PROJECT SUMMARY It is well known that age-related changes in the immune system contribute to declines in the ability to mount a highly protective response following either infection or vaccination. While vaccination does improve the outcome of influenza (flu) infection in older adults, it is still foremost among all infectious diseases causing death and disability in this population. Importantly, aging impacts almost every aspect of the adaptive immune response to influenza including generation of virus-specific CD4 and CD8 T cell effectors, high affinity antibody production and generation of protective immune memory. One of the most prominent features of aging is the accumulation of senescent cells (SC) in various tissues and in this project, we will explore the role of SC in shaping the generation of protective immune memory following influenza infection. Cellular senescence is characterized by irreversible growth arrest that occurs when cells experience a stressor. Senescence has two main roles in an adult: one is to suppress cells that have incurred DNA or other damage to prevent them from transitioning into cancer, the other is to aid in wound healing. While SC are efficiently cleared by the immune system in young individuals, this is not the case as we get older. With chronological aging, the number of senescent cells increases, resulting in many age-related pathologies and diseases. In addition, factors secreted by senescent cells (the Senescence Associated Secretory Phenotype, SASP) can also have a direct impact on surrounding cells driving dysfunction and misdirected differentiation. In this project, we will use two experimental models to examine the impact of SC on the immune responses generated following an influenza infection, with a focus on generation of protective immune memory. The first is the p16-Trimodality Reporter (p16-3MR) transgenic mouse model developed in the Campisi lab and the second is the treatment of aged C57BL/6 mice with senolytics. Importantly, our preliminary studies have shown that eliminating SC in aged mice prior to flu infection has a negative impact on the generation of protective immune memory. The goal of this proposal is to further explore how deleting SC in aged mice impacts immunity and the transition from the effector phase to the generation of durable protective memory. This proposal has high translational significance as clinical trials for the senolytics for infectious diseases, such as COVID-19, are already underway and it is important to determine if this treatment could impair protective memory formation and leave at-risk older adults at risk for severe reinfection.