ABSTRACT
Hematology has experienced a particularly productive period of exploration and clinical application during the past half-century. Subjects such as cellular origins, in vitro and in vivo cell culture, the identication and genetic recombinative production of hemopoietic factors, cell surface structure, and transplantation have been addressed with signicant achievement. Among the most notable accomplishments has been the verication of the existence of the pluripotent hematopoietic stem cell (PHSC, HSC), its isolation, and harvest from the bone marrow and blood. Its quality of self-renewal has been experimentally established. The hematopoietic stem cell has been recognized on the basis of its unique identifying cell surface molecule, CD34+ (cluster of differentiation, CD), and its descendants have also been similarly classied on the basis of their specic individual cell surface clusters of differentiation (CD). The hematopoietic stem cell and the progenitor cells it generates are normally present in hemopoietic bone marrow but are not morphologically identiable in standard preparations such as Wright-stained dry lm smears. They are identied immunologically on the basis of their cell surface markers. The hemopoietic stem cell’s cascades of progeny are not routinely morphologically recognizable until they have differentiated to the level of the pronormoblast, myeloblast, megakaryoblast, and so on. The present-day nomenclature of the hemopoietic stem cell’s descendants continues to employ laboratory operational titles to signify them (such as CFUGEMM, colony-forming unit-granulocyte erythrocyte monocyte megakaryocyte, the stem cell for the myeloid lines). In regard to the erythroid lineage specically, its developmental ancestry is the following. The hemopoietic stem cell is envisioned as mitotically giving rise to two identical cells. One of the daughter cells persists as a hemopoietic stem cell (self-renewal) while the other enters hemopoiesis by evolving into a stem cell for the myeloid lineage, or alternatively into the stem cell for the lymphoid cells. If the cell assumes the myeloid pathway, it evolves into the CFUGEMM. Depending on the microenvironment and ambient hemopoietic factors, this cell enters the maturational lineages of specic myeloid cells (e.g., the erythroid, neutrophilic, megakaryocytic cell lines). If the erythroid lineage is entered, the next progenitor is termed as the burst-forming unit-erythroid (BFU-E) (so-called because of its rapid and robust proliferation in cell culture systems), which in turn evolves into the further developed colony-forming unit-erythroid (CFU-E). The latter cell
proliferates and differentiates into the pronormoblast, the most immature erythroid cell that is morphologically recognizable in routine preparations as a cell solely committed to the erythrocytic lineage (Figure 10).
