The primary objective of the study is to longitudinally profile immunoglobulin levels and autoantibody levels in subjects with myasthenia gravis (MG) who receive therapeutic plasma exchange (TPE).

This is a prospective, multi-center, pilot biomarker study in subjects receiving TPE for the treatment of MG. No study medications will be given.

Ten (10) AChR antibody positive MG subjects will be enrolled in the study at 2 sites. Of these 10 MG subjects, up to 5 may be receiving chronic TPE.

The study period will be approximately 3 months and will consist of:

• Screening/baseline visit,
• TPE visit where subjects will undergo clinical evaluations and blood draws for immunological assays,
• End of TPE visit where information on the TPE procedure will be recorded, clinical measurements will be performed, and a blood sample will be drawn.
• Post-TPE period where subjects will undergo clinical evaluations and blood draws for immunological assays at week 1, week 2, week 3, week 6, and week 12 after TPE.

Study procedures performed outside of usual care will include optional single-fiber electromyography (SFEMG) studies, blood draws and optional skin biopsies.

Inclusion Criteria:

• has the capacity to understand and sign an informed consent form
• 18 years or older
• diagnosis of MG based on clinical features
• has detectable serum autoantibodies to AChR
• has a clinical indication for the use of TPE to treat MG

Exclusion Criteria:

• unable or unwilling to comply with study procedures that include multiple venipunctures
• weighs less than 50Kg
• has a contraindication to treatment with TPE (e.g. clinically significant bleeding disorder)
• has muscle specific tyrosine kinase or low-density lipoprotein receptor-related protein 4 (LRP4) antibody positive MG
• has prior or current history of thymoma
• had a thymectomy in the past 6 months
• has received rituximab in the past 12 months
• has another coexisting autoimmune disease that is not clinically controlled or may preclude accurate study assessments according to the judgment of the PI
• has current signs or symptoms of severe, progressive, or uncontrolled renal, hepatic, hematological, gastrointestinal, endocrine, pulmonary, cardiac, or central nervous system disease
• has participated in an interventional clinical trial with a novel therapeutic agent in the past 6 months
• is cognitively impaired, a prisoner, or otherwise institutionalized at the time of screening

Potentially eligible subjects with MG that will receive TPE as part of their clinical care will be identified from clinic encounters, emergency department visits, and hospitalizations.