REVIEW. TRANSLATING MOLECULAR BIOLOGY INTO CLINICAL PRACTICE: THE ROLE OF TNF-α IN CROHN S DISEASE. William J. Sandborn, MD* ABSTRACT

Transcription

1 TRANSLATING MOLECULAR BIOLOGY INTO CLINICAL PRACTICE: THE ROLE OF TNF-α IN CROHN S DISEASE William J. Sandborn, MD* ABSTRACT Crohn s disease (CD) is characterized by intestinal inflammation and tissue destruction that are mediated in part by the inappropriate release of inflammatory cytokines. During the last decade, the inhibition of tumor necrosis factor (TNF)-α and other inflammatory cytokines has emerged as a therapeutic strategy for CD and other disorders that are associated with elevated TNF-α production. Monoclonal antibodies against TNF-α (eg, infliximab, adalimumab) have been shown to be effective for the induction and long-term maintenance of remission in CD. Antibody Fab fragments have also been shown to improve the symptoms of CD, and an anti-tnf-α Fab conjugated with polyethylene glycol (certolizumab pegol) may soon become available for the treatment of CD. Other potential therapeutic strategies include the use of recombinant soluble TNF-α receptor, which binds to and inactivates circulating TNF-α; agents that block leukocyte adhesion and transendothelial migration; and antibodies that target other inflammatory cytokines. Recent analyses of clinical trial data have suggested that elevated levels of the inflammatory marker C-reactive protein (CRP) may help to identify patients who are most likely to benefit from TNF-based therapies. Additional research is required to develop algorithms to incorporate information about CRP concentration or other biomarkers into clinical decision making for CD. (Adv Stud Med. 2005;5(9C):S852-S859) *Professor of Medicine, Division of Gastroenterology and Hepatology, Mayo Clinic College of Medicine, Rochester, Minnesota. Address correspondence to: William J. Sandborn, MD, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, MN sandborn.william@mayo.edu. Crohn s disease (CD) is characterized by a sustained inappropriate immune response by a variety of cell types in the intestinal mucosa, resulting in persistent intestinal inflammation and tissue destruction. 1 The tissue injury of CD is primarily mediated by the release of a number of proinflammatory cytokines from T helper type 1 (Th1) lymphocytes, including interleukin (IL)-12, tumor necrosis factor (TNF)-α, and interferon (IFN)-. 2 TNF-α is thought to be of particular importance in the pathogenesis of CD. 3 The concentration of TNF-α is elevated in the blood, stool, and intestinal mucosa of patients with CD. 3-6 TNF-α expression is closely related to the development of inflammatory bowel disease in animal models of CD 7,8 and a number of biologic agents that interfere with the activity of TNF-α have been shown to improve the symptoms of CD in clinical trials. 3-8 During the last decade, inhibition of TNF-α has emerged as a potential therapeutic strategy for CD and for other diseases that are associated with excessive production of Th1 cytokines, including rheumatoid arthritis, psoriatic arthritis, and psoriasis Several different biotechnology approaches to the inhibition of TNF-α have been developed, and the results of clinical trials have shown that some TNF-α inhibitors can help to induce or maintain remission in patients with CD. However, well-designed clinical trials have shown that not all agents that block the effects of TNF-α are effective treatments for CD. The reasons for the variable effectiveness of anti TNF-α in CD are not well understood. It may be the case that inhibition of TNF-α alone is not sufficient to improve the symptoms of CD, and that other mechanisms of action, such as the induction of T-cell apoptosis, are also required for clinical efficacy. Alternatively, differences in clinical efficacy between various biotechnology agents may be related to differences in binding affinity for a given antigen. S852 Vol. 5 (9C) October 2005

