CD34 and acute promyelocytic leukemia: We then compared the level of HHEX mRNA expression observed in either normal CD34+ cells or day 7 granulocytic cells, composed by a majority of normal promyelocytes, with the HHEX mRNA levels observed in fresh diagnostic APL blasts and we observed that HHEX levels were markedly lower in leukemic cells than in their normal counterpart (Fig. 1b).