NEW YORK (Reuters) - Swiss pharmaceutical company Roche Holding AG will suspend its HIV research because none of its pending medicines represent significant improvement over existing drugs, a company spokeswoman said on Friday.

“Research scientists currently working in HIV will be reassigned to other activities,” Linda Dyson, a spokeswoman in Roche’s U.S. office in New Jersey, said in an e-mail.

Dyson confirmed an e-mail sent on Wednesday to some activists informing them of the decision. In that e-mail, the company said it “decided to refocus our resources within virology on diseases in which we can deliver substantial improvements over existing medications.”

Dyson declined to specify how much Roche has been investing in HIV research.

She also said she could not specify how many employees worked in the HIV research division. Roche employs 5,000 people in the U.S. and 3,000 in its New Jersey office.

The company said in the e-mail to some activists that it initially had been excited about the potential for drugs in pre-clinical testing, but it has “concluded that none would provide a true incremental benefit for patients compared to medicines currently on the market.”

Roche said it would continue to support its molecular diagnostic tests and drugs already on the market, including the fusion-inhibitor Fuzeon.

Roche has partnered with Morrisville, North Carolina-based biotech Trimeris Inc to sell Fuzeon, which netted $266.8 million in sales last year.

But the drug struggled because of its cost -- $25,000 for a year’s supply -- exceeding the cost of other HIV drugs on the market, said Peter Staley, founder of AIDSmeds.com, which tracks HIV- related news.

The launch of new drugs and an uptick in HIV cases is set to make AIDS medicine a $10.6 billion market by 2015, according to a study published last year by independent market research firm Datamonitor.

More than 20 separate HIV drugs are available, with several combination pills also available. None can cure the fatal disease, which infects an estimated 33 million people globally and which has killed 25 million.

The drugs fall into various classes, each of which interferes with the replication of the virus at a different stage. The human immunodeficiency virus hijacks immune system cells, forcing them to create copies of itself.

Activists said they would not mourn the withdrawal of Roche from the field.

“They’re not beloved in the AIDS community,” said James Love, Director of Knowledge Ecology International, an advocacy group that focuses on access to medication.

“They are criticized a lot by people in the AIDS field because they are the least willing to give discounts on their AIDS drugs.”

The decision reflects “the lack of productivity among the groups that they have working in this area,” he said, adding that “a lot of the big pharma companies haven’t been very impressive in terms of their big internal pipeline.”

Staley said Roche has never come up with an AIDS drug that has sold really well.

“Roche is a big company and they’ve been trying to get this right for many, many years.” Staley said.

“It is disappointing that there is one less big pharmaceutical company in this field. I don’t think it’s a sign of a serious problem in pharma’s commitment.”