Persistent enteric murine norovirus infection is associated with functionally suboptimal virus-specific CD8 T cell responses

Norovirus (NV) gastroenteritis is a major contributor to global morbidity and mortality, yet little is known about immune mechanisms leading to NV control. Previous studies using the murine norovirus (MNV) model have established a key role for T cells in MNV clearance. Despite these advances, important questions remain regarding the magnitude, location, and dynamics of the MNV-specific T cell response. To address these questions, we identified MNV-specific major histocompatibility complex (MHC) class I immunodominant epitopes using an overlapping peptide screen. One of these epitopes (amino acids 519 to 527 of open reading frame 2 [ORF2(519-527)]) was highly conserved among all NV genogroups. Using MHC class I peptide tetramers, we tracked MNV-specific CD8 T cells in lymphoid and mucosal sites during infection with two MNV strains with distinct biological behaviors, the acutely cleared strain CW3 and the persistent strain CR6. Here, we show that enteric MNV infection elicited robust T cell responses primarily in the intestinal mucosa and that MNV-specific CD8 T cells dynamically regulated the expression of surface molecules associated with activation, differentiation, and homing. Furthermore, compared to MNV-CW3 infection, chronic infection with MNV-CR6 resulted in fewer and less-functional CD8 T cells, and this difference was evident as early as day 8 postinfection. Finally, MNV-specific CD8 T cells were capable of reducing the viral load in persistently infected Rag1(−/−) mice, suggesting that these cells are a crucial component of NV immunity. Collectively, these data provide fundamental new insights into the adaptive immune response to two closely related NV strains with distinct biological behaviors and bring us closer to understanding the correlates of protective antiviral immunity in the intestine

Vaccine-induced boosting of influenza virus-specific CD4 T cells in younger and aged humans.

Current yearly influenza virus vaccines induce strain-specific neutralizing antibody (NAb) responses providing protective immunity to closely matched viruses. However, these vaccines are often poorly effective in high-risk groups such as the elderly and challenges exist in predicting yearly or emerging pandemic influenza virus strains to include in the vaccines. Thus, there has been considerable emphasis on understanding broadly protective immunological mechanisms for influenza virus. Recent studies have implicated memory CD4 T cells in heterotypic immunity in animal models and in human challenge studies. Here we examined how influenza virus vaccination boosted CD4 T cell responses in younger versus aged humans. Our results demonstrate that while the magnitude of the vaccine-induced CD4 T cell response and number of subjects responding on day 7 did not differ between younger and aged subjects, fewer aged subjects had peak responses on day 14. While CD4 T cell responses were inefficiently boosted against NA, both HA and especially nucleocaspid protein- and matrix-(NP+M) specific responses were robustly boosted. Pre-existing CD4 T cell responses were associated with more robust responses to influenza virus NP+M, but not H1 or H3. Finally pre-existing strain-specific NAb decreased the boosting of CD4 T cell responses. Thus, accumulation of pre-existing influenza virus-specific immunity in the form of NAb and cross-reactive T cells to conserved virus proteins (e.g. NP and M) over a lifetime of exposure to infection and vaccination may influence vaccine-induced CD4 T cell responses in the aged

Genomic Circuitry Underlying Immunological Response to Pediatric Acute Respiratory Infection

Summary: Acute respiratory tract viral infections (ARTIs) cause significant morbidity and mortality. CD8 T cells are fundamental to host responses, but transcriptional alterations underlying anti-viral mechanisms and links to clinical characteristics remain unclear. CD8 T cell transcriptional circuitry in acutely ill pediatric patients with influenza-like illness was distinct for different viral pathogens. Although changes included expected upregulation of interferon-stimulated genes (ISGs), transcriptional downregulation was prominent upon exposure to innate immune signals in early IFV infection. Network analysis linked changes to severity of infection, asthma, sex, and age. An influenza pediatric signature (IPS) distinguished acute influenza from other ARTIs and outperformed other influenza prediction gene lists. The IPS allowed a deeper investigation of the connection between transcriptional alterations and clinical characteristics of acute illness, including age-based differences in circuits connecting the STAT1/2 pathway to ISGs. A CD8 T cell-focused systems immunology approach in pediatrics identified age-based alterations in ARTI host response pathways. : Henrickson et al. measure transcriptional alterations in blood CD8 T cells from pediatric patients with acute respiratory tract infections and correlate gene modules with clinical characteristics. This approach defines an influenza prediction signature that is effective across ages, revealing age-based alterations in genetic circuitry underlying host responses to influenza. Keywords: influenza, gene expression, rhinovirus, human immunology, CD8 T cel