2 This article reviews a number of potential therapeutic strategies that have been developed to improve the symptoms of CD by targeting the biological effects of TNF-α. Other possible approaches to the inhibition of T-cell mediated tissue injury are also briefly described. A companion article by Dr Stephen B. Hanauer discusses the integration of anti TNF-α therapies into clinical practice for the treatment of patients with CD. STRATEGIES TO INHIBIT TNF-α FUNCTION TNF-α produces several physiological effects that promote inflammation: it stimulates the production of other proinflammatory cytokines, such as IL-1, IL-6, and IFN- ; it stimulates further TNF-α production; it disrupts the intestinal endothelial cell boundary, increasing the permeability of the endothelial layer to antigens; and it increases the activity of antigen presenting cells. 12 One strategy to block these proinflammatory effects of TNF-α that has been extensively evaluated in CD is the administration of monoclonal antibodies against TNF-α. Infliximab, which is approved by the US Food and Drug Administration (FDA) for the treatment of CD, is a chimeric IgG1 monoclonal antibody to TNF-α that includes human constant domains and murine variable domains. 13 Controlled clinical trials have shown that infliximab is effective for both the induction and maintenance of remission in patients with CD A second anti TNF-α monoclonal antibody, adalimumab, is FDA-approved for the treatment of rheumatoid arthritis. 18 Adalimumab is a fully human recombinant IgG1 antibody to TNF-α, in which human heavy and light chains with binding affinity for TNF-α were independently identified and then combined, resulting in the removal of all murine sequences. 19 Adalimumab has been shown to be effective for the induction of remission in patients with CD. 20 Preliminary data also indicate that adalimumab is effective as maintenance therapy. 21 An investigational agent, CDP-571, is a humanized IgG4 monoclonal antibody to TNF-α. 22 In initial clinical trials, CDP-571 produced short-term improvement in CD symptoms after 2 to 4 weeks of treatment, but did not induce remission and was not associated with improvement in clinical outcomes after 6 months. 23,24 An alternative to the use of antibodies is the removal of the Fc antibody portion and the use of only the Fab fragment (the variable domains and hinge region). One example of this approach is certolizumab pegol (CDP-870), a humanized TNF-α Fab fragment in which the murine framework that surrounds the antigen-binding portion of the antibody has been replaced by human sequences and the Fc portion of the antibody has been removed (Figure 1). 19,25 The Fab fragment is linked to polyethylene glycol (PEG) to increase its half-life. 19 CDP-870 can be administered by intravenous or subcutaneous administration, and it is being developed as a subcutaneous treatment for CD. The removal of the Fc antibody portion has the Figure 1. Protein-Engineered Antibodies and Fusion Proteins Chimeric monoclonal antibody 75% Human Mouse Humanized monoclonal antibody Human CDR Human recombinant antibody 95% Human 100% Human VL Humanized Fab fragment VH CH1 Human recombinant receptor/ Fc fusion protein Fc 100% Human Receptor Constant 2 Constant 3 CDR = complementary determining region; CH1 = complementary heavy chain; PEG = polyethylene glycol; VH = immunoglobulin heavy chain; VL = variable light chain. Copyright MedReviews, LLC. Reprinted with permission of MedReviews, LLC. Hanauer SB. Rev Gastroenterol Disord. 2004;4(suppl 3):S18-S Reviews in Gastroenterological Disorders is a copyrighted publication of MedReviews, LLC. All rights reserved. PEG PEG Advanced Studies in Medicine S853

3 potential therapeutic advantage that it avoids complement fixation, and thereby reduces antibody-dependent cytotoxicity and T-cell apoptosis. However, it is also possible that antibody-mediated T-cell apoptosis is one mechanism by which the anti TNF-α antibodies produce their therapeutic effects. This is an important issue that has very recently evolved with respect to the results of clinical trials. CDP-870 significantly improved the symptoms of CD in 1 recent clinical trial, but only in patients with elevated C-reactive protein (CRP). 26,27 However, 2 subsequent, large clinical trials that prospectively evaluated CDP-870 in patients with elevated CRP and in those without elevated CRP demonstrated efficacy in both subgroups of patients (S. Schreiber et al, unpublished data, 2005). 28 TNF-α produces its effects by binding to 2 cell membrane receptors, p55 and p A third potential therapeutic strategy for CD is the administration of soluble TNF-α receptors, which bind to TNF-α and prevent it from activating its normal biological targets. Two different approaches to this strategy have been developed. The first is represented by onercept, a recombinant soluble TNF-α p55 receptor. Onercept has a relatively short half-life and must be administered at least 3 times a week by subcutaneous injection. One clinical trial that examined onercept for the treatment of CD found that it did not produce a significant beneficial effect. 