AQP4 and myeloid sarcoma: Notable examples of fluid biomarkers that are already in clinical use in MS include oligoclonal bands [52] (now part of MS diagnostic criteria), antibodies against aquaporin-4 [53] and myelin oligodendrocyte protein [54] (which define pathologically discrete disease entities which previously fell under the umbrella of MS), as well as serological assays for JC virus [55] (pre-immunosuppression risk stratification).