Influence of pre-existing influenza virus-specific CD4 T cells on TIV response.

<p>Representative flow cytometry plots of subjects without (top) or with (bottom) significant day 0 positive responses are shown (percent of responding CD4 T cells is indicated) (<b>A</b>). Pooled data summarize day 0 influenza virus-specific CD4 T cells for each viral protein in young (black) or aged (red) subjects (<b>B</b>). Dotted line indicated the limit of detection based on background (no stim control). Graphs of H1 responses over time after TIV in young (left) or aged (right) subjects with no day 0 influenza virus-specific CD4 T cells (green) or positive day 0 responses (blue) (limit of detection marked by dotted line) (<b>C</b>). Summary data with mean and standard error of CD4 TIV response in combined young and aged subjects with no day 0 influenza virus-specific CD4 T cells (green) or positive day 0 responses (blue) for each influenza virus protein (ANOVA) (<b>D</b>).</p

CD4 T cell response kinetics after TIV.

<p>(<b>A</b> and <b>B</b>) Vaccine-induced responses were defined as an increase in cytokine production compared to the d0 response and were examined over time for each subject. Representative flow cytometry plots (<b>A</b>) and kinetic graphs (<b>B</b>) show changes in cytokine production over time after vaccination. Examples of responses to H1 from young and aged are shown illustrating gating and changing percent of responding CD4 T cells over time (<b>A</b>). The numbers in <b>A</b> indicate the percent of CD4 T cells making IFNγ and/or TNFα. Line graphs for multiple subjects demonstrate the range and kinetics for multiple young (black) and aged (red) subjects (<b>B</b>). Summarized data for young (black) and aged (red) show the mean and standard error for responses to each protein over time (<b>C</b>). The number of subjects peaking on day 7 versus day 14 was compared between young (black bars) and aged (red bars) subjects for responses to H1, H3, or NP+M (D). Statistical testing was performed using the Fisher’s exact Chi-squared. Summary data for IL-2 production to each peptide pool is shown for young (black) and aged (red) (Mann-Whitney) (<b>E</b>). Differentiation phenotype (CD27+CD45RA- on left or PD-1+ on right) of influenza virus-specific CD4 T cells peaking on day 7 or day 14 post-TIV for individual influenza proteins (<b>F</b>). For this analysis young and aged subjects were combined to test whether CD4 T cell responses peaking on day 7 differed from those peaking on day 14. Separate analysis of expression of PD-1 on influenza virus-specific CD4 T cells from young (black symbols) versus aged (red symbols) subjects was performed on day 7 post-TIV (Mann-Whitney) (<b>G</b>).</p

Effect of pre-existing NAb on TIV CD4 responses.

<p>Day 0 NAb titers are shown for H1N1 (left) or H3N2 (right) in young (open symbols) or aged (closed symbols) subjects (<b>A</b>). Kinetics of CD4 T cell responses in young (left) or aged (right) to H1 (top) or H3 (bottom) in relation to presence or absence of day 0 NAb to H1 (black), H3 (blue) both H1 and H3 (green), or neither strain (red) (<b>B</b>). Magnitude of CD4 T cell responses combining data for young and aged subjects to H1 (left), H3 (center), or NP+M (right) for subjects with (red) or without (black) day 0 NAb titers (ANOVA) (<b>C</b>). Correlation of NAb to H3N2 (x axis) versus peak anti-influenza virus H3 CD4 T cell response (y axis) is shown for all subjects (young - open circles; aged - closed circles) (<b>D</b>).</p