Namen, Shelby

Abstract The contribution of antiviral resident memory T cells (TRM) to blood-brain barrier disruption has not been defined despite the implication of this lymphocyte in clinical encephalitis. We therefore evaluated the capacity of TRM cells to induce CNS vascular permeability in mice which resolved Theiler’s murine encephalomyelitis (TMEV) infection. Following TMEV infection of the brain, persistent populations of virus antigen specific resident memory T cells are induced within the brain. This population of resident memory T cells can be further reactivated at 60 dpi through administration of the cognate immunodominant virus peptide antigen, VP2, inducing blood brain barrier disruption in the process. We determined that brain resident memory T cells expand following reactivation with administered VP2 peptide. This reactivation is associated with infiltration of T cells, and inflammatory myeloid cells into the brain. Importantly, using depletion and T cell sequestrating strategies with low dose anti CD8 antibodies and FTY720, we determined that TRM induced blood-brain barrier disruption is independent of peripheral T cells. We conclude that reactivation of brain TRM cells during peptide administration occurs without dependency on peripheral responses, highlighting the importance of this cell type in inducing neuroinflammation and underlying neuropathology.

Abstract Brain resident memory T cells (TRM) have recently been phenotypically characterized. However, the function of these cells in the brain, and their changes during neurological insults, is not well understood. Using the described phenotype of brain TRMs (TCRB+, CD69+, CD4 or CD8+, CD103−, CD44+), we evaluated cellular responses of this population in the naïve brain and upon various neurological insults. We found that numbers of brain TRMs increased as a function of age. Additionally, TRM cells in the naïve brain produce TNFα constitutively, setting them apart from TRMs in other organs. Parabiosis studies revealed that circulating pools of memory T cells contributes to maintenance of TRM cells in the naïve brain. During neurological injury, we observed an increase in numbers of TRMs as early as 24 hours following physical insult induced by intracranial injection of PBS. During brain infection with Theiler’s Murine Encephalomyelitis virus, brain TRMs increased in number prior to detection of any virus-specific CD8 T cells. This implies TRMs respond to CNS viral infections prior to generation of virus antigen specific responses. This response is due to proliferation of TRM cells in the brain, as treatment with FTY720 did not inhibit TRM proliferation 24 hours post infection. In short, naïve brains harbor populations of TNFα producing TRM cells. And TRMs rapidly respond to neurological injuries through proliferation in an antigen independent manner. Understanding brain TRMs is crucial in investigating their role in neurodegenerative disorders or targeting this potent population of brain resident T cells in cancers of the CNS.

Abstract Brain tissue resident memory T cells (TRM) are an emerging lymphocyte of interest. While the phenotype and gene expression pattern of brain TRMs have recently been discussed, their function and response to neurologic insults is not yet understood. Using the described phenotype of TRMs (TCRB+, CD69+, CD4 or CD8+, CD103−, CD44+), we analyzed the reaction of this lymphocyte in the brain to various neurological insults. We found that physical insult induced by an intracranial(ic) injection of PBS resulted in increased TRM numbers within 24 hours post insult. This TRM population later decreased yet remained above baseline by 50 days post insult. Interestingly, TRM populations also increased in the brains of animals as a function of age, suggesting natural insults experienced by mice leads to an ever increasing TRM population in the brain. We then assessed the reaction of TRMs to virus in the brain. Mice infected ic with Theiler’s Murine Encephalomyelitis virus (TMEV) had a marked increase in brain TRMs one day later, which is 4 days prior to detection of traditional TMEV antigenspecific CD8 T cells. This implies TRMs respond to CNS viral infections prior to generation of virus antigen specific responses. Finally, we investigated the role of dendritic cell (DC) antigen presentation in generation of TRMs using our novel MHC class I conditional knockout mice. Conditional ablation of H-2Kb and H-2Db did not disrupt TRM populations in the brain. Our data is the first study to show: 1. Activation of TRMs in the brain preceded antigen specific cell infiltration and 2. MHC class I molecules on DCs are not required to generate brain resident TRMS. Understanding brain TRMs is crucial in elucidating their role in neurodegeneration and/or targeting them in CNS cancers.