30 The second approach is represented by etanercept, a fusion protein that combines the extracellular portion of the p75 receptor with the Fc portion of human IgG1 (Figure 2). 3,19 The addition of the Fc portion increases the half-life of the molecule. In a placebocontrolled trial of patients with CD, etanercept was not associated with significant improvement in symptoms. 31 One potential limitation with all of the antibody-based therapies is immunogenicity and the development of neutralizing antibodies. An important determinant of immunogenicity is the degree to which the antibody incorporates nonhuman components. In general, humanized antibodies (which contain approximately 5% murine sequences) or fully human antibodies (which contain no murine sequences) are less immunogenic than chimeric monoclonal antibodies (which contain approximately 25% murine sequences). However, it is possible for antibodies to develop in response to humanized or fully human antibodies, or even to endogenous antibodies. 32 Lower antibody doses tend to be more immunogenic, and higher doses are more likely to produce tolerance. Loading doses and the use of constant therapy (dosing based on the drug half-life to ensure that the patient is always exposed to the antibody) can also reduce the likelihood of immunogenicity. Immunogenic reactions can also be reduced by the coadministration of an immunosuppressant such as azathioprine, 6-mercaptopurine, or methotrexate. There may be a modest reduction in immunogenicity by pretreatment with a dose of intravenous corticosteroids before administering monoclonal antibodies. The risk of immunogenic reactions may also be greater Figure 2. Recruitment of Neutrophils into Inflamed Tissue L-selectin Neutrophil E/P-selectin Rolling 2 IL-8 PAF β2-integrin activation 1 3 L-selectin β2-integrin Tight adhesion ICAM-1 4 Transmigration Endothelium Recruitment of neutrophils into inflamed tissue results from rolling, tight adhesion, and transendothelial migration. TNF-α promotes all 3 steps by increasing the expression of E/P selectin by endothelial cells by (1) inducing the production of platelet activating factor (PAF) and interleukin (IL)-8 by endothelial cells; (2) increasing expression of intercellular adhesion molecule-1 (ICAM-1); and (3) inducing the local production of various chemotactic substances, such as IL-8 and leukotriene B4. Reprinted with permission from the BMJ Publishing Group. van Deventer SJ. Gut. 1997;40: S854 Vol. 5 (9C) October 2005

4 when antibodies are administered by subcutaneous administration than when administered intravenously. It is likely that combining the various strategies to reduce antibody development may produce additive reductions in the risk of clinically significant immunogenicity, although the optimal strategies to prevent immunogenic reactions have not been well defined by clinical trials. THE IMPORTANCE OF CRP IN PREDICTING RESPONSE TO THERAPY Although all of the anti TNF-α therapies block the effects of TNF-α, the efficacy of these agents in clinical trials of patients with CD has been quite variable. The reason for this variability is not well understood at present. One possibility is that only IgG1 antibodies are effective. However, as noted previously, the IgG4 antibody CDP-870 also improved the symptoms of CD during the first few weeks of treatment. In addition, the 2 soluble receptor agents were not at all effective for CD. It has long been recognized that there is an association between circulating levels of the acute-phase reactant CRP and the symptoms of active CD. 33,34 This relationship is not strong however, and it was initially believed by most clinicians that CRP and CD severity were not causally linked. As a result, treatment decisions have generally been made on the basis of clinical symptoms alone, without regard to CRP findings. More recently, post hoc subgroup analyses in a number of clinical trials of patients with CD have suggested that CRP may be more directly associated with the inflammation of CD, and that patients with elevated CRP levels are more likely to respond to some treatments than patients who do not have elevated CRP levels. However, this effect is largely due to differences in the response of patients to placebo between those with and without elevated CRP levels. During the induction of response or remission treatment, the placebo response rate is often quite pronounced in patients who have normal CRP levels at baseline. In contrast, the placebo response rate in some studies was lower among patients who have symptoms and elevated CRP levels. 