Iceland-based biosimilar developer Alvotech has sued AbbVie in a U.S. federal court, seeking to have AbbVie’s patents for its blockbuster arthritis drug Humira (adalimumab) declared invalid.

The case is a countersuit against AbbVie, which filed a lawsuit against Alvotech in March, alleging that the company recruited a former AbbVie employee to steal trade secrets in order to produce a biosimilar of Humira.

AbbVie filed suit in the U.S. District Court for the Northern District of Illinois, Eastern Division, while Alvotech has filed its suit in the U.S. District Court for the Eastern District of Virginia.

The Alvotech suit aims to end AbbVie’s monopoly on the lifechanging drug, allegedly maintained through “the acquisition and threatened enforcement of an outrageous number of patents of dubious validity.… Any competitor that desires to bring a biosimilar version of Humira to market is threatened with crushing, ruinous litigation on these patents.”