Page 1326 - Hematology_ Basic Principles and Practice ( PDFDrive )

1172 Part VII Hematologic Malignancies

LTD4, and LTE4, and cyclooxygenase-derived prostaglandin (PG) different tissues of the same organism. Although several techniques,
D2. These substances are involved in mediating vasodilation and including flow cytometry-based cell sorting, exist for ex vivo isolation
vasopermeability, smooth muscle constriction, mucus secretion, and of BM MCs, yields are typically low, reflecting the low numbers
other proinflammatory sequelae. IgE- and non-IgE–dependent of MCs in the BM and the difficulties in isolating them from
mechanisms (e.g., IgG, complement [C3a, C5a], neuropeptides, other tissues, such as the lung. Ex vivo generation of human cord
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narcotics, physical stimuli, and activation of Toll-like receptors by blood–derived or peripheral blood–derived MCs from their CD34
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bacterial products) can induce MCs to release a variety of cytokines or CD133 progenitor cells using SCF and IL-6, can generate large
(e.g., TNF-α, macrophage inflammatory protein [MIP]-1α and -1β, numbers of functionally mature MCs that can be interrogated for
monocyte chemoattractant protein [MCP]-1, IFN-α, β, and γ, and various types of biologic investigations. Many studies of MCs and/
various interleukins) and growth factors (see Table 72.1) that are or mastocytosis have relied on MC lines such as the SCF-dependent
implicated in the aforementioned physiologic roles of inflammation, cell lines LAD1/LAD2, derived from patients with MC sarcoma
allergic responses, and host defense. MCs mediate early-phase (e.g., with KIT D816V (this cell line actually has normal KIT despite
anaphylaxis, acute asthma) and late-phase allergic responses, as well its origin, and is SCF dependent); the LUVA cell line (derived
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as non–type I hypersensitivity reactions through their proinflamma- from CD34 cells, growth factor–independent, normal KIT, and
tory mediators. Furthermore, MCs mediate upregulation of Th2 tendency to lose FcεRI expression with long-term culture); and the
responses and allergen-specific IgE biosynthesis, which contribute to SCF-independent human mast cell line HMC-1 derived from a
host defense against parasitic infections. MCs have also been impli- patient with MCL. Two HMC-1 subclones are available—HMC-1.1,
cated in the pathogenesis of various nonallergic conditions such as which contains the KIT V560G mutation, and HMC-1.2, which
infectious or autoimmune diseases (e.g., multiple sclerosis, psoriasis, expresses both KIT V560G and D816V. Both clones have been
rheumatoid arthritis, inflammatory bowel disease), and also in repair useful for in vitro evaluation of the differential sensitivity of different
after tissue injury, such as wound healing, thrombolysis, or tissue small-molecule inhibitors of KIT. None of these human MC lines,
remodeling. however, express both a functional IgE receptor and KIT D816V.
