CD5 and B-cell chronic lymphocytic leukemia: On the other hand, SHP-1 exists in CLL cells as two distinct pools, one of which is bound to the Tyr-phosphorylated cytoplasmic tail of the transmembrane CLL marker CD5, most likely supporting pro-survival pathways, and the other that is located in the cytoplasm in an inactive form that can be reactivated by small molecules that disrupt the inhibitory intramolecular interactions.