Kinetics of pro- and anti-inflammatory spike-specific cellular immune responses in long-term care facility residents after COVID-19 mRNA primary and booster vaccination: a prospective longitudinal study in Japan

Abstract

Background: The magnitude and durability of cell-mediated immunity in older and severely frail individuals following coronavirus disease 2019 (COVID-19) vaccination remain unclear. A controlled immune response could be the key to preventing severe COVID-19; however, it is uncertain whether vaccination induces an anti-inflammatory cellular immune response. To address these issues, a 48-week-long prospective longitudinal study was conducted. A total of 106 infection-naive participants (57 long-term care facility [LTCF] residents [median age; 89.0 years], 28 outpatients [median age; 72.0 years], and 21 healthcare workers [median age; 51.0 years]) provided peripheral blood mononuclear cell (PBMC) samples for the assessment of spike-specific PBMC responses before primary vaccination, 24 weeks after primary vaccination, and three months after booster vaccination. Cellular immune responses to severe acute respiratory syndrome coronavirus 2 spike protein were examined by measuring interferon (IFN)-γ, tumor necrosis factor (TNF), interleukin (IL)-2, IL-4, IL-6, and IL-10 levels secreted from the spike protein peptide-stimulated PBMCs of participants.

Results: LTCF residents exhibited significantly lower IFN-γ, TNF, IL-2, and IL-6 levels than healthcare workers after the primary vaccination. Booster vaccination increased IL-2 and IL-6 levels in LTCF residents comparable to those in healthcare workers, whereas IFN-γ and TNF levels in LTCF residents remained significantly lower than those in healthcare workers. IL-10 levels were not significantly different from the initial values after primary vaccination but increased significantly after booster vaccination in all subgroups. Multivariate analysis showed that age was negatively associated with IFN-γ, TNF, IL-2, and IL-6 levels but not with IL-10 levels. The levels of pro-inflammatory cytokines, including IFN-γ, TNF, IL-2, and IL-6, were positively correlated with humoral immune responses, whereas IL-10 levels were not.

Conclusions: Older and severely frail individuals may exhibit diminished spike-specific PBMC responses following COVID-19 vaccination compared to the general population. A single booster vaccination may not adequately enhance cell-mediated immunity in older and severely frail individuals to a level comparable to that in the general population. Furthermore, booster vaccination may induce not only a pro-inflammatory cellular immune response but also an anti-inflammatory cellular immune response, potentially mitigating detrimental hyperinflammation.

Keywords: COVID-19; Cell-mediated immunity; Frailty; IFN-γ; IL-10; Interleukin; Older adults; SARS-CoV-2; Vaccination.

Fig. 1

Kinetics of spike-specific peripheral blood mononuclear cell responses. Cellular immune responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein, as examined by measuring (a) interferon (IFN)-γ, (b) tumor necrosis factor (TNF), (c) interleukin (IL)-2, (d) IL-6, (e) IL-10, and (f) IL-4 secreted from the spike protein peptide-stimulated peripheral blood mononuclear cells of participants before and six months after the primary vaccination and three months after the booster vaccination. Participants are stratified into three subgroups: healthcare workers (HW), outpatients (OP), and residents of long-term care facilities (LTCF). Each dot represents an individual participant, and the lines indicate corresponding pairs. The levels of each cytokine are logarithmically transformed. Boxes span the interquartile range; the line within each box denotes the median, and the whiskers are the largest and smallest values within the range of ±1.5-fold in the interquartile range from the first and third quartiles. P values were determined using one-sample Wilcoxon test with Bonferroni correction for multiple comparisons. N.S.; not significant

Fig. 2

Comparison of the spike-specific peripheral blood mononuclear cell response among subgroups. Cellular immune responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein, as examined by measuring (a) interferon (IFN)-γ, (b) tumor necrosis factor (TNF), (c) interleukin (IL)-2, (d) IL-6, (e) IL-10, and (f) IL-4 secreted from the spike protein peptide-stimulated peripheral blood mononuclear cells of participants before and six months after the primary vaccination, and three months after the booster vaccination. Participants are stratified into three subgroups: healthcare workers (HW), outpatients (OP), and residents of long-term care facilities (LTCF). Each dot represents the individual participant. The levels of each cytokine were logarithmically transformed into a plot. Boxes span the interquartile range; the line within each box denotes the median, and the whiskers are the largest and smallest values within the range of ±1.5-fold in the interquartile range from the first and third quartile. Between-group differences were tested pairwise using Dunn’s test for multiple comparisons. P values are indicated for each plot. N.A.; not applicable

Fig. 3

Correlations between age and IFN-γ, TNF, IL-2, IL-6, and IL-10 levels. The upper and lower rows show the correlations six months after primary vaccination and three months after booster vaccination, respectively. rS: Spearman rank correlation coefficient. Values of rS are shown in bold when P values are less than 0.05: * P<0.05, ** P<0.01, and *** P<0.001. The levels of each cytokine are logarithmically transformed. The 90% confidence ellipse region was drawn assuming a near-Gaussian distribution of the values

Fig. 4

Correlations between cytokine levels and humoral immune responses. Correlations between cytokine levels [interferon (IFN)-γ, tumor necrosis factor (TNF), interleukin (IL)-2, IL-6, and IL-10], serum antibodies to the receptor-binding domain (RBD) of the S1 subunit of the viral spike protein [IgG(S-RBD)] levels, and neutralizing antibody activity of sera against the wild-type virus and Delta and Omicron variants (a) six months after primary vaccination and (b) three months after booster vaccination. rS: Spearman rank correlation coefficient. Values of rS are shown in bold when P values are less than 0.05: * P<0.05, ** P<0.01, and *** P<0.001. The levels of each cytokine are logarithmically transformed. The 90% confidence ellipse region was drawn assuming a near-Gaussian distribution of the values

Fig. 5

Correlations between interferon (IFN)-γ, tumor necrosis factor (TNF), interleukin (IL)-2, IL-6, and IL-10 levels. Correlations between IFN-γ, TNF, IL-2, IL-6, and IL-10 levels at (a) six months after primary vaccination and (b) three months after booster vaccination. rS: Spearman rank correlation coefficient. Values of rS are shown in bold when P values are less than 0.05: * P<0.05, ** P<0.01, and *** P<0.001. The levels of each cytokine are logarithmically transformed. The 90% confidence ellipse region was drawn assuming a near-Gaussian distribution of the values