Since haematopoietic stem cells cannot be isolated as a pure population, it is not possible to identify them under a microscope.[ citation needed ] Therefore, there are many techniques to isolate haematopoietic stem cells (HSCs). HSCs can be identified or isolated by the use of flow cytometry where the combination of several different cell surface markers is used to separate the rare HSCs from the surrounding blood cells. HSCs lack expression of mature blood cell markers and are thus, called Lin-. Lack of expression of lineage markers is used in combination with detection of several positive cell-surface markers to isolate HSCs. In addition, HSCs are characterized by their small size and low staining with vital dyes such as rhodamine 123 (rhodamine lo) or Hoechst 33342 (side population).
CD34+ Cells can be isolated by 4 different techniques from peripheral blood samples
The classical marker of human HSC is CD34 first described independently by Civin et al. and Tindle et al. [1] [2] [3] [4] It is used to isolate HSC for reconstitution of patients who are haematologically incompetent as a result of chemotherapy or disease.
Many markers belong to the cluster of differentiation series, like: CD34, CD38, CD90, CD133, CD105, CD45, and also c-kit – the receptor for stem cell factor.
There are many differences between the human and murine hematopoietic cell markers for the commonly accepted type of hematopoietic stem cells. [5]
However, not all stem cells are covered by these combinations that, nonetheless, have become popular. In fact, even in humans, there are hematopoietic stem cells that are CD34 −/CD38 −. [6] [7] Also some later studies suggested that earliest stem cells may lack c-kit on the cell surface. [8] For human HSCs use of CD133 was one step ahead as both CD34 + and CD34 − HSCs were CD133 +.
Traditional purification method used to yield a reasonable purity level of mouse hematopoietic stem cells, in general, requires a large (~10–12) battery of markers, most of which were surrogate markers with little functional significance, and thus partial overlap with the stem cell populations and sometimes other closely related cells that are not stem cells. Also, some of these markers (e.g., Thy1) are not conserved across mouse species, and use of markers like CD34 − for HSC purification requires mice to be at least 8 weeks old.
Alternative methods that could give rise to a similar or better harvest of stem cells is an active area of research, and are presently[ when? ] emerging. One such method uses a signature of SLAM family cell surface molecules. The SLAM (Signaling lymphocyte activation molecule) family is a group of more than 10 molecules whose genes are located mostly tandemly in a single locus on chromosome 1 (mouse), all belonging to a subset of the immunoglobulin gene superfamily, and originally thought to be involved in T-cell stimulation. This family includes CD48, CD150, CD244, etc., CD150 being the founding member, and, thus, also known as slamF1, i.e., SLAM family member 1.
The signature SLAM codes for the hemopoietic hierarchy are:
For HSCs, CD150 + CD48 − was sufficient instead of CD150 + CD48 − CD244 − because CD48 is a ligand for CD244, and both would be positive only in the activated lineage-restricted progenitors. It seems that this code was more efficient than the more tedious earlier set of the large number of markers, and are also conserved across the mouse strains; however, recent work has shown that this method excludes a large number of HSCs and includes an equally large number of non-stem cells. [9] [10] CD150 + CD48 − gave stem cell purity comparable to Thy1 lo SCA-1 +lin− c-kit + in mice. [11]
Irving Weissman's group at Stanford University was the first to isolate mouse hematopoietic stem cells in 1986 [12] [13] and was also the first to work out the markers to distinguish the mouse long-term (LT-HSC) and short-term (ST-HSC) hematopoietic stem cells (self-renew-capable), and the Multi-potent progenitors (MPP, low or no self-renew capability – the later the developmental stage of MPP, the lesser the self-renewal ability and the more of some of the markers like CD4 and CD135):
Haematopoiesis is the formation of blood cellular components. All cellular blood components are derived from haematopoietic stem cells. In a healthy adult human, roughly ten billion to a hundred billion new blood cells are produced per day, in order to maintain steady state levels in the peripheral circulation.
Hematopoietic stem cells (HSCs) are the stem cells that give rise to other blood cells. This process is called haematopoiesis. In vertebrates, the first definitive HSCs arise from the ventral endothelial wall of the embryonic aorta within the (midgestational) aorta-gonad-mesonephros region, through a process known as endothelial-to-hematopoietic transition. In adults, haematopoiesis occurs in the red bone marrow, in the core of most bones. The red bone marrow is derived from the layer of the embryo called the mesoderm.
CD34 is a transmembrane phosphoglycoprotein protein encoded by the CD34 gene in humans, mice, rats and other species.
Cancer stem cells (CSCs) are cancer cells that possess characteristics associated with normal stem cells, specifically the ability to give rise to all cell types found in a particular cancer sample. CSCs are therefore tumorigenic (tumor-forming), perhaps in contrast to other non-tumorigenic cancer cells. CSCs may generate tumors through the stem cell processes of self-renewal and differentiation into multiple cell types. Such cells are hypothesized to persist in tumors as a distinct population and cause relapse and metastasis by giving rise to new tumors. Therefore, development of specific therapies targeted at CSCs holds hope for improvement of survival and quality of life of cancer patients, especially for patients with metastatic disease.
