The blood is rich in different types of mesoderm derived stem and progenitor cells

Abstract

The blood and bone marrow have been thoroughly investiagated for more than a century, but we are still gaining surprising new informations. Blood transports different mature cells such as erythrocytes, platelets and granulocytes, but curiously, the blood is also transporting a number of non-differentiated cells of various mesodermal lineages: hematopoietic and mesenchymal stem and progenitor cells, endothelial progenitor cells and very small embryonal like cells are some of the most impressive examples. In adults the bone marrow is the source of practiclly all cells that could be found in the blood. Stem and progenitor cells egress from the bone marrow and home to the bone marrow or various tissues in a highly regulated manner. The fact that the hematopoetic stem and progenitor cells traffi c through the blood and repopulate the bone marrow niche is largely explored in stem cell therapy in human medicine. In this review we will briefl y describe the main characteristics of stem and progenitor cells, the mechanisms of their mobilization from the bone marrow and homing to target tissues. Also, the history and importance of the fact that different stem, progenitor and precursor cells could be isolated from the blood circulation will be discussed in the light of informations concerning their use in human and veterinary medicine.