Identification of a Set of Seven Genes for the Monitoring of Minimal Residual Disease in Pediatric Acute Myeloid Leukemia

Abstract

Background: Monitoring of minimal residual disease (MRD) has become a strong diagnostic tool in acute lymphoblastic leukemia. It is used for risk-adapted therapy and for the recognition of pending relapses. In acute myeloid leukemia (AML), there is still a need for more suitable MRD markers. Experimental Design: A stepwise approach which combined genome-wide expression profiling, TaqMan low density arrays, and a TaqMan real-time PCR-based screening was used to identify new markers for the monitoring of MRD in AML. Leukemic cells from 52 children with AML and 145 follow-up samples from 25 patients were analyzed. Results: Seven genes were identified which are vastly overexpressed in many patients with AML compared with healthy bone marrow: CCL23, GAGED2, MSLN, SPAG6, and ST18 as well as the previously described markers WT1 and PRAME. The expression of all genes decreased to normal levels in patients who achieved a continuous complete remission. Elevated levels of at least one gene were found prior to relapse in 7 out of 10 patients who relapsed. Conclusions: This set of genes should allow a sensitive and specific monitoring of MRD in AML. Notably, some of these markers could also serve as therapeutic targets or might be involved in leukemogenesis. MSLN is already used as a target for immunotherapy in clinical trials in other malignancies.

A Causal Role for the Human Tumor Antigen Preferentially Expressed Antigen of Melanoma in Cancer

“…Various methods are used for the detection of MRD and several genes have been tested for their suitability as markers of MRD by qualitative and quantitative RT-PCR techniques. PRAME is one of the molecular markers that are being tested in AML and seems to be a promising diagnostic marker for the detection of MRD in AML (22). For the development of more effective and less toxic cancer therapies, increased selectivity of therapeutic agents is urgently needed.…”

What do we mean by sensitivity when we talk about detecting minimal residual disease?

“…4 It was highly expressed in AML samples but not in healthy bone marrow. However, we found that it was useless as an MRD marker because expression of CSPG4 was also high in bone marrow that was free of leukemia but was regenerating after chemotherapy.…”

“…They depend on the copy numbers of the leukemia-associated genes (WT1, PRAME and others [3][4][5] ) that are used for PCR or the quality of the leukemiaassociated phenotypes that are used for flow cytometry. 6 Therefore, any statement on the quality of a method of monitoring MRD should include the following data: the threshold that is used for clinical decision-making, sensitivity, specificity and the proportion of patients for whom this level of quality can be achieved.…”

“…Flow cytometry or real-time PCR for leukemia-associated genes (WT1, PRAME and others) always give a certain amount of positivity in leukemiafree samples (Lapillone et al; 3 Steinbach et al; 4 Matsushita et al; 5 Kern et al; 6 San Miguel et al; 8 Venditti et al; 9 and others). Therefore, the relevant question is what is the lowest proportion of leukemic cells that gives a test result that is higher than the one in any healthy bone marrow?…”

“…This was performed in a number of studies for flow cytometry (Kern et al; 6 San Miguel et al; 8 Venditti et al; 9 and others) and also for leukemia-specific genes (Lapillone et al; 3 Steinbach et al; 4 Matsushita et al; 5 …”