Neurotropic viral infections induce priming and maintenance of a novel antigen-specific CD8 T cell population within the bone marrow that dysregulates the stem cell niche upon reactivation

Bone marrow (BM) is the primary immune organ responsible for stem cell maintenance. Neurotropic infections elicit sequestration of T cells within the BM. Changes of the BM niche during brain viral infections are unknown. Intracranial infection with the neurotropic Theiler’s Murine Encephalomyelitis Virus (TMEV) in C57BL/6 mouse is cleared by 30 days due to generation of an antigen-specific CD8 T cell response. We determined that 1-10% of CD8 T cells present in the sternal, femoral, and cranial BM were virus antigen-specific 7 days post intracranial infection. Over 70% of these CD8 T cells were tissue resident. We determined antigen-specific CD8 T cells were generated in the BM within 4 days of infection, a timeline similar to lymph nodes. Continuous treatment with FTY720, which sequesters T cells outside of the blood, did not eliminate antigen-specific CD8 T cells in any BM compartment. CD8 T cells in the BM established durable memory populations and were reactivated upon antigen reencounter. Both acute infection and reactivation caused an increase in lineage^-, Sca-1⁺, ckit⁺ (LSK) cells in the BM. This LSK dysregulation was abrogated upon CD8 T cell depletion and was limited to the intracranial routes of infection. We conclude that brain viral infections induce in situ effector and memory T cell responses within the BM and cause stem cell dysregulation. Our data paves the way for crucial studies of BM resident antigen-specific CD8 T cells in health and disease.