US regulators are undertaking a priority review of Roche/Genentech's experimental multiple sclerosis therapy Ocrevus, which many believe has the potential to transform treatment of the disease.

Ocrevus (ocrelizumab) is an investigational, humanised monoclonal antibody designed to selectively target CD20-positive B cells, a specific type of immune cell thought to be a key contributor to myelin and axonal (nerve cell) damage, which can lead to disability in people with MS.

Data from the OPERA I and OPERA II Phase III trials involving patients with relapsing MS, which affects around 85 percent of people at time of diagnosis, found that the drug beat Rebif (interferon beta-1a) in reducing the three major markers of disease activity over a two-year period.

The trials showed a 46 percent and 47 percent reduction in the annualised relapse rate, as well as a 43 percent and 37 percent risk reduction in confirmed disability progression for 12 weeks compared with interferon beta-1a.

In the Phase III ORATORIO trial in people with primary progressive MS, a form of the disease marked by steadily worsening symptoms for which there is no approved treatment, Genentech's biologic significantly slashed the progression of clinical disability by 24 percent versus a for at least 12 weeks (the primary endpoint), and by 25 percent over 24 weeks (a secondary endpoint).

"Ocrevus is the first investigational medicine to significantly reduce disability progression in people with relapsing and primary progressive forms of MS," noted Sandra Horning, Roche's chief medical officer and head of Global Product Development.

"We are pleased by the FDA's decision to classify their review of the BLA as priority because we believe Ocrevus has the potential to help people living with either of these two forms of MS."

The drug is also the first investigational medicine to receive Breakthrough Therapy Designation from the US Food and Drug Administration in MS; a decision is expected by December 28.