Gilead Sciences is once again preparing to defend itself against a challenge to its hepatitis C intellectual property. The latest lawsuit comes from the University of Minnesota which filed a claim in its district court on Aug. 29, alleging patent infringement by the US drugmaker. The university believes that Gilead’s hepatitis C treatments, which include the blockbuster Sovaldi and two follow-up drugs Harvoni and Epclusa, infringe patent rights that were assigned by Carton Wagner, a professor and an endowed chair in the department of medicinal chemistry in its College of Pharmacy.

The university is reported to be seeking “damages adequate to compensate it for Gilead’s infringement, in no event less than a reasonable royalty”, and for the damages to be determined by a jury. It contends that Wagner received the patent in August 2014. Gilead has rejected the claim and said it strongly believes it has the sole right to sell the active ingredient, sofosbuvir, in the US. “We believe the University of Minnesota’s patent is invalid and is not infringed by the sale of Gilead’s medicines for chronic hepatitis C,” the California-based firm said in a statement.

In March, Gilead lost a high-profile patent dispute with US rival Merck over sofosbuvir.