How Adenovirus Vector COVID-19 Vaccine (Ad5-nCoV) works?

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How Adenovirus Vector COVID-19 Vaccine (Ad5-nCoV) works?

The dose of a vaccine is usually 0.5 ml. In order to make this 0.5 ml of transparent liquid effective to prevent the COVID-19 virus from infecting the human body and defeat the COVID-19 epidemic that is still spreading around the world, vaccine research and development workers have devoted themselves to nearly a year.

At the beginning of 2020, the COVID-19 epidemic broke out. On January 22, the adenovirus vector COVID-19 vaccine (Ad5-nCoV) project was officially launched.

The project uses adenovirus vector technology with proven safety and immunogenicity as the research and development route, becoming the world’s first COVID-19 vaccine to enter phase I clinical trials.

What kind of vaccine is the adenovirus vector COVID-19 vaccine (Ad5-nCoV)? How does it work? How safe is it?

In short, the adenovirus vector new coronavirus vaccine (Ad5-nCoV) is to construct the gene of the new coronavirus S protein into the adenovirus genome.

The coat is still the normal coat protein of adenovirus, but the gene inside contains the gene encoding the new coronavirus S protein.

Therefore, when adenovirus infects host cells, the genes encoding the S protein of the new coronavirus are released to the host cell, and S protein is synthesized in the cytoplasm, and the S protein stimulates a series of immune responses.

How Adenovirus Vector COVID-19 Vaccine (Ad5-nCoV) works? — *Picture: Schematic diagram of the working mechanism of Ad5 vector vaccine*

What is Ad5 adenovirus? Is it really safe to use it as a carrier?

Ad5 adenovirus is a double-stranded DNA virus without envelope and has a strong ability to infect human cells. Ad5 adenovirus vector is a relatively mature platform. It cuts off the key gene fragments responsible for replication in adenovirus so that it cannot replicate but retains its ability to infect human cells. It is called a replication-defective adenovirus vector.

Researchers have integrated the gene sequence encoding the COVID-19 S protein into the adenovirus genome through genetic recombination to become a replication-deficient adenovirus vector vaccine.

After the human body is vaccinated with the vaccine, with the strong infecting ability of the adenovirus vector, it can quickly enter the cell, release the gene sequence encoding the S protein in the cell to synthesize the S protein, and become an antigen that can be recognized by the body.

Adenovirus vectors that do not have the ability to replicate will be metabolized by the body.

As a genetically engineered vaccine, in addition to the above-mentioned safety, what other technical advantages does the adenovirus vector COVID-19 vaccine (Ad5-nCoV) have? The advantage of an adenovirus-based vaccine is that it can induce both humoral and cellular immunity.

How to understand humoral immunity and cellular immunity?

In short, humoral immunity produces antibodies that bind to viruses, preventing them from entering human cells, where they are recognized, swallowed, and degraded by macrophages. Viruses that have been lucky enough to enter cells can be recognized by cellular immune mechanisms.

Killer T cells secrete cytokines to lyse off infected cells. Of course, the process of humoral immune response and cellular immune response is very complicated. There are many cytokines and cells with different functions that cooperate to resist viruses.

If the immune response process is likened to a war between the immune system and foreign enemies, then the immune response induced by the adenovirus vector COVID-19 vaccine (Ad5-nCoV) is equivalent to a joint battle by sea, land and air to completely eliminate the enemy, and the immunogenicity is naturally better. .

Based on the immunological principles of COVID-19 vaccine candidates based on different technical routes, not all vaccines can stimulate cellular immunity.

So why is cellular immunity so important? Because the main battlefield dominated by humoral immunity is not able to eliminate all invading viruses in a single battle in the face of a virus with such a powerful infection like COVID-19, and the virus that escapes from the neutralizing antibody encirclement and suppression, once it enters the body’s cells, humoral immunity is It can’t work anymore, the task of digging out the hidden enemies one by one can only be done by the cellular immune unit.

In addition to the COVID-19 vaccine, based on the adenovirus vector technology platform, the team of Academician Chen Wei of the Chinese Academy of Military Sciences and Cansino Biosciences successfully developed a recombinant Ebola virus disease vaccine in 2017.

In the process of exploration and practice, the R&D team has accumulated core capabilities such as talents, technology, systems, and hardware that are compatible with the adenovirus platform, thereby helping the development of the COVID-19 vaccine.

Currently, the Phase III clinical trials of the adenovirus vector COVID-19 vaccine (Ad5-nCoV) are underway in many countries around the world, and we look forward to more good news together!