Pluripotential hemopoietic stem cell
Encyclopedia
Hematopoietic stem cells (HSCs), also spelled Hæmatopoietic stem cells, are multipotent stem cell
s that give rise to all the blood cell types from the myeloid
(monocytes and macrophages, neutrophils, basophils, eosinophils, erythrocytes, megakaryocytes/platelets, dendritic cells), and lymphoid
lineages (T-cells, B-cells, NK-cells). The definition of haematopoietic stem cells has undergone considerable revision in the last two decades. The hematopoietic tissue contains cells with long-term and short-term regeneration capacities and committed multipotent, oligopotent, and unipotent progenitors. HSCs constitute 1:10.000 of cells in myeloid tissue
.
HSCs are a heterogeneous population. Three classes of stem cells exist, distinguished by their ratio of lymphoid to myeloid progeny (L/M) in blood. Myeloid-biased (My-bi) HSC have low L/M ratio (>0, <3), whereas lymphoid-biased (Ly-bi) HSC show a large ratio (>10). The third category consists of the balanced (Bala) HSC for which 3 ≤ L/M ≤ 10. Much work is currently being undertaken to investigate the properties of these different classes of HSCs, but it appears that only the myeloid-biased and -balanced HSCs have durable self-renewal properties. In addition, serial transplantation experiments have shown that each subtype preferentially re-creates its blood cell type distribution, suggesting an inherited epigenetic program for each subtype.
of adults, which includes femur
s, hip, ribs, sternum, and other bones. Cells can be obtained directly by removal from the hip using a needle and syringe, or from the blood following pre-treatment with cytokine
s, such as G-CSF (granulocyte colony-stimulating factors), that induce cells to be released from the bone marrow compartment. Other sources for clinical and scientific use include umbilical cord
blood, peripheral blood a small number of stem and progenitor cells circulate in the bloodstream, in the past 10 years, researchers have found that they can coax the cells to migrate from marrow to blood in greater numbers by injecting the donor with a cytokine, such as granulocyte-colony stimulating factor (GCSF)and recent study shown that ex-vivo expansion of HSCs is possible in 3D bioreactor. Because HSCs are not generated in the adult but during the embryogenesis, many scientific groups are studying HSCs during the embryonic development. It is now well described in mammalians that the first definitive HSCs are detected in the AGM (Aorta-gonad-mesonephros
), and then massively expanded in the Fetal Liver prior to colonize before birth the bone marrow. Such fundamental research could help to understand the mechanisms that are responsible of HSCs generation and/or amplification, and to the discovery of new molecules that could eventually be used to maintain or expand HSCs in vitro.
It is known that a small number of HSCs can expand to generate a very large number of daughter HSCs. This phenomenon is used in bone marrow transplantation, when a small number of HSCs reconstitute the hematopoietic system. This indicates that, subsequent to bone marrow transplantation, symmetrical cell divisions into two daughter HSCs 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. 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.
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) HSC 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) HSC give rise to too few lymphocytes resulting in ratios 0<ρ<3, while lymphoid-biased (Ly-bi) HSC generate too few myeloid cells, which results in lymphoid-to-myeloid ratios of 10<ρInterleukin 7
(IL-7).
Subsequent to this, other groups confirmed and highlighted the original findings (refer to the excellent mini-review by Timm Schroeder). 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. In 2010, the Goodell group provided additional insights about the molecular basis of lineage bias in side population Side population
(SP) SCA-1+ lin- c-kit+ HSC. 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.
is a cell culture-based empirical assay. When plated onto a confluent culture of stromal feeder layer, a fraction of HSCs 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., thymocyte
s into thymic
nurse cell
s); 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 HSC field by the cell culture terminology cobble stone area-forming cells (CAFC), which means areas of cluster of cells that look dull cobblestone
-like under phase contrast microscopy, compared to the other HSCs, 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 integrin
s.
, they will develop into T cells. In the case of fetuses and other extramedullary hematopoiesis
, HSCs may also settle in the liver
or spleen
and develop.
This ability is the reason why HSCs may be harvested directly from the blood.
series, like: CD34
, CD38
, CD90
, CD133
, CD105, CD45
, and also c-kit, - the receptor for stem cell factor
. The haematopoietic stem cells are negative for the markers that are used for detection of lineage commitment, and are, thus, called Lin-; and, during their purification by FACS
, a bunch of up to 14 different mature blood-lineage marker, e.g., CD13 & CD33
for myeloid, CD71 for erythroid, CD19
for B cells, CD61
for megakaryocytic, etc. for humans; and, B220 (murine CD45
) for B cells, Mac-1
(CD11b
/CD18
) for monocytes, Gr-1 for Granulocyte
s, Ter119 for erythroid cells, Il7Ra, CD3
, CD4
, CD5
, CD8
for T cells, etc. (for mice) antibodies are used as a mixture to deplete the lin+ cells or late multipotent progenitors (MPP)s.
There are many differences between the human and mice hematopoietic cell markers for the commonly accepted type of haematopoietic stem cells.http://stemcells.nih.gov/info/scireport/chapter5.asp.
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
-. Also some later studies suggested that earliest stem cells may lack c-kit on the cell surface. 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 haematopoietic 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.
, CD150, CD244
, etc., CD150 being the founding member, and, thus, also called slamF1, i.e., SLAM family member 1.
The signature SLAM code 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.
. CD150+CD48
- gave stem cell purity comparable to Thy1loSCA-1+lin-c-kit+ in mice.
