Anti-adhesion molecule therapy for inflammatory bowel disease.

Within the intestinal mucosa, adhesion molecules are involved in local lymphocyte stimulation and antigen presentation, as well as in the regulation of leukocyte influx. In inflammation, many adhesion molecules are upregulated, but [[alpha].sub.4]-integrins likely hold a key position in directing leukocytes into the inflamed bowel wall. Compounds directed against leukocyte trafficking have been designed and are being developed as a novel class of drugs in the treatment of Crohn's disease and ulcerative colitis. In the near future, some of these novel biologic agents may prove valuable therapeutic tools in the management of refractory IBD.

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The inflammatory bowel diseases (IBD), Crohn's disease and ulcerative colitis, are immune-mediated intestinal disorders of uncertain pathogenesis that have emerged principally in the developed areas of the world. Refractory Crohn's disease impairs quality of life and eventually causes debilitating complications that frequently necessitate bowel resection. Patients with refractory ulcerative colitis ultimately require colectomy.

The long-term outcome of the ileo-anal pouch used in IBD is far from optimal. Moreover, medical therapies for IBD, such a cortico-steroids, carry a heavy burden of undesired side effects.

In the last decade, management of refractory IBD has changed dramatically, with the increasing use of immunosuppressive drugs and the advent of biologic therapies. Most patients with refractory disease now receive azathioprine/ 6-mercaptopurine or methotrexate as maintenance therapy.

Novel biological therapies, created with genetic technology and directed against specific inflammatory mediators, have found some of their first clinical applications in the management of IBD. The chimeric anti-TNF antibody infliximab has proven very efficacious in patients with both active refractory and fistulizing Crohn's disease failing standard therapy. This compound has set the standard for the future development of IBD therapies. Several second-generation anti-TNF drugs are now in testing, including small molecule compounds for oral administration.

Still, 30 to 40% of patients with refractory Crohn's disease do not respond to infliximab treatment. Moreover, the long-term use of this drug is hampered by immunogenicity and the risk of infectious complications. Therefore, biologic therapies based on alternative pathways in the inflammatory cascade would be valuable.

Circulating leukocytes are crucial in the pathogenesis of IBD and are important targets for drug development. T lymphocytes are very mobile cells, involved in a continuous journey from the blood, to the gut mucosa, and back into the blood and primary lymphoid organs. Adhesion molecules regulate this cornerstone phenomenon in immunology, known as T-cell trafficking. Modulating T-cell adhesion may alter the course of the local inflammatory reaction in the intestinal wall and thus offers therapeutic potential for the management of IBD.

Adhesion Molecules Assist in T-Cell Migration

Though the pathogenesis of Crohn's disease and ulcerative colitis is still incompletely understood, the crucial role played by T cells in these disorders is clear.

T cells originate in the bone marrow and mature in the primary lymphoid organs. To reach the gastrointestinal tract, where they patrol for antigens and assist in intestinal inflammatory reactions, T cells rely on an elaborate system of traffic signals, termed adhesion molecules. These molecules direct the journey from the blood to antigen-rich organs, such as the gut or lungs. On average, T cells do not stay in the bloodstream for more than 30 minutes.

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On reaching the intestine, leukocytes interact with the endothelium of postcapillary vessels (i.e., high endothelial venules), before they migrate into the tissues. This interaction is hindered by the relative high speed at which T cells travel, creating an important shear stress in the blood-stream.

A highly effective and sequential system of adhesion molecules has emerged to overcome these physical forces. Initial tethering occurs through the interaction between selectins (L, P, and E selectins) and oligosaccharide moieties acting as ligands. L-selectins are expressed on leukocytes, whereas P- and E-selectins are found on the endothelium.

Selectin bonds provide a high tensile strength but are short lived, and the T cells roll over the endothelium from one selectin bond to the next.

To definitively stop the lymphocyte and allow migration into tissue requires secondary adhesion molecules, all members of the integrin family. The integrins that direct T-cell migration are leukocyte function-associated antigen 1 (LFA-1, or [[alpha].sub.2][[beta].sub.2] integrin) and the two [[alpha].sub.4] integrins, [[alpha].sub.4][[beta].sub.1] and [[alpha].sub.4][[beta].sub.7]

In contrast to selectins, which are constitutively expressed, integrins must be activated before they can engage in rolling. Integrin activation is mediated by chemokines that appear at the endothelial surface and bind to G-protein-coupled receptors on the lymphocyte surface.

