Page 364 - Hematology_ Basic Principles and Practice ( PDFDrive )

300 Part IV Disorders of Hematopoietic Cell Development

expressed among BFU-E. This may relate to variations in their cycling The correlation between phenotype and function of cells isolated
status, because myeloid progenitors in S phase have relatively higher on the basis of these antigenic expression profiles is not maintained
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expression of class II antigens. The presence of HLA class II antigens under conditions of perturbed or stressed erythropoiesis. Stress
(DR and, to a lesser extent, DP and DQ) most likely allows BFU-E to activates the bone morphologic protein 4 (BMP4)/Hedgehog signal-
recognize and interact with the immunoregulatory cells (e.g., T cells, ing, which induces the generation of erythroid progenitor cells with
pos
55
pos
pos
monocytes), which also express class II determinants. In addition a unique phenotype, KIT , CD71 , and TER-119 (TER-119
to HLA antigens, several other antigenic structures are found on recognizes the murine equivalent of glycophorin A). 80,81 The expres-
cells within the BFU-E compartment (see Table 26.1). The best sion on these cells of “true” markers of terminal erythroid maturation
representative of these is the CD34 antigen, which has been success- suggests that stress-specific erythroid progenitors may be related to
fully exploited for isolation of BFU-E and other progenitors. CD34 the proerythroblasts with extensive proliferative potential generated
is a highly O-glycosylated cell surface glycoprotein. It is expressed in in mice after EPO treatment or anemia challenge, 82,83 thereby indicat-
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all hematopoietic progenitors and vascular endothelial cells. The ing that stress may uncouple proliferation and differentiation pro-
role of CD34 in human hematopoiesis is not clearly defined. The grams during terminal erythroid maturation. The proliferation and
numbers of all hematopoietic progenitors were reduced in CD34 differentiation programs are also during ontogenesis. The number
“null” murine embryos and adult animals, but no other abnormali- of erythroblasts generated in vitro by embryonic/primitive (E7.5
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ties were identified. Expression of CD34 was low or absent in a yolk sac), embryonic/definitive (E8.5-9.5 yolk sac and E12.5 fetal
58
population of adult long-term repopulating cells in mouse and in liver), and adult/definitive murine erythroid progenitors in the pres-
84
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man. However, the clinical significance of this finding is not clear ence of EPO, KL, and dexamethasone differ widely. Embryonic/
60
because of the fluctuating expression of CD34 and the difference definitive proerythroblasts originating from a transient wave of
in regulatory mechanisms of CD34 gene expression in mouse and early fetal erythropoiesis are capable of generating large numbers
10
30
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human stem cells. Furthermore, use of antibodies or conjugated (10 - to 10 -fold expansion) of proerythroblasts that, because of
ligands determined that BFU-E present in enriched progenitor their great expansion potential, were characterized as extensively
preparations display receptors for KL, EPO, TPO, GM-CSF, IL-3, self-renewing erythroblasts (ESREs). By contrast, under the same
IL-6, and IL-11. However, the majority of BFU-E, in contrast to conditions, embryonic/primitive proerythroblasts failed to expand
2
5
myeloid progenitors (colony-forming unit–granulocyte-macrophage and adult/definitive proerythroblasts expanded only 10 - to 10 -fold.
[CFU-GM]), do not express the restricted hematopoietic phosphatase Interestingly, human erythroblasts generated in the presence of dexa-
CD45RA. 62,63 Furthermore, BFU-E appears to share with late colony- methasone also express high levels of C-KIT and acquire self-renewal
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forming unit–megakaryocyte (CFU-Mk) progenitors the expression potential. In addition to steroids, polymeric immunoglobulin A1
of the TPO receptor (c-Mpl or TPO-R) 63,64 and glycoprotein IIb/IIIa (IgA1) has also been shown to control erythroblast proliferation and
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(CD41), a marker of the divergence between definitive hematopoiesis to accelerate erythropoiesis recovery in anemia. These observations
and endothelial cells during development. 65,66 challenge the notion that erythroblasts are capable of a limited (at
As BFU-E mature to the CFU-E stage, they begin to express most two to four) number of divisions.