's group at Stanford University
was the first to isolate mouse hematopoietic stem cells in 1988 and was also the first to work out the markers to distinguish the mouse long-term (LT-HSC) and short-term (ST-HSC) haematopoietic stem cells (self-renew-capable), and the Multipotent 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
):
The root for CFU-E is "rubri", for CFU-GM is "granulo" or "myelo" and "mono", for CFU-L is "lympho" and for CFU-Meg is "megakaryo". According to this terminology, the stages of red blood cell formation would be: rubriblast, prorubricyte, rubricyte, metarubricyte, and erythrocyte. However, the following nomenclature seems to be, at present, the most prevalent:
| Committee >
"lympho"
"rubri"
"granulo" or "myelo"
"mono"
"megakaryo"
>-
| Lineage
Lymphoid
Myeloid
Myeloid
Myeloid
| CFU CFU-L
CFU-GEMM
→CFU-E
CFU-GEMM→CFU-GM
→CFU-G
CFU-GEMM→CFU-GM
→CFU-M
CFU-Meg
>-
| Process
lymphocytopoiesis
erythropoiesis
granulocytopoiesis
monocytopoiesis
| [root]blast Lymphoblast
Proerythroblast
Myeloblast
Monoblast
Megakaryoblast
>-
| pro[root]cyte
Prolymphocyte
Polychromatophilic erythrocyte
Promyelocyte
Promonocyte
Promegakaryocyte
>-
| [root]cyte
-
Normoblast
Eosino/neutro/basophilic myelocyte
Megakaryocyte
>-
| meta[root]cyte
Large lymphocyte
Reticulocyte
Eosinophilic/neutrophilic/basophilic metamyelocyte
, Eosinophilic/neutrophilic/basophilic band cell
Early monocyte
| mature cell name Small lymphocyte
Erythrocyte
granulocytes (Eosino/neutro/basophil)
Monocyte
thrombocytes (Platelets)
Osteoclasts also arise from haemopoietic cells of the monocyte/neutrophil lineage, specifically CFU-GM.
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 haematopoietic 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.
The reconstitution kinetics are very heterogeneous. However, using symbolic dynamics
, one can show that they fall into a limited number of classes. To prove this, several hundred experimental repopulation kinetics from clonal Thy-1lo SCA-1+ lin- 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 haematopoietic stem cell compartment is also heterogeneous by dynamical criteria.
Stem cell
This article is about the cell type. For the medical therapy, see Stem Cell TreatmentsStem cells are biological cells found in all multicellular organisms, that can divide and differentiate into diverse specialized cell types and can self-renew to produce more stem cells...
s that give rise to all the blood cell types from the myeloid
Myeloid
The term myeloid suggests an origin in the bone marrow or spinal cord, or a resemblance to the marrow or spinal cord.In hematopoiesis, the term "myeloid cell" is used to describe any leukocyte that is not a lymphocyte...
(monocytes and macrophages, neutrophils, basophils, eosinophils, erythrocytes, megakaryocytes/platelets, dendritic cells), and lymphoid
Lymphoid
Lymphoid is a term used to describe lymph or the lymphatic system.In the context of lymphoid leukemia, it refers specifically to lymphocytes Lymphoid leukemias and lymphomas are now considered to be tumors of the same type of cell lineage. They are called "leukemia" when in the blood or marrow and...
lineages (T-cells, B-cells, NK-cells). The definition of haematopoietic stem cells has undergone considerable revision in the last two decades. The hematopoietic tissue contains cells with long-term and short-term regeneration capacities and committed multipotent, oligopotent, and unipotent progenitors. HSCs constitute 1:10.000 of cells in myeloid tissue
Myeloid tissue
Myeloid tissue is a biologic tissue with the ability to perform hematopoiesis. It is mainly found as the red bone marrow in bones, and is often synonymous with this. However, myeloid can also be present in the liver and spleen in fetuses ....
.
HSCs are a heterogeneous population. Three classes of stem cells exist, distinguished by their ratio of lymphoid to myeloid progeny (L/M) in blood. Myeloid-biased (My-bi) HSC have low L/M ratio (>0, <3), whereas lymphoid-biased (Ly-bi) HSC show a large ratio (>10). The third category consists of the balanced (Bala) HSC for which 3 ≤ L/M ≤ 10. Much work is currently being undertaken to investigate the properties of these different classes of HSCs, but it appears that only the myeloid-biased and -balanced HSCs have durable self-renewal properties. In addition, serial transplantation experiments have shown that each subtype preferentially re-creates its blood cell type distribution, suggesting an inherited epigenetic program for each subtype.
Source
HSCs are found in the bone marrowBone marrow
Bone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg , bone marrow accounts for approximately 2.6 kg...
of adults, which includes femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
s, hip, ribs, sternum, and other bones. Cells can be obtained directly by removal from the hip using a needle and syringe, or from the blood following pre-treatment with cytokine
Cytokine
Cytokines are small cell-signaling protein molecules that are secreted by the glial cells of the nervous system and by numerous cells of the immune system and are a category of signaling molecules used extensively in intercellular communication...
s, such as G-CSF (granulocyte colony-stimulating factors), that induce cells to be released from the bone marrow compartment. Other sources for clinical and scientific use include umbilical cord
Umbilical cord
In placental mammals, the umbilical cord is the connecting cord from the developing embryo or fetus to the placenta...
blood, peripheral blood a small number of stem and progenitor cells circulate in the bloodstream, in the past 10 years, researchers have found that they can coax the cells to migrate from marrow to blood in greater numbers by injecting the donor with a cytokine, such as granulocyte-colony stimulating factor (GCSF)and recent study shown that ex-vivo expansion of HSCs is possible in 3D bioreactor. Because HSCs are not generated in the adult but during the embryogenesis, many scientific groups are studying HSCs during the embryonic development. It is now well described in mammalians that the first definitive HSCs are detected in the AGM (Aorta-gonad-mesonephros
Aorta-gonad-mesonephros
The aorta-gonad-mesonephros is a region of embryonic mesoderm that develops during embryonic development from the para-aortic splanchnopleura in chick, mouse and human embryos...
