LEF1 and B-cell chronic lymphocytic leukemia: LEF-1 is expressed by B cell precursors in the bone marrow and is critical during B cell development.[8] Mature B and plasma cells lose expression of LEF-1 during B cell development.[9] Similarly, this study has demonstrated that stimulating CLL cells to acquire a further stage of differentiation, i.e., ISC, leads to a decrease in LEF-1 expression while the plasma cell specific transcription factor, PRDM1, increases.