Human Genome Sciences Inc said on Monday that its experimental lupus drug had succeeded in a late-stage clinical trial, shocking many who had written the product off as dead and fueling a 228 per cent stock jump.

The results, which were announced just after midnight on Sunday, showed patients who took the drug, Benlysta, demonstrated a statistically significant improvement in the symptoms of their disease compared with those taking a placebo.

Results of the 52-week trial - the first of two requested by US regulators - showed 57.6 per cent of patients taking a high dose of Benlysta experienced an improvement in their symptoms, compared with 43.6 per cent who took a placebo.

The result was statistically significant and met the main goal of the clinical trial.

Of patients who took a low dose of the drug, which is administered once a month by IV infusion, 51.7 per cent showed improvement in their symptoms, a figure that was also statistically significant.

The main goal of the trial was to show a four-point or greater improvement in disease symptoms as measured by a scale known as Selena Sledai. A four-point reduction on a scale of 10 constitutes a good, or meaningful, response. The lower the score, the less disease activity a patient has. All patients entering the trial had a score of six or higher.

The trial also required that patients did not experience a worsening of their disease in any organ beyond the originally affected one. The trial met all of these goals at both doses.

Lupus is a complex disease that causes the immune system to attack the body's own tissue and organs, including the joints, kidneys, heart, lungs, brain, blood or skin. Symptoms include achy joints, fever, arthritis, kidney damage, chest pain and skin rash, among others.

Data from the 867-person trial, known as BLISS-52, take the company one step closer to being the first to have a new lupus drug approved in 50 years. Multiple drugs are approved for other indications and used to treat lupus, but none has been approved specifically for the disease in decades.

The disease affects an estimated 1.5 million people in the United States and 5 million worldwide, according to the Lupus Foundation of America.

Human Genome's drug is not expected to treat all patients, but is aimed at a subgroup who have mild to moderate disease. That is because an earlier trial failed to meet its main goal, but investigators noticed that a subset of patients did very well.

The late-stage, or Phase III trials were designed in conjunction with the US Food and Drug Administration to test those patients most likely to benefit from the drug.

The initial market for Benlysta, therefore, consists of some 300,000 patients, Human Genome chief executive Thomas Watkins said in an interview.

Roughly 150,000 patients in the United States stand to benefit from the drug, if it is approved. While that may represent a small portion of the total number affected by lupus, it is nonetheless an important advance, and Watkins said that from a corporate perspective, it represents a substantial revenue opportunity.

'A drug like this, with this kind of promise, has the potential to be a blockbuster drug,' Watkins said. Drugs are typically referred to as blockbusters when they generate $1 billion or more in revenue. Profit would be split between Human Genome and its partner, GlaxoSmithKline.

The second of the two late-stage trials is due to be reported in November. There are no substantive differences between the two trials, the company said. The first was conducted in Asia, Latin America and Eastern Europe, and the second in Europe and North America.

If the second, confirmatory trial, replicates the findings in this trial, Human Genome and GlaxoSmithKline would aim to file for approval of the drug by early 2010, according to David Stump, the company's head of re