Shares of Roche Holding AG /zigman2/quotes/206324342/delayed CH:ROG -0.79% gained 2.4% in premarket trading on Thursday after the drugmaker said it is testing a combination of its rheumatoid arthritis drug Actemra with Gilead Sciences Inc.'s /zigman2/quotes/210293917/composite GILD -0.39% remdesivir in hospitalized COVID-19 patients. Gilead's stock was down 0.4%. Roche has previously announced it is studying Actemra in 450 hospitalized COVID-19 patients participating in a randomized, double-blind, placebo-controlled late-stage trial; results from that trial are expected "this summer," Roche said. The new Phase 3, randomized, double-blind, multicenter study will test Actemra and remdesivir against placebo and remdesivir in about 450 patients hospitalized with severe COVID-19 pneumonia. Trial sites are in Canada, Europe, and the U.S. The Food and Drug Administration granted an emergency use authorization to remdesivir on May 1 as a treatment for some severely ill COVID-19 patients. The experimental drug has not been approved as a treatment for the disease caused by the coronavirus. Since the start of the year, Roche's stock is up 8.2%, Gilead's stock has gained 15.2%, and the S&P 500 /zigman2/quotes/210599714/realtime SPX +0.24% has declined 6.0%.