The human bone marrow macro-environment is constantly changing. At the age of twenty these changes become apparent as MRI studies demonstrate a transition from a red marrow (rich in blood vessels) to a yellow marrow (rich in fat). Why this changes occur and how they are related to the other phenotype of the aged marrow is unclear. Reduced diversity of B and T cell repertoire is another change in the environment and its role in shaping the evolution of the rest of the hematopoietic system is also unclear. Studying the interaction between the changing environment and preleukemic hematopoiesis is another focus of our lab.