Minimal residual disease in leukemia: studies in an animal model for acute myelocytic leukemia (BNML)

The possibilities for studying minimal residual disease (MRD) in human acute myelocytic leukemia (AML) are limited. Animal models are, therefore, indispensable for gaining insight into the characteristics of leukemia growth during the MRD phase. Studies were done to compare AML to acute myelocytic leukemia in the Brown Norway rat (BNML). The BNML model exhibited a high degree of similarity to human AML with regard to its general growth characteristics, its cell kinetic parameters, its biophysical parameters and its response to chemotherapy. This implied that studies of the BNML model have predictive value for clinical application. In the BNML model a number of independent methods are available to quantify the number of leukemic cells, i.e., indirectly by means of various bioassays or directly by using monoclonal antibody labeling and flow cytometry. Studies of the BNML model in relation to the understanding of various aspects of MRD in leukemia are discussed in this concise review. Insight has been obtained with regard to the kinetics of MRD; the efficacy of certain treatment modalities, e.g., cytostatic drug treatment with or without total body irradiation to eradicate MRD; the efficacy of various methods for eliminating residual leukemic cells from autologous marrow grafts; the emergence of drug resistance during MRD; and the progression of residual disease during the remission phase ultimately leading to a relapse and the implications of these observations for staging leukemia patients during the phase of MRD.