), and then massively expanded in the Fetal Liver prior to colonize before birth the bone marrow. Such fundamental research could help to understand the mechanisms that are responsible of HSCs generation and/or amplification, and to the discovery of new molecules that could eventually be used to maintain or expand HSCs in vitro.
Multipotency and self-renewal
As stem cells, HSC are defined by their ability to replenish all blood cell types (Multipotency) and their ability to self-renew.It is known that a small number of HSCs can expand to generate a very large number of daughter HSCs. This phenomenon is used in bone marrow transplantation, when a small number of HSCs reconstitute the hematopoietic system. This indicates that, subsequent to bone marrow transplantation, symmetrical cell divisions into two daughter HSCs must occur.
Stem cell self-renewal is thought to occur in the stem cell niche
Stem cell niche
Stem cell niche is a phrase loosely used in the scientific community to describe the microenvironment in which stem cells are found, which interacts with stem cells to regulate stem cell fate. The word 'niche' can be in reference to the in vivo or in vitro stem cell microenvironment...
in the bone marrow, and it is reasonable to assume that key signals present in this niche will be important in self-renewal. 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.
Stem cell heterogeneity
It was originally believed that all HSC 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-1lo SCA-1+ lin- c-kit+ HSC. 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) HSC 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) HSC give rise to too few lymphocytes resulting in ratios 0<ρ<3, while lymphoid-biased (Ly-bi) HSC generate too few myeloid cells, which results in lymphoid-to-myeloid ratios of 10<ρInterleukin 7
IL-7 a hematopoietic growth factor secreted by stromal cells in the red marrow and thymus. It is also produced by keratinocytes, dendritic cells, hepatocytes, neurons, and epithelial cells but is not produced by lymphocytes.- Genetics :...
(IL-7).
Subsequent to this, other groups confirmed and highlighted the original findings (refer to the excellent mini-review by Timm Schroeder). 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. In 2010, the Goodell group provided additional insights about the molecular basis of lineage bias in side population Side population
Side population
In flow cytometry, a side population is a sub-population of cells that is distinct from the main population on the basis of the markers employed...
(SP) SCA-1+ lin- c-kit+ HSC. As previously shown for IL-7 signaling, it was found that a member of the transforming growth factor
Transforming growth factor
Transforming growth factor is used to describe two classes of polypeptide growth factors, TGFα and TGFβ....
family (TGF-beta) induces and inhibits the proliferation of My-bi and Ly-bi HSC, respectively.
Functional assays
A cobblestone area-forming cell (CAFC) assayAssay
An assay is a procedure in molecular biology for testing or measuring the activity of a drug or biochemical in an organism or organic sample. A quantitative assay may also measure the amount of a substance in a sample. Bioassays and immunoassays are among the many varieties of specialized...
is a cell culture-based empirical assay. When plated onto a confluent culture of stromal feeder layer, a fraction of HSCs 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
Emperipolesis
In medicine, emperipolesis is the presence of an intact cell within the cytoplasm of another cell. It is derived from Greek ....
is the in vivo phenomenon in which one cell is completely engulfed into another (e.g., thymocyte
Thymocyte
Thymocytes are hematopoietic progenitor cells present in the thymus. Thymopoiesis is the process in the thymus by which thymocytes differentiate into mature T lymphocytes. The primary function of thymocytes is the generation of T lymphocytes . The thymus provides an inductive environment, which...
s into thymic
Thymus
The thymus is a specialized organ of the immune system. The thymus produces and "educates" T-lymphocytes , which are critical cells of the adaptive immune system....
nurse cell
Nurse cell
-Human physiology:Nurse cells are specialized macrophages residing in the bone marrow that assist in the development of red blood cells. They absorb the nuclei of immature red blood cells and may provide growth factors to help the red blood cells mature...
s); 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 HSC field by the cell culture terminology cobble stone area-forming cells (CAFC), which means areas of cluster of cells that look dull cobblestone
Cobblestone
Cobblestones are stones that were frequently used in the pavement of early streets. "Cobblestone" is derived from the very old English word "cob", which had a wide range of meanings, one of which was "rounded lump" with overtones of large size...
-like under phase contrast microscopy, compared to the other HSCs, 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
CXCR4
C-X-C chemokine receptor type 4 also known as fusin or CD184 is a protein that in humans is encoded by the CXCR4 gene.- Function :...
(CD184) the receptor for CXC Chemokines (e.g., SDF1
SDF-1 (biology)
SDF-1 is small cytokine belonging to the chemokine family that is officially designated Chemokine ligand 12 ....
) and α4β1 integrin
Integrin
Integrins are receptors that mediate attachment between a cell and the tissues surrounding it, which may be other cells or the ECM. They also play a role in cell signaling and thereby regulate cellular shape, motility, and the cell cycle....
s.
