The Stem Cell Core will include a state-of-the-art flow cytometry facility. The Core will: 1. Provide investigators with pluripotent hematopoietic stem cells. 2. Provide T and B lymphoid progenitors. 3. Provide stromal cell co-culture systems and cytokine-driven colony assays. 4. Provide animal marrow transplantation models. 5. Provide monoclonal antibodies conjugated to fluorochromes. 6. Develop new technologies to improve core services.