PI3Kδ kinase is expressed in normal and malignant B-cells. By inhibiting it, idelalisib induces apoptosis and prevents proliferation in cell lines derived from malignant B-cells and in primary tumor cells. It also inhibits several cell signaling pathways, including B-cell receptor (BCR) signaling and the CXCR4 and CXCR5 signaling, which are involved in trafficking and homing of B-cells to the lymph nodes and bone marrow.[