Mobility
HSCs 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 thymusThymus
The thymus is a specialized organ of the immune system. The thymus produces and "educates" T-lymphocytes , which are critical cells of the adaptive immune system....
, they will develop into T cells. In the case of fetuses and other extramedullary hematopoiesis
Extramedullary hematopoiesis
Extramedullary hematopoiesis refers to hematopoiesis occurring outside of the medulla of the bone.In some cases, it may be physiologic. For example, during fetal development, hematopoiesis occurs at many different locations, such as the liver and spleen....
, HSCs may also settle in the liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
or spleen
Spleen
The spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock...
and develop.
This ability is the reason why HSCs may be harvested directly from the blood.
Physical characteristics
With regard to morphology, hematopoietic stem cells resemble lymphocytes. They are non-adherent, and rounded, with a rounded nucleus and low cytoplasm-to-nucleus ratio. Since PHSC cannot be isolated as a pure population, it is not possible to identify them in a microscope. The above description is based on the morphological characteristics of a heterogeneous population, of which PHSC are a component.Markers
In reference to phenotype, hematopoeitic stem cells are identified by their small size, lack of lineage (lin) markers, low staining (side population) with vital dyes such as rhodamine 123 (rhodamineDULL, also called rholo) or Hoechst 33342, and presence of various antigenic markers on their surface.Cluster of differentiation and other markers
Many of these markers belong to the cluster of differentiationCluster of differentiation
The cluster of differentiation is a protocol used for the identification and investigation of cell surface molecules present on white blood cells, providing targets for immunophenotyping of cells...
series, like: CD34
CD34
CD34 molecule is a cluster of differentiation molecule present on certain cells within the human body. It is a cell surface glycoprotein and functions as a cell-cell adhesion factor. It may also mediate the attachment of stem cells to bone marrow extracellular matrix or directly to stromal cells...
, CD38
CD38
CD38 , also known as cyclic ADP ribose hydrolase is a glycoprotein found on the surface of many immune cells , including CD4+, CD8+, B and natural killer cells...
, CD90
CD90
Thy-1 or CD90 is a 25–37 kDa heavily N-glycosylated, glycophosphatidylinositol 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...
, CD133
CD133
CD133, originally known as AC133. CD133 is a glycoprotein also known in humans and rodents as Prominin 1 . Currently the function of CD133 is unknown...
, CD105, CD45
CD45
Protein tyrosine phosphatase, receptor type, C also known as PTPRC is an enzyme that, in humans, is encoded by the PTPRC gene. PTPRC is also known as CD45 antigen , which was originally called leukocyte common antigen.- Function :The protein encoded by this gene is a member of the protein tyrosine...
, and also c-kit, - the receptor for stem cell factor
Stem cell factor
Stem Cell Factor is a cytokine that binds to the c-Kit receptor . SCF can exist both as a transmembrane protein and a soluble protein...
. The haematopoietic stem cells are negative for the markers that are used for detection of lineage commitment, and are, thus, called Lin-; and, during their purification by FACS
Flow cytometry
Flow cytometry is a technique for counting and examining microscopic particles, such as cells and chromosomes, by suspending them in a stream of fluid and passing them by an electronic detection apparatus. It allows simultaneous multiparametric analysis of the physical and/or chemical...
, a bunch of up to 14 different mature blood-lineage marker, e.g., CD13 & CD33
CD33
CD33 or Siglec-3 is a transmembrane receptor expressed on cells of myeloid lineage. It is usually considered myeloid-specific, but it can also be found on some lymphoid cells.It binds sialic acids, therefore is a member of the SIGLEC family of lectins....
for myeloid, CD71 for erythroid, CD19
CD19
B-lymphocyte antigen CD19 also known as CD19 , is a protein that in humans is encoded by the CD19 gene.- Function :...
for B cells, CD61
CD61
Integrin beta-3 or CD61 is a protein that in humans is encoded by the ITGB3 gene. CD61 is a cluster of differentiation found on thrombocytes.-Structure and function:...
for megakaryocytic, etc. for humans; and, B220 (murine CD45
CD45
Protein tyrosine phosphatase, receptor type, C also known as PTPRC is an enzyme that, in humans, is encoded by the PTPRC gene. PTPRC is also known as CD45 antigen , which was originally called leukocyte common antigen.- Function :The protein encoded by this gene is a member of the protein tyrosine...
) for B cells, Mac-1
Mac-1
MAC-1 may refer to:* Macrophage-1 antigen* Integrin alpha M...
(CD11b
Integrin alpha M
Integrin alpha M is one protein subunit that forms the heterodimeric integrin alpha-M beta-2 molecule, also known as macrophage-1 antigen or complement receptor 3 . ITGAM is also known as CR3A, and cluster of differentiation molecule 11B...
/CD18
CD18
Integrin beta-2 is a protein that in humans is encoded by the ITGB2 gene.It is the beta subunit of four different structures:* LFA-1 * Macrophage-1 antigen * Integrin alphaXbeta2...
) for monocytes, Gr-1 for Granulocyte
Granulocyte
Granulocytes are a category of white blood cells characterized by the presence of granules in their cytoplasm. They are also called polymorphonuclear leukocytes because of the varying shapes of the nucleus, which is usually lobed into three segments...
s, Ter119 for erythroid cells, Il7Ra, CD3
CD3
CD3 or CD-3 may be:* CD3 , an antigen, cluster of differentiation protein , part of the T cell receptor complex on a mature T lymphocyte* Ford CD3 platform* MediaMax CD-3, copy protection scheme* MiniCD, a 3-inch CD...
