CTLA4 and B-cell chronic lymphocytic leukemia: Using fluorescently labeled flow cytometry antibodies to detect both intracellular and surface CTLA4 in the blood from Eμ-MTCP1 mice, we found that, like human CLL and unlike Eμ-TCL1 CLL-like cells, CTLA4 expression was restricted to the intracellular compartment (Supplementary Fig. 3F).