On May 20, pharmaceutical company Gilead Sciences, Inc. announced that the U.S. Patent and Trademark Office (PTO) upheld one of four recently challenged patents for Gilead’s AIDS drug Viread, Reuters reports (reuters.com, 5/20).

Last year, the nonprofit group Public Patent Foundation challenged the Viread patents, saying that the scientific knowledge on which the patents were based existed prior to the patents’ approval.

“We have always believed that the U.S. PTO would recognize that Viread is a novel product, and we remain confident that the office will rule similarly on the remaining three patents under review,” said Gregg Alton, Gilead’s general counsel, in a statement. According to the article, Gilead said that the PTO has not announced a ruling on the remaining three patents.