Trimeris reported some positive news about its HIV drug Fuzeon this week, but that wasn’t enough to prevent a downgrade of its stock on Thursday.

Legg Mason cut its rating on Trimeris (Nasdaq: TRMS) to “sell” from “hold.” It had upgraded to “hold” from “sell” in July.

The stock fell 10 percent, or $1.49, to close at $13.56. Its 52-week low is $10.58; the high is $28.49.

On Tuesday, Trimeris and its partner Roche announced that tests of patients receiving Fuzeon along with other AIDS drugs demonstrated a clear improvement over those who were taking drugs without Fuzeon. Fuzeon is designed to assist patients who have undergone previous AIDS treatments. It attacks the HIV virus outside of healthy cells.

The inhibitor regime produced “undetectable levels of HIV” among 52 percent of the patients compared to 27 percent without Fuzeon, Trimeris said.

“These results are particularly compelling given that they are derived from one of the largest prospective databases evaluating optimal treatment regimens selected with the assistance of resistance testing,” Trimeris said in a statement.