In immunology, central tolerance is the process of eliminating any developing T or B lymphocytes that are autoreactive, i.e. reactive to the body itself. Through elimination of autoreactive lymphocytes, tolerance ensures that the immune system does not attack self peptides. Lymphocyte maturation occurs in primary lymphoid organs such as the bone marrow and the thymus. In mammals, B cells mature in the bone marrow and T cells mature in the thymus.
Hemangioblasts are the multipotent precursor cells that can differentiate into both hematopoietic and endothelial cells. In the mouse embryo, the emergence of blood islands in the yolk sac at embryonic day 7 marks the onset of hematopoiesis. From these blood islands, the hematopoietic cells and vasculature are formed shortly after. Hemangioblasts are the progenitors that form the blood islands. To date, the hemangioblast has been identified in human, mouse and zebrafish embryos.
Thy-1 or CD90 is a 25–37 kDa heavily N-glycosylated, glycophosphatidylinositol (GPI) anchored conserved cell surface protein with a single V-like immunoglobulin domain, originally discovered as a thymocyte antigen. Thy-1 can be used as a marker for a variety of stem cells and for the axonal processes of mature neurons. Structural study of Thy-1 led to the foundation of the Immunoglobulin superfamily, of which it is the smallest member, and led to some of the initial biochemical description and characterization of a vertebrate GPI anchor and also the first demonstration of tissue specific differential glycosylation.
Lymphopoiesis (lĭm'fō-poi-ē'sĭs) is the generation of lymphocytes, one of the five types of white blood cells (WBCs). It is more formally known as lymphoid hematopoiesis.
Proto-oncogene c-KIT is the gene encoding the receptor tyrosine kinase protein known as tyrosine-protein kinase KIT, CD117 or mast/stem cell growth factor receptor (SCFR). Multiple transcript variants encoding different isoforms have been found for this gene. KIT was first described by the German biochemist Axel Ullrich in 1987 as the cellular homolog of the feline sarcoma viral oncogene v-kit.
Integrin α4β1 is an integrin dimer. It is composed of CD49d and CD29. The alpha 4 subunit is 155 kDa, and the beta 1 subunit is 150 kDa.
CD16, also known as FcγRIII, is a cluster of differentiation molecule found on the surface of natural killer cells, neutrophils, monocytes, macrophages, and certain T cells. CD16 has been identified as Fc receptors FcγRIIIa (CD16a) and FcγRIIIb (CD16b), which participate in signal transduction. The most well-researched membrane receptor implicated in triggering lysis by NK cells, CD16 is a molecule of the immunoglobulin superfamily (IgSF) involved in antibody-dependent cellular cytotoxicity (ADCC). It can be used to isolate populations of specific immune cells through fluorescent-activated cell sorting (FACS) or magnetic-activated cell sorting, using antibodies directed towards CD16.
Stem cell factor is a cytokine that binds to the c-KIT receptor (CD117). SCF can exist both as a transmembrane protein and a soluble protein. This cytokine plays an important role in hematopoiesis, spermatogenesis, and melanogenesis.
Fms-related tyrosine kinase 3 ligand (FLT3LG) is a protein which in humans is encoded by the FLT3LG gene.
Signaling lymphocytic activation molecule 1 is a protein that in humans is encoded by the SLAMF1 gene. Recently SLAMF1 has also been designated CD150.
CD109 is a human gene.
Stem cell markers are genes and their protein products used by scientists to isolate and identify stem cells. Stem cells can also be identified by functional assays. Below is a list of genes/protein products that can be used to identify various types of stem cells, or functional assays that do the same. The initial version of the list below was obtained by mining the PubMed database as described in
KSL cells in cell biology are an early form of mouse/murine hematopoietic stem cells. Characteristics are Kit (+), Sca-1 (+) and Lin (-). HSCs [Hematopoietic stem cells] in murine cultures show phenotypic markers as being CD34-, CD150+, and Flt3- for LTR [long-term reconstitution]. These phenotypic markers are used when purifying hematopoietic stem cells from the many other differentiated cells in the bone marrow.
Sca-1 stands for "Stem cells antigen-1". It consist of 18-kDa mouse glycosyl phosphatidylinositol-anchored cell surface protein (GPI-AP) of the LY6 gene family. It is the common biological marker used to identify hematopoietic stem cell (HSC) along with other markers.
Islet resident macrophages are the predominant myeloid cell of the pancreatic islets of langerhans.
OP9 cells are a cell line derived from mouse bone marrow stromal cells (mesenchyme). These cells are now characterized as stem cells. When co-cultured with embryonic stem cells (ESC), OP9 cells can induce ESC to differentiate into blood cells by serving as a feeder layer. They have the potential to be used in cell therapy, regenerative medicine and as immunomodulators.