Varicella-Zoster Virus-Specific Cellular Immune Responses to the Live Attenuated Zoster Vaccine in Young and Older Adults

Abstract

The incidence and severity of herpes zoster (HZ) increases with age. The live attenuated zoster vaccine generates immune responses similar to HZ. We compared the immune responses to zoster vaccine in young and older to adults to increase our understanding of the immune characteristics that may contribute to the increased susceptibility to HZ in older adults. Young (25-40 y; n = 25) and older (60-80 y; n = 33) adults had similar magnitude memory responses to varicella-zoster virus (VZV) ex vivo restimulation measured by responder cell-frequency and flow cytometry, but the responses were delayed in older compared with young adults. Only young adults had an increase in dual-function VZV-specific CD4⁺ and CD8⁺ T cell effectors defined by coexpression of IFN-γ, IL-2, and CD107a after vaccination. In contrast, older adults showed marginal increases in VZV-specific CD8⁺CD57⁺ senescent T cells after vaccination, which were already higher than those of young adults before vaccination. An increase in VZV-stimulated CD4⁺CD69⁺CD57⁺PD1⁺ and CD8⁺CD69⁺CD57⁺PD1⁺ T cells from baseline to postvaccination was associated with concurrent decreased VZV-memory and CD8⁺ effector responses, respectively, in older adults. Blocking the PD1 pathway during ex vivo VZV restimulation increased the CD4⁺ and CD8⁺ proliferation, but not the effector cytokine production, which modestly increased with TIM-3 blockade. We conclude that high proportions of senescent and exhausted VZV-specific T cells in the older adults contribute to their poor effector responses to a VZV challenge. This may underlie their inability to contain VZV reactivation and prevent the development of HZ.

Figure 1. VZV-specific memory responses after ZV administration to young and older adults

The bars represent medians and upper quartiles of measurements from 25 young and 33 older recipients of ZV. Memory responses were measured by RCF (panel A) and flow cytometry (panel B) at the indicated time points. Asterisks indicate significant and changes from baseline (p < 0.05) within each age group. Hash tags indicate significant differences between groups. The gating strategy used for panel 1B is shown in Supplemental Figure 2A.

Figure 2. VZV-specific Effector CD4 (A) and CD8 (B) Responses to ZV in Young (Left) and Older Adults (Right)

The data were derived from 25 young and 33 older adults whose PBMC were ex vivo restimulated with live VZV and mock-infected control. The data show expression of IFNγ, IL2 and CD107a measured by flow cytometry after subtraction of background. The bars show the mean% of the T cell subsets expressing the number of markers (variables) indicated on the x axis at the time points indicated in the legend. Marginal and significant differences are highlighted by crosses above the bars. The tables show p values for changes at the times indicated in the column headings compared with D0 in each T cell subsets grouped by the number of expressed markers (category). Young adults showed increases of dual function VZV-effectors at D7, which were marginal for CD4 (p=0.08) and significant for CD8 effectors (p=0.008), whereas older adults showed a marginal decrease in single function CD8 effectors at D30 (p=0.05).

Figure 3. VZV-specific Exhausted and Senescent CD8 T cells in Young and Older Adults

The data were derived from 25 young and 33 older adults whose PBMC were ex vivo restimulated with live VZV and mock-infected control. The data show expression of PD1 and CD57 on CD69+ T cells measured by flow cytometry in VZV-restimulated PBMC after subtraction of background control. Panel A: Pies show the distribution of CD8+ T cells expressing both PD1 and CD57 (red slices), only CD57 (teal slices), only PD1 (green slices), neither PD1 nor CD57 (blue slices) at D0 in young (left) and older adults (right). The light green arc indicates total CD57 and the red arc total PD1. The table shows that the distributions were significantly different (p=0.03) between young and older adults. Panel B: Bars show mean and SEM of the VZV-specific CD8+CD69+PD1+% (left graph) and CD8+CD69+CD57+% (right graph) at each visit in young and older adults. The horizontal continuous lines indicate significant differences between young and older adults; dotted lines indicate marginal differences. Asterisk indicates a marginal increase compared to D0 in senescent VZV-specific CD8+ T cells in older adults (p=0.06).

Figure 4. Increases of VZV-Specific CD4+ or CD8+ T Cells Expressing both CD57 and PD1 Correlate with Decreases in RCF (Left) and CD8+ CTL (Right), Respectively, in Older Adults

Data were derived from 33 older adults. Peak response for RCF memory was D30 and for CD8+IFNγ+CD107a effector was D7. P values and coefficients of correlation calculated by Pearson correlation analyses are shown on each graph. The gating strategy used for the flow cytometry data is shown in Supplemental Figure 2B.

Figure 5. Increased ex-vivo VZV-specific proliferation of PBMC from older adults by blockade of the PD1 pathway

Panel A shows the gating strategy in a sample with a response to anti-PDL1. Data in panel B used PBMC collected from 11 older adults at 7 to 14 days after vaccination. Dots represent results of each participant. Bars and whiskers indicate medians and lower and upper quartiles of the composite results, which did not have a normal distribution. Stimulation conditions are listed under each bar: mock=mock-stimulated background control; aPDL1= anti-PDL1; VZV= VZV-stimulated. P values calculated by Wilcoxon matched-pairs signed rank test showed significant increases both in CD4+ and CD8+ VZV-specific T cell proliferation after addition of anti-PDL1.

Figure 6. Effect of Inhibitory Pathway Blockades on VZV-Specific Effector T-Cell Responses in Older Adults

Data were derived from PBMC collected from 11 older adults at 14 days after ZV administration. Panel A shows the gating strategy for CD8+IFNγ+ T cells. In Panel B the dots indicate the values of each of the 11 participants and the bars indicate means and SEM of the composite results, which had a normal distribution. P values were calculated by paired Student’s T-test