Integrins interact with specific ligands, the addressins, on the endothelium. LFA-1 ([[alpha].sub.2][[beta].sub.2] integrin), expressed on neutrophils, interacts with intercellular adhesion molecule 1 and 2 (ICAM-1 and -2).

[[alpha].sub.4] integrins, predominantly expressed on lymphocytes, interact with addressins expressed on the endothelium. [[alpha].sub.4][[beta].sub.1] integrin binds to vascular cell adhesion molecule 1 (VCAM-1), and [[alpha].sub.4][[beta].sub.7] integrin binds with mucosal addressin-cell adhesion molecule 1 (MAdCAM-1). MAdCAM-1 is typically associated with murine Peyer's patches and also with human gut-associated lymphoid tissue.

Because there is a certain specificity to addressin distribution, adhesion molecules not only serve to facilitate lymphocyte migration but also contribute to tissue-specific lymphocyte trafficking. For example, in lymph nodes, naive T cells start the slow rolling process when L-selectin engages with peripheral node addressin, whereas in intestinal Peyer's patches, the additional interaction of [[alpha].sub.4][[beta].sub.7] integrin with MAdCAM-1 is required for rolling.

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Moreover, in intestinal high endothelial venules, naive T cells first use L-selectin to engage with the endothelium, whereas effector T cells and memory T cells, with a high density of membrane-bound [[alpha].sub.4][[beta].sub.7] integrin (so-called gut-homing cells), engage directly with MAdCAM-1. Naive T cells and effector T cells also can engage their [[alpha].sub.L][[beta].sub.2] integrin to connect with ICAM-1, but this interaction is not gut specific.

Tissue-specific lymphocyte trafficking may have important implications for efficacy and toxicity of anti-adhesion molecule therapies.

Adhesion Molecules Are Upregulated in IBD

Recruitment of effector and memory T cells that recognize antigens encountered in the gut lumen is crucial in disease states such as acute intestinal inflammation due to luminal pathogens. Alterations to vascular endothelium in tissues that contain potential pathogens allow leukocyte adhesion and migration, whereas these micro-vessels prevent leukocyte diapedesis in basal conditions.

Inflammatory cytokines such as tumor necrosis factor (TNF) and interleukin-1 (IL-1) induce the expression of ICAM-1, E-selectin, and probably also MAdCAM-1 on endothelium in inflamed tissue. An upregulation of MAdCAM-1 can be deduced from the observation that intestinal endothelium from IBD patients has a higher adhesiveness for [[alpha].sub.4] integrins. VCAM-1, the other ligand of [[alpha].sub.4] integrins, does not account for this observation because it is sparsely expressed in the gut microcirculation.

Also, chemokines secreted by inflammatory cells in the diseased tissue activate integrins expressed on membranes of T cells rolling over the endothelium. In surgical resection specimens from patients with IBD, ICAM-1 and -2 expression is increased on the endothelium. The ligands for ICAM, the [[beta].sub.2] integrins, also are upregulated in both Crohn's disease and ulcerative colitis.

Intravital microscopy studies, done in rat intestine in which inflammation was induced by serosal application of Escherichia coli lipopolysaccharides, have shown that in early inflammation, leukocyte rolling is mediated by P-selectin, but in a more advanced inflammatory phase, L-selectin and [[alpha].sub.4] integrins mediate this process.

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Notably, the clinical response to anti-TNF therapy in patients with Crohn's disease is associated with a marked decrease in ICAM-1 expression in the intestinal endothelium. The same decrease is seen in the endothelium of synovial venules in patients with rheumatoid arthritis treated with infliximab.

T-cell migration into the inflamed bowel segments is probably of paramount importance in the pathogenesis of IBD. However, a decreased exit of lymphocytes from the mucosa and an increased local activation and/or proliferation of these cells also could contribute to the perpetuation of inflammatory reactions in IBD.