Coupling of MCs and eosinophils often occurs in the same tissue However, more recently, a human cord blood–derived cell line that
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niches in allergic/inflammatory and neoplastic disorders such as is SCF dependent and FcεRI (ROSA KIT WT ), and that converts to
eosinophilic esophagitis, chronic gastritis, gastrointestinal neoplasms, SCF independence and tumorigenic growth with transfection by
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parasitic infections, and inflammatory bowel disease. MCs can initi- KIT D816V (ROSA KIT D816V ), has been established, and should be a
ate the allergic inflammatory cascade, resulting in recruitment of useful tool for studying the biology and pharmacologic aspects of
eosinophils during the later phases of an allergen encounter. Both mastocytosis. 10
MCs and eosinophils express CCR3 and respond to eotaxins and
RANTES (CCL5), leading to recruitment of both cell types into
inflamed tissue. Moreover, MC-derived heparin can bind and stabilize Mouse Models to Study Human Mastocytosis
eotaxins. In addition, MCs and eosinophils can interact with each
other through soluble mediators or via direct cell-to-cell contact. At A number of murine models of mastocytosis are available, including
least in the murine system, MCs can also be induced to produce IL-3 several transgenic models and xenotransplantation models. First, all
and IL-5, which can potentiate eosinophil recruitment in tissues. The the cell lines described earlier have been applied successfully in
two principle MC-derived proteases exert dual actions on eosinophils. xenotransplantation models. In most instances, NSG mice were
For example, MC-derived chymase suppresses eosinophil apoptosis employed. In addition, several transgenic models have been estab-
and induces release of IL-6, CXCL8, CCL2, and CXCL1 from lished. In one model, transgenic mice harboring a fusion transgene
eosinophils. In contrast, β-tryptase can cleave eotaxin and RANTES, consisting of the 571-bp primate chymase gene (Δ571-bchm) pro-
and can limit eosinophil chemotaxis. Eosinophils in turn produce moter fragment and the human Kit proto-oncogene cDNA with
SCF, which can attract more tissue MCs and protect them from the codon 816 Asp→Val substitution were generated. These mice
apoptosis. were found to slowly develop a MC disease-like condition with
IgE-mediated hypersensitivity reactions (e.g., allergic rhinitis or focal accumulations of MCs in the spleen and other organs, resem-
asthma, anaphylaxis) are mediated by binding of allergen-specific bling indolent SM (ISM). In another model, a transgenic mouse
IgE to the high-affinity FcεRI receptor, which is constitutively exhibiting murine KIT D814V was established. These mice devel-
expressed at a high level on MCs. Engagement of FcεRI leads to its oped gastrointestinal MC accumulations. Both models may not
inclusion in lipid rafts, and phosphorylation of its β- and γ-chain reflect all aspects of the human disease, but may be helpful in basic
immunoreceptor tyrosine-based activation motifs (ITAMs) by Lyn science.
kinase and subsequent activation of Syk kinase through its binding
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to the ITAMs. These proximal signaling events also activate Fyn
kinase, which is important for phosphorylation of the adaptor FIP1L1-PDGFRA- and NPM-ALK-Based Murine Models
protein Gab2 and activation of the PI3K pathway. Lyn kinase also
regulates phosphorylation of the protein scaffolds LAT and NTAL, Expression of the FIP1L1-PDGFRA fusion alone in murine BM cells
which coordinate multiple signaling pathways including Ras/MAP was not sufficient to cause eosinophilia, but only a general myelopro-
kinase, TEC family kinases, and PLCγ activation. PLCγ, in turn, is liferative disease. However, overexpression of IL-5 together with
a critical mediator of MC cytokine production and degranulation. FIP1L1-PDGFRA produced typical features closely resembling HES,
Experimental data indicate that the functions of KIT and FcεRI in including tissue infiltration by eosinophils. However, a phenotype of
MCs are interdependent. It has been observed that SCF enhances mastocytosis in addition to eosinophilia developed in another murine
FcεRI-mediated MC degranulation, and that phosphorylation of model by introducing FIP1L1-PDGFRA into hematopoietic stem
the membrane adaptor molecule NTAL is a crucial link between the cells and progenitors with T-cell overexpression of IL-5. Transplanta-
signaling cascades following KIT activation and FcεRI aggregation. tion of NPM-ALK (nucleophosmin-anaplastic lymphoma kinase)–
In addition, BTK is a mediator of FcεRI-mediated MC degranulation transduced progenitors into normal mice or IL-9–transgenic mice
and plays a critical role in the amplification of FcεRI activation without NPM-ALK each result in MC hyperplasia; however, both
by KIT. “single-hit” models are insufficient to generate a histopathologic
picture of SM. SM is only observed when NPM-ALK is transduced
into mouse BM progenitors of lethally irradiated IL-9 transgenic
TOOLS TO STUDY HUMAN MAST CELLS mice. Similar to the model of FIP1L1-PDGFRA and IL-5, this model
of the NPM-ALK fusion and IL-9 highlights the biologic interdepen-
The challenges of studying MCs relate to heterogeneity in their dence of a fusion oncogene and cytokine-related pathways in promot-
morphology and function between different species, and also within ing the full expression of neoplastic MC growth.