• J K MacDonald and J W D McDonald.
• Robarts Research Institute, Robarts Clinical Trials, P.O. Box 5015, 100 Perth Drive, London, Ontario, CANADA, N6A 5K8. jmacdon1@uwo.ca
• Cochrane Db Syst Rev. 2007 Jan 1(1):CD006097.

BackgroundThe pathogenesis of Crohn's disease involves migration of leukocytes into gut tissue and subsequent inflammation. Natalizumab (Tysabri(R), Elan Pharmaceuticals and Biogen Idec) a recombinant humanized IgG4 monoclonal antibody that blocks adhesion and subsequent migration of leukocytes into the gut by binding the alpha4 integrin is a member of a new class of molecules known as selective adhesion molecule (SAM) inhibitors. The results of animal studies suggest that alpha4 integrin blockade could be a useful therapy for inflammatory bowel disease. The results of randomized controlled trials suggest that natalizumab may be an effective therapy for active Crohn's disease. This systematic review summarizes the current evidence on the use of natalizumab for the induction of remission in Crohn's disease.ObjectivesTo determine the efficacy and safety of natalizumab for induction of remission in Crohn's disease.Search StrategyA computer assisted search of the Cochrane Central Register of Controlled Trials, the Cochrane Inflammatory Bowel Disease and Functional Bowel Disorders Review Group Specialized Trials Register, MEDLINE and EMBASE was performed to identify relevant publications between 1966 and September 2006. The medical subject heading (MeSH) terms "Crohn disease" or "inflammatory bowel disease", "Natalizumab" or "Antegren" or "Tysabri" and "Antibodies, Monoclonal" were used to perform key word searches of each database. Manual searches of reference lists from potentially relevant papers were performed in order to identify additional studies that may have been missed using the computer-assisted search strategy. Abstracts from major gastroenterological meetings were searched to identify research submitted in abstract form only. Personal contacts, leaders in the field, and the manufacturers were contacted to identify other studies which may not be published.Selection CriteriaWe included only randomized controlled trials comparing natalizumab to a placebo or control therapy for the induction of remission in Crohn's disease.Data Collection And AnalysisData were analyzed using Review Manager (RevMan 4.2.8). All data were analyzed on an intention-to-treat basis. For pooled data, summary test statistics were derived using the relative risk and 95% confidence intervals. Fixed and random effects models were used where appropriate. The definitions of treatment success, remission and clinical improvement were set by the authors of each paper, and the data were combined for analysis only if these definitions were sufficiently similar.Main ResultsPooled data from the four included studies suggest that natalizumab (300 mg or 3 to 4 mg/kg) is effective for induction of clinical response and remission in patients with moderately to severely active Crohn's disease. This benefit is statistically significant for one, two and three infusion treatments. There was a trend toward increased benefit with additional infusions of natalizumab. Natalizumab appears to provide greater benefit for patient subgroups characterized by objective confirmation of active inflammation or chronically active disease despite conventional therapies. These subgroup analyses demonstrated significantly greater clinical response and remission rates for natalizumab compared with placebo in patients with elevated C-reactive protein levels, active disease despite the use of immunosuppressants, or prior anti-tumor necrosis factor therapy. These benefits were apparent for both short term (one infusion) and longer term treatment (two or three infusions). Natalizumab was generally well tolerated and the safety profile observed in the four included studies was similar. Adverse events occurred infrequently and were experienced by a similar proportion of natalizumab and placebo treated patients. There were no statistically significant differences between natalizumab and placebo treated patients in the proportions of patients who withdrew due to adverse events or those who experienced serious adverse events. The included trials lacked adequate power to detect serious adverse events that occur infrequently. Recently, two patients with multiple sclerosis treated with natalizumab in combination with interferon beta-1a and one patient with Crohn's disease treated with natalizumab in combination with azathioprine developed progressive multifocal leukoencephalopathy (PML) resulting in two patient deaths. A retrospective investigation was conducted to assess the risk of PML in natalizumab treated patients and no new cases were identified.Authors' ConclusionsPooled data suggest that natalizumab is effective for induction of clinical response and remission in some patients with moderately to severely active Crohn's disease. The clinical benefit of induction therapy with natalizumab in Crohn's disease should be weighed against the potential risk of serious adverse events. Preliminary data from the retrospective investigation of adverse events associated with natalizumab suggest that it may be possible to identify patients at risk for PML by testing for the appearance of JC virus in plasma.

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