In recent years, there has been rapid expansion of the clinical use of hematopoietic stem cells as well as its concomitant understanding of its basic biology. to a significantly lesser rate of bone marrow transplantation failures as sufficient number of stem cells will make sure engraftment of stem cells. 1. Introduction Peripheral blood-derived stem cells (PBSCs) have been used in bone marrow transplantation ever since its first report was published in the late 70s . In recent years, there has been rapid expansion of the clinical use of hematopoietic stem cells as well as its concomitant understanding of its basic biology. These stem cells, which are a crucial DMT1 blocker 1 component of transplantation, are progenitors to the blood cells of the body that constitutes the myeloid and erythroid lineage . They constantly provide mature blood cells during the lifespan of the individual. These are one of the best characterized stem cells in the body that are clinically applicable in the treatment of diseases such as breast malignancy, leukemias, and congenital immunodeficiencies . Hematopoietic stem cells (HSCs) belong to a group of multipotent precursors that have a self-renewal capacity and the ability to generate different cell types that comprise of the blood-forming system . Transplantation of HSCs forms the basis of consolidation therapy in cancer treatments and is used to remedy or ameliorate a number of hematologic and genetic disorders . HSCs are also an attractive target cell populace for gene therapies because they are readily accessible for ex vivo genetic modification and allow for the possibility of sustained transgene expression in circulating peripheral blood cells throughout the lifetime of an individual . PBSC transplantation (PBSCT) has become increasingly common with PBSCs largely replacing bone marrow (BM) as the preferred stem cell source due largely to quicker engraftment kinetics and ease of collection. In the peripheral blood, stem cells are found in limited numbers (less than 0.1% of all nucleated cells). Stem cell progenitor cells circulate in the periphery, as this ensures an even distribution of hematopoiesis within the bone marrow. 1.1. Hematopoietic Stem Cell Morphology PBSCs consist of a subpopulation of hematopoietic progenitor cells (CD34+), DMT1 blocker 1 which is usually morphologically difficult to identify. These cells can be distinguished by their immunophenotypic patterns as CD34+/CD38?. They do not express a full complement of either myeloid or lymphoid lineage-specific markers (Lin?) but do express the Thy-1 differentiation antigen. The CD34+/CD38?/Lin?/Thy-1+ cells are responsible for initiating long-term culture initiating colony (LTC-IC) assays . There are numerous methods for stem cell quantification after collection but the most common method used today is the flow cytometric evaluation of CD34+ cell numbers. Enumeration of CD34+/CD38?, CD34+/CD33?, and CD34+/Thy-1+ cell subsets has proven to be a useful technique in the estimation of stem cell numbers . Other methods such as colony forming models (CFU) of granulocyte-macrophage were also used to estimate stem cell numbers. This method is much less reliable due to the variation in culture techniques, media preparation, CD282 and several human factors . 1.2. Mobilization and Collection of PBSCs Hematopoietic stem cells have an inherent property to constantly leave the bone marrow and penetrate tissues thereafter returning to the BM or peripheral niches via the blood or lymphatic system . A niche is usually a subgroup of tissue cells and extracellular substrates that can indefinitely harbor one or more stem cells and control their self-renewal and progeny in vivo . Levels of pluripotent hematopoietic stem cells rise up to 50-fold in the recovery phase after myelosuppressive chemotherapy and can be DMT1 blocker 1 collected for autologous transplantation. In order to achieve circulating levels high enough to ensure a harvest capable of reconstituting a mature hematopoietic system after allogeneic donation, healthy donors must be primed with hematopoietic.