In addition, CD39+ Treg cells have also been reported as a subset of the CD4+ CD25highFoxP3+ Treg cells in association with chronic infections like tuberculosis (TB) [12], hepatitis B (HBV) and in graft rejections [13], [14] and the ability of CD8+ CD39+ Treg cells to suppress antigen specific CD4+ proliferation clearly demonstrated the importance of this sub-population [15]. The gene discussed is ENTPD1; the disease is hepatitis B virus infection.