Clinical implications of PRAME gene expression in childhood acute myeloid leukemia

The expression of the PRAME gene (preferentially expressed antigen of melanoma) was measured by quantitative reverse transcriptase polymerase chain reaction in 50 children with newly diagnosed acute myeloid leukemia (AML), three samples of CD34+ stem cells, six bone marrow samples, and 10 peripheral blood samples of healthy donors, as well as three AML cell-lines (KG-1, U937, and HL-60). Eight patients were also analyzed in relapse. Contrary to previous reports, we could show that the PRAME gene is expressed by CD34+ stem cells. This might constitute a problem in using PRAME for tumor immunotherapy. Overexpression of PRAME was found in 62% (n=31) of our patients. The rates of overall and disease-free survival in this group were higher than in patients with no or low expression (P<0.05). PRAME expression was negatively correlated to the white blood cell count at diagnosis (P<0.05) and significantly higher in patients with t(8;21). The levels of expression at diagnosis corresponded with those at relapse (P<0.001) and increased levels could be found prior to the relapse in one patient who was regularly monitored. Our results suggest that the expression of PRAME is an indicator of favorable prognosis and could be a useful tool for monitoring minimal residual disease in childhood AML.