Comparison of blood samples before idelalisib treatment initiation and during the treatment revealed a reduced frequency of circulating Tregs (148) as well as a reduced fraction of KI-67+, proliferating Tregs, in comparison to pre-treatment samples (136), implicating that idelalisib treatment of CLL patients likely reduces accumulation and proliferation of Tregs (Figure 3). The gene discussed is MKI67; the disease is B-cell chronic lymphocytic leukemia.