The role of CD4 T cell help in primary and secondary CD8 T cell responses to infectious pathogens remains incompletely defined. The primary CD8 T response to infections was initially thought to be largely independent of CD4 T cells, but it is not clear why some primary, pathogen-specific CD8 T cell responses are CD4 T cell dependent. Furthermore, although the generation of functional memory CD8 T cells is CD4 T cell help dependent, it remains controversial when the “help” is needed. In this study, we demonstrated that CD4 T cell help was not needed for the activation and effector differentiation of CD8 T cells during the primary response to vaccinia virus infection. However, the activated CD8 T cells showed poor survival without CD4 T cell help, leading to a reduction in clonal expansion and a diminished, but stable CD8 memory pool. In addition, we observed that CD4 T cell help provided during both the primary and secondary responses was required for the survival of memory CD8 T cells during recall expansion. Our study indicates that CD4 T cells play a crucial role in multiple stages of CD8 T cell response to vaccinia virus infection and may help to design effective vaccine strategies.
CD4 T cell help plays an important role in promoting CD8 T cell immunity to pathogens. In models of infection with vaccinia virus (VV) and Listeria monocytogenes, CD4 T cell help is critical for the survival of activated CD8 T cells during both the primary and memory recall responses. Still unclear, however, is how CD4 T cell help promotes CD8 T cell survival. In this study, we first showed that CD4 T cell help for the CD8 T cell response to VV infection was mediated by IL-21, a cytokine produced predominantly by activated CD4 T cells, and that direct action of IL-21 on CD8 T cells was critical for the VV-specific CD8 T cell response in vivo. We next demonstrated that this intrinsic IL-21 signaling was essential for the survival of activated CD8 T cells and the generation of long-lived memory cells. We further revealed that IL-21 promoted CD8 T cell survival in a mechanism dependent on activation of the STAT1 and STAT3 pathways and subsequent upregulation of the prosurvival molecules Bcl-2 and Bcl-xL. These results identify a critical role for intrinsic IL-21 signaling in CD8 T cell responses to an acute viral infection in vivo and may help design effective vaccine strategies.
Background: In the United States, meningococcal serogroup B (MenB) vaccination is recommended for 16-23-year-olds based on shared clinical decision-making. We estimated series completion among individuals initiating MenB vaccination for the 2 available vaccines: MenB 4-component (MenB-4C, doses at 0 and ≥1 month) and MenB factor H binding protein (MenB-FHbp, doses at 0 and 6 months). Methods: This retrospective health insurance claims data analysis included 16-23-year-olds who initiated MenB vaccination (index date) during January 2017 to November 2018 (MarketScan Commercial Claims and Encounters Database) or January 2017 to September 2018 (MarketScan Multi-State Medicaid Database) and had continuous enrollment for ≥6 months before and ≥15 months after index. The main outcome was MenB vaccine series completion within 15 months. Among noncompleters, preventive care/wellchild and vaccine administrative office visits were identified as potential missed opportunities for series completion. Robust Poisson regression models identified independent predictors of series completion. Results: In the Commercial (n = 156,080) and Medicaid (n = 57,082) populations, series completion was 56.7% and 44.7%, respectively, and was higher among those who initiated MenB-4C versus MenB-FHbp (61.1% versus 49.8% and 47.8% versus 33.9%, respectively; both P < 0.001). Among noncompleters, 40.2% and 34.7% of the Commercial and Medicaid populations, respectively, had ≥1 missed opportunity for series completion. Receipt of MenB-4C and younger age were independently associated with a higher probability of series completion. Conclusions: Series completion rates were suboptimal but were higher among those who initiated MenB-4C. To maximize the benefits of MenB vaccination, interventions to improve completion and reduce missed opportunities should be implemented.
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