discovery 19, 305-306 (2020). doi: 10.1038/d41573-020-00073-5
Lurie D, et al. Developing COVID-19 vaccines at pandemic speed. The New England Journal of Medicine. 2020; doi:10.1056/NEJMp2005630
https://www.mayoclinic.org/diseases-conditions/coronavirus/in-depth/coronavirus-vaccine/art-20484859
The race for corona virus vaccines by Ewen Callaway.Nature 580, 576-577 (2020). doi: 10.1038/d41586-020-01221-y
https://www.niaid.nih.gov/research/vaccine-types
About the Author
Vigneshwar Senthilvel is a graduate student at the CSIR Institute of Genomics and Integrative Biology (CSIR-IGIB) . He can be reached on twitter handle @vickymj93
All opinions expressed are personal and do not reflect the stated opinions of any of the organisations affiliated.
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