* 43.2 pct of patients respond vs 33.8 pct for placebo

* Paves way for approval of first new lupus drug in 50 yrs

* Human Genome stock up 33 pct

(Updates with details, analysis)

By Toni Clarke and Ben Hirschler

BOSTON/LONDON, Nov 2 (Reuters) - Human Genome Sciences Inc (HGSI.O: Quote, Profile, Research) said its experimental lupus drug Benlysta eased symptoms in more than 43 percent of patients who took it in a clinical trial, paving the way for approval of the first new treatment for the disease in 50 years.

The news sent Human Genome's shares up 33 percent, adding $1 billion to its market value and turning the once unloved company into the hottest biotech story of the year.

Data from a late-stage clinical trial showed patients who took a high dose of the drug, in combination with standard therapies, experienced a significant improvement in symptoms compared with those taking standard treatments in combination with a placebo.

The results met the main goal of the trial, which was the second of two needed for the drug to be considered for approval by the U.S. Food and Drug Administration.