Dec 15 (Reuters) - Bristol Myers Squibb Co"s (BMY.N) Orencia on Wednesday became the first drug to win U.S. approval for the prevention of acute Graft versus Host Disease (aGvHD), a potentially fatal complication that could occur after a stem cell transplant. The Food and Drug Administration (FDA) has cleared the drug in combination with certain immunosuppressants for use in adults and children aged two and older who are undergoing stem cell transplantation from an unrelated donor. The disease, in which the immune cells of the donor attack the recipient"s body, can be acute or chronic. The former could affect the gastrointestinal tract, skin and liver, with symptoms likely appearing within weeks of the transplant. In 2019, Incyte"s (INCY.O) Jakafi had won the first U.S. approval for the treatment of aGvHD patients 12 years and older. Orencia"s approval was based on real-world clinical evidence of the drug"s efficacy and results from a mid-stage study showing a combination of Orencia and immunosuppressive drugs boosted aGvHD-free survival rates. Immunosuppressive medicines are generally used to treat the chronic form of the disease, whose symptoms may take months to appear after the transplant. The FDA originally approved Orencia in 2005 for the treatment of adult rheumatoid arthritis and later also cleared it for two other types of arthritis. Bristol Myers said on Wednesday it would price the entire course of treatment at $14,742, similar to the pricing for arthritis. Orencia for aGvHD consists of four infusions given over a 29-day period. The average cost per infusion is $3,685. The company"s shares were 1.9% higher on Wednesday, bucking broader market weakness.