Shares of Eli Lilly & Co. /zigman2/quotes/200106384/composite LLY +1.11% were down 1.1% in premarket trading on Monday after the drugmaker said the first patient had been enrolled in a late-stage trial assessing rheumatoid arthritis drug Olumiant as a treatment for COVID-19. Olumiant, which was developed by Incyte Corp. /zigman2/quotes/204510994/composite INCY -4.01% and is licensed by Lilly, generated $426.9 million in revenue for Lilly in 2019. Several drugs developed to treat rheumatoid arthritis have become clinical targets in the hunt for COVID-19 treatments. This includes Olumiant, Roche Holdings' /zigman2/quotes/206324342/delayed CH:ROG +1.84% Actemra, and Regeneron Pharmaceuticals Inc. [: regn] and Sanofi /zigman2/quotes/201967021/composite SNY +0.71% 's Kevzara. The Phase 3 randomized, controlled clinical trial is testing Olumiant in hospitalized COVID-19 patients; it's expected to enroll 400 participants in the U.S., Europe, and Latin America, with an aim of reducing the cytokine storms that present in some of these patients. The National Institutes of Health is also conducting a trial evaluating Olumiant in combination with Gilead Sciences Inc.'s /zigman2/quotes/210293917/composite GILD +0.02% remdesivir. Lilly's stock has gained 9.2% year-to-date, while the S&P 500 /zigman2/quotes/210599714/realtime SPX -1.12% is down 5.8%.