Eosinophils and their mediators play a crucial role in various reactive states such as bacterial and viral infections, chronic inflammatory disorders, and certain hematologic malignancies. Depending ...on the underlying pathology, molecular defect(s), and the cytokine- and mediator-cascades involved, peripheral blood and tissue hypereosinophilia (HE) may develop and may lead to organ dysfunction or even organ damage which usually leads to the diagnosis of a HE syndrome (HES). In some of these patients, the etiology and impact of HE remain unclear. These patients are diagnosed with idiopathic HE. In other patients, HES is diagnosed but the etiology remains unknown — these patients are classified as idiopathic HES. For patients with HES, early therapeutic application of agents reducing eosinophil counts is usually effective in avoiding irreversible organ damage. Therefore, it is important to systematically explore various diagnostic markers and to correctly identify the disease elicitors and etiology. Depending on the presence and type of underlying disease, HES are classified into primary (clonal) HES, reactive HES, and idiopathic HES. In most of these patients, effective therapies can be administered. The current article provides an overview of the pathogenesis of eosinophil-associated disorders, with special emphasis on the molecular, immunological, and clinical complexity of HE and HES. In addition, diagnostic criteria and the classification of eosinophil disorders are reviewed in light of new developments in the field.
Chronic myeloid leukemia (CML) is a stem cell (SC) neoplasm characterized by the BCR/ABL1 oncogene. Although mechanisms of BCR/ABL1-induced transformation are well-defined, little is known about ...effector-molecules contributing to malignant expansion and the extramedullary spread of leukemic SC (LSC) in CML. We have identified the cytokine-targeting surface enzyme dipeptidylpeptidase-IV (DPPIV/CD26) as a novel, specific and pathogenetically relevant biomarker of CD34+/CD38─ CML LSC. In functional assays, CD26 was identified as target enzyme disrupting the SDF-1-CXCR4-axis by cleaving SDF-1, a chemotaxin recruiting CXCR4+ SC. CD26 was not detected on normal SC or LSC in other hematopoietic malignancies. Correspondingly, CD26+ LSC decreased to low or undetectable levels during successful treatment with imatinib. CD26+ CML LSC engrafted NOD-SCID-IL-2Rγ−/− (NSG) mice with BCR/ABL1+ cells, whereas CD26─ SC from the same patients produced multilineage BCR/ABL1– engraftment. Finally, targeting of CD26 by gliptins suppressed the expansion of BCR/ABL1+ cells. Together, CD26 is a new biomarker and target of CML LSC. CD26 expression may explain the abnormal extramedullary spread of CML LSC, and inhibition of CD26 may revert abnormal LSC function and support curative treatment approaches in this malignancy.
•DPPIV (CD26) is a new specific marker of CML LSC that aids CML diagnostics and the measurement, characterization, and purification of LSC.•DPPIV on CML LSC degrades SDF-1 and thereby promotes the niche-escape of LSC, which may contribute to extramedullary myeloproliferation in CML.
BET inhibitors (BETi) target bromodomain-containing proteins and are currently being evaluated as anti-cancer agents. We find that maximal therapeutic effects of BETi in a Myc-driven B cell lymphoma ...model required an intact host immune system. Genome-wide analysis of the BETi-induced transcriptional response identified the immune checkpoint ligand Cd274 (Pd-l1) as a Myc-independent, BETi target-gene. BETi directly repressed constitutively expressed and interferon-gamma (IFN-γ) induced CD274 expression across different human and mouse tumor cell lines and primary patient samples. Mechanistically, BETi decreased Brd4 occupancy at the Cd274 locus without any change in Myc occupancy, resulting in transcriptional pausing and rapid loss of Cd274 mRNA production. Finally, targeted inhibition of the PD-1/PD-L1 axis by combining anti-PD-1 antibodies and the BETi JQ1 caused synergistic responses in mice bearing Myc-driven lymphomas. Our data uncover an interaction between BETi and the PD-1/PD-L1 immune-checkpoint and provide mechanistic insight into the transcriptional regulation of CD274.
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•BETi require an intact host immune system to promote robust anti-tumor responses•BRD4 inhibition inhibits PD-L1 transcription independently from MYC expression•BRD4 and IRF1 co-regulate interferon-induced PD-L1 transcription•Combinations of BET inhibitor and immune modulating therapy are efficacious in vivo
Hogg et al. find that BET bromodomain inhibitors promote anti-tumor immune responses through transcriptional repression of immune checkpoint ligand PD-L1 in genetically diverse tumor models and in response to inflammatory stimuli. Moreover, BET inhibitors enhance the efficacy of immune modulating therapies, such as checkpoint blockade.
