The Utility of Myositis Specific Antibodies in Clinical Practice.

BACKGROUND: Fifteen myositis-specific antibodies have been described and characterized over the past 40 years. Approximately two thirds of patients with idiopathic inflammatory myositis have a myositis-specific antibody and only rarely more than one. Assays to detect them are now widely available within clinical practice. CONTENT: We describe the original description and clinical phenotype of the myositis-specific antibodies, forming the antisynthetase syndrome group, anti-MDA-5 and rapidly progressive interstitial lung disease, anti-SRP/HMGCR and necrotizing myositis, anti-TIF-1γ/NXP-2 and malignancy, anti-SAE and esophageal disease, and anti-Mi-2 and classic dermatomyositis skin disease. SUMMARY: Clinical practice is likely to be refined, with diagnosis and classification of the idiopathic inflammatory myositides based primarily on myositis-specific antibody, rather than directed by muscle histology or the broader clinical characteristics of polymyositis and dermatomyositis. All patients newly presenting with idiopathic inflammatory myositis should be routinely screened for myositis-specific antibodies. A positive result will usefully provide diagnostic and prognostic information, guide selection of therapy, and prompt surveillance for potential organ involvement and other features, such as cancer, throughout the disease course.

Case report: Interference from isatuximab on serum protein electrophoresis prevented demonstration of complete remission in a myeloma patient.

Multiple myeloma is a haematological cancer caused by malignant plasma cells in the bone marrow that can result in organ dysfunction and death. Recent novel treatments have contributed to improved survival rates, including monoclonal antibody therapies that target the CD38 protein on the surface of plasma cells. Anti-CD38 therapies are IgG kappa monoclonal antibodies that are given in doses high enough for the drug to be visible on serum protein electrophoresis as a small paraprotein. We present a case where isatuximab, the most recent anti-CD38 monoclonal antibody to be approved for treatment of myeloma, obscured the patient's paraprotein on gel immunofixation, so that complete remission could not be demonstrated. This was resolved using the isatuximab Hydrashift assay. The interference on gel immunofixation was unexpected because isatuximab migrated in a position distinct from the patient's paraprotein on capillary zone electrophoresis. We demonstrate the surprising finding that isatuximab migrates in a different position on gel electrophoresis compared to capillary zone electrophoresis. It is vital that laboratories are aware of the possible interference on electrophoresis from anti-CD38 monoclonal antibody therapies, and are able to recognise these drugs on protein electrophoresis. The difference in isatuximab's electrophoretic mobility on capillary and gel protein electrophoresis makes this particularly challenging. Laboratories should have a strategy for alternative analyses in the event that the drugs interfere with assessment of the patient's paraprotein.

Development and preparation of a new serum protein reference material: feasibility studies and processing.

BACKGROUND: The availability of matrix reference materials is essential for the standardisation of (immuno)assays used to measure proteins. The reference material ERM-DA470 (previously called CRM470) certified in 1993 has led to a large degree of harmonisation of these assays. A new serum protein reference material has now been produced (ERM-DA470k). It is intended to replace ERM-DA470, and will additionally be certified for beta(2)-microglobulin (B2M). METHODS: Serum from 390 healthy donors was pooled and processed so as to stabilise, delipidate and 'maturate' it. Purified C-reactive protein (CRP) and recombinant B2M were added. Pilot batches were produced to study the stability, homogeneity, and commutability of the material. On the basis of the results with the trial batches it was decided to proceed with the processing of the main batch of a candidate reference material. RESULTS: Two pilot batches were produced and the processed and spiked serum lyophilised after filling (1 mL). The B2M in the material was shown to be stable and commutable. For CRP, it was discovered that freeze-drying led to a decrease in measurable protein. The main batch of candidate reference material was produced and fulfilled the required criteria in terms of optical transparency, homogeneity and stability. CONCLUSIONS: A new serum protein reference material has been produced with the properties required for a serum protein reference material for 14 proteins. An apparent loss of CRP of approximately 20% was observed upon freeze-drying of the material.