There is some evidence to support a role for adhesion molecules in interactions between T cells and resident dendritic cells or mesenchymal cells in the intestinal mucosa and submucosa. The extracellular matrix protein fibronectin, for instance, is an [[alpha].sub.4][[beta].sub.7] integrin ligand, and its interaction may influence the function of stromal cells, such as antigen-presenting dendritic cells or fibroblasts.

Other extravascular ligands for [[alpha].sub.4] integrins include matrix molecules such as osteopontin, thrombospondin, and ADAM28, a metalloproteinase domain constitutively expressed on lymphocytes.

Binding of ICAM-1 and [[alpha].sub.4] integrins to their respective addressins induces a costimulatory signal in antigen presentation to T cells, inducing lymphocyte proliferation and cytokine production. Moreover, expression of ICAM-1 in Crohn's disease is not only increased in the intestinal mucosa, but also in the submucosa and in the muscle layers. Intestinal smooth muscle expresses ICAM-1 when stimulated by proinflammatory cytokines in vitro, and this may contribute to local interactions with lymphocytes that have penetrated into the deeper layers of the intestinal wall.

Therefore, the therapeutic benefit of anti-adhesion molecule treatments

might be explained by:

* a decrease in T-cell recruitment at the endothelial surface,

* an inhibition of costimulatory effects of adhesion molecules in local leukocyte activation within the mucosa, or

* a combination of both of these mechanisms.

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Extraintestinal inflammatory events, such as reactive arthritis and erythema nodosum, are frequent in both Crohn's disease and ulcerative colitis. It may be that activated gut-homing lymphocytes also travel to synovial microvasculature to contribute to IBD-associated arthritis.

Marko Salmi and Sirpa Jalkanen, from the University of Turku, Finland, have shown convincingly that several leukocyte populations originating from the inflamed gut adhere to synovial vessels. However, these cells engage CD44 to interact with vascular adhesion protein in the synovial venules, whereas [[alpha].sub.4][[beta].sub.7] integrin- MAdCAM-1 interactions dominate in the intestine.

Anti-Adhesion Molecule Strategies Focus on the [[alpha].sub.4] Integrins

The crucial role of adhesion molecules in inflammatory disorders has prompted interest in them as potential targets for drug development. Pioneering studies with anti-adhesion strategies have been performed in asthma, where antagonists of [T.sub.H.]2-specific chemokines and inhibitors of [[alpha].sub.4][[beta].sub.1] integrins have been shown to induce marked anti-inflammatory effects.

In IBD, anti-adhesion therapy has focused on two pathways: the [[alpha].sub.4] integrin-MAdCAM-1 interaction and the [[beta].sub.2] integrin-ICAM-1 interaction.

Two anti-[[alpha].sub.4] monoclonal antibodies have been developed and subsequently tested in a primate model and in clinical trials. A specific humanized [[alpha].sub.4][[beta].sub.7] integrin monoclonal antibody, MLN02, was developed by Millenium Pharmaceuticals, and a humanized monoclonal [[alpha].sub.4] integrin-IgG4 antibody, natalizumab (Tysabri[R]), was introduced by Biogen Idec/Elan Pharmaceuticals. The only conceptual difference between the two compounds lies in the specificity of MLN02 for blocking the [[alpha].sub.4][[beta].sub.7]--MAdCAM-1 interaction, whereas natalizumab also inhibits [[alpha].sub.4][[beta].sub.1]--VCAM-1 binding.

The compounds were first tested in the cotton-top tamarin, a South American primate that, when kept in captivity, spontaneously develops a chronic colitis resembling human IBD. Both antibodies produced rapid and marked improvement in clinical and histologic scores in colitic animals. In addition, the anti-[[alpha].sub.4][[beta].sub.7] antibody MLN02 also achieved a reduction in mucosal T-cell and neutrophil counts.

Natalizumab (Humanized Anti-[[alpha].sub.4] Integrin-IgG4 Antibody)

Natalizumab was developed in parallel for the management of IBD and multiple sclerosis. Indeed, whereas the [[alpha].sub.4][[beta].sub.7]-MAdCAM-1 interaction is pivotal in gut lymphocyte homing, [[alpha].sub.4][[beta].sub.1]-VCAM-1 binding appears to be a crucial step in experimental encephalomyelitis.

