Scientific Abstract

Proposal No.  IBD-0143
Principal Investigator:  Rainer Duchmann, M.D.
Applicant Organization:  Charité - Universitätsmedizin Berlin; Campus Benjamin Franklin (Germany)
Project Title:  CD4+CD25+ T regulatory cells in inflammatory bowel disease
Period of Award:  May 15, 2005 – August 14, 2007

Research in inflammatory bowel disease (IBD) has had a strong focus on inflammatory mechanisms.  However, it is clear that intestinal immune responses are regulated by both specialised inflammatory and regulatory (or suppressive) T cell populations. Among the latter, CD4+CD25+ T_reg are a new and very interesting T cell subset.  Although there is a large literature on these cells in general, including detailed studies demonstrating that they can both prevent and treat chronic intestinal inflammation in animal models, their role in human IBD is still in a very early stage of exploration.

Different from mice, humans show a heterogeneous population of CD4+CD25+ T cells that express either moderate, intermediate, or high levels of CD25.  We have previously isolated these populations using established procedures with high purity following a combination of MACS and FACS and confirmed results from other laboratories showing that the regulatory population is present in the CD25^high fraction.  Using different techniques (flow cytometry for CD4+CD25^high T cells, detection of CD3/FOXP3 and CD25/FOXP3 double-positive cells in cytospins and tissues by immunochemistry, real time PCR for FOXP3 and a cellular assay to assess the suppressive function of CD4+CD25^high T cells in response to allogeneic stimulation), we already showed that there is an increased and potentially protective level of functionally active CD4+CD25+T_reg in peripheral blood of IBD patients in remission, but an insufficient level in peripheral blood and involved intestinal mucosa of patients with active disease.

Our submitted project builds on these results.  It aims to further investigate the role of CD4+CD25+T_reg in IBD pathogenesis and to determine whether measurement of their frequency provides a (sub)clinical marker of disease activity.  In more detail, we want to perform a clinical long-term follow-up study in patients with Crohn’s disease to assess whether there is a correlation between the level (or intra-individual changes thereof) of CD4+CD25+ T_reg and clinical course.  Thus, we hope to identify CD4+CD25+ T_reg as a subclinical marker of disease activity that might predict relapse or identify patients with increased risk for relapse.  This could improve patient care and outcome, e.g., by providing a rationale for starting preventive therapy.  The basic research suggested in this project aims to identify whether (and which) antigen(s) activate and expand CD4+CD25+ Treg in IBD. In addition, we hypothesize that although CD4+CD25+ T_reg show a normal suppressive function to polyclonal or allogeneic stimuli, some bacterial antigens (e.g., the most relevant in IBD) may not or only insufficiently activate T_reg function.  To test this hypothesis, suppressive function of IBD T_reg will be studied in an antigen specific system.  We expect that results from this work will further our understanding of the role of CD4+CD25+ T_reg in IBD pathogenesis.  In addition, information on the antigens driving CD4+CD25+ T_reg in IBD and their functionality may be relevant to better assess the rational basis of potentially forthcoming therapies, which are likely to involve their in vitro propagation and reinfusion.  The proposed studies on human CD4+CD25+ T reg are thus hoped to provide new information relating to IBD pathogenesis, clinical management and therapy.