, CD4
CD4
CD4 is a glycoprotein expressed on the surface of T helper cells, monocytes, macrophages, and dendritic cells. It was discovered in the late 1970s and was originally known as leu-3 and T4 before being named CD4 in 1984...
, CD5
CD5
CD5 or CD-5 may be:* Child development-5, for five-year old children, a more developmentally appropriate acronym for kindergarten* cluster of differentiation 5 molecule, type I transmembrane protein* compact disc, 5-inch CD, usually music CD...
, CD8
CD8
CD8 is a transmembrane glycoprotein that serves as a co-receptor for the T cell receptor . Like the TCR, CD8 binds to a major histocompatibility complex molecule, but is specific for the class I MHC protein. There are two isoforms of the protein, alpha and beta, each encoded by a different gene...
for T cells, etc. (for mice) antibodies are used as a mixture to deplete the lin+ cells or late multipotent progenitors (MPP)s.
There are many differences between the human and mice hematopoietic cell markers for the commonly accepted type of haematopoietic stem cells.http://stemcells.nih.gov/info/scireport/chapter5.asp.
- Mouse HSC : CD34CD34CD34 molecule is a cluster of differentiation molecule present on certain cells within the human body. It is a cell surface glycoprotein and functions as a cell-cell adhesion factor. It may also mediate the attachment of stem cells to bone marrow extracellular matrix or directly to stromal cells...
lo/-, SCA-1+, Thy1.1+/lo, CD38CD38CD38 , also known as cyclic ADP ribose hydrolase is a glycoprotein found on the surface of many immune cells , including CD4+, CD8+, B and natural killer cells...
+, C-kit+, lin- - Human HSC : CD34CD34CD34 molecule is a cluster of differentiation molecule present on certain cells within the human body. It is a cell surface glycoprotein and functions as a cell-cell adhesion factor. It may also mediate the attachment of stem cells to bone marrow extracellular matrix or directly to stromal cells...
+, CD59CD59Protectin, a complement regulatory protein, also known as ', or MIRL is a human gene and protein....
+, Thy1/CD90CD90Thy-1 or CD90 is a 25–37 kDa heavily N-glycosylated, glycophosphatidylinositol 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...
+, CD38CD38CD38 , also known as cyclic ADP ribose hydrolase is a glycoprotein found on the surface of many immune cells , including CD4+, CD8+, B and natural killer cells...
lo/-, C-kit/CD117CD117Mast/stem cell growth factor receptor also known as proto-oncogene c-Kit or tyrosine-protein kinase Kit or CD117 is a protein that in humans is encoded by the KIT gene...
+, lin-
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
CD34
CD34 molecule is a cluster of differentiation molecule present on certain cells within the human body. It is a cell surface glycoprotein and functions as a cell-cell adhesion factor. It may also mediate the attachment of stem cells to bone marrow extracellular matrix or directly to stromal cells...
-/CD38
CD38
CD38 , also known as cyclic ADP ribose hydrolase is a glycoprotein found on the surface of many immune cells , including CD4+, CD8+, B and natural killer cells...
-. Also some later studies suggested that earliest stem cells may lack c-kit on the cell surface. For human HSCs use of CD133
CD133
CD133, originally known as AC133. CD133 is a glycoprotein also known in humans and rodents as Prominin 1 . Currently the function of CD133 is unknown...
was one step ahead as both CD34
CD34
CD34 molecule is a cluster of differentiation molecule present on certain cells within the human body. It is a cell surface glycoprotein and functions as a cell-cell adhesion factor. It may also mediate the attachment of stem cells to bone marrow extracellular matrix or directly to stromal cells...
+ and CD34
CD34
CD34 molecule is a cluster of differentiation molecule present on certain cells within the human body. It is a cell surface glycoprotein and functions as a cell-cell adhesion factor. It may also mediate the attachment of stem cells to bone marrow extracellular matrix or directly to stromal cells...
- HSCs were CD133
CD133
CD133, originally known as AC133. CD133 is a glycoprotein also known in humans and rodents as Prominin 1 . Currently the function of CD133 is unknown...
+.
Traditional purification method used to yield a reasonable purity level of mouse haematopoietic 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
CD34
CD34 molecule is a cluster of differentiation molecule present on certain cells within the human body. It is a cell surface glycoprotein and functions as a cell-cell adhesion factor. It may also mediate the attachment of stem cells to bone marrow extracellular matrix or directly to stromal cells...
- for HSC purification requires mice to be at least 8 weeks old.
SLAM code
Alternative methods that could give rise to similar or better harvest of stem cells is a hot area of research and are presently emerging. One such method uses a signature of SLAM family of cell surface molecules. SLAM (Signaling lymphocyte activation molecule) family is a group of >10 molecules whose genes are located mostly tandemly in a single locus on chromosome 1 (mouse), all belonging to a subset of immunoglobulin gene superfamily, and originally thought to be involved in T-cell stimulation. This family includes CD48CD48
CD48 is a human protein encoded by the gene....
, CD150, CD244
CD244
CD244 is a human protein encoded by the gene. It is also known as Natural Killer Cell Receptor 2B4-External links:...
, etc., CD150 being the founding member, and, thus, also called slamF1, i.e., SLAM family member 1.
