This article may be too technical for most readers to understand.(August 2015) |
Hematopoietic stem cell | |
---|---|
Details | |
Precursor | Hemangioblast |
System | Hematopoietic system |
Location | Bone marrow |
Function | Stem cells that give rise to other blood cells |
Identifiers | |
Latin | cellula haematopoietica praecursoria |
Acronym(s) | HSC |
MeSH | D006412 |
TH | H2.00.01.0.00006 |
Anatomical terms of microanatomy |
Hematopoietic stem cells (HSCs) are the stem cells [1] that give rise to other blood cells. This process is called haematopoiesis. [2] 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. [3] [4] 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.
Haematopoiesis is the process by which all mature blood cells are produced. It must balance enormous production needs (the average person produces more than 500 billion blood cells every day) with the need to regulate the number of each blood cell type in the circulation. In vertebrates, the vast majority of hematopoiesis occurs in the bone marrow and is derived from a limited number of hematopoietic stem cells that are multipotent and capable of extensive self-renewal.
Hematopoietic stem cells give rise to different types of blood cells, in lines called myeloid and lymphoid. Myeloid and lymphoid lineages both are involved in dendritic cell formation. Myeloid cells include monocytes, macrophages, neutrophils, basophils, eosinophils, erythrocytes, and megakaryocytes to platelets. Lymphoid cells include T cells, B cells, natural killer cells, and innate lymphoid cells.
The definition of hematopoietic stem cell has developed since they were first discovered in 1961. [5] The hematopoietic tissue contains cells with long-term and short-term regeneration capacities and committed multipotent, oligopotent, and unipotent progenitors. Hematopoietic stem cells constitute 1:10,000 of cells in myeloid tissue.
HSC transplants are used in the treatment of cancers and other immune system disorders [6] due to their regenerative properties. [7]
They are round, non-adherent, with a rounded nucleus and low cytoplasm-to-nucleus ratio. In shape, hematopoietic stem cells resemble lymphocytes.
The very first hematopoietic stem cells during (mouse and human) embryonic development are found in aorta-gonad-mesonephros region and the vitelline and umbilical arteries. [8] [9] [10] Slightly later, HSCs are also found in the placenta, yolk sac, embryonic head, and fetal liver. [3] [11]
Stem and progenitor cells can be taken from the pelvis, at the iliac crest, using a needle and syringe. [12] The cells can be removed as liquid (to perform a smear to look at the cell morphology) or they can be removed via a core biopsy (to maintain the architecture or relationship of the cells to each other and to the bone).[ citation needed ]
A colony-forming unit is a subtype of HSC. (This sense of the term is different from colony-forming units of microbes, which is a cell counting unit.) There are various kinds of HSC colony-forming units:
The above CFUs are based on the lineage. Another CFU, the colony-forming unit–spleen (CFU-S), was the basis of an in vivo clonal colony formation, which depends on the ability of infused bone marrow cells to give rise to clones of maturing hematopoietic cells in the spleens of irradiated mice after 8 to 12 days. It was used extensively in early studies, but is now considered to measure more mature progenitor or transit-amplifying cells rather than stem cells[ citation needed ].
Since hematopoietic stem cells cannot be isolated as a pure population, it is not possible to identify them in a microscope.[ citation needed ] Hematopoietic stem cells can be identified or isolated by the use of flow cytometry where the combination of several different cell surface markers (particularly CD34) are used to separate the rare hematopoietic stem cells from the surrounding blood cells. Hematopoietic stem cells 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 hematopoietic stem cells. In addition, hematopoietic stem cells are characterised by their small size and low staining with vital dyes such as rhodamine 123 (rhodamine lo) or Hoechst 33342 (side population).
Hematopoietic stem cells are essential to haematopoiesis, the formation of the cells within blood. Hematopoietic stem cells can replenish all blood cell types (i.e., are multipotent) and self-renew. A small number of hematopoietic stem cells can expand to generate a very large number of daughter hematopoietic stem cells. This phenomenon is used in bone marrow transplantation, [13] when a small number of hematopoietic stem cells reconstitute the hematopoietic system. This process indicates that, subsequent to bone marrow transplantation, symmetrical cell divisions into two daughter hematopoietic stem cells must occur.
