Page 135 - Hematology_ Basic Principles and Practice ( PDFDrive )

106 Part II Cellular Basis of Hematology

TABLE Soluble Proteins and Small Molecules That Regulate that PGE 2 modulates WNT signaling via regulation of β-catenin
9.2 Hematopoietic Stem Cell Self-Renewal degradation and PGE 2/WNT activation regulated both hematopoi-
etic regeneration in the zebrafish and long-term HSC repopulation
Function in HSC in mice. Hoggatt et al also showed that short-term exposure to
447
Growth Factor Self-Renewal Reference a PGE 2 promoted the enhanced homing and repopulation of human
NOTCH ligands Sufficient, not necessary 167, 171–173, CB HSCs in immune-deficient mice caused by increased CXCR4
177, 178 expression on PGE 2-treated CB HSCs. Ex vivo treatment with PGE 2
was subsequently shown to increase human CB CFC content and
WNT proteins Sufficient, ? necessary 185, 189, 201, engraftment capacity after transplant into immune-deficient mice,
203
and PGE 2-treated BM cells were also found to provide more than
BMPs ? Sufficient, SMAD4 220 one year of multilineage reconstitution in a nonhuman primate
necessary model. Based on these encouraging results, a phase I clinical trial
448
SCF Necessary, not sufficient 439 was undertaken, in which one unmanipulated CB unit and a second
TPO Necessary, not sufficient 440 CB unit that was cultured for two hours in the presence of
16,16-dimethyl PGE 2 (dmPGE 2) were transplanted into adult
CXCL12 Necessary 239, 242 patients after nonmyeloablative conditioning. dmPGE 2-treated CB
RAR-γ Necessary 117 cells resulted in accelerated neutrophil recovery (17.5 days versus 21
ANGPTL Sufficient 441, 442 days) and long-term engraftment in 10 of 12 patients. 449
Recently, screening strategies in human cells have been success-
Sufficient 445, 448
fully used to identify novel growth factors, developmental factors
PGE 2
PTN Necessary, sufficient 107, 454 and chemical compounds, for HSCs. Himburg et al identified
AHR antagonist Sufficient 456 pleiotrophin (PTN), a heparin binding growth factor, from a gene
a References are representative, not all-inclusive. expression analysis of human brain-derived endothelial cells (ECs)
450–453
AHR, aryl hydrocarbon receptor; ANGPTL, angiopoietin-like protein; BMP, bone that support human HSC expansion in vitro. Treatment of
morphogenetic protein; CXCL12, C-X-C motif chemokine 12; HSC, murine BM HSCs with PTN produced a 10-fold expansion of long-
hematopoietic stem cell; PGE 2 , prostaglandin E 2 ; PTN, pleiotrophin; RAR-γ, term repopulating HSCs in culture, and systemic administration of
retinoic acid receptor γ; SCF, stem cell factor; TPO, thrombopoietin. PTN to irradiated mice caused a 20-fold increase in the recovery
Adapted from Zon L: Intrinsic and extrinsic control of haematopoietic stem cell 107
self-renewal. Nature 453:306, 2008, with permission. of BM LTC-ICs in vivo. Mechanistically, PTN signaling caused
the upregulation of PI3K/AKT signaling and Hes1 expression in
HSCs, suggesting that activation of these signaling cascades may
107
contribute to PTN-mediated HSC expansion. Mice lacking Ptn
454
NOVEL GROWTH FACTORS FOR HEMATOPOIETIC STEM had 11-fold less BM HSC content than their wild-type littermates.
Interestingly, LT-HSC content, as measured in tertiary and quater-
CELLS AND CLINICAL TESTING nary transplants, was increased in chimeric mice with Ptn deletion
455
in the BM microenvironment compared with wild-type mice.