The signature SLAM code for the hemopoietic hierarchy are:
- Hematopoietic stem cells (HSC) : CD150+CD48CD48CD48 is a human protein encoded by the gene....
-CD244CD244CD244 is a human protein encoded by the gene. It is also known as Natural Killer Cell Receptor 2B4-External links:...
- - Multipotent progenitor cells (MPPs) : CD150-CD48CD48CD48 is a human protein encoded by the gene....
-CD244CD244CD244 is a human protein encoded by the gene. It is also known as Natural Killer Cell Receptor 2B4-External links:...
+ - Lineage-restricted progenitor cells (LRPs) : CD150-CD48CD48CD48 is a human protein encoded by the gene....
+CD244CD244CD244 is a human protein encoded by the gene. It is also known as Natural Killer Cell Receptor 2B4-External links:...
+ - Common myeloid progenitor (CMP) : linLinLin may refer to:People*Lin , usually Chinese*Lin, variant of Lyn or Lynn*Lin, short for Linda*Lin , Chinese ninja characterPlaces*Lin, Korçë, village in Pogradec District, Albania...
-SCA-1-c-kit+CD34CD34CD34 molecule is a cluster of differentiation molecule present on certain cells within the human body. It is a cell surface glycoprotein and functions as a cell-cell adhesion factor. It may also mediate the attachment of stem cells to bone marrow extracellular matrix or directly to stromal cells...
+CD16/32mid - Granulocyte-macrophage progenitor (GMP) : linLinLin may refer to:People*Lin , usually Chinese*Lin, variant of Lyn or Lynn*Lin, short for Linda*Lin , Chinese ninja characterPlaces*Lin, Korçë, village in Pogradec District, Albania...
-SCA-1-c-kit+CD34CD34CD34 molecule is a cluster of differentiation molecule present on certain cells within the human body. It is a cell surface glycoprotein and functions as a cell-cell adhesion factor. It may also mediate the attachment of stem cells to bone marrow extracellular matrix or directly to stromal cells...
+CD16/32hi - Megakaryocyte-erythroid progenitor (MEP) : linLinLin may refer to:People*Lin , usually Chinese*Lin, variant of Lyn or Lynn*Lin, short for Linda*Lin , Chinese ninja characterPlaces*Lin, Korçë, village in Pogradec District, Albania...
-SCA-1-c-kit+CD34CD34CD34 molecule is a cluster of differentiation molecule present on certain cells within the human body. It is a cell surface glycoprotein and functions as a cell-cell adhesion factor. It may also mediate the attachment of stem cells to bone marrow extracellular matrix or directly to stromal cells...
-CD16/32low
For HSCs, CD150+CD48
CD48
CD48 is a human protein encoded by the gene....
- was sufficient instead of CD150+CD48
CD48
CD48 is a human protein encoded by the gene....
-CD244
CD244
CD244 is a human protein encoded by the gene. It is also known as Natural Killer Cell Receptor 2B4-External links:...
- 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.
. CD150+CD48
CD48
CD48 is a human protein encoded by the gene....
- gave stem cell purity comparable to Thy1loSCA-1+lin-c-kit+ in mice.
LT-HSC/ST-HSC/Early MPP/Late MPP
Irving WeissmanIrving Weissman
Irving Lerner "Irv" Weissman M.D. is a Professor of Pathology and Developmental Biology at Stanford University where he is the Director of the Stanford Institute of Stem Cell Biology and Regenerative Medicine....
's group at Stanford University
Stanford University
The Leland Stanford Junior University, commonly referred to as Stanford University or Stanford, is a private research university on an campus located near Palo Alto, California. It is situated in the northwestern Santa Clara Valley on the San Francisco Peninsula, approximately northwest of San...
was the first to isolate mouse hematopoietic stem cells in 1988 and was also the first to work out the markers to distinguish the mouse long-term (LT-HSC) and short-term (ST-HSC) haematopoietic stem cells (self-renew-capable), and the Multipotent 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
CD135
Cluster of differentiation antigen 135 also known as Fms-like tyrosine kinase 3 or receptor-type tyrosine-protein kinase FLT3 is a protein that in humans is encoded by the FLT3 gene...
):
- LT-HSC : CD34CD34CD34 molecule is a cluster of differentiation molecule present on certain cells within the human body. It is a cell surface glycoprotein and functions as a cell-cell adhesion factor. It may also mediate the attachment of stem cells to bone marrow extracellular matrix or directly to stromal cells...
-, SCA-1+, Thy1.1+/lo, C-kit+, linLineage markersThe lineage markers are a standard cocktail of antibodies designed to remove mature hematopoietic cells from a sample. Those antibodies are targeted to CD2, CD3, CD4, CD5, CD8, NK1.1, B220, TER-119, and Gr-1 in mice and CD3 , CD14 , CD16 , CD19 , CD20 , and CD56 in humans....
-, CD135CD135Cluster of differentiation antigen 135 also known as Fms-like tyrosine kinase 3 or receptor-type tyrosine-protein kinase FLT3 is a protein that in humans is encoded by the FLT3 gene...
-, Slamf1/CD150+ - ST-HSC : CD34CD34CD34 molecule is a cluster of differentiation molecule present on certain cells within the human body. It is a cell surface glycoprotein and functions as a cell-cell adhesion factor. It may also mediate the attachment of stem cells to bone marrow extracellular matrix or directly to stromal cells...
