Drug company Allergan transferred its Restasis drug patents to a Mohawk tribe in upstate NY. Under the deal, Allergan paid the Indian tribe $13.75 million and agreed to further payment of $15 million in annual royalties while the patents were in force. In exchange, the tribe agreed to lease the patents back to Allergan and promised to claim sovereign immunity in any USPTO patent challenges. Under the law, Indian tribes possess inherent sovereignty; however, this sovereignty may be limited through treaty or federal statute. Additionally, Congress possesses plenary power over tribes, allowing it to alter or abolish tribal sovereignty at will. The US Supreme Court recently held that Indian tribes cannot use sovereign immunity to shield themselves from patent challenges brought within the USPTO. The court did not decide whether sovereign immunity claims could be used by states.