Stem cell self-renewal is thought to occur in the stem cell niche in the bone marrow, and it is reasonable to assume that key signals present in this niche will be important in self-renewal. [2] There is much interest in the environmental and molecular requirements for HSC self-renewal, as understanding the ability of HSC to replenish themselves will eventually allow the generation of expanded populations of HSC in vitro that can be used therapeutically.
Hematopoietic stem cells, like all adult stem cells, mostly exist in a state of quiescence, or reversible growth arrest. The altered metabolism of quiescent HSCs helps the cells survive for extended periods of time in the hypoxic bone marrow environment. [14] When provoked by cell death or damage, Hematopoietic stem cells exit quiescence and begin actively dividing again. The transition from dormancy to propagation and back is regulated by the MEK/ERK pathway and PI3K/AKT/mTOR pathway. [15] Dysregulation of these transitions can lead to stem cell exhaustion, or the gradual loss of active Hematopoietic stem cells in the blood system. [15]
Hematopoietic stem cells have a higher potential than other immature blood cells to pass the bone marrow barrier, and, thus, may travel in the blood from the bone marrow in one bone to another bone. If they settle in the thymus, they may develop into T cells. In the case of fetuses and other extramedullary hematopoiesis. Hematopoietic stem cells may also settle in the liver or spleen and develop.
This enables Hematopoietic stem cells to be harvested directly from the blood.
Hematopoietic stem cell transplantation (HSCT) is the transplantation of multipotent hematopoietic stem cells, usually derived from bone marrow, peripheral blood, or umbilical cord blood. [16] [17] [13] It may be autologous (the patient's own stem cells are used), allogeneic (the stem cells come from a donor) or syngeneic (from an identical twin). [16] [17]
It is most often performed for patients with certain cancers of the blood or bone marrow, such as multiple myeloma or leukemia. [17] In these cases, the recipient's immune system is usually destroyed with radiation or chemotherapy before the transplantation. Infection and graft-versus-host disease are major complications of allogeneic HSCT. [17]
In order to harvest stem cells from the circulating peripheral blood, blood donors are injected with a cytokine, such as granulocyte-colony stimulating factor (G-CSF), that induces cells to leave the bone marrow and circulate in the blood vessels. [18] In mammalian embryology, the first definitive Hematopoietic stem cells are detected in the AGM (aorta-gonad-mesonephros), and then massively expanded in the fetal liver prior to colonising the bone marrow before birth. [11]
Hematopoietic stem cell transplantation remains a dangerous procedure with many possible complications; it is reserved for patients with life-threatening diseases. As survival following the procedure has increased, its use has expanded beyond cancer to autoimmune diseases [19] [20] and hereditary skeletal dysplasias; notably malignant infantile osteopetrosis [21] [22] and mucopolysaccharidosis. [23]
Stem cells can be used to regenerate different types of tissues. HCT is an established as therapy for chronic myeloid leukemia, acute lymphatic leukemia, aplastic anemia, and hemoglobinopathies, in addition to acute myeloid leukemia and primary immune deficiencies. Hematopoietic system regeneration is typically achieved within 2–4 weeks post-chemo- or irradiation therapy and HCT. HSCs are being clinically tested for their use in non-hematopoietic tissue regeneration. [24]
DNA strand breaks accumulate in long term hematopoietic stem cells during aging. [25] This accumulation is associated with a broad attenuation of DNA repair and response pathways that depends on HSC quiescence. [25] Non-homologous end joining (NHEJ) is a pathway that repairs double-strand breaks in DNA. NHEJ is referred to as "non-homologous" because the break ends are directly ligated without the need for a homologous template. The NHEJ pathway depends on several proteins including ligase 4, DNA polymerase mu and NHEJ factor 1 (NHEJ1, also known as Cernunnos or XLF).
DNA ligase 4 (Lig4) has a highly specific role in the repair of double-strand breaks by NHEJ. Lig4 deficiency in the mouse causes a progressive loss of hematopoietic stem cells during aging. [26] Deficiency of lig4 in pluripotent stem cells results in accumulation of DNA double-strand breaks and enhanced apoptosis. [27]
In polymerase mu mutant mice, hematopoietic cell development is defective in several peripheral and bone marrow cell populations with about a 40% decrease in bone marrow cell number that includes several hematopoietic lineages. [28] Expansion potential of hematopoietic progenitor cells is also reduced. These characteristics correlate with reduced ability to repair double-strand breaks in hematopoietic tissue.
