TNFSF13B and B-cell chronic lymphocytic leukemia: To also examine the contributions of APRIL, BAFF, and CD40L on CLL cell survival, we performed the 10-day CellTiter-Glo luminescent viability assay following 24 h co-culture with either control fibroblasts, GFP-APRIL + CD40L fibroblasts or GFP-APRIL, GFP-BAFF, and GFP-APRIL + CD40L fibroblasts (Fig. 2a, b).