Hypocretin-specific CD4+ T cells in narcolepsy patients and controls: in vivo clonal expansion and phenotypes

Individuals with narcolepsy suffer from abnormal sleep patterns due to loss of neurons that uniquely supply hypocretin (HCRT). Previous studies found the associations of narcolepsy with human leukocyte antigen (HLA)-DQ6 allele and T-cell receptor α (TRA) J24 gene segment and also suggested that in vitro-stimulated T cells can target HCRT. However, DQ6+ individuals generate DQ6-HCRT tetramer+/TRAJ24+ TCRs. Without a proof that an HCRT-reactive cell expressing such TCRs has expanded in vivo, T cell-mediated autoimmunity in narcolepsy remains speculative. Here, we isolated DQ6-HCRT tetramer+/CD4+ T cells (low frequency, <0.04%) from DQ6+ individuals with/without narcolepsy. Within 74 informative TRAJ24+ TCRαβ from 8/12 patients and 11/12 controls, we identified a conserved family of clonotypes shared by 2 patients and 2 controls using identical α/β genes. TRAJ24-G allele+ clonotypes only expanded in the two patients, whereas a TRAJ24-C allele+ clonotype expanded in a control. A representative tetramer+/G-allele+ TCR showed signaling reactivity to the physiologically modified form of the epitope HCRT87-97. Clonally expanded G-allele+ T cells also exhibited an unconventional effector phenotype. In vivo expansion of HCRT-reactive TRAJ24-G allele+ cells provides critical evidence for an autoimmune contribution to narcolepsy development. DQ6/hypocretin peptide tetramer+/CD4+ T cells were isolated from the peripheral blood of 12 narcoleptic patients and 12 DQ6 allele-matched controls. Four different tetramers were used.