FRONT PAGE: Study Shows Immune Cells Against Covid-19 Stay High In Number Six Months After Vaccination

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Newswise — A recent study by Johns Hopkins Medicine researchers provides evidence that CD4+ T lymphocytes — immune system cells also known as helper T cells — produced by people who received either of the two available messenger RNA (mRNA) vaccines for COVID-19 persist six months after vaccination at only slightly reduced levels from two weeks after vaccination and are at significantly higher levels than for those who are unvaccinated.

The researchers also found that the T cells they studied recognize and help protect against the delta variant of SARS-CoV-2, the virus that causes COVID-19. The U.S. Centers for Disease Control and Prevention state that the delta variant of SARS-CoV-2, currently the most prevalent strain in the United States, causes more infections and spreads quicker than other forms.

The study findings were first reported online Oct. 25, 2021, in the journal Clinical Infectious Diseases.

“Previous research has suggested that humoral immune response — where the immune system circulates virus-neutralizing antibodies — can drop off at six months after vaccination, whereas our study indicates that cellular immunity — where the immune system directly attacks infected cells — remains strong,” says study senior author Joel Blankson, M.D., Ph.D., professor of medicine at the Johns Hopkins University School of Medicine. “The persistence of these vaccine-elicited T cells, along with the fact that they’re active against the delta variant, has important implications for guiding COVID vaccine development and determining the need for COVID boosters in the future.”

To reach these findings, Blankson and his colleagues obtained blood from 15 study participants (10 men and five women) at three times: prior to vaccination, between seven and14 days after their second Pfizer/BioNTech or Moderna vaccine dose, and six months after vaccination. The median age of the participants was 41 and none had evidence of prior SARS-CoV-2 infection.

CD4+T lymphocytes are called helper T cells. They assist another type immune system cell, B lymphocytes (B cells), to respond to antigens on viruses like SARS-CoV-2. The CD4+ T cell activation activates immature B cells into either plasma cells that make antibodies to mark infected bodies for elimination or memory cells that “remember the antigen’s structure for a quicker response to future infections. A CD4+ T-cell response can be used to measure how well the immune system responds and produces humoral immunity. Blankson and his colleagues discovered that helper T cells were not recognizing the SARS-CoV-2 spike proteins prior to vaccination. They had a median of 2.7 spots-forming units (SFUs), which is a measure for T cell frequency, per million peripheral blood mononuclear cell (PBMCs), which are blood cells with a round nucleus including lymphocytes. Between 7 and 14 days after vaccination, the T cell frequency rose to a median of 237 SFUs per million PBMCs. Six months later, the T cell frequency dropped to a median 122 SFUs/million PBMCs. This is still a significantly higher level than before vaccination.

The researchers also examined six months after vaccination the ability of CD4+ cells to recognize spike proteins at the top of the SARS-CoV-2 Delta variant. The researchers found that the number of T-cells capable of recognizing the spike protein of the delta variant virus strain was not significantly different than the number of cells that were attuned with the original virus strain’s protein.

Although the study was small due to the limited number of participants, Blankson believes it highlights areas that warrant further investigation.

” The robust expansion of T cells upon stimulation with spike proteins is clearly indicated. This supports the need to conduct more research to prove that booster shots can increase the frequency and type of SARS-CoV-2-specific-T cells in the blood.” Blankson says. “The added bonus is finding that this response also is likely strong for the delta variant.”

Along with Blankson, the members of the study team from Johns Hopkins Medicine are study lead author Bezawit Woldemeskel and Caroline Garliss.

This study was supported by the Johns Hopkins COVID-19 Vaccine-related Research Fund.

The authors do not have financial or conflict of interest disclosures.

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