Deficiency of NHEJ factor 1 in mice leads to premature aging of hematopoietic stem cells as indicated by several lines of evidence including evidence that long-term repopulation is defective and worsens over time. [29] Using a human induced pluripotent stem cell model of NHEJ1 deficiency, it was shown that NHEJ1 has an important role in promoting survival of the primitive hematopoietic progenitors. [30] These NHEJ1 deficient cells possess a weak NHEJ1-mediated repair capacity that is apparently incapable of coping with DNA damages induced by physiological stress, normal metabolism, and ionizing radiation. [30]
The sensitivity of hematopoietic stem cells to Lig4, DNA polymerase mu and NHEJ1 deficiency suggests that NHEJ is a key determinant of the ability of stem cells to maintain themselves against physiological stress over time. [26] Rossi et al. [31] found that endogenous DNA damage accumulates with age even in wild type Hematopoietic stem cells, and suggested that DNA damage accrual may be an important physiological mechanism of stem cell aging.
A study shows the clonal diversity of hematopoietic stem cells gets drastically reduced around age 70 to a faster-growing few, substantiating a novel theory of ageing which could enable healthy aging. [32] [33] Of note, the shift in clonal diversity during aging was previously reported in 2008 [34] for the murine system by the Christa Muller-Sieburg laboratory in San Diego, California.
A cobblestone area-forming cell (CAFC) assay is a cell culture-based empirical assay. When plated onto a confluent culture of stromal feeder layer, [35] a fraction of hematopoietic stem cells creep between the gaps (even though the stromal cells are touching each other) and eventually settle between the stromal cells and the substratum (here the dish surface) or trapped in the cellular processes between the stromal cells. Emperipolesis is the in vivo phenomenon in which one cell is completely engulfed into another (e.g. thymocytes into thymic nurse cells); on the other hand, when in vitro, lymphoid lineage cells creep beneath nurse-like cells, the process is called pseudoemperipolesis. This similar phenomenon is more commonly known in the HSC field by the cell culture terminology cobble stone area-forming cells (CAFC), which means areas or clusters of cells look dull cobblestone-like under phase contrast microscopy, compared to the other hematopoietic stem cells, which are refractile. This happens because the cells that are floating loosely on top of the stromal cells are spherical and thus refractile. However, the cells that creep beneath the stromal cells are flattened and, thus, not refractile. The mechanism of pseudoemperipolesis is only recently coming to light. It may be mediated by interaction through CXCR4 (CD184) the receptor for CXC Chemokines (e.g., SDF1) and α4β1 integrins. [36]
Hematopoietic stem cells (HSC) cannot be easily observed directly, and, therefore, their behaviors need to be inferred indirectly. Clonal studies are likely the closest technique for single cell in vivo studies of HSC. Here, sophisticated experimental and statistical methods are used to ascertain that, with a high probability, a single HSC is contained in a transplant administered to a lethally irradiated host. The clonal expansion of this stem cell can then be observed over time by monitoring the percent donor-type cells in blood as the host is reconstituted. The resulting time series is defined as the repopulation kinetic of the HSC.
The reconstitution kinetics are very heterogeneous. However, using symbolic dynamics, one can show that they fall into a limited number of classes. [37] To prove this, several hundred experimental repopulation kinetics from clonal Thy-1lo SCA-1+ lin−(B220, CD4, CD8, Gr-1, Mac-1 and Ter-119) [38] c-kit+ HSC were translated into symbolic sequences by assigning the symbols "+", "-", "~" whenever two successive measurements of the percent donor-type cells have a positive, negative, or unchanged slope, respectively. By using the Hamming distance, the repopulation patterns were subjected to cluster analysis yielding 16 distinct groups of kinetics. To finish the empirical proof, the Laplace add-one approach was used to determine that the probability of finding kinetics not contained in these 16 groups is very small. By corollary, this result shows that the hematopoietic stem cell compartment is also heterogeneous by dynamical criteria.