A first phase I/II randomized placebo-controlled trial of natalizumab included 30 patients. This study was not powered to assess the therapeutic potential of natalizumab, but at week 2, 39% (n=7) of the natalizumab-treated patients versus 8% (n=1) of placebo-treated patients had achieved clinical remission (reduction in Crohn's disease activity index [CDAI] <150), though the effect was short lived.

In a larger trial, 248 patients with moderately to severely active Crohn's disease were treated twice at 4-week intervals intravenously with 3 or 6 mg/kg of natalizumab or placebo. The primary endpoint was the number of patients in remission (CDAI <150) at week 6.

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A significantly greater number of patients achieved remission at 6 weeks in the 3 + 3 mg/kg group only [44% (29/66) vs 27% (17/63) for placebo, p<0.05]. Clinical response, defined as a [greater than or equal to] 70% drop in CDAI, was seen at week 6 in 38% of the placebo group, versus 59% of the 3 + 0 mg/kg group (p<0.03 vs placebo), 71% of the 3 + 3 mg/kg group (p<0.001), and 57% of the 6 + 6 mg/kg group (p<0.05). The response persisted through week 12 in those receiving re-treatment at week 4.

In 2005, results of the large phase III ENACT-1 trial, enlisting patients with moderate to severe Crohn's disease, were reported. This trial included 905 patients and is probably the largest phase III, randomized controlled trial ever conducted in Crohn's disease. Patients were treated intravenously with a fixed dose of 300 mg of natalizumab or placebo at week 0, 4, and 8 in a 4:1 randomization. The primary endpoints were both clinical response ([greater than or equal to] 70 point reduction in CDAI) and clinical remission at week 10. Roughly 40% of patients in both groups had been treated previously with the anti-TNF agent infliximab.

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Although the trial did not meet its primary endpoint, the response and remission rates were significantly higher for the actively treated patient group. In addition, when patients with elevated C-reactive protein (CRP) and concomitant immunosuppressive therapy were analyzed separately, larger differences between patients receiving natalizumab and placebo became apparent: remission rates at 10 weeks were 41% for the natalizumab group versus 18% for the placebo group--although this difference appeared to be due to a decrease in placebo response rates among the placebo group over time.

Also, the long-term treatment extension study (ENACT-2) found an advantage for continued treatment with natalizumab, with good tolerability. Steroid-free remission after 9 months of treatment was 45% in patients treated with natalizumab 300 mg intravenously every 4 weeks versus 22% in placebo-treated patients.

The experience with natalizumab in ulcerative colitis has been more limited. Ten patients with moderate active ulcerative colitis were treated in a small open-label trial. The results suggest a therapeutic benefit of natalizumab, but controlled evidence is needed.

The original safety data from the three trials of natalizumab in Crohn's disease were excellent, with only 8% of patients developing anti-natalizumab antibodies and <1% experiencing a severe infusion reaction. Interestingly, a transient increase in circulating lymphocytes was consistently observed in natalizumab-treated patients across all clinical trials, indicating that the antibody really prevented the diapedesis of these cells through the vascular wall.

Similar clinical efficacy and tolerability data resulted in FDA approval in late 2004 for natalizumab in combination with interferon-[alpha] to treat refractory multiple sclerosis.

However, by early 2005, the commercial use of natalizumab was halted due to the development of progressive multifocal leukoencephalopathy (PML) in three patients. Two of these patients had multiple sclerosis treated with natalizumab and interferon-[alpha], and one patient with Crohn's disease received natalizumab monotherapy.

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PML is a rare and often lethal brain disease predominantly occurring in immunosuppressed persons and associated with reactivation of JC virus replication in glial cells. Most immunocompetent subjects (80%) carry JC virus as a latent infection without clinical effects. Natalizumab, however, impairs T-cell migration to the brain, which probably results in an impaired control of JC virus replication by the adaptive immune system.

