MS4A1 and B-cell chronic lymphocytic leukemia: FMC7 is strongly expressed by CLL cells when they proceed to prolymphocytoid transformation.[44] Although a major proportion of (81%) the CLL cells in the ex vivo sample was FMC7 positive, the established MEC1 line contained only 8% positive cells.[20] In our present analysis, the majority of the MEC1 cells expressed FMC7 (74%) and all MEC2 cells expressed this marker.