Treatment of inflammatory bowel disease by chemokine receptor-targeted leukapheresis

Highlights

• A new monocyte-targeting apheresis for IBD.

• Elimination of gut-homing CCR9-expressing cells by immobilized CCL25.

• Positive response in a pilot-patient with ulcerative colitis.

Abstract

Leukapheresis removes circulating leukocytes en route to the target organ. Hitherto unspecific matrixes have been used to remove leukocytes in inflammatory bowel disease (IBD). This report describes a novel selective leukapheresis column based on chemokine–chemokine receptor interaction. We found an increased expression of the gut homing chemokine receptor CCR9 on CD14⁺ monocytes and on CD3⁺ T lymphocytes from IBD patients. Biologically active CCL25 was coupled to a Sepharose matrix and demonstrated to selectively remove CCR9-expressing cells leaving other cell populations largely unaffected. A patient with active ulcerative colitis, was subjected to CCL25-column leukapheresis. Four days after treatment, he experienced clinical improvement and stable disease improvement ensued. The study illustrates that specific cells can be targeted using high affinity interactions, i.e., CCL25–CCR9 interactions to remove pathogenic gut-homing cells. Leukapheresis using the bCCL25 column should be investigated in a clinical phase I trial of patients with inflammatory bowel disease.

Introduction

Inflammatory bowel diseases (IBD), i.e. Crohn's disease (CD) and ulcerative colitis (UC), are chronic inflammatory disorders of the gastrointestinal tract associated with high morbidity and significant health care-related costs [1]. Research in later years has emphasized the central role of the immune system in the pathogenesis of IBD [2]. Current IBD treatment includes oral corticosteroids and azathioprine, which both are broadly acting immunosuppressants which suffer from complications associated with increased patient susceptibility to infection as well as other side effects. During the last decade, biological agents such as the monoclonal antibodies Infliximab and Adalimumab have been introduced. These anti-TNF antibodies neutralize the TNF-signaling pathways and have proved efficacious for severe IBD. However, close to one third of CD patients are primary non-responders to the drug and around 60% of the responders will eventually become refractory to the therapy according to some studies [3], [4], [5]. Moreover, biologics are associated with side effects such as immunogenicity and opportunistic infections [5], [6], [7], [8].

Disease pathogenesis in IBD is largely unknown even though complex; multiple genetic and immunological aberrations have been identified [9]. In addition, several factors such as infections in early life, changes in commensal flora and the interaction with the immune system may result in intestinal inflammation. When the balance of the immune system is disturbed, through genetic or environmental challenges, the activated blood cells enter the intestinal submucosa and induce inflammation, which in turn attracts additional immune cells in a vicious circle. Patients with active IBD display increased numbers of circulating granulocytes and monocytes [10], [11], which are assumed to be en route to the inflamed bowel mucosa. Subsequent differentiation of the CD14⁺ monocytes into TNF-α-producing (M1) macrophages in the mucosa fuels the inflammation and contributes to epithelial disruption and inflammation [12].

A key component for directing the transmigration of circulating cells to the gut is the signaling induced by chemokines which are small proteins that direct the circulating leukocytes to target organs such as the intestine, skin or respiratory system. This migratory apparatus is often organ-specific and the chemokines induce chemotaxis by recruiting immune cells that express the appropriate G-protein-coupled chemokine receptor; thereby accomplishing both tissue- and cell-specific migration [13]. In IBD, cells expressing the gut-homing chemokine receptor 9 (CCR9) are recruited through binding to the chemokine CCL25, also referred to as the thymus-expressed chemokine (TECK). The CCR9–CCL25 interaction is one of the crucial homing mechanisms in this context and previous animal models have identified its importance in the migration especially to the small intestine [14]. Consequently, CCR9 blockade is of therapeutic interest and has recently been used in clinical trials for IBD.

Leukapheresis has also been used in the treatment of IBD, with the premise of trapping leukocytes en route to the target organ and thereby reducing the inflammation. Two different approaches have been employed: leukocytapheresis (LCAP) with the Cellsorba™ device, which removes lymphocytes, granulocytes and monocytes; and granulocyte–monocyte apheresis (GMA) using the Adacolumn [15]. In LCAP, cell depletion is accomplished by non-selective adsorption to a non-woven polyester fabric [16], whereas the Adacolumn apheresis system consists of a column filled with cellulose acetate beads. During apheresis, serum immunoglobulins and complement fragments are deposited on the beads which causes adhesion of cells equipped with Fc and complement receptors; mainly granulocytes and monocytes [15]. Both LCAP and GMA have shown results in IBD and share an excellent safety profile [17], [18], making them interesting alternatives to the immunosuppressive drugs. Clinical studies using both LCAP and GMA have indicated effect but clinically significant differences have not been found. In a recent, randomized sham-controlled trial of Adacolumn in UC, the apheresis treatment failed to reach a significant response compared to control [19].

We have recently demonstrated that the major pro-inflammatory TNF-α producing monocyte population in the circulation defined as CD14⁺DR^hi, expresses the highest levels of CCR9 [20]. Therefore taken together with the well-established role of the high-affinity binding between the chemokine CCL25 and its receptor CCR9 to specifically attract and fuel the gastrointestinal inflammation we decided to develop a selective CCR9 removing medical device. The study describes the development of a novel concept in leukapheresis using specific chemokine–ligand binding in an extracorporeal apheresis column for the treatment of inflammatory bowel disease.