In mid-2006, natalizumab was returned to the U.S. market for the treatment of relapsing multiple sclerosis, with the proviso that patients are not immunocompromised and receive no concomitant immunosuppressive therapy (except for intermittent steroids). This restricted program is designed to prevent reactivation of the JC virus that causes PML.

MLN02 (Humanized Anti-[[alpha].sub.4][[beta].sub.7] Integrin Antibody)

MLN02, an anti-[[alpha].sub.4][[beta].sub.7] integrin antibody, has been studied most extensively in ulcerative colitis.

In 2000, Brian Feagan and colleagues reported on a randomized placebo-controlled trial involving 28 patients with moderate ulcerative colitis, who received increasing doses of MLN02 or placebo. While the trial was designed to evaluate tolerability and not efficacy, complete endoscopic and clinical remission at day 30 was observed in 3 of 5 patients receiving the highest dose (0.5 mg/kg intravenously). This dose saturated [[alpha].sub.4][[beta].sub.7] binding for up to 30 days.

In a follow-up phase II trial reported in 2005, Feagan and coworkers treated 181 patients with either 0.5 or 2.0 mg/kg of MLN02 or placebo twice at 28 days apart. Remission rates on day 43 were significantly higher in MLN02-treated patients (33% at 0.5 mg/kg, 34% at 2.0 mg/kg) than in placebo-treated patients (15%; p = 0.03). The drug was generally well tolerated, with an infusion reaction with angioedema seen in 1 patient.

Given that MLN02 selectively blocks leukocyte trafficking to the gut, one may speculate that systemic immunity is less impaired with this antibody than with less-selective adhesion molecule inhibitors. However, MLN02 induces neutralizing antibodies in patients, and immunogenicity can impair long-term efficacy and tolerance. Clinical trials with long-term administration of MLN02 would be needed to assess this risk (though development has now been halted).

MLN02 also was assessed in Crohn's disease, in a placebo-controlled trial with 185 patients having mild to moderately active disease. Patients received either 0.5 or 2.0 mg/kg of MLN02 or placebo twice with a 28-day interval. At 2

In June 2006, natalizumab was approved in the European Union for use in relapsing MS without restrictions. months, there was no difference in clinical response between MLN02and placebo-treated patients.

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Anti-ICAM-1 Therapy Inhibits the [[beta].sub.2] Integrin Interaction

In inflamed tissues, the release of cytokines induces the expression of ICAM-1 and other addressins on endothelial surfaces. Rolling leukocytes use [[beta].sub.2] and [[alpha].sub.4] integrins on their surfaces to engage with ICAM1 and -2 to halt their movement. This interaction induces a costimulatory signal in T cells, promoting lymphocyte proliferation and cytokine production.

An upregulation in the expression of ICAM-1 and -2 on endothelium, as well as expression their [[beta].sub.2] integrin ligands on leukocytes, has been reported in both Crohn's disease and ulcerative colitis.

In human disease, the efficacy of anti-ICAM strategies was first shown in rheumatoid arthritis, a [T.sub.H]1-driven inflammatory disorder that bears similarities to Crohn's disease. Treatment with neutralizing anti-ICAM-1 antibodies has produced sustained improvement in RA symptoms, even after short treatment courses of 2 or 5 days.

The proof of concept for use of anti-ICAM therapy in human IBD was realized in animal models, where both anti-ICAM-1 monoclonal antibodies and ICAM-1 antisense oligonucleotides achieved some effectiveness.

In one model of dextran sulfate sodium-induced murine colitis, intracolonic administration of anti-ICAM antibodies was effective in reducing signs of colonic inflammation, including histologic damage. In a second study, in the mouse SAMP1/Yit ileitis model, anti-ICAM-1 given alone produced no significant benefits, but was effective when administered in combination with anti-VCAM-1 or anti-[[alpha].sub.4] antibodies, suggesting a redundancy in the adhesion pathways in acute inflammation.

Interestingly, the use of VCAM-1 inhibition for human IBD can be questioned in that VCAM-1 is expressed sparsely in human intestinal epithelium, even in inflammation. Furthermore, the combination ICAM-1/VCAM-1 treatment affected only the acute component of the ileitis, and not signs of chronic inflammation (e.g., architectural changes in the mucosa, muscle hypertrophy).