Several novel proteins and small molecules have been reported to Taken together, these results suggest that PTN regulates BM HSC
promote potent expansion of murine or human HSCs in culture expansion and regeneration, and in the context of constitutive Ptn
(Table 9.2). 107,439,440 Moreover, leveraging insights into the mecha- knockout, Ptn loss in hematopoietic cells may dominate over effects
nisms which regulate HSC self-renewal and differentiation, several of Ptn loss in the niche. 109,455 Further studies will be necessary to
different approaches to expand human CB HSCs have been tested in resolve these questions and define the potential therapeutic efficacy
456
441
early clinical trials. Zhang et al reported the discovery of the pro- of PTN. Boitano et al described a screening approach of more than
teins angiopoietin-like 2 (ANGPTL2) and ANGPTL3 in a fetal liver 100,000 heterocyclic compounds for the capacity to maintain human
+
stromal cell line and demonstrated that the addition of ANGPTL2 CD34 cells in culture for five days. This screen yielded the discovery
or ANGPTL3 to cytokine cultures supported a 24- to 30-fold expan- of the purine derivative StemRegenin 1 (SR1), which was shown to
456
sion of human BM cells capable of long-term repopulation in promote the expansion of human CB repopulating cells in vitro.
+
442
NOD/SCID mice. Subsequently, Zhang et al demonstrated that Three-week cultures of human CB CD34 cells with thrombopoietin,
the addition of ANGPTL5 and insulin-like growth factor binding SCF, FLT3 ligand, interleukin-6 (IL-6), and SR1 promoted a 17-fold
protein 2 (IGFBP2) to the combination of SCF, TPO, and FGF1 increase in SCID-repopulating cells compared with the progeny of
supported up to a 20-fold increase in human CB cells capable of cultures containing thrombopoietin, SCF, FLT3 ligand, and IL-6
456
8-week engraftment in NOD/SCID mice. Of note, because the alone. SR1 appears to mediate its effects via inhibition of the aryl
addition of ANGPTL5 and IGFBP2 did not substantially increase hydrocarbon receptor. Aryl hydrocarbon receptors are expressed by
total cell expansion compared with SCF, TPO, and FGF1 alone, it HSCs, but the downstream signaling mechanism through which SR1
456
remains possible that treatment with ANGPTL proteins or IGFBP2 mediates HSC expansion remains unknown. Recently, Dahlberg
may enhance the homing of HSCs in immune-deficient transplant et al reported that the combination of SR1 with the NOTCH ligand,
442
models. Because of their potency in expanding human CB HSCs Delta Ext-IgG , caused a threefold increase in human CB-derived myeloid
in preclinical models, ANGPTL proteins represent attractive targets repopulation in NSG mice at two weeks compared to CB cells
457
for translation into the clinic. Recently, several ANGPTL proteins, cultured with Delta Ext-IgG or SR1 alone. Preliminary results from
including ANGPTL2 and ANGPTL5 have been found to bind and a phase I trial of transplantation with SR1-treated CB cells have
activate the immune-inhibitory receptor human leukocyte demonstrated the feasibility and safety of this approach. 458
443
immunoglobulin-like receptor B2 (LILRB2). Interestingly, studies In a recent analysis of growth factors elaborated by an AGM-
in zebrafish and human cells indicate that ANGPTL2, through its derived stromal cell line, Wohrer et al reported that nerve growth
interaction with LILRB2, leads to cleavage and activation of the factor and collagen 1, when added to a defined serum-free medium
NOTCH receptor, ultimately inducing MYC target genes stimulat- containing SCF and IL-11, produced fourfold expansion of murine
ing HSPC formation and expansion. 444 long-term repopulating HSCs in seven-day cultures compared to
445
North et al reported that prostaglandin E 2 (PGE 2) positively SCF and IL-11 alone. 459,460 Separately, treatment of human CB HSCs
regulates HSC formation in the zebrafish model. These authors also with a pyrimidoindole derivative, UM171, was shown to promote a
demonstrated that short-term (2-hour) treatment of murine HSCs 13-fold expansion of CB cells capable of repopulating NSG mice at
461
with PGE 2 produced a two- to threefold increase in donor cell 20 weeks posttransplantation. Although the mechanism of action
repopulation in transplanted mice compared with mice transplanted of UM171 has not been elucidated, preliminary analyses suggested
445
446
with untreated cells. Subsequently, Goessling et al showed that UM171 inhibited erythroid and megakaryocytic differentiation