IL21 and B-cell chronic lymphocytic leukemia: In proliferating primary CLL cells (NTL-CD40L/IL21 co-culture), mTOR-selective inhibitors induced a significant decrease in the S phase of cell cycle alone and in the RAP/IB combination compared to ibrutinib (IB) or NDC controls, indicative of an mTORC1-mediated reduction in cell cycle (Fig. 6A–C, Supplementary Fig. 10).