1. Departments of Pathology and Developmental Biology, Stanford University School of Medicine, Stanford, California 94305 , USA
2. These authors contributed equally to this work
3. Present address: Department of Cancer Immunology and AIDS, Dana-Farber Cancer Institute, 44 Binney Street, Boston, Massachusetts 02115, USA.

Correspondence to: Koichi Akashi^1,2 Correspondence and requests for materials should be addressed to K.A. (e-mail: Email: akashi@leland.stanford.edu).

Abstract

Haematopoietic stem cells give rise to progeny that progressively lose self-renewal capacity and become restricted to one lineage^{1, 2}. The points at which haematopoietic stem cell-derived progenitors commit to each of the various lineages remain mostly unknown. We have identified a clonogenic common lymphoid progenitor that can differentiate into T, B and natural killer cells but not myeloid cells³. Here we report the prospective identification, purification and characterization, using cell-surface markers and flow cytometry, of a complementary clonogenic common myeloid progenitor that gives rise to all myeloid lineages. Common myeloid progenitors give rise to either megakaryocyte/erythrocyte or granulocyte/macrophage progenitors. Purified progenitors were used to provide a first-pass expression profile of various haematopoiesis-related genes. We propose that the common lymphoid progenitor and common myeloid progenitor populations reflect the earliest branch points between the lymphoid and myeloid lineages, and that the commitment of common myeloid progenitors to either the megakaryocyte/erythrocyte or the granulocyte/macrophage lineages are mutually exclusive events.