More importantly, data presented herein, indicate that CD154 is capable of significantly protecting T-cell leukemia or lymphoma cell lines from Fas-mediated death, through activation mainly of the PI-3k/Akt pathway but also of the p38 and ERK1/2 MAPK cascades as well as via the inhibition of caspase-8 cleavage. This evidence concerns the gene CD40LG and T-cell leukemia.