The Immune Response to SARS-CoV-2 Vaccine in a Cohort of Family Pediatricians from Southern Italy

Abstract

In Italy, from January 2021, the Ministry of Health indicated a vaccination plan against COVID for frail patients and physicians based on a three-dose scheme. However, conflicting results have been reported on which biomarkers permit immunization assessment. We used several laboratory approaches (i.e., antibodies serum levels, flow cytometry analysis, and cytokines release by stimulated cells) to investigate the immune response in a cohort of 53 family pediatricians (FPs) at different times after the vaccine. We observed that the BNT162b2-mRNA vaccine induced a significant increase of specific antibodies after the third (booster) dose; however, the antibody titer was not predictive of the risk of developing the infection in the six months following the booster dose. The antigen stimulation of PBMC cells from subjects vaccinated with the third booster jab induced the increase of the activated T cells (i.e., CD4⁺ CD154⁺); the frequency of CD4⁺ CD154⁺ TNF-α⁺ cells, as well as the TNF-α secretion, was not modified, while we observed a trend of increase of IFN-γ secretion. Interestingly, the level of CD8⁺ IFN-γ⁺ (independently from antibody titer) was significantly increased after the third dose and predicts the risk of developing the infection in the six months following the booster jab. Such results may impact also other virus vaccinations.

Keywords: COVID-19; IFN-γ; SARS-CoV2 antibodies; T-cell; TNF-α.

Figure 1

(A) Serum levels of IgG (AU/mL) targeting the Receptor-Binding Domain (RBD) in 53 family pediatricians at different times (see Table 1); ** p < 0.001. (B) Comparison of IgG levels among FPs who developed acute SARS-CoV-2 infection (A, n = 20) and FPs who did not develop acute SARS-CoV-2 infection (B, n = 33) during the 6 months following the third dose of vaccine; n.s. not significant. Means and SD are shown. Statistical analysis was performed as reported in the methods.

Figure 2

(A) CD4⁺ CD154⁺ T cells (percent of total lymphocytes) in 53 family pediatricians (FPs) at T3 compared to T2 (left panel). Differences in the percent of CD4⁺ CD154⁺ cells between patients of group A (n = 20) and group B (n = 33) (right panel). (B) CD4⁺ CD154⁺ TNF-α⁺ cells (percent of total lymphocytes) in FP at different time points (left panel). Differences in the percent of CD4⁺ CD154⁺ TNF-α⁺ cells between patients of group A and group B (right panel). (C) CD8⁺ IFN-γ⁺ cells (percent of total lymphocytes) in FP at different time points (left panel). Differences in the percent of CD8⁺ IFN-γ⁺ cells between patients of group A and group B; In (A–C), ** p < 0.001; * p < 0.05; n.s. not significant. Means and SD are shown. Statistical analysis was performed as reported in the methods.

Figure 3

Correlation between serum levels of IgG (AU/mL) targeting the Receptor-Binding Domain (RBD) and percent of CD8⁺ IFN-γ⁺ cells at T2 (left) and T3 (right). Statistical analysis was performed as reported in the methods.

Figure 4

Release (stimulation index, SI) of IFN-γ (panel (A)) and TNF-α (panel (B)) at T2 and T3 (left panel) in 53 FPs; differences of cytokine release between family pediatricians of group A (n = 20) and group B (n = 33) (right panel). n.s. not significant. Means and SD are shown. Statistical analysis was performed as reported in the methods.