Conversion of antigen-specific effector/memory T cells into Foxp3-expressing Treg cells by inhibition of CDK8/19

A promising way to restrain hazardous immune responses, such as autoimmune disease and allergy, is to convert disease-mediating T cells into immunosuppressive regulatory T (T-reg) cells. Here, we show that chemical inhibition of the cyclin-dependent kinase 8 (CDK8) and CDK19, or knockdown/knockout of the CDK8 or CDK19 gene, is able to induce Foxp3, a key transcription factor controlling T(reg )cell function, in antigen-stimulated effector/memory as well as naive CD4(+) and CD8(+) T cells. The induction was associated with STAT5 activation, independent of TGF-beta action, and not affected by inflammatory cytokines. Furthermore, in vivo administration of a newly developed CDK8/19 inhibitor along with antigen immunization generated functionally stable antigen-specific Foxp3(+)T(reg) cells, which effectively suppressed skin contact hypersensitivity and autoimmune disease in animal models. The results indicate that CDK8/19 is physiologically repressing Foxp3 expression in activated conventional T cells and that its pharmacological inhibition enables conversion of antigen-specific effector/memory T cells into Foxp3(+) T-reg cells for the treatment of various immunological diseases.