Brain infection would be bad news for Roche's MS drug Ocrevus

Roche is investigating a case of a potentially deadly brain infection in a patient with its new multiple sclerosis drug, Ocrevus.

Analysts have predicted that Ocrevus (ocrelizumab) could generate sales of more than $4 billion by 2022, but any confirmed signs of serious side-effects would be bad news.

The company is looking into the case of Progressive Multifocal Leukoencephalopathy (PML) – although the suggestion is that the infection was caused by a prior treatment.

The patient had previously been treated for three years Biogen’s Tysabri (natalizumab), and had received only a single dose of Ocrevus in April.

Reuters reports that Roche is trying to determine the source of the infection, which is associated with MS drugs like Tysabri that suppress the immune system.

In a statement cited by the news agency, Roche said the doctor treating the patient had reported the infection as related to the previous treatment with Tysabri.

No cases of PML occurred in clinical trials for Ocrevus, and the patient had previously tested positive for John Cunningham virus, which is normally harmless but can lead to the brain disease in MS patients with weakened immune systems.

Approved by the FDA in March, Ocrevus is an important part of Roche’s strategy to replace lost sales as its three biggest selling drugs, MabThera, Herceptin and Avastin become vulnerable to cheaper competition from biosimilars.

As well as working in relapsing disease, Ocrevus is the first disease-modifying drug approved for the debilitating primary progressive form of MS.

A humanised monoclonal antibody, Ocrevus targets CD20-positive B cells, thought to contribute to damage in myelin nerve insulation and nerve cells.

By targeting CD20 on B cells, but not on stem cells or plasma cells, Ocrevus is designed to preserve other functions of the immune system.

Roche’s Swiss rival Novartis is developing a rival MS drug, BAF312, for secondary progressive multiple sclerosis, which could be approved in the second half of this year.