Irving Weissman, M.D., Ph.D.

Professor of Pathology and Developmental Biology

Our lab’s research encompasses the developmental biology, self-renewal, homing, and functions of the cells that make up the blood-forming and immune systems. The main focus for the past several years has been the purification, biology, transplantation, and evolution of stem cells. We were the first to isolate in pure form any stem cells from any tissue in any species. The isolation of mouse hematopoietic stem cells (HSC) was followed by the isolation of human HSC. Purified human HSC have been successfully used to provide cancer-free autologous stem cell transplants into patients receiving otherwise lethal doses of chemotherapy and radiotherapy for their cancers. We have gone on to identify the stages of development between stem cells and mature blood cells. These include the common lymphocyte progenitor (CLP), the common myeloid progenitor (CMP), and the descendents of the CMP^- the common granulocyte and monocyte progenitor (GMP) and megakaryocyte/erythrocyte progenitors (MEP). Similarly, we have identified the several stages of thymic lymphocyte development. Recently, accurate mouse models of human leukemias have been made, and have been used to show the central role of inhibition of programmed cell death in that process. Current projects also include investigations of neural stem cells.

The Weissman laboratory also has a group at Hopkins Marine Station where they work with a protochordate between invertebrates and vertebrates. These organisms contain both germline and somatic (body and blood) stem cells that are used every week in an asexual developmental process that forms entire new organisms derived from these cells. Most interestingly, these organisms can connect their extracorporeal blood vessels to those of genetically identical or genetically distinct siblings. We have found that both germline and somatic stem cells from one can participate in competition for developmental sites of the other. We found that these animals have a transplantation gene locus very similar to the one that limits transplants in man for the apparent purpose of limiting parasitic germline stem cells from spreading too far through the species. Thus the work in our lab extends from developmental and population genetics of primitive chordates to basic discoveries in stem cell biology to the clinic.