Life science
Medical & healthcare

Identification of the mechanism by which thymoma implicates autoimmune
neuromuscular diseases, including myasthenia gravis
Department of Neurology, Graduate School of Medicine
Associate Professor Tatsusada Okuno		

https://researchmap.jp/neuroimmunology?lang=en

Department of Frontier Research in Tumor Immunology, Graduate School of Medicine
Specially Appointed Professor Naganari Ohkura

https://researchmap.jp/read0007148?lang=en

Department of Neurology, Graduate School of Medicine

Life science

Professor Hideki Mochizuki				https://researchmap.jp/read0207787?lang=en

Abstract
Myasthenia gravis (MG) is an autoimmune disease characterized by autoantibodies against acetylcholine receptors at theneuromuscular junction. MG commonly occurs in patients withthymoma. In addition to MG, autoimmune neurological diseases
such as autoimmune encephalitis and stiff-person syndrome arealso accompanied by thymoma. In this study, we try to elucidate
the mechanism by which these autoimmune neuromuscular diseases occur in patients with thymoma by analyzing open databaseof thymoma, pathological and clinical data and single cell RNA
Sequencing(scRNASeq). We found that thymomas show high levels of various neuromuscular antigens with chemokines, such as
CXCL12. In addition, we were able to identify neuromuscular TECs(nmTECs), which have the ability to trigger autoimmune reactions
by presenting autoantigens and recruiting lymphocytes.

▍ Background & Results
MG is an autoimmune disease in which the neuromuscular junction is disrupted by acetylcholine receptor antibodies and is highly
associated with thymoma. Thymoma is a tumor composed of tumorigenic thymic epithelium (TEC) and lymphocytes. In a normal thymus,
TEC induces immune tolerance by expressing autoantigens, however, the relationship to pathogenesis of MG remains unknown.
In an attempt to further understand this relationship, we analyzed
the thymoma data in The Cancer Genome Atlas and searched for
MG-related genes. Among the genes identified were target antigens

for autoantibodies that appear in thymoma patients, including neurofilament, GABA receptor, potassium channel, glycine receptor,
ryanodine receptor, and myosin. To examine which cells express
these MG-related genes, scRNASeq of thymoma and peripheral
blood mononuclear cells from patients with thymoma-associatedMG was performed. As a result, we found that they cluster in thesubpopulation of TECs not consistent with known TEC. Consistently,
immunohistochemistry revealed expression of neuromuscular-related
proteins including neurofilaments and GABA receptors in TEC. We
termed these cells neuromuscular-TECs (nmTECs), meaning TECs
expressing neuromuscular antigens. Gene-set analysis showed that
Class I and II MHC antigen processing and presentation pathways
are enriched in nmTECs. These cells also highly expressing thechemokine CXCL12/SDF-1, which was postulated to form a microenvironment that attracts lymphocytes to the thymoma. This result
could suggest that the induction of neuromuscular antigen-reactive
lymphocytes by nmTEC in thymomas plays a crucial role in the development of autoimmune neuromuscular diseases including MG.

▍ Significance of the research and Future perspective
Our findings suggest that the nmTECs we identified could trigger
thymoma-associated autoimmune neuromuscular diseases including MG. We believe that further studies on nmTECs could possibly
contribute to the unveiling of the pathogenesis of organ-specificautoimmune diseases, as well as the development of the spontaneous animal model of MG and the therapies selectively targeting
nmTEC.

Figure 1. Identification of nmTec. (a)design of the scRNAseq analysis. Immune cells and non-immune cells from MG-type thymoma and immune cells
FIThe
GUexperimental
RE 1.
from the blood of patients were collected for scRNAseq. (b). UMAP plot for 65,935 cells displaying the clusters from the thymoma and blood of patients with MG. Arrow
indicates nmTec. (c). Violin plots of mean expression of the REACTOME gene sets; neuronal system (left) and muscle contraction (right) in TEC clusters. (d). Immunohistochemistry of the neuronal genes in nmTec. [Scale bar: 20 μm]. GABRA5; gamma-aminobutyric acid type A receptor subunit alpha5, GLI2; GLI Family Zinc Finger 2,MAP2; microtubule associated protein 2, NEFL; Neurofilament Light Chain, NEFM; Neurofilament Medium Chain, These figures were reproduced from Yasumizu et al.
doi: 10.1111/cen3.12743

P a t e n t
Tr e a t i s e

Yasumizu, Yoshiaki; Okuno, Tatsusada; Mochizuki, Hideki et al. Myasthenia gravis-specific aberrant neuromuscular gene expression by medullary thymic
epithelial cells in thymoma. Nature Communications 2022, 13(1), 4230. doi: 10.1038/s41467-022-31951-8

URLK e y w o r d myasthenia gravis, thymoma, nmTEC, autoimmune neuromuscular diseases