Gilead Sciences took the unusual step of mounting a challenge to U.S. government patents on Wednesday, saying the government’s claim to have invented the use of the drug Truvada for HIV prevention is invalid.

The pharmaceutical company filed a petition with the U.S. Patent and Trademark Office, asking for a reexamination of the government’s patents. Gilead says medical professionals were widely discussing Truvada, approved in 2004 for treating people already infected with HIV, for prevention of the disease before the government filed its patent claim in 2006.

“That was already known in the public domain, and you can’t take that back,’’ Gilead patent lawyer Patricia Thayer said in an interview Wednesday. Gilead’s filing included reams of documents the company says prove that the concept of using Truvada for prevention was widely known several years before the government’s application.

The Department of Health and Human Services declined to comment. “We do not comment about matters in litigation,” spokeswoman Caitlin Oakley said.

Gilead’s battle over Truvada for PREP, as the prevention dose is known, has spawned a broad controversy since The Washington Post reported in March on the government’s decision not to seek enforcement in the courts of its own patents.

Truvada for PREP is the linchpin of public health strategies to eradicate HIV and AIDS by 2030, a goal adopted by President Trump.

The U.S. Centers for Disease Control and Prevention won its Truvada for PREP patents in 2015 after a nine-year patent application. The CDC said government scientists in government labs, working with government primates, showed that Truvada worked for prevention. Using tens of millions of dollars in federal and private foundation grants, researchers later proved it could work in humans.

The government has collected no royalties from Gilead for its contributions. It has written letters to Gilead asserting its patent but stopped short of going to court with an infringement case.

HIV/AIDS activists have slammed Gilead for its $20,000 annual price tag for Truvada for PREP, saying its monopoly pricing is curbing use of the lifesaving drug. Members of Congress say the cost is a prime example of a drug company profiteering on a medical therapy developed with taxpayer dollars.

The Justice Department launched a review of the patents in April, and Gilead said Wednesday it has not heard from Justice Department lawyers.

The company said the patent fight is distracting from efforts to reduce stigma and more widely distribute Truvada for PREP.

“Our hope and our belief is that taking this step is potentially the most rapid path to getting the issue resolved,’’ said Amy Flood, Gilead’s senior vice president for public affairs. “The true barriers to access to PREP don’t involve the patents themselves. There’s a lot of work to be done.’’

The Gilead filing Wednesday includes a sworn statement by a British researcher, Michael Youle, who said he publicly declared in 2002 that antiretroviral drugs could be used to prevent HIV infection. His lengthy affidavit describes the various hypotheses in play among providers and researchers before 2006.

But activists dismissed Gilead’s assertions and said the move was a sign that the company is worried the government will take action.

Gilead’s arguments in Wednesday’s petition “point to early speculation about the possibility of Truvada as PREP,’’ said Nick Faust of the advocacy group PrEP4All. “Speculation is not the same thing as invention. The CDC invented PREP.’’

Gilead has agreed to provide free Truvada for the government’s efforts to eradicate HIV/AIDS but has said the offer is not related to its patent dispute with the government.