24,26,35 It has been hypothesized that some patients who have symptoms of CD may actually have other conditions, such as short-bowel syndrome, bile-salt diarrhea, irritable bowel syndrome, partial mechanical obstructions caused by fibrosis of CD or from previous operations, bacterial overgrowth, or other causes of symptoms. When these patients are entered in clinical trials, a substantial number may improve spontaneously, whereas patients with biologically driven inflammation tend to have a less benign clinical course and less likelihood of a significant improvement with placebo. However, although it has been observed in post hoc subgroup analyses from several studies that the placebo response rate is greater in patients with low CRP levels, the explanation for this phenomenon remains speculative at present. The results from 2 large clinical trials, which prospectively evaluated CDP-870 in patients with and without elevated CRP, did not demonstrate an effect of elevated CRP on either the placebo response rate or efficacy (S. Schreiber et al, unpublished data, 2005). 28 It is also possible that there are groups of patients with similar clinical manifestations but distinct pathophysiological processes that produce CD, and that therapies that block TNF-α are beneficial in some subgroups but not in others. Additional clinical trials are in progress to clarify the relationship between CD symptoms, biological markers such as CRP, and endoscopy findings. 36 These studies may eventually lead to the development of algorithms to guide clinical decision making for patients with CD. Until such guidelines have been developed, a reasonable approach is to assess CRP values for patients with symptoms of CD. If CRP is elevated and there are no symptoms that suggest that emergency treatment is required (eg, obstructive symptoms), therapy may be initiated with an immunosuppressive or biologic agent without the need for a structural evaluation with endoscopy or radiographic studies. For a patient who is symptomatic but who has a normal CRP value, a structural evaluation should be considered. However, there is no single approach to the integration of CRP findings into the management of CD at present. THE ROLE OF T-CELL APOPTOSIS IN CD TREATMENT The first 2 anti TNF-α medications that were examined for the treatment of CD were infliximab and etanercept. Infliximab was effective in patients with CD, whereas etanercept was not. 16,31 It was hypothesized that infliximab may induce apoptosis of T cells. In vivo experiments found that that infliximab, but not etanercept, induced T-cell apoptosis Advanced Studies in Medicine S855

5 Subsequent research found that adalimumab and infliximab both induced T-cell apoptosis, and that etanercept did not. 40 These findings provide an appealing explanation for the differences in clinical efficacy of these agents that were observed in patients with CD, and suggest that apoptosis was linked to IgG1 monoclonal antibody therapeutic agents. However, the CDP-870 (humanized Fab antibody fragment) is also effective for CD. Therefore, more research is needed to further define the role of T-cell apoptosis in the treatment response with these agents. OTHER INFLAMMATORY CYTOKINES IN CD: IL-12, IFN-, IL-6 As noted previously, CD is generally thought to develop as a consequence of the abnormal production of Th1 proinflammatory cytokines. Therefore, it has been hypothesized that other Th1 cytokines may be important in the pathogenesis of CD, and that therapeutic interventions to block these cytokines might improve symptoms in these patients. Antibodies have been developed against IL-6, IL-12, and IFN-, and initial clinical trials have evaluated the effectiveness of these antibodies for patients with CD. The effects of an anti IL-12 antibody were examined in a phase 2 clinical trial, which found that 7 weeks of treatment reduced the expression of inflammatory cytokines within the colonic lamina propria, and resulted in clinical improvement in more patients than with placebo administration. 