Tysabri is a humanized monoclonal antibody approved for adult patients with relapsing forms of multiple sclerosis (MS), to slow the worsening of disability that is common in patients with MS and decrease the number of flare-ups (relapses), and in adult patients with Crohn’s disease. Because Tysabri increases the risk of progressive multifocal leukoencephalopathy (PML), a rare brain infection that usually causes death or severe disability, Tysabri is generally recommended for patients that have not been helped enough by, or cannot tolerate, another treatment for MS. Tysabri does not cure MS and has not been studied for longer than two years or in patients with chronic progressive MS. In a 2-year study, some people taking Tysabri were considered to be free from MS disease activity because they had fewer flare-ups, no disease progression and no new or newly active MRI lesions. Tysabri is marketed in the United States by Biogen Idec.
How Tysabri Works
Tysabri binds to the α4 integrin, reducing the transfer of inflammatory immune cells into the central nervous system and the intestine. Its ability to inhibit the transfer of such cells into the central nervous system is important because MS involves an autoimmune process whereby immune cells destroy the myelin sheath, which surrounds and protects neurons much like an insulator surrounding an electrical wire. When the myelin sheath is damaged, neurons are unable to effectively conduct electrical signals and communicate throughout the nervous system, resulting in the various kinds of physical disabilities seen in MS. Tysabri’s ability to inhibit the transfer of inflammatory immune cells into the intestine is important in Crohn’s disease because the infiltration of such cells into the gastrointestinal tract is believed to cause the inflammation characteristic of Crohn’s disease.
Tysabri was launched for MS in late 2004 and then withdrawn from the market in early 2005 due to safety concerns. Three cases of PML, a viral infection of the brain that usually leads to death or severe disability, were reported (two in MS patients and one in a Crohn’s disease patient). Tysabri was re-introduced to the market for MS in June 2006 with revised labeling, greater safety warnings and a risk management plan entitled TOUCH. In 2008 Tysabri was launched in the US for patients with moderate to severe Crohn’s disease who have had an inadequate response to, or are unable to tolerate, conventional treatments for Crohn’s disease or TNF inhibitors.