CD4 and myeloid sarcoma: TGF-β released by Treg cells promotes the CD103 expression in the brain-infiltrated T cells.427 Moreover, PD-L1+glial cells combine with brain-CD103+CD69+CD8+TRM cells expressing PD-1, and promote their development.428 CD8+TRM cells can trigger pathological neuroinflammation and impair neurons with the assistance of CD4+T cells.429,430 Moreover, CD103+CD69+CD49a+CD8+TRM cells located in the white matter lesions of progressive MS have been demonstrated to promote inflammatory activity.431 Therefore, CD8+TRM cells are likely to be the pathogenic factors for MS progression.