41 Studies of anti IFN- antibody failed to demonstrate significant clinical benefit in the study primary endpoint for patients in general, but for the subgroup of patients with elevated CRP, repeated dosing did appear to produce some benefit. 42 IL-6 is a major stimulant of the production of CRP by the liver, and a single small study suggested that an antibody against the IL-6 receptor (MRA) produced some clinical benefit in patients with elevated CRP at baseline. 43 Thus, the results of these preliminary studies suggest that treatments that target any of several Th1 cytokines may improve symptoms in patients with CD. CELL ADHESION MOLECULES Activated T lymphocytes migrate from the circulation to peripheral sites of inflammation by means of a carefully coordinated series of interactions between cell adhesion molecules on lymphocytes and receptor molecules on endothelial cells. 3 Agents that interrupt these adhesion molecule interactions and prevent the transendothelial migration of T lymphocytes have been evaluated for the treatment of CD. One approach is an antisense oligonucleotide against the ribonucleic acid for intercellular adhesion molecule-1. This antisense oligonucleotide (alicaforsen; ISIS- 2302) improved symptoms of CD in some preliminary clinical trials, 44 but was not effective in a larger phase 3 study. 45 Post hoc subgroup analyses suggested that the dose of alicaforsen used may have been too low, and a high-dose trial was initiated, which also failed to demonstrate significant improvement in patients with CD. 46 Topical alicaforsen is being tested as therapy for pouchitis and for proctitis. Natalizumab is an IgG4 humanized monoclonal antibody to α4 integrin, a cellular adhesion molecule that is important in the homing of lymphocytes to the gut. Natalizumab was developed primarily for the treatment of multiple sclerosis (MS) and CD. It was approved by the FDA in December 2004, and withdrawn from the market in February 2005 after 2 patients who received natalizumab in combination with PEG-interferon developed progressive multifocal leukoencephalopathy (PML). 47 In another clinical trial, a patient with CD treated with natalizumab in combination with azathioprine who was initially thought to have had a fatal astrocytoma was reclassified as having PML. 48 Natalizumab was clearly effective for the treatment of MS, and was approved under an accelerated approval program on the basis of 1-year data in patients with MS that demonstrated that it was approximately twice as effective as IFN-beta. An intensive safety evaluation of all of the patients with MS who were treated with natalizumab has been completed, and no additional cases of PML were identified. 49 Regulatory review of these safety data to determine whether natalizumab should return to clinical use for MS is anticipated in the latter half of Safety evaluation of patients with CD and rheumatoid arthritis who were treated with natalizumab is still ongoing. In patients with CD, a phase 3 clinical trial for induction of response and remission failed to demonstrate the efficacy of natalizumab in the overall patient population, but demonstrated efficacy in a subgroup of patients with elevated CRP. 35 A second phase 3 trial for induction of response and remission in patients with elevated CRP also demonstrated efficacy with natalizumab. 50 In addition, a phase 3 trial for maintenance of response and remission S856 Vol. 5 (9C) October 2005

6 with natalizumab demonstrated a significant maintenance benefit throughout 12 months. 35 A second antibody, MLN-02 (also referred to as LDP-02), is a fully human IgG1 monoclonal antibody against α4β7, a cell adhesion molecule that interacts with mucosal addressin cell adhesion molecule 1 in the gut mucosa. MLN-02 is thought to affect lymphocyte homing specifically in the gut, with less effect on lymphocyte trafficking in other tissues. 51 Thus, it is expected that MLN-02 should be associated with a lower risk of PML. A phase 2 clinical trial that examined this agent for ulcerative colitis demonstrated significant effects for induction of response, remission, and endoscopic healing. 