Immune-deficient mice as models of normal and leukemic human hematopoiesis

A complete understanding of the organization of the human hematopoietic stem cell hierarchy and of the molecular events regulating the stem cell developmental program has been hampered by the absence of suitable in vivo stem cell assays. Perturbations in the normal stem cell program that lead to neoplastic growth are also difficult to study because leukemic cells do not grow readily in culture. Recent advances in the transplantation of human cells into immune-deficient mice provide an unprecedented opportunity to study human hematopoiesis--both normal and abnormal--in the context of a small animal model. Here I review several of these new animal models and the basic concepts of murine and human hematopoiesis which led to their development.