Leveraging an ongoing longitudinal study of influenza vaccination to define immune signatures of response and risk of infection in older adults >75

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Project summary Seasonal influenza (“flu”) remains a serious public health threat with the highest burden of severe disease and complications affecting older adults, particularly those over age 75. In addition to vaccine itself, responses to vaccination and vaccine effectiveness in older adults are likely influenced by comorbidity (e.g., frailty), immune senescent remodeling (i.e., immunosenescence and inflammaging), repeated annual vaccination, intra-seasonal immune waning, and virus strain variations both in vaccine formula and in circulation. Since 2014, we have established a study cohort in community-dwelling older adults >75. The cohort has accumulated 815 person-seasons with comprehensive demographic, clinical, functional and laboratory data, as well as banked pre- and post-vaccination serum, plasma, and peripheral blood mononuclear cell (PBMC) samples. We also identified 15 breakthrough flu infection cases with banked post-infection serum, plasma and PBMC samples. Importantly, 20 subjects participated in all 7 seasons, 36 in 6 seasons, 31 in 5 seasons, 16 in 4 seasons, and 165 in 3 seasons or less. Here, we propose to leverage this unique cohort and employ cutting edge immunologic research tools to develop state-of-the-art “immune signatures” reflecting both general immune status (distribution and function of immune cell subsets through high-dimensional flow analysis and RNA-Seq; cytokine profiling) and influenza-specific immunity (breadth and depth of flu-specific T cell repertoire; distribution/function of homotypic/heterotypic anti-flu T cells through flow analysis and scRNA-Seq; deep serological profiling of strain-specific and cross-reactive flu antibodies). Our objective is to characterize immune signatures and their intra- and inter-seasonal changes over time as determinants of vaccine responses and risk of breakthrough infection in older adults >75. Our specific aims are: 1) Characterize seasonal baseline (pre-existing) immune signatures as determinants of vaccine response and how they change over time. We will not only determine inter-season longitudinal trajectory, but also identify specific baseline immune signatures predict responses to vaccination; 2) Characterize seasonal immune signature responses to vaccination as determinants of risk of breakthrough infection and how they change over time. We will evaluate and compare differences and similarities of immune signature responses elicited by vaccination vs natural infection to explore immune mechanisms of vulnerability; and 3) Characterize intra-seasonal waning of immune signature responses to vaccination and its change across seasons through monthly blood sampling until the end of each flu season across multiple seasons. Upon completion, the proposed studies will advance our understanding of immune signatures as key immunologic mechanisms for vaccine responses and risk of breakthrough infection in a typical geriatric population. Ultimately, these studies will help define correlates of protection and develop more effective immunization strategies including a universal vaccine for this highly vulnerable subset of older adults.