Making Progress in Cancer Detection
Morris Kletzel, MD, MBA is one of the foremost authorities on pediatric stem cell transplants in the U.S. His laboratory has developed molecular techniques to detect minimal residual disease (MRD) in patients with neuroblastoma and leukemia. This refers to the presence of a small number of residual tumor cells left within the patient after treatment or removal of the primary tumor. There are different methods of detecting MRD in leukemias, each with different levels of detection. Compared with flow cytometry-based methods, which have a sensitivity of about 1:10,000, DNA-based methods allow for detection of leukemic blasts as low as 1 in 106 normal cells.
In a substantial fraction of acute myeloid leukemia (AML) patients, however, neither the flow cytometry nor the DNA-based method is useful. MRD detection by measuring WT1 expression is an attractive alternative, as the assay does not require bone marrow aspirate samples; peripheral blood can be used for all AML patients.
The Kletzel lab uses qRT-PCR (quantitative reverse transcriptase polymerase chain reaction) to detect two genes transcripts: tyrosine hydroxylase in peripheral blood and bone marrow as a marker of MRD in neuroblastoma, and the Wilms’ tumor gene (WT1) for all leukemias. High levels of WT1 expression have been reported in 90 to 100 percent of AML and 60 to 90 percent of acute lymphoblastic leukemia (ALL) blasts. This has led to its increasing use in measuring MRD in leukemia patients after initial therapy. Kletzel’s studies indicate that the detection of over-expression of WT1 in blood samples obtained following induction therapy in patients with leukemia is associated with poor prognosis.
Experts agree on these findings. There is a growing consensus that the level of MRD in patients after therapy can serve as an important prognostic factor that determines long-term outcomes. Patients with undetectable levels of MRD demonstrate improved survival after hematopoietic stem cell transplant (HSCT). The Kletzel lab doesn’t yet understand the mechanism; in fact, the literature confirms that there is widespread uncertainty throughout the scientific community on how WT1 functions. Kletzel hypothesizes that WT1 is a surrogate marker for proliferation, and the data support that hypothesis. There are other investigators who have said that WT1 may be involved in the development of leukemia. What is very difficult to determine is whether it regulates proliferation, promotes leukemogenesis or acts according to an internal signaling. “So we’re working on that,” says Kletzel. “Actually, as we speak we’re presenting a paper in Italy on the role of WT1 correlating juvenile myelomonocytic leukemia (JMML), a rare stem cell disease and its unique proliferative charcteristic. It has never been reported.” He is referring to the International Conference on WT1 in Human Neoplasia, which met in April. According to Marie Olszewski, a member of the Kletzel lab who coordinates the MRD project and attended the meeting, the organization is quite focused. “I learned so much from the science being presented. Questions continue to be posted: Is WT1 an oncogene? Or a tumor suppressor? Or bidirectional? It’s a very complex gene”.
The MRD project’s clinical impact is immediate; in fact, it is beginning to be used with patients. The lab is one of 16 major pediatric transplant centers throughout the U.S. involved in a clinical trial to measure WT1 in patients with AML. Patients going to transplant will have their marrow and/or peripheral blood screened at baseline, and again post-transplant. Kletzel’s group will be the reference lab to measure WT1 messenger RNA levels using qRT-PCR, and their association with long-term outcome. This trial is being supported and certified by the Center for International Blood and Marrow Transplant Research (CIBMTR), which is a combined research program of the National Marrow Donor Program® and the Medical College of Wisconsin. CIBMTR serves as the national registry of transplantation for patients with AML. Kletzel says, “We are going to see how patients who go to transplant with MRD do after they get transplant.”
Morris Kletzel heads the Children’s Memorial Center for Cancer and Blood Disorders, which is a part of the Robert H. Lurie Comprehensive Cancer Center of Northwestern University. Kletzel is Professor of Pediatrics at Northwestern University Feinberg School of Medicine and the Meryl Suzanne Weiss Distinguished Professor in Hematology, Oncology and Stem Cell Transplant. He is also a member of the Clinical and Translational Research Program of the research center.