Chronic SIV-Induced neuroinflammation disrupts CCR7+ CD4+ T cell immunosurveillance in the rhesus macaque brain.

CD4+ T cells survey and maintain immune homeostasis in the brain, yet their differentiation states and functional capabilities remain unclear. Our approach, combining single-cell transcriptomic analysis, ATAC-Seq, spatial transcriptomics, and flow cytometry, revealed a distinct subset of CCR7+ CD4+ T cells resembling lymph node central memory (TCM) cells. We observed chromatin accessibility at the CCR7, CD28, and BCL-6 loci, defining molecular features of TCM. Brain CCR7+ CD4+ T cells exhibited recall proliferation and interleukin-2 production ex vivo, showcasing their functional competence. We identified the skull bone marrow as a local niche for these cells alongside CNS border tissues. Sequestering TCM cells in lymph nodes using FTY720 led to reduced CCR7+ CD4+ T cell frequencies in the cerebrospinal fluid, accompanied by increased monocyte levels and soluble markers indicating immune activation. In macaques chronically infected with SIVCL757 and experiencing viral rebound due to cessation of antiretroviral therapy, a decrease in brain CCR7+ CD4+ T cells was observed, along with increased microglial activation and initiation of neurodegenerative pathways. Our findings highlight a role for CCR7+ CD4+ T cells in CNS immune surveillance, and their decline during chronic SIV highlights their responsiveness to neuroinflammation.

CCR7+ CD4 T Cell Immunosurveillance Disrupted in Chronic SIV-Induced Neuroinflammation in Rhesus Brain.

CD4 T cells survey and maintain immune homeostasis in the brain, yet their differentiation states and functional capabilities remain unclear. Our approach, combining single-cell transcriptomic analysis, ATAC-seq, spatial transcriptomics, and flow cytometry, revealed a distinct subset of CCR7+ CD4 T cells resembling lymph node central memory (T CM ) cells. We observed chromatin accessibility at the CCR7, CD28, and BCL-6 loci, defining molecular features of T CM . Brain CCR7+ CD4 T cells exhibited recall proliferation and interleukin-2 production ex vivo, showcasing their functional competence. We identified the skull bone marrow as a local niche for these cells alongside other CNS border tissues. Sequestering T CM cells in lymph nodes using FTY720 led to reduced CCR7+ CD4 T cell frequencies in the cerebrospinal fluid, accompanied by increased monocyte levels and soluble markers indicating immune activation. In macaques chronically infected with SIVCL57 and experiencing viral rebound due to cessation of antiretroviral therapy, a decrease in brain CCR7+ CD4 T cells was observed, along with increased microglial activation and initiation of neurodegenerative pathways. Our findings highlight a role for CCR7+ CD4 T cells in CNS immune surveillance and their decline during chronic SIV-induced neuroinflammation highlights their responsiveness to neuroinflammatory processes. In Brief: Utilizing single-cell and spatial transcriptomics on adult rhesus brain, we uncover a unique CCR7+ CD4 T cell subset resembling central memory T cells (T CM ) within brain and border tissues, including skull bone marrow. Our findings show decreased frequencies of this subset during SIV- induced chronic neuroinflammation, emphasizing responsiveness of CCR7+ CD4 T cells to CNS disruptions. Highlights: CCR7+ CD4 T cells survey border and parenchymal CNS compartments during homeostasis; reduced presence of CCR7+ CD4 T cells in cerebrospinal fluid leads to immune activation, implying a role in neuroimmune homeostasis. CNS CCR7+ CD4 T cells exhibit phenotypic and functional features of central memory T cells (T CM ) including production of interleukin 2 and the capacity for rapid recall proliferation. Furthermore, CCR7+ CD4 T cells reside in the skull bone marrow. CCR7+ CD4 T cells are markedly decreased within the brain parenchyma during chronic viral neuroinflammation.

Pseudouridylation of Epstein-Barr virus noncoding RNA EBER2 facilitates lytic replication.

Epstein-Barr virus (EBV) expresses two highly abundant noncoding RNAs called EBV-encoded RNA 1 (EBER1) and EBER2, which are preserved in all clinical isolates of EBV, thus underscoring their essential function in the viral life cycle. Recent epitranscriptomics studies have uncovered a vast array of distinct RNA modifications within cellular as well as viral noncoding RNAs that are instrumental in executing their function. Here we show that EBER2 is marked by pseudouridylation, and by using HydraPsiSeq the modification site was mapped to a single nucleotide within the 3' region of EBER2. The writer enzyme was identified to be the snoRNA-dependent pseudouridine synthase Dyskerin, which is the catalytic subunit of H/ACA small nucleolar ribonucleoprotein complexes, and is guided to EBER2 by SNORA22. Similar to other noncoding RNAs for which pseudouridylation has a positive effect on RNA stability, loss of EBER2 pseudouridylation results in a decrease in RNA levels. Furthermore, pseudouridylation of EBER2 is required for the prolific accumulation of progeny viral genomes, suggesting that this single modification in EBER2 is important for efficient viral lytic replication. Taken together, our findings add to the list of RNA modifications that are essential for noncoding RNAs to implement their physiological roles.