Rapamycin inhibits B-cell growth but not survival. (A) BLyS-dependent ex vivo B-cell survival is resistant to rapamycin. Small resting B cells from normal donors were cultured for 4 days with and without 100 ng/mL rhuBLyS, vehicle, or 50 nM rapamycin, which was used to pretreat B cells before culture, added directly to cultures on initiation and readded every 2 days. Viable cells were determined at day 4. Data are the arithmetic mean (±SD) and the results of 3 independent experiments. (B,C) Rapamycin inhibits BLyS-dependent maintenance of B cell size. CD23⁺ B cells from (B) normal or (C) Pim 1^−/− 2^−/− double-deficient donors were cultured with and without BLyS and with vehicle or rapamycin for 5 days. Cell size was determined for viable cells daily by a Coulter Z2 size analyzer. Results are the arithmetic mean (±SD) from 3 independent experiments. Statistical comparisons are between BLyS and BLyS plus rapamycin cell populations (* P < .05; ** P < .01).