Shrestha, Ramila Barun

ABSTRACT Interferon-γ (IFNγ) signaling is prominent in inflammatory CNS microenvironments across many neurological disorders, but the neuronal peptides presented on HLA class I under these conditions and their functional consequences for CD8 + T cells remain incompletely defined. Here we combine human iPSC-derived human neural aggregates (HNAs), HLA class I immunoprecipitation coupled to LC-MS/MS immunopeptidomics, and microfluidic co-culture assays to map IFNγ-induced neuronal antigen presentation and test antigen-specific cytotoxicity. IFNγ stimulation induced robust HLA class I expression in HNAs and enabled recovery of a canonical 8-12-mer class I ligandome enriched for 9-mers. Neuron-restricted expression of a synapsin-driven polyepitope cassette yielded presentation of defined neoantigen 9-mer peptides on donor HLA class I molecules and, in the presence of IFNγ, elicited activation of autologous antigen-specific CD8 + T cells and consequent antigen-dependent neurite injury. Across four donors, comparative immunopeptidomics identified large IFNγ-unique neural peptide repertoires distinct from matched fibroblasts and revealed a consistent enrichment of predicted high-affinity binders on HLA-B allotypes. Finally, β2-microglobulin deletion ablated peptide recovery, and neuron-restricted β2-microglobulin reconstitution enabled identification of neuron-derived peptides, including peptides derived from neurofilament light (NEFL) that were shared across donors and presented on multiple HLA allotypes. Together, these data provide an integrated platform for neuronal autoantigen discovery and functional validation and support a model in which IFNγ-driven neuronal HLA class I presentation creates an HLA-B-weighted epitope landscape that can be recognized by autoreactive cytotoxic CD8 + T cells.

Abstract Description CD8+ T cell responses to neuronal antigens are believed to contribute to CNS autoimmune diseases and neurodegenerative disease pathophysiology. However, the specific endogenous human neuron antigens and their MHC restrictions remain unknown. We characterized the immunopeptidome of human iPSC-derived neurons and verified their ability to elicit cytopathic responses in autologous T cells. After maturation, >100M neurons were treated with IFNg to induce MHC I expression. MHC class I molecules were immunoprecipitated, and associated peptides were analyzed using mass spectrometry. For comparison we also analyzed identically treated human adult dermal fibroblasts and neural ectoderm cells, and neurons differentiated from B2M KO NSCs. Immunopeptidomes were analyzed my Gibbs clustering, netMHC affinity and immunogenicity prediction for patient allotypes. We identified peptides uniquely presented by IFNg-treated neurons and analyzed these for brain enrichment. Among neural enriched proteins detected across multiple subjects, proteins for which CNS autoimmunity has been described were found to be enriched. We also identified putative immunodominant peptides from 29 potential MS patient autoantibody targets (including CRYAB) presented by MHC I on human neurons. Finally, human neurons transduced to express immunodominant peptides from CMV, EBV, and influenza (CEF) showed detectable MHC I peptide presentation and could be injured by autologous CEF-stimulated CD8+ T cells by live imaging. Funding Sources Don and Fran Herdrich NIH grant NS064571 (to CLH) Mayo Clinic Eugene and Marcia Applebaum fellowship award (to BDSC) The Center for Multiple Sclerosis and Autoimmune Neurology at Mayo Clinic (to CLH). Topic Categories Neuroimmunology (NEUR)

Abstract We recently reported normalization of CSF cytokine levels following successful treatment of drug-resistant epilepsy (DRE) with recombinant interleukin-1 receptor antagonist (rIL1RA). To further understand the mechanism of this therapeutic outcome, we interrogated the ability of serum and CSF factors that are elevated in drug resistant-seizure disorders to promote inflammatory responses in astrocytes and human brain microvessel endothelial cells (HBMVECs). We report that CCL2, TNFa, IL6, and CXCL8/1 were strongly induced in 1) astrocytes and HBMVECs stimulated with IL1β (blocked by rIL1RA) and 2) astrocytes but not HBMVECs in response to DRE patient serum but not control serum (partially blocked by rIL1RA). This suggested that other serum factors contribute to astrocyte activation in this DRE. HMGB1 and IL18 were also dysregulated in DRE patient serum; however, IL18 failed to stimulate cytokine secretion from astrocytes. In contrast, HMGB1 induced cytokine secretion from astrocytes, which was blocked by the TLR4 inhibitor TAK242. Remarkably, TAK242 also prevented cytokine production by astrocytes in response to serum from some patients with DRE. Finally, IL1β induced the polarized uptake and secretion of HMGB1 across transwell inserts harboring confluent monolayers of HBMVECs suggesting that IL1b signaling may cause endothelial cells to transport serum HMGB1 into the perivascular space—promoting TLR4-dependent cytokine release from astrocytes. This translation of an “outside” inflammatory signal into an “inside” inflammatory response may underlie seizure disorders that are resistant to anti-seizure drugs.