+, SCA-1+, Thy1.1+/lo, C-kit+, linLineage markersThe lineage markers are a standard cocktail of antibodies designed to remove mature hematopoietic cells from a sample. Those antibodies are targeted to CD2, CD3, CD4, CD5, CD8, NK1.1, B220, TER-119, and Gr-1 in mice and CD3 , CD14 , CD16 , CD19 , CD20 , and CD56 in humans....
-, CD135CD135Cluster of differentiation antigen 135 also known as Fms-like tyrosine kinase 3 or receptor-type tyrosine-protein kinase FLT3 is a protein that in humans is encoded by the FLT3 gene...
-, Slamf1/CD150+, Mac-1 (CD11b)lo - Early MPP : CD34CD34CD34 molecule is a cluster of differentiation molecule present on certain cells within the human body. It is a cell surface glycoprotein and functions as a cell-cell adhesion factor. It may also mediate the attachment of stem cells to bone marrow extracellular matrix or directly to stromal cells...
+, SCA-1+, Thy1.1-, C-kit+, linLineage markersThe lineage markers are a standard cocktail of antibodies designed to remove mature hematopoietic cells from a sample. Those antibodies are targeted to CD2, CD3, CD4, CD5, CD8, NK1.1, B220, TER-119, and Gr-1 in mice and CD3 , CD14 , CD16 , CD19 , CD20 , and CD56 in humans....
-, CD135CD135Cluster of differentiation antigen 135 also known as Fms-like tyrosine kinase 3 or receptor-type tyrosine-protein kinase FLT3 is a protein that in humans is encoded by the FLT3 gene...
+, Slamf1/CD150-, Mac-1 (CD11b)lo, CD4CD4CD4 is a glycoprotein expressed on the surface of T helper cells, monocytes, macrophages, and dendritic cells. It was discovered in the late 1970s and was originally known as leu-3 and T4 before being named CD4 in 1984...
lo - Late MPP : CD34CD34CD34 molecule is a cluster of differentiation molecule present on certain cells within the human body. It is a cell surface glycoprotein and functions as a cell-cell adhesion factor. It may also mediate the attachment of stem cells to bone marrow extracellular matrix or directly to stromal cells...
+, SCA-1+, Thy1.1-, C-kit+, linLineage markersThe lineage markers are a standard cocktail of antibodies designed to remove mature hematopoietic cells from a sample. Those antibodies are targeted to CD2, CD3, CD4, CD5, CD8, NK1.1, B220, TER-119, and Gr-1 in mice and CD3 , CD14 , CD16 , CD19 , CD20 , and CD56 in humans....
-, CD135CD135Cluster of differentiation antigen 135 also known as Fms-like tyrosine kinase 3 or receptor-type tyrosine-protein kinase FLT3 is a protein that in humans is encoded by the FLT3 gene...
high, Slamf1/CD150-, Mac-1 (CD11b)lo, CD4CD4CD4 is a glycoprotein expressed on the surface of T helper cells, monocytes, macrophages, and dendritic cells. It was discovered in the late 1970s and was originally known as leu-3 and T4 before being named CD4 in 1984...
lo
Nomenclature of hematopoietic colonies and lineages
Between 1948 and 1950, the Committee for Clarification of the Nomenclature of Cells and Diseases of the Blood and Blood-forming Organs issued reports on the nomenclature of blood cells. An overview of the terminology is shown below, from earliest to final stage of development:- [root]blast
- pro[root]cyte
- [root]cyte
- meta[root]cyte
- mature cell name
The root for CFU-E is "rubri", for CFU-GM is "granulo" or "myelo" and "mono", for CFU-L is "lympho" and for CFU-Meg is "megakaryo". According to this terminology, the stages of red blood cell formation would be: rubriblast, prorubricyte, rubricyte, metarubricyte, and erythrocyte. However, the following nomenclature seems to be, at present, the most prevalent:
>-
| Lineage
Lymphoid
Lymphoid is a term used to describe lymph or the lymphatic system.In the context of lymphoid leukemia, it refers specifically to lymphocytes Lymphoid leukemias and lymphomas are now considered to be tumors of the same type of cell lineage. They are called "leukemia" when in the blood or marrow and...
Myeloid
The term myeloid suggests an origin in the bone marrow or spinal cord, or a resemblance to the marrow or spinal cord.In hematopoiesis, the term "myeloid cell" is used to describe any leukocyte that is not a lymphocyte...
| CFU
CFU-GEMM
CFU-GEMM is a colony forming unit that generates myeloid cells.CFU-GEMM cells are multipotential progenitor cells.The "GEMM" stands for ""granulocyte, erythrocyte, monocyte, megakaryocyte".CFU-GEMM gives rise to CFU-GM....
→CFU-E
CFU-E
CFU-E is a colony forming unit.It arises from CFU-GEMMUnderstanding the murine CFU-e assay :CFU-e is a stage of erythroid development between the BFU-e stage and the pro-erythroblast stage...
CFU-GM
CFU-GM is a colony forming unit. It is derived from CFU-GEMM.The "GM" stands for "granulocyte, monocyte".It is the precursor for monoblasts and myeloblasts....
→CFU-G
CFU-GM
CFU-GM is a colony forming unit. It is derived from CFU-GEMM.The "GM" stands for "granulocyte, monocyte".It is the precursor for monoblasts and myeloblasts....
→CFU-M
CFU-Meg
CFU-Meg is a colony forming unit.It leads to the production of megakaryocytes.Some sources prefer the term "CFU-Mega"....
