IntroductionAfter spending several billion dollars and a decade or more in development and clinical trial, only approximately 10% of new drugs show efficacy and reach the market for patient use. This apparent inefficiency, however, masks enormous opportunities to repurpose existing drugs to treat diseases for which they were not originally intended, especially diseases with limited therapeutic options (1, 2). Therapies for inflammatory diseases are an attractive choice for drug repositioning because of the complexity of the immune response, the hit-or-miss nature of treatment (which is often by trial and error), and the number of traditional drugs and new biologics for inflammatory diseases.Determining which drugs to reposition, however, is not trivial. Among a heterogeneous patient population that seems affected by the same autoimmune condition, one cannot be sure if the disease is in fact the same, or at what progressive stage a patient is presenting. Currently, most predictions of patients that would benefit from drug repositioning are drawn from retrospective computational methods, genomic analyses, BACKGROUND. In patients with limited response to conventional therapeutics, repositioning of already approved drugs can bring new, more effective options. Current drug repositioning methods, however, frequently rely on retrospective computational analyses and genetic testing -time consuming methods that delay application of repositioned drugs. Here, we show how proteomic analysis of liquid biopsies successfully guided treatment of neovascular inflammatory vitreoretinopathy (NIV), an inherited autoinflammatory disease with otherwise poor clinical outcomes.