Impaired Functional T-Cell Response to SARS-CoV-2 After Two Doses of BNT162b2 mRNA Vaccine in Older People

Abstract

Long-term care facility (LTCF) older residents display physiological alterations of cellular and humoral immunity that affect vaccine responses. Preliminary reports suggested a low early postvaccination antibody response against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The aim of this study was to focus on the specific T-cell response. We quantified S1-specific IgG, neutralizing antibody titers, total specific IFNγ-secreting T cells by ELISpot, and functionality of CD4⁺- and CD8⁺-specific T cells by flow cytometry, after two doses of the BNT162b2 vaccine in younger and older people, with and without previous COVID-19 infection (hereafter referred to as COVID-19-recovered and COVID-19-naive subjects, respectively). Frailty, nutritional, and immunosenescence parameters were collected at baseline in COVID-19-naive older people. We analyzed the immune response in 129 young adults (median age 44.0 years) and 105 older residents living in a LCTF (median age 86.5 years), 3 months after the first injection. Humoral and cellular memory responses were dramatically impaired in the COVID-19-naive older (n = 54) compared with the COVID-19-naive younger adults (n = 121). Notably, older participants' neutralizing antibodies were 10 times lower than the younger's antibody titers (p < 0.0001) and LCTF residents also had an impaired functional T-cell response: the frequencies of IFNγ⁺ and IFNγ⁺IL-2⁺TNFα⁺ cells among specific CD4⁺ T cells, and the frequency of specific CD8⁺ T cells were lower in COVID-19-naive older participants than in COVID-19-naive young adults (p < 0.0001 and p = 0.0018, respectively). However, COVID-19-recovered older participants (n = 51) had greater antibody and T-cell responses, including IFNγ⁺ and IFNγ⁺IL-2⁺TNFα⁺-specific CD4⁺ T cells (p < 0.0001), as well as TNFα⁺-specific CD8⁺ T cells (p < 0.001), than COVID-19-naive older adults. We also observed that "inflammageing" and particularly high plasma levels of TNFα was associated to poor antibody response in the older participants. In conclusion, our results show that the COVID-19-naive older people had low counts and impaired specific CD4⁺ and CD8⁺ T cells, in addition to impaired antibody response, and that specific studies are warranted to assess the efficiency of SARS-CoV-2 mRNA-based vaccines, as in other immunocompromised subjects. Our study also shows that, despite their physiological alterations of immunity, vaccination is highly efficient in boosting the prior natural memory response in COVID-19-recovered older people.

Keywords: SARS – CoV – 2; T cells response; mRNA vaccination; older people and ageing; vaccine.

Figure 1

Flow chart of the study.

Figure 2

Specific antibody and T-cell responses in older and in young adults before (D0) and 3 months (D90) after the first injection of BNT162b2. (A) Anti-S1 IgG, (B) serum neutralization assay against live virus, and (C) S1-reactive T cells (ELISpot) in COVID-19-naïve and in COVID-19-recovered participants. Wilcoxon matched-pairs signed rank test was used for paired comparisons. ^* p-values < 0.05; ^** p-values < 0.01; ^**** p-values < 0.0001. CTL, IFNγ SFCs, interferon gamma spot-forming cells.

Figure 3

Specific antibody and T-cell responses in older and in young adults 3 months after the first injection of BNT162b2. (A) Antibody responses assessed by ELISA (anti-S1 IgG) (COVID-19-naive younger n = 121, COVID-19-naive older n = 54, COVID-19-recovered young n = 8, COVID-19-recovered older n = 47; median [interquartile range (IQR)] are shown). (B) Serum neutralization assay against live virus (COVID-19-naive young adults n = 101, COVID-19-naive older n = 52, COVID-19-recovered young n = 7, COVID-19-recovered older n = 51; geometric median and 95% confidence interval are shown). (C) Participants with detectable neutralizing antibodies according to live virus-neutralizing assay (titer ≥1:20). (D) Number of S1 peptide pool reactive T cells (ELISpot) (COVID-19-naive young adults n = 121, COVID-19-naive older n = 52, COVID-19-recovered young n = 8, COVID-19-recovered older n = 50; median [interquartile range (IQR)] are shown). (E) Correlations between age and main immune parameters of the postvaccinal response at 3 months in COVID-19-naive older and COVID-19-naive young adults. Values are Spearman’s rank correlation (r) coefficients. The number of pairs that were analyzed, p-values and 95% confidence intervals of significant correlations are detailed in Table 2 . ^** p-values <0.01; ^*** p-values < 0.001; ^**** p-values < 0.0001; ns, not significant. IFNγ SFCs, interferon gamma spot-forming cells; LV-NT50, 50% serum neutralization titer in live virus neutralization assay; pV-NT50, 50% serum neutralization titer in pseudovirus neutralization assay.