Chronic myelomonocytic leukemia (CMML) is a stem cell-derived neoplasm characterized by dysplasia, uncontrolled expansion of monocytes, and substantial risk to transform to secondary acute myeloid ...leukemia (sAML). So far, little is known about CMML-initiating cells. We found that leukemic stem cells (LSC) in CMML reside in a CD34
/CD38
fraction of the malignant clone. Whereas CD34
/CD38
cells engrafted NSGS mice with overt CMML, no CMML was produced by CD34
/CD38
progenitors or the bulk of CD34
monocytes. CMML LSC invariably expressed CD33, CD117, CD123 and CD133. In a subset of patients, CMML LSC also displayed CD52, IL-1RAP and/or CLL-1. CMML LSC did not express CD25 or CD26. However, in sAML following CMML, the LSC also expressed CD25 and high levels of CD114, CD123 and IL-1RAP. No correlations between LSC phenotypes, CMML-variant, mutation-profiles, or clinical course were identified. Pre-incubation of CMML LSC with gemtuzumab-ozogamicin or venetoclax resulted in decreased growth and impaired engraftment in NSGS mice. Together, CMML LSC are CD34
/CD38
cells that express a distinct profile of surface markers and target-antigens. During progression to sAML, LSC acquire or upregulate certain cytokine receptors, including CD25, CD114 and CD123. Characterization of CMML LSC should facilitate their enrichment and the development of LSC-eradicating therapies.
Abstract Chronic myeloid leukemia (CML) is a stem cell-derived leukemia in which neoplastic cells exhibit the Philadelphia (Ph) chromosome and the related oncoprotein, BCR-ABL1. The disease is ...characterized by an accumulation of myeloid precursor cells in the peripheral blood (PB) and bone marrow (BM). A small fraction of neoplastic cells in the CML clone supposedly exhibits self-renewal and thus long-term disease-propagating ability. However, so far, little is known about the phenotype, function, and target expression-profiles of these leukemic stem cells (LSC). Recent data suggest that CML LSC aberrantly express the interleukin-2 receptor alpha chain CD25. Whereas normal CD34+ /CD38− BM stem cells display only low amounts of CD25 or lack CD25, CD34+ /CD38− LSC strongly express CD25 in over 90% of all patients with untreated CML. As a result, CD25 can be employed to identify and quantify CML LSC. In addition, it has been described that CD25 serves as a negative growth regulator of CML LSC. In the current article, we review the value of CD25 as a novel marker and potential drug-target in CML LSC.
Mast cell leukemia (MCL) is a highly fatal malignancy characterized by devastating expansion of immature mast cells in various organs. Although considered a stem cell disease, little is known about ...MCL-propagating neoplastic stem cells. We here describe that leukemic stem cells (LSCs) in MCL reside within a CD34
/CD38
fraction of the clone. Whereas highly purified CD34
/CD38
cells engrafted NSG
mice with fully manifesting MCL, no MCL was produced by CD34
/CD38
progenitors or the bulk of KIT
/CD34
mast cells. CD34
/CD38
MCL cells invariably expressed CD13 and CD133, and often also IL-1RAP, but did not express CD25, CD26 or CLL-1. CD34
/CD38
MCL cells also displayed several surface targets, including CD33, which was homogenously expressed on MCL LSCs in all cases, and the D816V mutant form of KIT. Although CD34
/CD38
cells were resistant against single drugs, exposure to combinations of CD33-targeting and KIT-targeting drugs resulted in LSC-depletion and markedly reduced engraftment in NSG
mice. Together, MCL LSCs are CD34
/CD38
cells that express distinct profiles of markers and target antigens. Characterization of MCL LSCs should facilitate their purification and should support the development of LSC-eradicating curative treatment approaches in this fatal type of leukemia.
In chronic myelogenous leukemia (CML), leukemic stem cells (LSC) represent a critical target of therapy. However, little is known about markers and targets expressed by LSCs. The aim of this project ...was to identify novel relevant markers of CML LSCs.
CML LSCs were examined by flow cytometry, qPCR, and various bioassays. In addition, we examined the multipotent CD25(+)CML cell line KU812.
In contrast to normal hematopoietic stem cells, CD34(+)/CD38(-)CML LSCs expressed the IL-2 receptor alpha chain, IL-2RA (CD25). STAT5 was found to induce expression of CD25 in Lin(-)/Sca-1(+)/Kit(+)stem cells in C57Bl/6 mice. Correspondingly, shRNA-induced STAT5 depletion resulted in decreased CD25 expression in KU812 cells. Moreover, the BCR/ABL1 inhibitors nilotinib and ponatinib were found to decrease STAT5 activity and CD25 expression in KU812 cells and primary CML LSCs. A CD25-targeting shRNA was found to augment proliferation of KU812 cellsin vitroand their engraftmentin vivoin NOD/SCID-IL-2Rγ(-/-)mice. In drug-screening experiments, the PI3K/mTOR blocker BEZ235 promoted the expression of STAT5 and CD25 in CML cells. Finally, we found that BEZ235 produces synergistic antineoplastic effects on CML cells when applied in combination with nilotinib or ponatinib.
CD25 is a novel STAT5-dependent marker of CML LSCs and may be useful for LSC detection and LSC isolation in clinical practice and basic science. Moreover, CD25 serves as a growth regulator of CML LSCs, which may have biologic and clinical implications and may pave the way for the development of new more effective LSC-eradicating treatment strategies in CML.
