Natalizumab Natalizumab (Tysabri) is a novel monoclonal antibody (mAb) dimmed againts the adhesion molecule very late antigen-4 (VLA-4) that is expressed on leukocytes (except neutrophils). This agent is the first and currently the only mAb approved for use in MS. Natalizumab prevents leukocytes from binding to the vascular endothelium, especially
during inflammation and ultimately prevents their transmigration into the CNS. Natalizumab had promising results in a phase II trial and two phase III clinical trials. In the phase III trial
AFFIRM, sustained progression of disability Was reduced by 42%, clinical relapse rate was reduced by 68%, and MRI activity (enhancing lesions) was reduced by 92% in the natalizumab- treated group compared to placebo. Natalizumab was removed from the market in early 2005 after tWO MS patients from the seond phase III trial (SENTINEL) developed a rare, deadly viral infection of the brain called progressive multifocal leukocncephalopathy (PML). Both patients were on combination therapy ,Avonexe plus natalizumab