PIK3CD and B-cell chronic lymphocytic leukemia: Accordingly, mice deficient in p110δ (referred to as PI3Kδ henceforth) activity exhibit profound disruption of lymphocyte homeostasis and humoral immunity7 via effects centered upon antigen receptor signaling,7, 8 cytokine production8, 9 and Treg function.10 Consequently, δ isoform selective PI3K inhibitors (PI3Kδi) have provided encouraging therapeutic responses in clinical trials,11 particularly in combination with anti-CD20 monoclonal antibodies (mAb),12 culminating in the approval of Zydelig (idelalisib) for the treatment of relapsed refractory CLL in combination with rituximab.