Coexisting autoantibodies against transcription factor Sp4 are associated with decreased cancer risk in dermatomyositis patients with anti-TIF1γ autoantibodies

Objectives In dermatomyositis (DM), different autoantibodies are associated with unique clinical phenotypes. For example, anti-TIF1γ autoantibodies are associated with a substantially increased risk of cancer. The purpose of this study was to discover novel DM autoantibodies. Methods Phage ImmunoPrecipitation Sequencing using sera from 67 DM patients suggested that transcription factor Sp4 is a novel autoantigen; this was confirmed by showing that patient sera immunoprecipitated full-length Sp4 protein. Sera from 371 Johns Hopkins myositis patients (255 with DM, 28 with antisynthetase syndrome [ASyS], 40 with immune-mediated necrotizing myopathy [IMNM], 29 with inclusion body myositis [IBM], and 19 with polymyositis [PM]), 75 rheumatologic disease controls (25 with Sjogren’s syndrome, 25 with systemic lupus erythematosus, and 25 with rheumatoid arthritis), and 200 healthy comparators were screened for anti-SP4 autoantibodies by an enzyme-linked immune absorption assay. Serum from 23 Spanish TIF1γ-positive DM patients was also screened for anti-Sp4 autoantibodies Results Anti-Sp4 autoantibodies were present in 11.4% of DM and 8% of rheumatoid arthritis patients but not in any other clinical group. Among DM patients, 90% of anti-Sp4 autoantibodies were detected in patients with anti-TIF1γ autoantibodies. Among anti-TIF1γ-positive DM patients from Johns Hopkins and Spain, those with coexisting anti-Sp4 autoantibodies had a decreased risk of cancer (0% vs. 31%; p=0.001, Chi-squared test). Conclusions Anti-Sp4 autoantibodies are enriched in anti-TIF1γ-positive DM patients without cancer, suggesting that the development of an anti-Sp4 immune response may correlate with a relatively low risk of cancer in these patients. What is already known about this subject? What does this study add? How might this impact on clinical practice? Testing for anti-Sp4 autoantibodies may define a population of anti-TIF1γ-positive dermatomyositis patients without a substantially increased risk of cancer. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work was supported, in part, by the Intramural Research Program of the National Institutes of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health. The Johns Hopkins Rheumatic Diseases Research Core Center, where some of the autoantibodies were assayed, is supported by NIH P30-AR070254. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: IRB of Johns Hopkins gave ethical approval for this work. IRB of the National Institutes of Health gave ethical approval for this work. Ethics committee of the Vall dHebron and Clinic Hospitals gave ethical approval for this work. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data relevant to the study are either included in the article or will be shared upon request.