Biologic Therapy for Inflammatory Bowel Disease

Despite all of the advances in our understanding of the pathophysiology of inflammatory bowel disease (IBD), we still do not know its cause. Some of the most recently available data are discussed in this review; however, this field is changing rapidly and it is increasingly becoming accepted that immunogenetics play an important role in the predisposition, modulation and perpetuation of IBD. The role of intestinal milieu, and enteric flora in particular, appears to be of greater significance than previously thought. This complex interplay of genetic, microbial and environmental factors culminates in a sustained activation of the mucosal immune and non-immune response, probably facilitated by defects in the intestinal epithelial barrier and mucosal immune system, resulting in active inflammation and tissue destruction.

Under normal situations, the intestinal mucosa is in a state of ‘controlled’ inflammation regulated by a delicate balance of proinflammatory (tumour necrosis factor [TNF]-α, interferon [IFN]-γ, interleukin [IL]-1, IL-6, IL-12) and antiinflammatory cytokines (IL-4, IL-10, IL-11).

The mucosal immune system is the central effector of intestinal inflammation and injury, with cytokines playing a central role in modulating inflammation. Cytokines may, therefore, be a logical target for IBD therapy using specific cytokine inhibitors. Biotechnology agents targeted against TNF, leukocyte adhesion, T-helper cell (T_h)-1 polarisation, T-cell activation or nuclear factor (NF)-κB, and other miscellaneous therapies are being evaluated as potential therapies for IBD. In this context, infliximab is currently the only biologic agent approved for the treatment of inflammatory and fistulising Crohn’s disease. Other anti-TNF biologic agents have emerged, including CDP 571, certolizumab pegol (CDP 870), etanercept, onercept and adalimumab. However, ongoing research continues to generate new biologic agents targeted at specific pathogenic mechanisms involved in the inflammatory process. Lymphocyte-endothelial interactions mediated by adhesion molecules are important in leukocyte migration and recruitment to sites of inflammation, and selective blockade of these adhesion molecules is a novel and promising strategy to treat Crohn’ s disease. Therapeutic agents that inhibit leukocyte trafficking include natalizumab, MLN-02 and alicaforsen (ISIS 2302). Other agents being investigated for the treatment of Crohn’s disease include inhibitors of T-cell activation, peroxisome proliferator-activated receptors, proinflammatory cytokine receptors and T_h1 polarisation, and growth hormone and growth factors. Agents being investigated for treatment of ulcerative colitis include many of those mentioned for Crohn’s disease.

More controlled clinical trials are currently being conducted, exploring the safety and efficacy of old and new biologic agents, and the search certainly will open new and exciting perspectives on the development of therapies for IBD.