surface proteins characteristic of erythroblasts, the morphologically More recently, erythroid cells have been derived in vitro from stem
recognizable erythroid cells. For example, CFU-E expresses Rh cell sources with unlimited proliferation potential such as human
antigens and the erythroid-specific sialoglycoprotein glycophorin A. embryonic stem cells (hESCs) and induced pluripotent stem cells
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Blood group antigens of the ABH Ii type are detectable in a subset of (iPSCs). Seminal studies in 2008 from Hiroyama et al established
CFU-E. In contrast, CD34 molecules, class II antigens, and certain that red blood cells generated from murine ESCs are functional in vivo
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growth factor receptors (i.e., IL-3R, C-KIT) are greatly diminished because they protect mice from lethal hemolytic anemia. Methods
or virtually absent at the CFU-E stage (see Table 26.1). The most for generating red blood cells from hESCs have also been published,
important functional difference between BFU-E and CFU-E is the and the biologic properties of these hESC-derived red blood cells
abundance of erythropoietin receptors (EPORs) on CFU-E and have been extensively characterized. 89,90 A number of groups have also
their dependence on EPO for cell survival. CFU-E, in contrast to published methods for generating red blood cells from iPSCs. 91,92 In
BFU-E, cannot survive in vitro even for a few hours in the absence general, independently of their origin, ESC- or iPS-derived erythroid
of EPO. Although greater than 80% of CFU-E have detectable cells express mostly embryonic and fetal globins. In addition, several
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EPORs, only a small proportion of BFU-E have receptors 68,69 investigators are exploring the feasibility of reprogramming somatic
and can terminally differentiate in culture in the presence of EPO cells directly into erythroid cells, bypassing the pluripotent state
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alone. Direct binding studies show that the number of EPORs and/or generating stem cells with unlimited expansion potential
peaks at the CFU-E/proerythroblast level and progressively declines by epigenetic or genetic in vitro treatments. 93,94 In both cases, the
67
when cells mature further (see Table 26.1), reflecting the declining modified cells generated erythroblasts that mature into circulating red
null
influence of EPO. In addition to the abundance of EpoRs, erythroid cells when injected into immunodeficient NOD/SCID/γc mice.
progenitors are distinguished from other marrow progenitors by the
presence of high levels of transferrin receptors (TfRs). 68,71,72 Peak
levels of TfRs are seen on CFU-E and erythroid precursors, and ERYTHROID MORPHOLOGICALLY RECOGNIZABLE
lower levels are present on reticulocytes. 64,71 (For a detailed review PRECURSOR CELL COMPARTMENT
of iron metabolism and heme synthesis in erythroid cells, see
references 73–75). The erythroid precursor cell compartment, also termed the erythron,
In addition to the functional definition, the hemopoietic compart- includes cells that, in contrast to the erythroid progenitor cells
ments in the marrow of a normal adult mouse have been prospectively (BFU-E and CFU-E), are defined by morphologic criteria. The earli-
identified on the basis of expression of specific cell surface antigens est recognizable erythroid cell is the proerythroblast, which after four
10
neg
and subsequent differentiation in vitro and in vivo. The Lin IL- to five mitotic divisions and serial morphologic changes gives rise to
pos
neg
neg
neg
7R Thy1 C-KIT Sca1 fraction of the marrow of normal adult mature erythroid cells. Its progeny include basophilic erythroblasts,
mice has been subdivided into three populations based on the expres- which are the earliest daughter cells, followed by polychromatophilic
low
sion of CD34 and CD16/CD32: CD16/CD32 CD34 high represent- and orthochromatic erythroblasts. Their morphologic characteristics
low
low
ing the common myeloid progenitor (CMP), CD16/CD32 CD34 reflect the accumulation of erythroid-specific proteins (i.e., hemoglo-
representing the megakaryocyte/erythroid progenitor (MEP), and bin) and the decline in nuclear activity (Fig. 26.2). The last mitotic
CD16/CD32 high CD34 high representing the granulocyte/macrophage division involves elimination of unwanted organelles (mitochondria,
10
progenitor (see Fig. 26.1). Many laboratories have also prospectively ribosomes and other intracytoplasmic organelles) by the autophagic
95
96
identified the corresponding human compartments. 11,76,77 In humans, machinery, intense membrane trafficking, and asymmetric parti-
the transition from CMP to MEP is characterized by loss of aldehyde tioning of the remaining cell components between two morphologi-
78
dehydrogenase activity and acquisition of c-Mpl expression. 79 cally distinct daughter cells: one nucleated, the pyrenocyte, and one