10-Cl-BBQ is an orally bioavailable, non-toxic benzimidazoisoquinoline derivative that acts as an aryl hydrocarbon receptor (AhR) agonist via directly binding to AhR (IC50??= 2.6 nM in a competitive binding assay) and induces its nuclear translocation. 10-Cl-BBQ is shown to increase CD4+ ?T-cells that co-express CD25, CTLA-4 and ICOS, as well as several other genes associated with regulatory T cell (Treg) function in a graft versus host response model (GVH, C57BI/6 T cells injected into B6D2F1 host mice). 10-Cl-BBQ displays good pharmacokinetic profile in mice (t1/2 = 2 h, Cmax = 21.5 µg/L, 10 mg/kg, i.p.). Also shown to prevent insulitis in a NOD T1D mouse model which is independent of Fox3 + ?Tregs (60 mg/kg, p.o, q.o.d.).