Introduction

Abstract

The present generation of physicians are witnessing a remarkable development in hematology. In the 1950s, the major tools used in the study of blood cell formation in man and other mammals were the microscope and cytochemical techniques. In the subsequent decade use was made of the availability of radioactive nuclides and the dynamics of blood cell formation and turnover were quantitated, notably by the introduction first of radioactive iron, then of radioactively labeled molecules, such as tritiated thymidine, to label hemopoietic cells and study them from their formation to their death. The 1960s also saw the introduction of cell culture methods into hematologic research. With the use of chromosomal techniques it became possible to characterize hematopoietic disorders such as chronic granulocytic leukemia and to establish it as a stem cell disorder. Chromosomal techniques were also used in experimental hematology to explore the migration streams of different kinds of cells in the organism. A major step forward was the development of cell culture and cell transplantation techniques to characterize hematopoietic stem cells. Thus, by the 1970s we witnessed the advent of the characterization of the complex system of hemopoietic stem cells, consisting of those that have retained pluripotency and others that are “committed” in the sense that they will respond to specific humoral stimuli with a specific differentiation into the morphologically identifiable cell lineages, such as erythropoiesis, granulocytopoiesis, megakaryocytopoiesis, and lymphocytopoiesis. While a spectrum of stem cell assay methods have become available for the mouse, they are still limited as far as clinical hematology is concerned. The availability of some test systems has just started to become useful in the practice of hematology, such as the semisolid agar system for the demonstration of “colony-forming units in culture” representing granulocytic “progenitor cells.”