A protective immune mechanism is formed in the body of the people who are infected with SARS-CoV-2, a causative agent of COVID-19, and then recover. The two major elements of the immune function are neutralizing antibodies and memory T cells, and there are increasing interests in the memory T cells compared to the neutralizing antibodies that decrease over time. The recent works by the research group of Professor Eui-Cheol Shin at the Center for Epidemic Preparedness are also directed to the memory T cells. They found that the memory T cells are retained for 10 months in the people who have recovered from COVID-19, and stem cell-like memory T cells are efficiently generated in them. Their results suggest that the memory T cells, protecting hosts against severe COVID-19, can be maintained for a long time.

|Contributions to the Establishment of Next-Generation Vaccine Strategies|

Generating and retaining of memory T cells have been confirmed.
Professor Shin says that the shares of neutralizing antibodies and memory T cells are half and half; the neutralizing antibodies prevent cells from being infected by virus, and T cells detect and remove virus-infected cells. “Simply speaking, the antibodies are like the front-line troops near to the ceasefire line, while the T cells are like the rear guards for responding to the enemy infiltration, such as the Capital Defense Command.”
The research group focuses on the memory T cells, because they can prevent post-infection serious cases and lower the fatality rate. In the collaborative study they conducted with Professor Won-Suk Choi’s group at the Korea University Ansan Hospital, they collected, during the follow-up period of 10 months from March 2020, the blood samples from those who had recovered from COVID-19, performed an immunological analysis, and found that the memory T cells were well retained during the study period. They also found that the memory T cells exhibited robust responses when they again encountered viral antigensafter 10 months.
When their paper was published (June 2021), their follow-up period was longest in the world. Besides that, their study has a pace-setting significance in another aspect; they became the first research group in the world that showed the successful generation of ‘stem cell-like memory cells,’ a type of memory T cell, in those who have recovered from COVID-19.
“The ‘stem cell-like memory cells’ are the memory T cells that have the regeneration function to keep the memory response for a long time. The verification of the cells suggests a very important point. In the past, we were able to confirm the retaining of the memory T cells after directly verifying their presence 10 months or 1 or 2 years later. However, the confirmation of the ’stem cell-like memory cells’ provide a rationale to expect that the T cells will be retained for a long time.”

Follow-up studies are carried out actively.
Many researchers are actively verifying the correlations between the vaccination and the retaining of antibodies or memory T cells. The works by Professor Shin’s group are in the middle of the same trend. “If you get the second shot, you are more likely to have the antibodies or memory T cells.” However, his group is moving on to another follow-up study.
“Currently, we are verifying, with those who have received COVID-19 mRNA vaccines, if ‘the memory T cell response is retained longer in the people in whom the stem cell-like memory cells are generated more.’ We hope that, through these studies, we can understand the mechanism that regulates the continuity of the protective immunity obtained by the vaccination, and to prepare a basis for developing next-generation vaccine strategies.”

Prof.Eui-Cheol Shin
2021 Annual Report