It was originally believed that all hematopoietic stem cells were alike in their self-renewal and differentiation abilities. This view was first challenged by the 2002 discovery by the Muller-Sieburg group in San Diego, who illustrated that different stem cells can show distinct repopulation patterns that are epigenetically predetermined intrinsic properties of clonal Thy-1 lo Sca-1+ lin− c-kit + HSC. [39] [40] [41] The results of these clonal studies led to the notion of lineage bias. Using the ratio of lymphoid (L) to myeloid (M) cells in blood as a quantitative marker, the stem cell compartment can be split into three categories of HSC. Balanced (Bala) hematopoietic stem cells repopulate peripheral white blood cells in the same ratio of myeloid to lymphoid cells as seen in unmanipulated mice (on average about 15% myeloid and 85% lymphoid cells, or 3 ≤ ρ ≤ 10). Myeloid-biased (My-bi) hematopoietic stem cells give rise to very few lymphocytes resulting in ratios 0 < ρ < 3, while lymphoid-biased (Ly-bi) hematopoietic stem cells generate very few myeloid cells, which results in lymphoid-to-myeloid ratios of ρ > 10. All three types are normal types of HSC, and they do not represent stages of differentiation. Rather, these are three classes of HSC, each with an epigenetically fixed differentiation program. These studies also showed that lineage bias is not stochastically regulated or dependent on differences in environmental influence. My-bi HSC self-renew longer than balanced or Ly-bi HSC. The myeloid bias results from reduced responsiveness to the lymphopoetin interleukin 7 (IL-7). [40]
Subsequently, other groups confirmed and highlighted the original findings. [42] For example, the Eaves group confirmed in 2007 that repopulation kinetics, long-term self-renewal capacity, and My-bi and Ly-bi are stably inherited intrinsic HSC properties. [43] In 2010, the Goodell group provided additional insights about the molecular basis of lineage bias in side population (SP) SCA-1+ lin− c-kit+ HSC. [44] As previously shown for IL-7 signaling, it was found that a member of the transforming growth factor family (TGF-beta) induces and inhibits the proliferation of My-bi and Ly-bi HSC, respectively.
From Greek haimato-, combining form of haima 'blood', and from the Latinized form of Greek poietikos 'capable of making, creative, productive', from poiein 'to make, create'. [45]
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.
Bone marrow is a semi-solid tissue found within the spongy portions of bones. In birds and mammals, bone marrow is the primary site of new blood cell production. It is composed of hematopoietic cells, marrow adipose tissue, and supportive stromal cells. In adult humans, bone marrow is primarily located in the ribs, vertebrae, sternum, and bones of the pelvis. Bone marrow comprises approximately 5% of total body mass in healthy adult humans, such that a man weighing 73 kg (161 lbs) will have around 3.7 kg (8 lbs) of bone marrow.
Hematopoietic stem-cell transplantation (HSCT) is the transplantation of multipotent hematopoietic stem cells, usually derived from bone marrow, peripheral blood, or umbilical cord blood, in order to replicate inside a patient and produce additional normal blood cells. HSCT may be autologous, syngeneic, or allogeneic.
CD34 is a transmembrane phosphoglycoprotein protein encoded by the CD34 gene in humans, mice, rats and other species.
Cell therapy is a therapy in which viable cells are injected, grafted or implanted into a patient in order to effectuate a medicinal effect, for example, by transplanting T-cells capable of fighting cancer cells via cell-mediated immunity in the course of immunotherapy, or grafting stem cells to regenerate diseased tissues.
Myeloid tissue, in the bone marrow sense of the word myeloid, is tissue of bone marrow, of bone marrow cell lineage, or resembling bone marrow, and myelogenous tissue is any tissue of, or arising from, bone marrow; in these senses the terms are usually used synonymously, as for example with chronic myeloid/myelogenous leukemia.
Extramedullary hematopoiesis refers to hematopoiesis occurring outside of the medulla of the bone. It can be physiologic or pathologic.
The aorta-gonad-mesonephros (AGM) is a region of embryonic mesoderm that develops during embryonic development from the para-aortic splanchnopleura in chick, mouse and human embryos. The very first adult definitive haematopoietic stem cells, capable of long-term multilineage repopulation of adult irradiated recipients, originate from the ventral endothelial wall of the embryonic dorsal aorta, through an endothelial transdifferentiation process referred to as an 'endothelial-to-haematopoietic transition' (EHT). In the mouse embryo, these very first HSCs are characterised by their expression of Ly6A-GFP (Sca1), CD31, CD34, cKit, CD27, CD41, Gata2, Runx1, Notch1, and BMP amongst others.