52 A second phase 2 trial in patients with CD has been completed, and the result for the primary study endpoint of clinical response was not significant, but the result for the secondary study endpoint of clinical remission was significant. 53 The doses of MLN-02 that were used in the CD study did not completely block α4β7 receptors. In addition, although fully human antibodies are generally less immunogenic than chimeric or humanized antibodies, MLN-02 was highly immunogenic in the ulcerative colitis study in which approximately 40% of patients developed antibodies to MLN-02 after 2 doses, and approximately 25% of patients developed neutralizing antibodies. 52 GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR The treatment strategies described above are based on the hypothesis that CD reflects an abnormally high level of activation of immune cells within the intestinal tract. An alternative view of CD, which suggests that the disorder is actually an immune deficiency disease, has recently been proposed. 54 This concept is based on the observation that certain aspects of CD resemble a number of relatively uncommon disorders that have in common neutrophil dysfunction. These include chronic granulomatous disease, Chediak Higashi syndrome, glycogen storage disease, and other disorders, which primarily affect children. As many as one third to one half of patients with these various neutrophil dysfunction syndromes also develop intestinal inflammation, diarrhea, and perianal fistulas that are indistinguishable from CD, with the exception that they are accompanied by neutrophil dysfunction. Therefore, it has been proposed that therapies to stimulate neutrophil function might be an effective therapy of CD. The efficacy of recombinant granulocytemacrophage colony-stimulating factor (GM-CSF; sargramostim) for the treatment of CD has been evaluated in a placebo-controlled study. 55 In this study of 124 patients, treatment with daily injections of sargramostim for 8 weeks did not improve the primary study endpoint of treatment response, but did improve a secondary endpoint, remission. 55 One patient in the GM-CSF treatment arm developed neutralizing antibodies to GM-CSF. This patient did not experience any clinically significant neutropenia during the study, although the long-term risk is not clear. Approximately 40% of the patients reported bone pain, and 90% had injection-site reactions. Although this study provides some evidence supporting the potential therapeutic role of GM-CSF in CD, the need for daily injections and high incidence of painful side effects may limit its clinical usefulness, especially in comparison with TNF-α treatments, which are generally well tolerated but have rare, potentially serious side effects. SUMMARY Considerable evidence suggests that the proinflammatory cytokine TNF-α is central to the pathogenesis of CD, and that interventions that target TNF-α significantly improve the severity of symptoms, induce remission, and maintain remission in patients with CD. Not all of the anti-tnf-α therapies have been equally effective for the treatment of CD symptoms in clinical trials, and it appears that inhibition of TNF-α alone may not be sufficient to improve symptoms. Some studies have suggested that the induction of T-cell apoptosis may also be required to effectively treat CD, although additional research is required to clarify this issue. Anti TNF-α Fab fragments have also been shown to improve the symptoms of CD in some studies. Administration of soluble T-cell receptors or receptor fusion proteins has not been shown to be effective. Biological markers of inflammation such as CRP may help to identify patients who are most likely to benefit from anti TNF-α or other immunosuppressive therapies. REFERENCES 1. Fiocchi C. Inflammatory bowel disease: etiology and pathogenesis. Gastroenterology. 1998;115: Advanced Studies in Medicine S857

