Induction of proliferation in vitro using CD40L stimulation results in high ki67 levels in CXCR4loCD5hi cells with CXCR4 expression increasing as CLL cells progress through S and G2/M‐phases, while CXCR4hiCD5lo CLL cells remained quiescent. Here, CD40LG is linked to B-cell chronic lymphocytic leukemia.