Cellular immune responses in children and adults receiving inactivated or live attenuated influenza vaccines

Abstract

The patterns of cellular immune responses induced by live attenuated influenza vaccine (LAIV) versus those of the trivalent inactivated influenza vaccine (TIV) have not been studied extensively, especially in children. The goals of this study were to evaluate the effects of TIV and LAIV immunization on cellular immunity to live influenza A virus in children and adults and to explore factors associated with variations in responses to influenza vaccines among individuals. A gamma interferon (IFN-gamma) flow cytometry assay was used to measure IFN-gamma-producing (IFN-gamma+) NK and T cells in peripheral blood mononuclear cell cultures stimulated with a live influenza A virus strain before and after LAIV or TIV immunization of children and adults. The mean percentages of influenza A virus-specific IFN-gamma+ CD4 and CD8 T cells increased significantly after LAIV, but not TIV, immunization in children aged 5 to 9 years. No increases in the mean levels of influenza A virus-reactive IFN-gamma+ T cells and NK cells were observed in adults given LAIV or TIV. TIV induced a significant increase in influenza A virus-reactive T cells in 6-month- to 4-year-old children; LAIV was not evaluated in this age group. The postvaccination changes (n-fold) in the percentages of influenza A virus-reactive IFN-gamma+ T and NK cells in adults were highly variable and correlated inversely with the prevaccination percentages, in particular with that of the CD56(dim) NK cell subset. In conclusion, our findings identify age, type of vaccine, and prevaccination levels of immune reactivity to influenza A virus as factors significantly associated with the magnitude of cellular immune responses to influenza vaccines.

Figures

FIG. 1.

Percentages of IFN-γ+ cells in CD4 and CD8 T cells and CD56bright and CD56dim NK cells at day 0 (d0; baseline), day 10 (d10), and day 28 (d28) after immunization with TIV or LAIV in children aged 5 to 9 years and adults. The bars denote the GMP of IFN-γ+ cells as estimated by GEE regression analysis. The criteria for statistical significance were adjusted across all four cell subsets within each vaccine and age group to control the type I error rate at 5% across these multiple comparisons. **, result that remained statistically significant after the adjustment; *, result with a P value of <0.05 in an individual test but that became nonsignificant after the adjustment.

FIG. 2.

Differences in LAIV- versus TIV-induced changes (n-fold) in IFN-γ+ CD4 and CD8 T cells in children aged 5 to 9 years. The height of each bar denotes the estimated change (n-fold; days 0 to 10 or days 0 to 28, as indicated) in the GMP (plus 1 standard error). The estimates and P values were from GEE regression analysis. FC, change (n-fold).

FIG. 3.

Differences in the change (n-fold) in GMP for IFN-γ+ CD4 and CD8 T cells after immunization with one dose of LAIV in children aged 5 to 9 years versus adults. The height of each bar denotes the estimated change (n-fold; days 0 to 10 or days 0 to 28, as indicated) in the GMP (plus 1 standard error). The estimates and P values were from GEE regression analysis. FC, change (n-fold).

FIG. 4.

NK cell and T-cell responses to TIV in children aged 6 months to 4 years. (A) Percentages of IFN-γ+ cells in the NK and T-cell subsets measured at baseline (d0; n = 24) before the first dose of TIV was given and at day 10 (range, 9 to 11) after dose 1 (n = 7) or dose 2 (n = 10) of TIV, which was given approximately 28 days after the first dose. The GMP of IFN-γ+ cells before and after each dose of TIV were compared via GEE regression analysis. The criteria for statistical significance were adjusted across all four cell subsets to control the type I error rate at 5% across these multiple comparisons. **, result that remained statistically significant after the adjustment; *, result with a P value of <0.05 in an individual test but that became nonsignificant after the adjustment. (B) Comparison of T-cell or NK cell responses at day 10 after dose 1 versus day 10 after dose 2 of TIV. The estimated changes (n-fold) in the GMP of IFN-γ+ cells (plus 1 standard error) were compared via GEE regression analysis. *, result with a P value of <0.05 in an individual test but that became nonsignificant after adjustment for multiple comparisons. FC, change (n-fold).

FIG. 5.

Association between age and T- and NK cell responses to TIV. Child and adult subjects in all three age groups receiving TIV were pooled for this analysis, consisting of children aged 6 months to 4 years (n = 24 at day 0; n = 7 at day 10), children aged 5 to 9 years (n = 17 at day 0; n = 20 at day 10), and adults (n = 21 at day 0; n = 23 at day 10). The base 10 logarithms of the percentages of IFN-γ+ cells in each of the cell subsets at day 0 (d0; baseline) and day 10 (d10) after the first dose of TIV were regressed on age using GEE. The GMP of IFN-γ+ cells was estimated from the regression fit at the median age for each of the three groups: 3, 7, and 30 years. (A) Fitted GEE regression model (lines) and raw data (symbols) for CD4 T cells. (B) Estimated baseline GMP (plus 1 standard error) of IFN-γ+ cells in each lymphocyte subset for the three median ages. (C) Estimated change (n-fold; day 0 to day 10) in the GMP of IFN-γ+ cells in each lymphocyte subset for the three median ages. P values are provided for comparisons of baseline GMP (panel B) or change (n-fold) in the GMP (panel C) between adjacent median ages. The criteria for statistical significance were adjusted across all four cell subsets to control the type I error rate at 5% across these multiple comparisons. **, result that remained statistically significant after the adjustment; *, result with a P value of <0.05 in an individual test but that became nonsignificant after the adjustment. FC, change (n-fold).

FIG. 6.

Associations between baseline percentages of IFN-γ+ cells and changes (n-fold) in the percentages after influenza vaccination. All subjects with data available for day 0 (baseline) and day 10 were included. (A) Scatter plots for the change (n-fold) in IFN-γ+ CD4 T cells versus baseline percentages of IFN-γ+ cells in CD4 and CD8 T-cell subsets and CD56bright and CD56dim NK cell subsets in adult and child (5- to 9-year-old) groups receiving LAIV or TIV. For reference, the dotted lines indicate a change (n-fold) of 1. (B) Complete list of estimated Spearman correlation coefficients, rS, for change (n-fold) versus the baseline level of IFN-γ+ cells in all lymphocyte subsets. The criteria for statistical significance were adjusted across four cell subsets within each vaccine/age group to control the type I error rate at 5% across the 16 multiple comparisons. **, result that remained statistically significant after the adjustment; *, result with a P value of <0.05 in an individual test but that became nonsignificant after the adjustment. The average rS was calculated across the change for four lymphocyte subsets versus the baseline percentage of each cell type in each age/vaccine group. FC, change (n-fold).

FIG. 7.

Estimated partial correlation coefficients for change (n-fold) versus baseline levels of IFN-γ+ cells, with the baseline level of each other lymphocyte subset held constant. The partial correlation coefficients (47) were calculated using the rS between the change (n-fold) in IFN-γ+ cells and the baseline percentage of IFN-γ+ cells (Fig. 6B) and the rS between the baseline percentage of IFN-γ+ cells in each cell subset. FC, change (n-fold).