We recently found that miR-29 is over-expressed in indolent human CLL, compared to aggressive CLL and normal CD19+ B-cells. To elucidate the role of miR-29 in B-cell leukemias we created transgenic mice over-expressing miR-29 in B-cells and recently we reported the phenotype of this new mouse model [55]. Immunophenotypic profile of spleen lymphocytes from miR-29 transgenics showed increased populations of CD5+CD19+IgM+ B-cells, a typical feature of CLL. Between the age of 12 and 24 months a markedly expanded CD5+ B-cell population was evident in spleens of 34 of 40 (85%) miR-29 transgenic mice; ~50% of B-cells in these transgenics were CD5 positive [55]. Interestingly, of 20 miR-29 transgenic mice followed to 24–26 months of age, only 4 (20%) developed frank leukemia and died of the disease. Since almost all miR-29 transgenics showed expanded CD5+CD19+IgM+ B-cell populations, but only 20% developed a frank leukemia, we concluded that miR-29 transgenics developed a disease similar to indolent CLL [55]. Moreover, miR-29 mice showed significant increases in % of leukemic cells with age. In mice younger than 15 months, CD5+ leukemic cells were only