Clinical trials assessing the therapeutic potential of anti-ICAM agents have been conducted exclusively with antisense oligonucleotides to ICAM-1. Antisense oligonucleotides hybridize to a specific RNA molecule, usually mRNA, and prevent subsequent translation of the protein encoded by the RNA.

The antisense concept is appealing, in that a disease-causing pathway can be targeted before translation has produced numerous proteins from a limited mRNA pool. However, selection of the correct site in the target mRNA to obtain optimal inhibition of translation is a complex process. Also, stability and resistance against enzymatic degradation are crucial for in vivo use of an antisense compound.

ISIS Pharmaceuticals has developed several clinically applicable antisense oligonucleotides. ICAM-1 was identified early as an important target for both the treatment of IBD and rheumatoid arthritis. One ICAM antisense oligonucleotide, alicaforsen (ISIS-2302), has been evaluated in several placebo-controlled randomized trials in active Crohn's disease, but so far with conflicting results.

Alicaforsen binds to the 3' untranslated region of the mRNA to prevent translation.

An pilot trial in 20 patients suggested a therapeutic potential for ICAM-1 antisense oligonucleotides in chronic active Crohn's disease. Two larger multicenter trials followed: one in Germany using a novel subcutaneous formulation, and one at centers in the United States and Europe using intravenous alicaforsen.

In the German trial, 75 patients with steroid-dependent, moderately active Crohn's disease were injected subcutaneously with 0.5 mg/kg of alicaforsen or placebo. However, only 3% of the patients achieved steroid-free clinical remission by 14 weeks, and the authors concluded that the drug had no therapeutic benefit in steroid-refractory Crohn's disease.

The other large multicenter study, done in the U.S. and Europe, involved 299 patients also with moderately active, steroid-dependent Crohn's disease. Patients received an intensified regimen of 2 mg/kg of alicaforsen intravenously three times a week for 2 or 4 weeks or placebo. After 1 month drug-free, the same treatment schedule was repeated.

Again, there were no differences in remission rates between treatment and placebo groups. Steroid-free remission at week 14 was seen in 20% of patients in both alicaforsen groups versus 18% in the placebo group. However, in a post hoc analysis using the AUC of alicaforsen plasma concentration, patients in the highest AUC group (AUC >65 [micro]g x hr/mL, 9 patients) showed a consistent, increased improvement rate for most of the clinical endpoints (remission, median CDAI, and IBDQ scores).

Taken together, these studies do not convincingly show efficiency of anti-ICAM oligonucleotides in IBD, although the question of whether alicaforsen should be used at higher doses remains undecided. High-dose exposure was reported in one small open-label trial of 20 patients, given 250 to 350 mg of alicaforsen. They showed a 41% remission rate, but 5 of these 20 patients withdrew due to infusion reactions.

The lack of clinical efficacy of alicaforsen also might be related to the inability of the intravenous compound to penetrate to the inflamed bowel. In several randomized trials to date, alicaforsen administered as a rectal enema to patients with left-sided ulcerative colitis (affecting the descending and sigmoid colon) has led to improvement in disease activity scores and endoscopic healing. Alicaforsen enema also appeared to induce long-lasting effects in ulcerative colitis that have not been observed with other topical agents.

In all the clinical trials, the typical side effects of alicaforsen were infusion site reactions or infusion reactions and moderate, noncritical increases in activated partial thromboplastin time (aPTT).

Use of anti-adhesion molecule therapy for IBD is an appealing concept with a sound immunologic basis. Anti-[[alpha].sub.4][[beta].sub.7] integrin therapy (natalizumab and MLN02) is theoretically the most gut-selective approach, and results from the first clinical trials appeared promising. More specifically, the ENACT phase III trial with natalizumab suggests that anti-adhesion molecule therapy is efficacious, even in patients refractory to anti-TNF antibodies. However, the occurrence of PML has limited the use of this compound, and it is unclear if these restrictions will allow all its use in IBD.

More gut-selective anti-adhesion molecules directed against MAdCAM-1 and [[alpha].sub.4][[beta].sub.7] integrins have entered clinical trials in ulcerative colitis and Crohn's disease. Although the development of MLN02 has been halted, a fully human anti-MAd-CAM1 monoclonal antibody is in phase II trials for ulcerative colitis.