>-
| Process
Erythropoiesis
Erythropoiesis is the process by which red blood cells are produced. It is stimulated by decreased O2 in circulation, which is detected by the kidneys, which then secrete the hormone erythropoietin...
Monocytopoiesis
Monocytopoiesis is the process which leads to the production of monocytes Monocytopoiesis is the process which leads to the production of monocytes Monocytopoiesis is the process which leads to the production of monocytes (and, subsequently, macrophages.It can be induced by macrophage...
| [root]blast
Lymphoblast
Lymphoblasts are immature cells which typically differentiate to form mature lymphocytes. Normally lymphoblasts are found in the bone marrow, but in acute lymphoblastic leukemia , lymphoblasts proliferate uncontrollably and are found in large numbers in the peripheral blood.The size is between 10...
Proerythroblast
A proerythroblast is the earliest of four stages in development of the normoblast.In histology, it is very difficult to distinguish it from the other "-blast" cells...
Myeloblast
The myeloblast is a unipotent stem cell, which will differentiate into one of the actors of the Granulocyte series.- Origin :These cells descend from the primitive reticulum cells, which are found in the stroma of the marrow. There is also an intermediate phase between the myeloblast and these...
Monoblast
Monoblasts are normally found in bone marrow and do not appear in the normal peripheral blood. They mature into monocytes which, in turn, develop into macrophages.-Structure:...
Megakaryoblast
A megakaryoblast is a precursor cell to a promegakaryocyte, which in turn becomes a megakaryocyte during haematopoiesis. It is the beginning of the thrombocytic series....
>-
| pro[root]cyte
Prolymphocyte
Found during lymphocytopoiesis, a prolymphocyte is the immediate precursor of a lymphocyte, derived from a lymphoblast.The size is between 10 and 18 μm.-External links:*...
Promyelocyte
A promyelocyte is a granulocyte precursor, developing from the myeloblast and developing into the myelocyte.-External links: - "18. Bone Marrow and Hemopoiesis: bone marrow smear, promyelocyte and erythroblasts " "Bone marrow" "Bone marrow"* - "Bone marrow smear"...
Promonocyte
A promonocyte is a cell arising from a monoblast and developing into a monocyte.-External links:* * - "Bone marrow smear"*...
Promegakaryocyte
A promegakaryocyte is a precursor cell for a megakaryocyte, arising from a megakaryoblast.The developmental stages of the megakaryocyte are:CFU-Me → megakaryoblast → promegakaryocyte → megakaryocyte.-External links:* *...
>-
| [root]cyte
Normoblast
An erythroblast is a type of red blood cell which still retains a cell nucleus. It is the immediate precursor of a normal erythrocyte.-Nomenclature:...
Megakaryocyte
The megakaryocyte is a bone marrow cell responsible for the production of blood thrombocytes , which are necessary for normal blood clotting...
>-
| meta[root]cyte
Lymphocyte
A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...
Reticulocyte
Reticulocytes are immature red blood cells, typically composing about 1% of the red cells in the human body.Reticulocytes develop and mature in the red bone marrow and then circulate for about a day in the blood stream before developing into mature red blood cells. Like mature red blood cells,...
Metamyelocyte
A metamyelocyte is a cell undergoing granulopoiesis, derived from a myelocyte, and leading to a band cell.It is characterized by the appearance of a bent nucleus, cytoplasmic granules, and the absence of visible nucleoli...
, Eosinophilic/neutrophilic/basophilic band cell
Band cell
A band cell is a cell undergoing granulopoiesis, derived from a metamyelocyte, and leading to a mature granulocyte.It is characterized by having a nucleus which is curved, but not lobar....
| mature cell name
Lymphocyte
A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...
Monocyte
Monocytes are a type of white blood cell and are part of the innate immune system of vertebrates including all mammals , birds, reptiles, and fish. Monocytes play multiple roles in immune function...
Osteoclasts also arise from haemopoietic cells of the monocyte/neutrophil lineage, specifically CFU-GM.
Colony-forming units
There are various kinds of colony-forming units:- Colony-forming unit lymphocyteLymphocyteA lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...
(CFU-L) - Colony-forming unit erythrocyte (CFU-E)
- Colony-forming unit granulo-monocyteMonocyteMonocytes are a type of white blood cell and are part of the innate immune system of vertebrates including all mammals , birds, reptiles, and fish. Monocytes play multiple roles in immune function...
(CFU-GM) - Colony-forming unit megakaryocyteMegakaryocyteThe megakaryocyte is a bone marrow cell responsible for the production of blood thrombocytes , which are necessary for normal blood clotting...
(CFU-Me) - Colony-forming unit Basophil (CFU-B)
- Colony-forming unit Eosinophil (CFU-Eo)
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 haematopoietic 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.
HSC Repopulation Kinetics
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
Symbolic dynamics
In mathematics, symbolic dynamics is the practice of modeling a topological or smooth dynamical system by a discrete space consisting of infinite sequences of abstract symbols, each of which corresponds to a state of the system, with the dynamics given by the shift operator...
, one can show that they fall into a limited number of classes. To prove this, several hundred experimental repopulation kinetics from clonal Thy-1lo SCA-1+ lin- 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
Hamming distance
In information theory, the Hamming distance between two strings of equal length is the number of positions at which the corresponding symbols are different...
, 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 haematopoietic stem cell compartment is also heterogeneous by dynamical criteria.