David is the Gerald and Darlene Jordan Professor of Medicine at Harvard University. He and Professor Douglas Melton founded and jointly direct the Harvard Stem Cell Institute, the largest institute dedicated to bringing stem cell biology to medical care in the world.

He is a hematologist/oncologist and directs the Center for Regenerative Medicine at the Massachusetts General Hospital. He previously chaired the Hematologic Malignancies program in the MGH Cancer Center. He is an expert on the medical applications of stem cell biology, with a particular emphasis on their uses in treating cancer and AIDS.

David has published over 300 scientific papers and book chapters. His laboratory has made fundamental contributions in research on how the stem cell niche regulates stem cell function in normal and disease-corrupted hematopoiesis. He is a member of the National Academy of Medicine and the American Academy of Arts and Sciences, and he has received awards from the Doris Duke Charitable Trust, the Ellison Medical Foundation, the Burroughs Welcome Fund, and the Leukemia and Lymphoma Society. He is the recipient of multiple honorary degrees.