CD4 + T cells are also called helper T cells because they help another type of cell in the immune system, B cells, respond to surface proteins – antigens – on viruses such as SARS-CoV-2. Activated by CD4 + T cells, immature B cells become either plasma cells which produce antibodies to mark infected cells for elimination from the body, or memory cells which “remember” the biochemical structure of the antigen for a more responsive response. fast to future infections. Therefore, a CD4 + T cell response can serve as a measure of how the immune system responds to a vaccine and produces humoral immunity.
Cellular immunity and vaccination reminders
CD4 + T lymphocytes (or helper T) precisely target the peak protein of the SARS-CoV-2 virus and these direct antibodies against the COVID-19 virus – including associated with the Delta variant – persist 6 months after vaccination with a vaccine to mRNA. “Previous research has suggested that the humoral immune response (the immune system circulates antibodies that neutralize the virus) may drop 6 months after vaccination however our study indicates that cellular immunity (the immune system directly attacks infected cells via these T cells) remain elevated, summarizes lead author Dr. Joel Blankson, professor of medicine at Johns Hopkins University School of Medicine. “The persistence of these vaccine-induced T cells, as well as the fact that they are active against the delta variant, has important implications for guiding the development of the COVID vaccine and determining the need for boosters.”
The study: to reach these conclusions, the team analyzed the blood of 15 participants (10 men and 5 women), on average 40 years old, before vaccination, between 7 and 14 days after the second dose of Pfizer / BioNTech vaccine or Moderna, and 6 months after vaccination. None of the participants had been infected with SARS-CoV-2 before vaccination. This analysis finds that the number of helper T cells recognizing the SARS-CoV-2 spike proteins
- was extremely low before vaccination (median 2.7 SFU (spot-forming units) per million peripheral blood mononuclear cells (PBMCs);
- between 7 and 14 days after vaccination, increases to a median of 237 SFU per million PBMCs;
- 6 months after vaccination, the level dropped slightly to reach a median of 122 SFU per million PBMCs: this is, however, a level of T cells still significantly higher than before vaccination, comment the authors.
- Still 6 months after vaccination, the ability of CD4 + T cells to recognize the peak proteins at the top of the delta variant of SARS-CoV-2 remains intact.
Admittedly, the analysis was carried out on a limited number of participants, but these first results suggest a certain persistence in the duration of the cellular immunity and deserve further studies, which could help to clarify the necessity and the timeframe. vaccination reminders.