The anti-ICAM antisense oligonucleotide alicaforsen has shown efficacy when used topically in ulcerative colitis, but its potential in Crohn's disease will be reconsidered in view of the negative trials.

Considering the immunology of IBD, other potential targets for research involving anti-adhesion molecule therapy have been identified and include chemokines and their receptors. The chemokine receptor CCR9 appears to be selectively involved in the migration of T cells to the gut and likely will meet future drug development. Also, several small molecule antagonists of the chemokine receptors are already available. Finally, adhesion molecules could be used to direct genetically modified counter-regulatory human T cells into the gut mucosa to induce anti-inflammatory effects.

Publication date: 14 Mar 2007

CDAI--Crohn's disease activity index

IBDQ--inflammatory bowel disease questionnaire

RECENT REVIEWS

Ulrich H. von Andrian and Charles R. Mackay: T-Cell function and migration--two sides of the same coin. N Engl J Med ; 343:1020-1034, 5 Oct 2000.

Paul Rutgeerts, Sander van Deventer, and Stefan Schreiber: The expanding role of biological agents in the treatment of inflammatory bowel disease--focus on selective adhesion molecule inhibition. Aliment Pharmacol Ther 17:1435-1450, June 2003.

Gert Van Assche and Paul Rutgeerts: Physiological basis for novel drug therapies used to treat the inflammatory bowel diseases: I. Immunology and therapeutic potential of antiadhesion molecule therapy in inflammatory bowel disease. Am J Physiol Gastrointest Liver Physiol 288:G169-G174, Feb 2005.

Gert Van Assche, Severine Vermeire, and Paul Rutgeerts: Medical treatment of inflammatory bowel diseases. Curr Opin Gastroenterol 21:443-447, Jul 2005.

ORIGINAL PAPERS

Subrata Ghosh, Eran Goldin, Fiona H. Gordon, et al: Natalizumab for active Crohn's disease. N Engl J Med 348:24-32, 2 Jan 2003.

Gert Van Assche, Marc Van Ranst, Raf Sciot, et al: Progressive multifocal leukoencephalopathy after natalizumab therapy for Crohn's disease. N Engl J Med 353:362-368, 28 Jul 2005.

William J. Sandborn, Jean Frederic Colombel, Roberts Enns, et al: Natalizumab induction and maintenance therapy for Crohn's disease. N Engl J Med 353:1912-1925, 30 Nov 2005. [ENACT-1 and 2]

Brian G. Feagan, Gordon R. Greenberg, Gary Wild, et al: Treatment of ulcerative colitis with a humanized antibody to the [[alpha].sub.4][[beta].sub.7] integrin. N Engl J Med 352:2499-2507, 16 Jun 2005.

GERT VAN ASSCHE, MD, PhD SEVERINE VERMEIRE, MD, PhD and PAUL RUTGEERTS, MD, PhD, FRCP are in the Division of Gastroenterology, Department of Medicine, at the University Hospital Leuven, Leuven, Belgium.

[e-mail]

PATIENTS IN REMISSION AT WK 10 (%)

                        PLACEBO   NATALIZUMAB

INTENTION TO TREAT         30          37
  (n = 905)
CRP > ULN                  28          40
  >2.87 mg/L
  (n = 660)
CONCOM.                    25          40
  IMMUNO-SUPPRESSANTS
  (n = 300)
CRP +                     18           41
  IMMUNO-SUPPRESSANTS
  (n = 222)

Post-hoc analysis of the ENACT-1 trial
demonstrated that remission rates with
natalizumab, 300 mg iv, were significantly
higher in patients with elevated
C-reactive protein (CRP) or the concomitant
use of immunomodulators at baseline.
However, concurrent use of immunosuppressant
drugs is now restricted
with natalizumab in light of its association
with PML.

DATA FROM SANDBORN WJ, ET AL: N ENGL J MED 353:1912-1925, 3 NOV 2005.

Note: Table made from bar graph.

