Marrow stromal cells and NLCs protect CLL cells against F-ara-A-induced apoptosis. (A-B) Cultivation on stromal cells protected CLL cells from F-ara-A-induced apoptosis. (A) CLL cell viability after 48-hour treatment with the indicated F-ara-A concentrations. Cells were cultivated with or without M2-10B4 stromal cells and treated with the indicated F-ara-A concentrations. CLL cell viability was determined after 48-hour treatment. Results are represented relative to untreated controls (100%) and are the mean ± SEM values of 4 different patients. (B) CLL cell viability with or without M2-10B4 stromal cells after 24-, 48-, and 72-hour treatment with 10 μM F-ara-A. Results are represented relative to untreated controls (100%) and are the mean ± SEM values of 10 patients. ^*Significant differences of CLL cell viability with stromal cells compared with CLL cell viability without stromal cells (P < .05). (C) NLCs protect CLL B cells against F-ara-A-induced apoptosis. CLL cells were grown in the presence of NLCs for 14 days and reseeded with or without NLCs before treatment with 10 μM F-ara-A. CLL cell viability was determined after 48 hours. Data are the mean ± SEM values of 6 patients (^*P < .05).