7 2. Romagnani S. Th1/Th2 cells. Inflamm Bowel Dis. 1999;5: van Deventer SJ. Tumour necrosis factor and Crohn s disease. Gut. 1997;40: Murch SH, Lamkin VA, Savage MO, Walker-Smith JA, MacDonald TT. Serum concentrations of tumour necrosis factor alpha in childhood chronic inflammatory bowel disease. Gut. 1991;32: Murch SH, Braegger CP, Walker-Smith JA, MacDonald TT. Location of tumour necrosis factor alpha by immunocytochemistry in chronic inflammatory bowel disease. Gut. 1993;34: Braegger CP, Nichols S, Murch SH, Stephens S, MacDonald TT. Tumour necrosis factor alpha in stool as a marker of intestinal inflammation. Lancet. 1992;339: Spencer DM, Veldman GM, Banerjee S, Willis J, Levine AD. Distinct inflammatory mechanisms mediate early versus late colitis in mice. Gastroenterology. 2002;122: Kontoyiannis D, Pasparakis M, Pizarro TT, Cominelli F, Kollias G. Impaired on/off regulation of TNF biosynthesis in mice lacking TNF AU-rich elements: implications for joint and gut-associated immunopathologies. Immunity. 1999;10: Tobin AM, Kirby B. TNF alpha inhibitors in the treatment of psoriasis and psoriatic arthritis. BioDrugs. 2005;19: Schwartzman S, Fleischmann R, Morgan GJ Jr. Do anti-tnf agents have equal efficacy in patients with rheumatoid arthritis? Arthritis Res Ther. 2004;6(suppl 2):S3-S Hochberg MC, Lebwohl MG, Plevy SE, Hobbs KF, Yocum DE. The benefit/risk profile of TNF-blocking agents: findings of a consensus panel. Semin Arthritis Rheum. 2005; 34: Sands BE. Why do anti-tumor necrosis factor antibodies work in Crohn s disease? Rev Gastroenterol Disord. 2004;4(suppl 3):S10-S Remicade (infliximab) [package insert]. Malvern, Pa: Centocor, Inc; Present DH, Rutgeerts P, Targan S, et al. Infliximab for the treatment of fistulas in patients with Crohn s disease. N Engl J Med. 1999;340: Sands BE, Anderson FH, Bernstein CN, et al. Infliximab maintenance therapy for fistulizing Crohn s disease. N Engl J Med. 2004;350: Targan SR, Hanauer SB, van Deventer SJ, et al. A short-term study of chimeric monoclonal antibody ca2 to tumor necrosis factor alpha for Crohn s disease. Crohn s Disease ca2 Study Group. N Engl J Med. 1997;337: Hanauer SB, Feagan BG, Lichtenstein GR, et al. Maintenance infliximab for Crohn s disease: the ACCENT I randomised trial. Lancet. 2002;359: Humira (adalimumab) [package insert]. North Chicago, Ill: Abbott Laboratories; Fleischmann R, Shealy D. Developing a new generation of TNFalpha antagonists for the treatment of rheumatoid arthritis. Mol Interventions. 2003;3: Hanaeur S, Lukas M, MacIntosh D, et al. A randomized, double-blind, placebo-controlled trial of the human anti-tnfα monoclonal antibody adalimumab for the induction of remission in patients with moderate to severely active Crohn s disease. Gastroenterology. 2004;127: Sandborn WJ, Hanauer SB, Lukas M, et al. Maintenance of remission over 1 year in patients with active Crohn s disease treated with adalimumab: results of a blinded placebo-controlled trial. Am J Gastroenterol. In press. 22. Stephens S, Emtage S, Vetterlein O, et al. Comprehensive pharmacokinetics of a humanized antibody and analysis of residual anti-idiotypic responses. Immunology. 1995; 85: Sandborn WJ, Feagan BG, Hanauer SB, et al. An engineered human antibody to TNF (CDP571) for active Crohn s disease: a randomized double-blind placebo-controlled trial. Gastroenterology. 2001;120: Sandborn WJ, Feagan BG, Radford-Smith G, et al. CDP571, a humanised monoclonal antibody to tumour necrosis factor alpha, for moderate to severe Crohn s disease: a randomised, double blind, placebo controlled trial. Gut. 2004;53: Hanauer SB. Efficacy and safety of tumor necrosis factor antagonists in Crohn s disease: Overview of randomized clinical studies. Rev Gastroenterol Disord. 2004;4(suppl 3):S18-S Schreiber S, Rutgeerts P, Fedorak RN, et al. A randomized, placebo-controlled trial of certolizumab pegol (CDP870) in active Crohn s disease. Gastroenterology. In press. 27. Winter TA, Wright J, Ghosh S, Jahnsen J, Innes A, Round P. Intravenous CDP870, a PEGylated Fab fragment of a humanized antitumour necrosis factor antibody, in patients with moderate-to-severe Crohn s disease: an exploratory study. Aliment Pharmacol Ther. 2004;20: CIMZIA demonstrates positive results in two pivotal phase III Crohn s disease trials [press release]. Brussels, Belgium: UCB Pharma; July 26, Shalaby MR, Sundan A, Loetscher H, Brockhaus M, Lesslauer W, Espevik T. Binding and regulation of cellular functions by monoclonal antibodies against human tumor necrosis factor receptors. J Exp Med. 1990;172: Rutgeerts P, Fedorak RN, Rachmilevich D, et al. Onercept (recombinant human p55 tumour necrosis factor receptor) treatment in patients with active Crohn s disease: randomized, placebo-controlled dose-finding phase II study. Gut. 2004;53(suppl VI):A Sandborn WJ, Hanauer SB, Katz S, et al. Etanercept for active Crohn s disease: a randomized, double-blind, placebocontrolled trial. Gastroenterology. 