Modulation of regulatory T cells by targeting the NFAT-FOXP3 protein : protein interaction

Cancer vaccines often generate elevated numbers of tumour- specific T-cells however these are generally insufficient to con- trol disease. Considerable evidence suggests that CD4+CD25+ regulatory T-cells (Treg) are largely responsible for preventing effective anti-tumour immune responses. Thus the develop- ment of novel strategies to manipulate the suppressive activity of Treg remains an important goal for cancer immunotherapy. Agents targeting Treg in the clinic have shown variable efficacy and considerable toxicity, e.g. the use of anti-CTLA4 antibod- ies has achieved some significant successes in clinical trials for several malignancies. Although effective, these antibodies have a relatively long clearance time which is thought to promote aggressive autoimmune responses.
CD4+CD25+ Treg cells are characterized by the transcription factor FOXP3 which is a master regulator of the function and development of Tregs. FOXP3 functions through the obligatory interaction with another transcription factor NFAT (nuclear fac- tor of activated T cells) resulting in repression of cytokine gene expression as well as the activation of the Treg marker genes CTLA4 and CD25. We have taken a novel approach to targeting Treg by developing a peptide (HWFT) that disrupts the interac- tion between the Treg specific transcription factor, FOXP3 and its obligatory co-factor NFAT. In mice HWFT triggers apoptosis
specifically in Treg in vitro, whilst in humans it inhibits their sup- pressive capacity without killing. At the molecular level we have shown that the DNA binding ability of FOXP3 is abolished in
the presence of HWFT. In order to evaluate the effect of HWFT treatment in mouse tumour models, the CD4+CD25+ subset in peripheral blood, spleen lymphocytes and tumour-infiltrating lymphocytes from HWFT-treated compared to untreated CT26 colon-carcinoma-bearing BALB/c mice will be analyzed by flow cytometry. The findings from these animal experiments will also be presented. This novel approach of targeting the FOXP3/NFAT complex may provide an additional strategy for abrogating local immune suppression in tumours exerted by Treg.