title: A novel class of somatic mutations in blood detected preferentially in CD8+ cells.
abstract: Somatic mutations have a central role in cancer but their role in other diseases such as autoimmune disorders is poorly understood. Earlier work has provided indirect evidence of rare somatic mutations in autoreactive T-lymphocytes in multiple sclerosis (MS) patients but such mutations have not been identified thus far. We analysed somatic mutations in blood in 16 patients with relapsing MS and 4 with other neurological autoimmune disease. To facilitate the detection of somatic mutations CD4+, CD8+, CD19+ and CD4-/CD8-/CD19- cell subpopulations were separated. We performed next-generation DNA sequencing targeting 986 immune-related genes. Somatic mutations were called by comparing the sequence data of each cell subpopulation to other subpopulations of the same patient and validated by amplicon sequencing. We found non-synonymous somatic mutations in 12 (60%) patients (10 MS, 1 myasthenia gravis, 1 narcolepsy). There were 27 mutations, all different and mostly novel (67%). They were discovered at subpopulation-wise allelic fractions of 0.2%-4.6% (median 0.95%). Multiple mutations were found in 8 patients. The mutations were enriched in CD8+ cells (85% of mutations). In follow-up after a median time of 2.3years, 96% of the mutations were still detectable. These results unravel a novel class of persistent somatic mutations, many of which were in genes that may play a role in autoimmunity (ATM, BTK, CD46, CD180, CLIP2, HMMR, IKFZF3, ITGB3, KIR3DL2, MAPK10, CD56/NCAM1, RBM6, RORA, RPA1 and STAT3). Whether some of this class of mutations plays a role in disease is currently unclear, but these results define an interesting hitherto unknown research target for future studies.
authors.affiliation: Molecular Neurology, Research Programs Unit, University of Helsinki, Department of Neurology, Helsinki University Hospital, Haartmaninkatu 8, FIN-00290 Helsinki, Finland. Electronic address: miko.valori@helsinki.fi.
authors.forename: Miko
authors.initials: M
authors.lastname: Valori
authors.affiliation: Molecular Neurology, Research Programs Unit, University of Helsinki, Department of Neurology, Helsinki University Hospital, Haartmaninkatu 8, FIN-00290 Helsinki, Finland. Electronic address: lilja.jansson@hus.fi.
authors.forename: Lilja
authors.initials: L
authors.lastname: Jansson
authors.affiliation: Molecular Neurology, Research Programs Unit, University of Helsinki, Department of Neurology, Helsinki University Hospital, Haartmaninkatu 8, FIN-00290 Helsinki, Finland. Electronic address: anna.kiviharju@helsinki.fi.
authors.forename: Anna
authors.initials: A
authors.lastname: Kiviharju
authors.affiliation: Finnish Institute for Molecular Medicine (FIMM), University of Helsinki, Helsinki, Finland. Electronic address: pekka.ellonen@helsinki.fi.
authors.forename: Pekka
authors.initials: P
authors.lastname: Ellonen
authors.affiliation: Hematology Research Unit Helsinki, University of Helsinki and Helsinki University Hospital Comprehensive Cancer Center, Haartmaninkatu 8, FIN-00029 Helsinki, Finland. Electronic address: hanna.rajala@helsinki.fi.
authors.forename: Hanna
authors.initials: H
authors.lastname: Rajala
authors.affiliation: Hematology Research Unit Helsinki, University of Helsinki and Helsinki University Hospital Comprehensive Cancer Center, Haartmaninkatu 8, FIN-00029 Helsinki, Finland; Department of Clinical Chemistry, University of Helsinki, Helsinki, Finland. Electronic address: shady.awad@helsinki.fi.
authors.forename: Shady Adnan
authors.initials: SA
authors.lastname: Awad
authors.affiliation: Hematology Research Unit Helsinki, University of Helsinki and Helsinki University Hospital Comprehensive Cancer Center, Haartmaninkatu 8, FIN-00029 Helsinki, Finland; Department of Clinical Chemistry, University of Helsinki, Helsinki, Finland. Electronic address: satu.mustjoki@helsinki.fi.
authors.forename: Satu
authors.initials: S
authors.lastname: Mustjoki
authors.affiliation: Molecular Neurology, Research Programs Unit, University of Helsinki, Department of Neurology, Helsinki University Hospital, Haartmaninkatu 8, FIN-00290 Helsinki, Finland. Electronic address: pentti.tienari@hus.fi.
authors.forename: Pentti J
authors.initials: PJ
authors.lastname: Tienari
mesh_terms: D000328:Adult; D000368:Aged; D020274:Autoimmune Diseases of the Nervous System / Q000097:blood / Q000276:immunology; D015551:Autoimmunity / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000097:blood / Q000276:immunology; D009154:Mutation / Q000235:genetics*; D009157:Myasthenia Gravis / Q000097:blood; D009290:Narcolepsy / Q000097:blood / Q000276:immunology; D055815:Young Adult
keywords: Autoimmune disease; CD8; Multiple sclerosis; STAT3; Somatic mutation