2001;121: Baidoo L, Lichtenstein GR. What next after infliximab? Am J Gastroenterol. 2005;100: Pepys MB, Druguet M, Klass HJ, Dash AC, Mirjah DD, Petrie A. Immunologic studies in inflammatory bowel disease. Ciba Found Symp. 1977;46: Andre C, Descos L, Landais P, Fermanian J. Assessment of appropriate laboratory measurements to supplement the Crohn s disease activity index. Gut. 1981;22: Sandborn WJ, Colombel JF, Enns R, et al. Natalizumab induction and maintenance therapy for Crohn s disease: the ENACT-1 and ENACT-2 trials. N Engl J Med. In press. 36. Solem CA, Loftus EV Jr, Tremaine WJ, Harmsen WS, Zinsmeister AR, Sandborn WJ. Correlation of C-reactive protein with clinical, endoscopic, histologic, and radiographic activity in inflammatory bowel disease. Inflamm Bowel Dis. 2005;11: Lugering A, Schmidt M, Lugering N, Pauels HG, Domschke W, Kucharzik T. Infliximab induces apoptosis in monocytes from patients with chronic active Crohn s disease by using a caspase-dependent pathway. Gastroenterology. 2001;121: ten Hove T, van Montfrans C, Peppelenbosch MP, van Deventer SJ. Infliximab treatment induces apoptosis of lami- S858 Vol. 5 (9C) October 2005

8 na propria T lymphocytes in Crohn s disease. Gut. 2002;50: Van den Brande JM, Braat H, van den Brink GR, et al. Infliximab but not etanercept induces apoptosis in lamina propria T-lymphocytes from patients with Crohn s disease. Gastroenterology. 2003;124: Shen C, Assche GV, Colpaert S, et al. Adalimumab induces apoptosis of human monocytes: a comparative study with infliximab and etanercept. Aliment Pharmacol Ther. 2005;21: Mannon PJ, Fuss IJ, Mayer L, et al. Anti-interleukin-12 antibody for active Crohn s disease. N Engl J Med. 2004;351: Erratum in: N Engl J Med. 2005;352: Hommes D, Mikhajlova T, Stoinov S, et al. Fontolizumab (HuZAF), a humanized anti-ifn-gamma antibody, has clinical activity and excellent tolerability in moderate to severe Crohn s disease. Gastroenterology. 2004;127: Ito H, Takazoe M, Fukuda Y, et al. A pilot randomized trial of a human anti-interleukin-6 receptor monoclonal antibody in active Crohn s disease. Gastroenterology. 2004; 126: Yacyshyn BR, Bowen-Yacyshyn MB, Jewell L, et al. A placebo-controlled trial of ICAM-1 antisense oligonucleotide in the treatment of Crohn s disease. Gastroenterology. 1998;114: Erratum in: Gastroenterology. 2001;121: Yacyshyn BR, Chey WY, Goff J, et al. Double blind, placebo controlled trial of the remission inducing and steroid sparing properties of an ICAM-1 antisense oligodeoxynucleotide, alicaforsen (ISIS 2302), in active steroid dependent Crohn s disease. Gut. 2002;51: Chey WY, Volfova M, Konecny M, et al. Two phase 3 studies of alicaforsen (ISIS-2302), an antisense oligonucleotide to human ICAM-1, in the treatment of moderate to severe Crohn s disease [abstract]. Gastroenterology. 2005;128(suppl 2):A Adelman B, Ekman L. Important drug warning. Voluntary suspension of Tsybari (natalizumab) marketing. Cambridge, Mass, San Diego, Calif: Biogen Idec, Inc., Elan Pharmaceuticals; Van Assche G, Van Ranst M, Sciot R, et al. Progressive multifocal leukoencephalopathy after natalizumab therapy for Crohn s disease. N Engl J Med. 2005;353: Biogen Idec and Elan announce TYSABRI safety evaluation update [press release]. Cambridge, Mass, Dublin, Ireland: Biogen Idec, Elan Corporation; August 9, TYSABRI phase III induction trial in Crohn s disease meets primary endpoint [press release]. Dublin, Ireland, Cambridge, Mass: Elan Corporation, Biogen Idec; June 30, Van Assche G, Rutgeerts P. Physiological basis for novel drug therapies used to treat that inflammatory bowel diseases. I. Immunology and therapeutic potential of antiadhesion molecule therapy in inflammatory bowel disease. Am J Physiol Gastrointest Liver Physiol. 2005;288:G169-G Feagan BG, Greenberg GR, Wild G, et al. Treatment of ulcerative colitis with a humanized antibody to the alpha4beta7 integrin. N Engl J Med. 2005;352: Feagan BG, Greenberg G, Wild G, et al. Efficacy and safety of a humanized a4ß7 antibody in active Crohn s disease (CD). Gastroenterology. 2003;124:A25-A Korzenik JR, Dieckgraefe BK. Is Crohn s disease an immunodeficiency? A hypothesis suggesting possible early events in the pathogenesis of Crohn s disease. Dig Dis Sci. 2000;45: Korzenik JR, Dieckgraefe BK, Valentine JF, et al. Sargramostim for active Crohn s disease. N Engl J Med. 2005;352: Advanced Studies in Medicine S859