Leukemic stem cells (LSCs) are an emerging target of curative anti-leukemia therapy. In acute lymphoblastic leukemia (ALL), LSCs frequently express CD34 and often lack CD38. However, little is known ...about markers and targets expressed in ALL LSCs. We have examined marker- and target expression profiles in CD34+/CD38− LSCs in patients with Ph+ ALL (n = 22) and Ph− ALL (n = 27) by multi-color flow cytometry and qPCR. ALL LSCs expressed CD19 (B4), CD44 (Pgp-1), CD123 (IL-3RA), and CD184 (CXCR4) in all patients tested. Moreover, in various subgroups of patients, LSCs also displayed CD20 (MS4A1) (10/41 = 24%), CD22 (12/20 = 60%), CD33 (Siglec-3) (20/48 = 42%), CD52 (CAMPATH-1) (17/40 = 43%), IL-1RAP (13/29 = 45%), and/or CD135 (FLT3) (4/20 = 20%). CD25 (IL-2RA) and CD26 (DPPIV) were expressed on LSCs in Ph+ ALL exhibiting BCR/ABL1p210, whereas in Ph+ ALL with BCR/ABL1p190, LSCs variably expressed CD25 but did not express CD26. In Ph− ALL, CD34+/CD38− LSCs expressed IL-1RAP in 6/18 patients (33%), but did not express CD25 or CD26. Normal stem cells stained negative for CD25, CD26 and IL-1RAP, and expressed only low amounts of CD52. In xenotransplantation experiments, CD34+/CD38− and CD34+/CD38+ cells engrafted NSG mice after 12–20 weeks, and targeting with antibodies against CD33 and CD52 resulted in reduced engraftment. Together, LSCs in Ph+ and Ph− ALL display unique marker- and target expression profiles. In Ph+ ALL with BCR/ABL1p210, the LSC-phenotype closely resembles the marker-profile of CD34+/CD38− LSCs in chronic myeloid leukemia, confirming the close biologic relationship of these neoplasms. Targeting of LSCs with specific antibodies or related immunotherapies may facilitate LSC eradication in ALL.
Despite new insights in molecular features of leukemic cells and the availability of novel treatment approaches and drugs, acute myeloid leukemia (AML) remains a major clinical challenge. In fact, ...many patients with AML relapse after standard therapy and eventually die from progressive disease. The basic concept of leukemic stem cells (LSC) has been coined with the goal to decipher clonal architectures in various leukemia‐models and to develop curative drug therapies by eliminating LSC. Indeed, during the past few years, various immunotherapies have been tested in AML, and several of these therapies follow the strategy to eliminate relevant leukemic subclones by introducing LSC‐targeting antibodies or LSC‐targeting immune cells. These therapies include, among others, new generations of LSC‐eliminating antibody‐constructs, checkpoint‐targeting antibodies, bi‐specific antibodies, and CAR‐T or CAR‐NK cell‐based strategies. However, responses are often limited and/or transient which may be due to LSC resistance. Indeed, AML LSC exhibit multiple forms of resistance against various drugs and immunotherapies. An additional problems are treatment‐induced myelotoxicity and other side effects. The current article provides a short overview of immunological targets expressed on LSC in AML. Moreover, cell‐based therapies and immunotherapies tested in AML are discussed. Finally, the article provides an overview about LSC resistance and strategies to overcome resistance.
Expression of cell surface target antigens on leukemic stem cells (LSC) in acute myeloid leukemia (AML) (left image) and on normal hematopoietic stem cells (right panel). Most of the clinically relevant surface target antigens are not only expressed on AML LSC but also in normal stem cells. In several instances, expression levels are higher on AML LSC than on normal stem cells providing a (small) therapeutic window. Only a few potential surface targets, such as CLL1 (CD371), are selectively (aberrantly) expressed on AML LSC but not on normal stem cells.
Little is known about the function and phenotype of leukemic stem cells (LSCs) in chronic myeloid leukemia (CML) or about specific markers that discriminate LSCs from normal hematopoietic stem cells ...(HSCs). CD26 has recently been described as a specific marker of CML LSCs. In the current study, we investigated this marker in a cohort of 31 unselected CML patients. BCR/ABL1 positivity was analyzed in highly enriched stem cell fractions using fluorescence in situ hybridization (FISH) and reverse transcription PCR (RT-PCR). The proportion of CD26+ LSCs and CD26- HSCs varied considerably among the patients analyzed, and the percentage of CD26+ cells correlated with leukocyte count. The CD26 expression robustly discriminated LSCs from HSCs. This required a strict gating of the stem cell compartment. Thus, in patients with very low LSC or HSC numbers, only the highly sensitive RT-PCR method discriminated between clonal and non-clonal cells, while a robust FISH analysis required larger numbers of cells in both compartments. Finally, our data show that the numbers of CD26+ CML LSCs correlate with responses to treatment with BCR-ABL1 inhibitors.
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