With regard to the first possibility, it has subsequently become clear that CLL cells recirculate between secondary lymphoid organs and peripheral blood and the latter contains subpopulations of resting or recently proliferating CLL cells which differ in their expression of surface receptors such as CD38, CD5 and CXCR4.(Calissano et al, 2011; Cuthill et al, 2015). Here, CD38 is linked to B-cell chronic lymphocytic leukemia.