PROM1 and leukemia: Moreover, PROM1/CD133 is expressed in most, but not all, KMT2A-rearranged acute leukemia patients, and its presence seems to reflect the immunophenotype and/or cell of origin of the leukemia, as HSCs and early progenitors typically express PROM1/CD133, while more differentiated B-cell progenitors do not [29, 54, 55].