Common Connective Tissue Disorder and Anti-Cytokine Autoantibodies are Enriched in Idiopathic Multicentric Castleman Disease Patients

Allan Feng ^1,2 Michael V Gonzalez ³ Muge Kalaycioglu ^1,2 Xihui Yin ^1,2 Melanie Mumau ³ Saishravan Shyamsundar ³ Mateo Sarmiento Bustamante ³ Sarah E Chang ^1,2 Shaurya Dhingra ^1,2 Tea Dodig-Crnkovic ⁴ Jochen Schwenk ⁴ Tarun Garg ⁵ Kazuyuki Yoshizaki ⁶ Frits van Rhee ⁵ David C Fajgenbaum ³ Paul J Utz ^1,2*

• ¹ Department of Medicine, Division of Immunology and Rheumatology, Stanford University School of Medicine, Stanford, United States
• ² Institute for Immunity, Transplantation and Infection, Stanford University School of Medicine, Stanford, United States
• ³ Center for Cytokine Storm Treatment & Laboratory, University of Pennsylvania, Philadelphia, United States
• ⁴ Science for Life Laboratory, Department of Protein Science, KTH Royal Institute of Technology, Stockholm, Sweden
• ⁵ Myeloma Center, University of Arkansas for Medical Sciences, Little Rock, United States
• ⁶ Department of Biomolecular Science and Regulation, The Institute of Scientific and Industrial Research, Osaka University, Osaka, Japan

Idiopathic Multicentric Castleman Disease (iMCD) is a polyclonal lymphoproliferative disorder involving cytokine storms that can lead to organ failure and death. The cause of iMCD is unknown, but some clinical evidence suggests an autoimmune etiology. For example, connective tissue disorders (CTDs) and iMCD share many clinical features, and autoantibodies have been anecdotally reported in individual iMCD patients. This study investigates whether common autoantibodies are shared across iMCD patients. We assembled custom bead-based protein arrays consisting of 52 autoantigens traditionally associated with CTDs and 38 full-length cytokines and screened serum samples from 101 iMCD patients for IgG autoantibodies. We also screened samples with a 1,103-plex array of recombinant human protein fragments to identify additional autoantibody targets. Finally, we performed receptor blocking assays on select samples with anti-cytokine autoantibodies (ACAs) identified by array. We found that an increased proportion of iMCD patients (47%) tested positive for at least one CTD-associated autoantibody compared to healthy controls (HC) (17%). Commonly detected CTD-associated autoantibodies were associated with myositis and overlap syndromes as well as systemic lupus erythematosus (SLE) and Sjögren's Syndrome (SS). ACAs were also detected in a greater proportion of iMCD patients (38%) compared to HC (10%), while the protein fragment array identified a variety of other autoantibody targets. One iMCD sample tested positive for receptor blocking against interferon-ω (IFNω). IgG autoantibodies binding autoantigens associated with common CTDs