Activation of mTOR signaling in DLBCL. (A) Constitutive activation of the mTOR signaling pathway in patient samples of DLBCL. Activation of Akt, mTOR, S6rp, and 4EBP1 was assessed in DLBCL tissue by immunohistochemistry with phospho-specific antibodies for Akt mTOR or S6rp or 4EBP1. (B-E) Effect of rapamycin on DLBCL survival. After DHL-6, Ly7, and Ly3 cell lines (B-D) or primary cells from 3 DLBCL patients (E) were treated with the indicated concentrations of rapamycin for 48 hours, survival was assessed using annexin and propidium iodide followed by flow cytometry. Data from 1 representative experiment are shown for each cell line (n = 3). Bar graph shows mean ± standard deviation (SD) from 3 determinations.