Recapitulating the effects of ITK deficiency, ibrutinib suppresses human CD4 T cells of healthy donors from differentiating into TH17 cells in vitro and reduces the in vivo frequencies of both TH17 and Tregs as well as the serum levels of TH17-associated cytokines IL-17A, IL-21 and IL-23 in CLL patients (Niemann et al., 2016; Eken et al., 2019; Mhibik et al., 2019). The gene discussed is ITK; the disease is B-cell chronic lymphocytic leukemia.