T cell/astrocyte fusions as a novel form of trained immunity to infection

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Abstract: Could fusion between two disparate cell types generate an unconventional memory of infection? Would this hybrid cell protect against tomorrow’s pandemics or promote neurodegeneration and cognitive decline? In virally infected mice, we serendipitously discovered the presence of long-lived cellular fusions between astrocytes, a major glial cell type in the central nervous system (CNS), and antiviral CD8+ T lymphocytes (T cells), which infiltrate the CNS following an upper airway infection. Remarkably, these T cell/astrocyte hybrids retain the cellular structure of an astrocyte but maintain gene expression only present in the T cell genome. While tissue- resident memory T cells are known to remain in the CNS after infection, T cell/astrocyte fusions represent an entirely novel cell fate that we consistently observe. This suggests that the transfer of genetic material from T cells could represent a widespread phenomenon associated with astrocyte reactivity. Histological studies of human brains have described hematopoietic fusions within the CNS, particularly in inflammatory settings, but the driving forces, mechanisms, and implications are unknown. Human pathogens, including those that cause upper respiratory infections (URI), directly infect or impact the CNS with symptoms ranging from mild inflammation to overt encephalitis and have been associated with cognitive changes and neurodegeneration, including “brain fog” associated with Influenza and Covid-19. These varying impacts on brain function are likely multifactorial but regional alterations in CNS gene expression are readily observed in animal models. We hypothesize that T cell/astrocyte hybrids represent a novel cell type possessing an engrained memory of inflammation that contributes to inflammatory and neurodegenerative processes. We will establish parameters that govern astrocyte and T cell hybrid formation and identify a core signature and biological consequences of infection-driven cell hybridization on inflammatory and immune processes.