Figure 4

Gating strategy for flow cytometry analyses of CD4⁺ and CD8⁺ T cells after BNT162b vaccination. (A) Identification of activation induced markers (AIM⁺ cells). Briefly, “living CD3⁺ T cells” are identified as 7-aminoactinomycine D (7AAD)-negative and CD3-positive cells. Among this population, CD4⁺ and CD8⁺ T cells are selected according to CD4⁺ and CD8⁺ expression, respectively. AIM⁺ cells among CD4⁺ T cells are both CD154⁺ and CD69⁺. AIM⁺ cells among CD8⁺ T cells are both CD107a⁺ and CD69⁺. (B) Representative plots displaying IFNγ, IL-2, and TNFα expression among AIM⁺CD4⁺ and CD8⁺ T cells.

Figure 5

Specific CD4⁺ T-cell response in older and in young adults 3 months after the first injection of BNT162b2. (A) Specific CD4⁺ T cells according to activation-induced markers (AIM), reported with their stimulation index. (B) Percentage of AIM⁺CD4⁺ T cells among total CD4⁺ T cells in responders, i.e., participants with a stimulation index ≥2. (C) Pie charts representing the relative proportions of AIM⁺CD4⁺ T cells producing none (white), one (light grey), two (medium grey), or three cytokines (dark grey) out of INFγ, IL-2, and TNFα according to participant group and past history of COVID-19 (naive and recovered). (D) Proportion of AIM⁺CD4⁺ cells producing IFNγ, IL-2, TNFα, and proportion of IFNγ⁺IL-2⁺TNFα⁺ (triple⁺) CD4⁺ T cells according to participant group and past history of COVID-19 (naive and recovered). (COVID-19-naive young adults n = 113, COVID-19-naive older n = 48, COVID-19-recovered young n = 8, COVID-19-recovered older n = 41; median [interquartile range (IQR)] are shown). ^* p-values < 0.05; ^**** p-values < 0.0001; ns, not significant. AIM⁺, cell-expressing activation-induced markers.

Figure 6

Specific CD8⁺ T-cell response in older and in young adults 3 months after the first injection of BNT162b2. (A) Specific CD8⁺ T cells according to activation-induced markers (AIM), reported with their stimulation index. (B) Percentage of AIM⁺CD8⁺ T cells among total CD8⁺ T cells in responders, i.e., participants with a stimulation index ≥2. (C) Pie charts representing the relative proportions of AIM⁺CD8⁺ T cells producing none (white), one (light grey), two (medium grey), or three cytokines (dark grey) out of INFγ, IL-2, and TNFα according to participant group and past history of COVID-19 (naive and recovered). (D) Proportion of AIM⁺CD4⁺ cells producing IFNγ, IL-2, TNFα, and proportion of IFNγ⁺IL-2⁺TNFα⁺ (triple⁺) CD4⁺ T cells according to participant group and past history of COVID-19 (naive and recovered). (COVID-19-naive young adults n = 113, COVID-19-naive older n = 48, COVID-19-recovered young n = 8, COVID-19-recovered older n = 41; median [interquartile range (IQR)] are shown). ^* p-values < 0.05; ^** p-values < 0.01; ^*** p-values < 0.001; ^**** p-values < 0.0001; ns, not significant. AIM⁺, cell-expressing activation-induced markers.

Figure 7

Unsupervised analysis of CD4⁺ and CD8⁺ T-cell functionality in older participants using t-distributed stochastic neighbor embedding (t-SNE). AIM⁺CD4⁺ (A) and AIM⁺CD8⁺ (B) T cells from older participants were concatenated and subjected to unsupervised analysis using t-SNE; highlighted (z-dimension) are areas with IFNγ, IL-2, or TNFα cell expression in COVID-19-naive and COVID-19-recovered older adults. To be noted, the higher frequency of IFNγ⁺CD4⁺ T cells and of TNFα⁺CD8⁺ T cells in COVID-19-recovered older adults (arrows).

Figure 8

Correlations between plasma cytokines levels at baseline, and main immune parameters of the postvaccinal response at 3 months in COVID-19-naive older subjects. The values correspond to Spearman’s rank correlation (r) coefficients. Only two correlations were found to be significant, between TNFα levels and NT50 LV-NT (r (95% CI) −0.35 [−0.62; 0.007], p = 0.048, sample size n = 33) and between TNFα levels and NT50 pV-NT (r (95% CI) −0.34 [−0.60; 0.02], p = 0.034, sample size n = 38). AIM⁺, cell-expressing activation-induced markers; NT50 LV-NT assay, 50% serum neutralization titer in live virus neutralization assay; NT50 PV-NT assay, 50% serum neutralization titer in pseudovirus neutralization assay.