Granulopoiesis is a part of haematopoiesis, that leads to the production of granulocytes. A granulocyte, also referred to as a polymorphonuclear leukocyte (PMN), is a type of white blood cell that has multi lobed nuclei, usually containing three lobes, and has a significant amount of cytoplasmic granules within the cell. Granulopoiesis takes place in the bone marrow. It leads to the production of three types of mature granulocytes: neutrophils, eosinophils and basophils.
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.
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.
Treosulfan, sold under the brand name Trecondi, is a medication given to people before they have a bone marrow transplant from a donor known as allogeneic hematopoietic stem cell transplantation. It is used as a 'conditioning' treatment to clear the bone marrow and make room for the transplanted bone marrow cells, which can then produce healthy blood cells. It is used together with another medicine called fludarabine in adults and children from one month of age with blood cancers as well as in adults with other severe disorders requiring a bone marrow transplant.
CFU-GEMM is a colony forming unit that generates myeloid cells. CFU-GEMM cells are the oligopotential progenitor cells for myeloid cells; they are thus also called common myeloid progenitor cells or myeloid stem cells. "GEMM" stands for granulocyte, erythrocyte, monocyte, megakaryocyte.
CFU-Meg is a colony forming unit. Haematopoiesis in the bone marrow starts off from a haematopoietic stem cell (HSC) and this can differentiate into the myeloid and lymphoid cell lineages. In order to eventually produce a megakaryocyte, the haematopoietic stem cell must generate myeloid cells, so it becomes a common myeloid progenitor, CFU-GEMM. This in turn develops into CFU-Meg, which is the colony forming unit that leads to the production of megakaryocytes.
Megakaryocyte–erythroid progenitor cells (MEPs), among other blood cells, are generated as a result of hematopoiesis, which occurs in the bone marrow. Hematopoietic stem cells (HSC) can differentiate into one of two progenitor cells: the common lymphoid progenitor and the common myeloid progenitor. MEPs derive from the common myeloid progenitor lineage. Megakaryocyte–erythroid progenitor cells must commit to becoming either platelet-producing megakaryocytes via megakaryopoiesis or erythrocyte-producing erythroblasts via erythropoiesis. Most of the blood cells produced in the bone marrow during hematopoiesis come from megakaryocyte–erythroid progenitor cells.
The haematopoietic system is the system in the body involved in the creation of the cells of blood.
Many human blood cells, such as red blood cells (RBCs), immune cells, and even platelets all originate from the same progenitor cell, the hematopoietic stem cell (HSC). As these cells are short-lived, there needs to be a steady turnover of new blood cells and the maintenance of an HSC pool. This is broadly termed hematopoiesis. This event requires a special environment, termed the hematopoietic stem cell niche, which provides the protection and signals necessary to carry out the differentiation of cells from HSC progenitors. This stem-cell niche relocates from the yolk sac to eventually rest in the bone marrow of mammals. Many pathological states can arise from disturbances in this niche environment, highlighting its importance in maintaining hematopoiesis.
GATA2 deficiency is a grouping of several disorders caused by common defect, namely, familial or sporadic inactivating mutations in one of the two parental GATA2 genes. Being the gene haploinsufficient, mutations that cause a reduction in the cellular levels of the gene's product, GATA2, are autosomal dominant. The GATA2 protein is a transcription factor critical for the embryonic development, maintenance, and functionality of blood-forming, lymphatic-forming, and other tissue-forming stem cells. In consequence of these mutations, cellular levels of GATA2 are deficient and individuals develop over time hematological, immunological, lymphatic, or other presentations that may begin as apparently benign abnormalities but commonly progress to severe organ failure, opportunistic infections, virus infection-induced cancers, the myelodysplastic syndrome, and/or leukemia. GATA2 deficiency is a life-threatening and precancerous condition.
Since haematopoietic stem cells cannot be isolated as a pure population, it is not possible to identify them under a microscope. 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 or Hoechst 33342.
Christa Edith Muller-Sieburg was a German-American immunologist and hematologist, whose work became central to the understanding of the clonal heterogeneity of hematopoietic stem cells (HSCs). Muller-Sieburg is known for her contributions to the purification of hematopoietic stem cells, the characterization of individual stem cell clones and her revision of the process of hematopoiesis.