STEROID-FREE REMISSION (%)

MONTHS
              p<0.003   p<.001

NATALIZUMAB      45       42
  (n = 67)
PLACEBO          22       15
  (n = 76)

Data from the ENACT-2 trial showed
the ability of continued treatment with
natalizumab, 300 mg iv every 4 weeks,
to maintain remissions with the discontinuation
of steroids.

DATA FROM SANDBORN WJ, ET AL: N ENGL J MED 353:1912-1925, 3 NOV 2005.

Note: Table made from line graph.

PATIENTS IN REMISSION AT WK 6 (%)

                   p<0.02

PLACEBO             14%
  (n = 9/63)
MLN02 0.5 mg/kg     33%
  (n = 19/55)
MLN02 2.0 mg/kg     32%
  (n = 19/60)

MLN02, a monoclonal antibody that
selectively binds [[alpha].sub.4][[beta].sub.7] integrins, was
significantly more efficacious than placebo
at inducing clinical remission in
patients with mild to moderate ulcerative
colitis (phase II trial).

ATA FROM FEAGAN BG, ET AL: N ENGL J MED 352:2499-2507, 16 JUN 2005.

Note: Table made from bar graph.

Adhesion Molecules Involved in Leukocyte Trafficking

                  Leukocyte Distribution

              Selectins and Selectin Ligands

L-selectin                                 Most leukocytes
Unknown (sialyl-[Lewis.sup.x]?)            Leukocytes
P-selectin glycoprotein                    Most leukocytes
  ligand 1

       [[beta].sub.2]-Integrins and Integrin Ligands

  [[alpha].sub.L][[beta].sub.2] (LFA-1)    All leukocytes
  [[alpha].sub.M][[beta].sub.2] (Mac-1)    Myeloid lineage
  [[alpha].sub.X][[beta].sub.2]            Dendritic cells
  [[alpha].sub.D][[beta].sub.2]            Monocytes, eosinophils

       [[alpha].sub.4]-Integrins and Addressin Ligands

  [[alpha].sub.4][[beta].sub.1] (VFA-1)    Most leukocytes, except
                                             neutrophils
  [[alpha].sub.4][[beta].sub.7]            Lymphocytes, NK cells,
                                           monocytes

                  Endothelial Distribution

               Selectins and Selectin Ligands

Peripheral node                            High endothelial venules in
  addressin                                  lymph nodes and inflamed
                                             tissues
E-selectin                                 Most endothelial cells
P-selectin                                 Endothelium, platelets

         [[beta].sub.2]-Integrins and Integrin Ligands

ICAM-1                                     Most cell types
ICAM-2                                     Endothelial cells,
                                             platelets
--
--

         [[alpha].sub.4]-Integrins and Addressin Ligands

VCAM-1                                     Endothelium, dendritic cells
MAdCAM-1                                   High endothelial venules
                                             in GALT
Fibronectin, osteopontin,                  Lamina propria
  ADAM28

Typical cellular distribution of adhesion molecules and ligands
is listed in the second column. GALT, gut-associated lymphoid tissue.

Anti-Adhesion Molecules in Clinical Trials in IBD

                                                 Efficacy in
Drug Name        Structure                     Crohn's Disease

Natalizumab      Humanized                  Efficacious in
  (Tysabri[R])   mouse anti-human           phase II/III trials
                 [[alpha].sub.4] integrin
                 IgG4 monoclonal Ab
MLN02            Humanized                  Not efficacious in
 (formerly       mouse anti-human           phase II trial
  LDP-02)        [[alpha].sub.4]
                 [[beta].sub.7] integrin
                 monoclonal Ab
Alicaforsen      Antisense                  Conflicting results in
  (ISIS 2302)    oligonucleotide            phase II/III trials
                 to ICAM-1 mRNA

                       Efficacy in
Drug Name          Ulcerative Colitis       Status

Natalizumab      Efficacious in             Phase III trials
  (Tysabri[R])   open-label                 completed
                 pilot study
MLN02            Efficacious in             Development
 (formerly       phase I/II trial           halted
  LDP-02)
Alicaforsen      Efficacious in             Phase II/III trials
  (ISIS 2302)    phase II trial             in UC ongoing