COVID-19 and T cell response after vaccination

Antibodies induced after coronavirus disease 2019 (COVID-19) vaccination or SARS-CoV-2 infection have the ability to cross-neutralize the variant of concern (VOC). It is declining. However, antibodies are not the only mediator of immunity.

New research published in the journal Immunology Frontier Investigate the cell-mediated immunity of BNT162b2COVID-19 mRNA vaccinated healthcare professionals and COVID-19 patients.

study: Long-lasting T cell response in BNT162b2 COVID-19 mRNA vaccine and COVID-19 convalescent patients.. Image Credit: Corona Borealis Studio / Shutterstock

Cell-mediated immunity

T cells A cell-based immune mediator. They play important roles in immune protection, recovery from acute infections, and long-term immunological memory.

The antigen-Presentation cells (APCs) present some short peptides of viral proteins to T cells. The T cell response is stimulated by these different short peptides. Therefore, T cell responses are not sensitive to viral protein mutations such as antibody responses.

CD8 + cytotoxic T lymphocytes (CTLs) identify and destroy virus-infected cells. CD4 + T helper (Th) cells regulate and enhance CTL response. They also stimulate antibody production by B cells.

Previous studies have shown that SARS-CoV-2 infection stimulates strong memory CD4 + and CD8 + T cell responses. This cell-mediated immunity may provide long-term protection against reinfection.

Evaluation of cell-mediated immunity

This study analyzes the lifespan of SARS-CoV-2 spike-specific antibodies and cell-mediated immunity in BNT162b2 vaccinated healthcare professionals and COVID-19 patients.

The study included 23 fully vaccinated medical personnel (two doses of BNT162b2 vaccine), 15 COVID-19 patients, and previously SARS-CoV-2 infection or COVID-19 vaccination. Included 13 individuals who did not receive it. Blood samples were collected from vaccinated individuals 6 weeks, 3 months, and 6 months after the first vaccination. Patients with convalescent COVID-19 18-45 days (33 days on average) after SARS-CoV-2 infection.

Peripheral blood mononuclear cells (PBMCs) were isolated from the blood and activated with peptides throughout the SARS-CoV-2 peplomer. T cell subtypes within the PBMC population were characterized using flow cytometry.

Expression of various cytokines was measured using RT-qPCR. In addition, Luminex was used to detect levels of cytokines and other molecules secreted by cells. Anti-SARS-CoV-2 antibody was measured using the enzyme immunoassay (EIA). The activation-inducing marker (AIM) assay was optimized prior to analyzing the sample.

PBMC was stimulated with the wild-type SARS-CoV-2 Wuhan virus spike peptide pool. 48 hours of stimulation and measurements of IFN-γ and IL-2 mRNA levels were selected for all analyses. Tetanus toxoid was used as a positive control. Both IFN-γ and IL-2 are Th1 cytokines.

T cell response

SARS-CoV-2 spike-specific CD4 + cellular responses were detected in all COVID-19 patients and vaccinated individuals 6 weeks, 3 months, and 6 months after the first vaccination.

A CD8 + cellular response was detected 6 weeks after the first dose in 80% of COVID-19 patients and 70% of vaccinated individuals. 67% of vaccinated individuals 3 months after the first dose. In 53% of vaccinated individuals, 6 months after the first dose. These T cell responses were similar in COVID-19 patients and vaccinated individuals.

The T cell response to VOCs was assessed by stimulating PBMCs with a peptide pool from. Spike protein Of alpha, beta, gamma, and delta variants. A CD4 + cellular response to all VOCs tested was detected in ≥71% of vaccinated individuals and ≥75% of COVID-19 patients.

CD8 + T cell responses to all VOCs tested were detected in ≥50% of vaccinated individuals and ≥75% of COVID-19 patients. However, a significant difference was observed between the wild-type and gamma mutants 6 weeks after vaccination and the wild-type and beta mutants 6 months after vaccination.

Patients with COVID-19 had a stronger response to CD4 + and CD8 + than those vaccinated. After 6 months, there was no decrease in cell-mediated immunity to VOCs.

Expression of IFN-γ and IL-2 mRNA was detected in 93% and 100% of vaccinated individuals after stimulation with wild-type and delta mutant spike peptide pools. mRNA levels were higher compared to PBMC mRNA levels collected from unvaccinated and uninfected individuals. Expression of IFN-γ and IL-2 mRNA was similar between COVID-19 patients and vaccinated individuals.

Correlation between humoral immunity and cell-mediated immunity after BNT162b2 vaccination n = 23 and SARS-CoV-2 infection. (A) Anti-SARS-CoV-2 S1-specific IgG, S1-total Ig, and N-protein-specific IgG antibody responses were measured from samples collected 6 weeks, 3 months, and 6 months after vaccination. .. After n = 23 or 1-month PCR confirms SARS-CoV-2 infection (n = 15). Serum antibody levels in vaccinated and infected individuals were compared to negative controls (n = 13) who had not been vaccinated with COVID-19 or had previously been infected with SARS-CoV-2. The bar represents the geometric mean titer. The cutoff value for positive test results is shown by the dotted line. Statistical analysis was performed with the Mann-Whitney U test to compare a 6-week vaccinated sample with a COVID-19 patient sample. **** p <0.0001. (B, C) Correlation between anti-SARS-CoV-2 S1 IgG antibody levels and SARS-CoV-2 (wt) spike-specific CD4 + and CD8 + T cell responses (B) Vaccinated medical personnel (sample 6 weeks, sample) Collected at 3 months), and 6 months after vaccination, n = 52) and (C) COVID-19 patients (sample collected 1 month after onset of symptoms, n = 15). The correlation is analyzed by Spearman's correlation and Spearman's r is shown in the figure.

After stimulating PBMC from individuals vaccinated with wild-type and delta mutant spike peptide pools, IFN-γ and IL-2 protein levels were significantly increased. Levels of IFN-γ and IL-2 were higher in vaccinated individuals and in COVID-19 patients than in unvaccinated, uninfected individuals. IFN-γ and IL-2 levels did not decrease 6 months after vaccination. In addition, stimulation with wild-type or delta mutant peptide pools produced comparable IFN-γ and IL-2 levels.

There was a high correlation between T cell activation and the production of IFN-γ and IL-2 cytokines.

All vaccinated individuals produced spike-specific anti-SARS-CoV-2 antibodies 6 weeks after the first vaccination. Antibody levels were higher than those in hospitalized COVID-19 patients. In vaccinated individuals, antibody levels gradually declined.

Levels of anti-SARS-CoV-2 antibody in vaccinated individuals did not correlate with CD4 + or CD8 + T cell responses. However, in COVID-19 patients, spike-specific anti-SARS-CoV-2 antibodies increased with increased CD4 + and CD8 + T cell responses.

Research limits

In this study, PBMCs were cryopreserved until analysis. This reduces cell viability and can result in the loss of some memory cells in the process. The number of participants evaluated in this study was relatively small. Only individuals vaccinated with BNT162b2 were studied. This study does not include vaccinated individuals over the age of 60. The AIM protocol did not test longer incubation times. Instead of 9-10 mer peptides, a longer 15 mer peptide pool was used for stimulation. This may underestimate SARS-CoV-2 specific CD8 + cells.

Conclusion

This study found that even if SARS-CoV-2 peplomer-specific antibodies declined over time after COVID-19 vaccination or spontaneous infection, cellular immunity was significantly retained and insensitive to viral peplomer mutations. Is shown.