Symptoms come and go in most cases of multiple sclerosis (MS), a chronic disease in which the immune system attacks myelin, the nonconductive sheath that surrounds neurons' axons. Yet 10 to 15 percent of cases are progressive rather than relapsing. This more severe version appears later in life and is marked by steadily worsening symptoms. No treatments are currently available, but that might be about to change.

In September pharmaceutical company Hoffmann–La Roche announced positive results from three large clinical trials of ocrelizumab, an injectable antibody medication that targets B cells, for both relapsing and progressive MS. They found that the drug was more effective at treating relapsing MS than interferon beta-1a (Rebif), a top-performing drug now used to treat the disease. Even more exciting, it slowed the advance of symptoms in patients with progressive MS for the entire 12-week duration of the study. “The drug has dramatic effects on relapsing MS, and we finally have our foot in the door with the progressive form,” says Stephen Hauser, a neurologist at the University of California, San Francisco, who was involved in the trials.

The fact that ocrelizumab works on both types of MS is a tantalizing clue for scientists trying to understand the root causes of the disease and figure out why the inflammation of the relapsing form eventually turns into progressive degeneration in some patients. “These results give evidence that the inflammatory and the degenerative components of MS are related,” Hauser says. “The big question now is, If we begin treatment really early, can we protect relapsing patients from developing the progressive problems later on?”

With these trials, Roche has cleared the last major hurdle in the FDA's drug-testing protocol. The company plans to file for approval to treat both forms of MS in early 2016, which means the drug could be on shelves as soon as 2017.