LONDON (Reuters) - A drug developed to fight leukemia appears to stop multiple sclerosis in its early stages and restore lost function to patients, British researchers said on Wednesday.

An undated image of the human brain taken through scanning technology. REUTERS/Sage Center for the Study of the Mind, University of California, Santa Barbara/Handout

The three-year study of Bayer AG and Genzyme Corp’s alemtuzumab for the first time show long-term improvement in disability, Alasdair Cole, a neurologist at the University of Cambridge, said in a telephone interview.

The drug, made under the brand name Campath, appears to regenerate brain cells and reverse the effects of relapsing-remitting multiple sclerosis, the researchers found.

“This is the first drug that has shown that people’s disability at the end of a period of time has actually improved,” Cole, who helped lead the study, said. “That is really encouraging for people with the disease.”

Multiple sclerosis is a disease in which the immune system mistakenly attacks and damages the myelin sheath that protects nerve cells. It affects 2.5 million people globally and can cause symptoms ranging from vague tingling to blindness and paralysis.

Standard treatments using a protein known as recombinant interferon beta include Biogen Idec Inc’s Avonex, the newer treatment Tysabri, developed by Biogen Idec and Elan, and Merck KGaA’s Rebif.

The study compared alemtuzumab to Rebif in 300 men and women with early stage MS, marked by flare-ups of numbness, vision loss and other problems that can last weeks or months.

Campath reduced the number of attacks by 74 percent compared to Rebif and reduced the risk of disability worsening by 71 percent.

More startling, Cole said, was that after three years people on the experimental drug showed better coordination, walked more quickly and had less brain tissue damage.

“The most remarkable thing is if you look at the disability of all the patients at the end of the treatment, the people on the standard treatment were more disabled,” he said.

“The patients on alemtuzumab have an increase in brain volume, which means the brain is repairing itself.”

The researchers did not compare the drug directly to Tysabri but based on existing data said they believe alemtuzumab is a more effective and safer treatment.

Tysabri is widely considered the most effective MS drug on the market, but its use has been crimped due to safety concerns.

Campath was first used in humans in the early 1980s to treat a form of leukemia. It is a monoclonal antibody, a lab-engineered immune system protein that attacks specific targets -- in this case white blood cells that cause damage to the myelin sheath around nerves.

Without this protection, the nerves are like bare wires that fuse together and short-circuit, leading to brain damage and producing symptoms of the disease, Cole said.

The drug, however, only works for people with early stage MS and also carries risks of serious but treatable side effects that included thyroid dysfunctions and a fatal blood condition.

Cole said the drug, about to go into final Phase III clinical trials, could hit the market in four years and could be a candidate for fast-track treatment from regulators.

“Whether or not alemtuzumab itself ends up on the market, this study will still be a landmark study showing you can improve the disability of people with multiple sclerosis if you treat it early enough and aggressively.”

“The point to me is we’ve drawn a line in the sand. We are in a new era and we can reverse disability.”