MTOR and B-cell chronic lymphocytic leukemia: Isoform PI3Kδ, the most critical in CLL, transmits pro-proliferative and pro-survival signals by Akt and mTOR and participates in other signaling derived from cell surface proteins including cluster-of-differentiation 40 (CD40), integrins, chemokine receptor type 4 (CXCR4), and other stromal factors.