Gilead Sciences is challenging the four patents held by the U.S. government on HIV-prevention drugs that lawmakers and patient advocates have urged HHS to use to cut the price of the pre-exposure prophylaxis treatments by licensing them to generic makers. “It doesn’t make much to sense to talk about licensing patents that we think are invalid,” said Patricia Thayer, Gilead intellectual property senior associate general counsel There is only one PrEP drug approved, Truvada, but FDA is expected to approve...