The anti-α4-integrin monoclonal antibody natalizumab (Tysabri) is effective in most patients in treating multiple sclerosis (MS), but a percentage of people develop infusion reactions or stop responding because they develop neutralizing antibodies, and some people may have neutralizing antibodies without symptoms. Expression of CD49d, a subunit of α4-integrin on peripheral blood mononuclear cells (PBMCs) fall with successful treatment. French researchers looked at a group of people with relapsing-remitting MS, and found that levels of CD49d expression rise early or do not fall in patients with neutralizing antibodies--this could be used as a surrogate biomarker of natalizumab efficacy. Abstract