Split anergized natural killer cells halt inflammation by inducing stem cell differentiation,resistance to NK cell cytotoxicity and prevention of cytokine and chemokine secretion

The mechanism of suppression of NK cytotoxicity in cancer patients is not clearly established. In this paper we provide evidence that anergized NK cells induce differentiation of healthy Dental Pulp Stem Cells (DPSCs) or transformed Oral Squamous Cancer Stem Cells (OSCSCs) resulting in cell growth inhibition, resistance to NK cell-mediated cytotoxicity and prevention of inflammatory mediators secretion. Induction of cytotoxicity resistance in differentiated cells correlated with increased CD54 and MHC class I surface expression and mediated by the combination of IFN-γ and TNF-α since antibodies to both, but not each cytokine alone, was able to inhibit resistance. In contrast, inhibition of cytokine and chemokine release was mediated by IFN-γ since the addition of anti-IFN-γ antibody, and not anti-TNF-α, restored secretion of inflammatory mediators in NK cell cultures with differentiated DPSCs and OSCSCs. There was a gradual and time dependent decrease in MHC class I and CD54 expression which correlated with the restoration of NK cell cytotoxicity, augmentation of cytokine secretion and increased cell growth from days 0–12 post NK removal. Continuous presence of NK cells is required for the maintenance of cell differentiation since the removal of NK cell-mediated function reverses the phenotype and function of differentiated cells to their stem-like cells.     

Activation of plasmacytoid dendritic cells promotes AML-cell fratricide

Acute myeloid leukemia (AML) is characterized by the proliferation of immature myeloid blasts and a suppressed immune state. Interferons have been previously shown to aid in the clearance of AML cells. Type I interferons are produced primarily by plasmacytoid dendritic cells (pDCs). However, these cells exist in a quiescent state in AML. Because pDCs express TLR 7–9, we hypothesized that the TLR7/8 agonist R848 would be able to reprogram them toward a more active, IFN-producing phenotype. Consistent with this notion, we found that R848-treated pDCs from patients produced significantly elevated levels of IFNβ. In addition, they showed increased expression of the immune-stimulatory receptor CD40. We next tested whether IFNβ would influence antibody-mediated fratricide among AML cells, as our recent work showed that AML cells could undergo cell-to cell killing in the presence of the CD38 antibody daratumumab. We found that IFNβ treatment led to a significant, IRF9-dependent increase in CD38 expression and a subsequent increase in daratumumab-mediated cytotoxicity and decreased colony formation. These findings suggest that the tolerogenic phenotype of pDCs in AML can be reversed, and also demonstrate a possible means of enhancing endogenous Type I IFN production that would promote daratumumab-mediated clearance of AML cells.     

Neutrophils with protumor potential could efficiently suppress tumor growth after cytokine priming and in presence of normal NK cells

In tumor-bearing state, the function of neutrophils is converted from tumor-suppressing to tumor-promoting. Here we report that priming with IFN-γ and TNF-α could convert the potential of neutrophils from tumor-promoting to tumor-suppressing. The neutrophils with protumor potential have not lost their responsiveness to IFN-γ and TNF-α. After priming with IFN-γ and TNF-α, the potential of the neutrophils to express Bv8 and Mmp9 genes was reduced. Conversely, the tumor-promotional neutrophils recovered the expression of Rab27a and Trail, resumed the activation levels of PI3K and p38 MAPK pathways in response to stimuli, and expressed higher levels of IL-18 and NK-activating ligands such as RAE-1, MULT-1, and H60. Therefore, the anti-tumor function of the neutrophils was augmented, including the cytotoxicity to tumor cells, the capability of degranulation, and the capacity to activate NK cells. Since the function of NK cells is impaired in tumor-bearing state, the administration of normal NK cells could significantly augment the efficiency of tumor therapy based on neutrophil priming. These findings highlight the reversibility of neutrophil function in tumor-bearing state, and suggest that neutrophil priming by IFN-γ/TNF-α might be a potential approach to eliminate residual tumor cells in comprehensive strategy for tumor therapy.     

Curcumin combined with FAPαc vaccine elicits effective antitumor response by targeting indolamine-2,3-dioxygenase and inhibiting EMT induced by TNF-α in melanoma

Fibroblast activation protein α (FAPα) is a potential target for cancer therapy. However, elimination of FAPα+ fibroblasts activates secretion of IFN-γ and TNF-α. IFN-γ can in turn induce expression indolamine-2,3-dioxygenase (IDO), thereby contributing to immunosuppression, while TNF-α can induce EMT. These two reactive effects would limit the efficacy of a tumor vaccine. We found that curcumin can inhibit IDO expression and TNF-α-induced EMT. Moreover, FAPαc vaccine and CpG combined with curcumin lavage inhibited tumor growth and prolonged the survival of mice implanted with melanoma cells. The combination of FAPαc vaccine, CpG and curcumin stimulated FAPα antibody production and CD8+ T cell-mediated killing of FAPα-expressing stromal cells without adverse reactive effects. We suggest a combination of curcumin and FAPαc vaccine for melanoma therapy.     

Direct RIG-I activation in human NK cells induces TRAIL-dependent cytotoxicity toward autologous melanoma cells

Activation of the innate immune receptor retinoic acid-inducible gene I (RIG-I) by its specific ligand 5′-triphosphate RNA (3pRNA) triggers anti-tumor immunity, which is dependent on natural killer (NK) cell activation and cytokine induction. However, to date, RIG-I expression and the functional consequences of RIG-I activation in NK cells have not been examined. Here, we show for the first time the expression of RIG-I in human NK cells and their activation upon RIG-I ligand (3pRNA) transfection. 3pRNA-activated NK cells killed melanoma cells more efficiently than NK cells activated by type I interferon. Stimulation of RIG-I in NK cells specifically increased the surface expression of membrane-bound TNF-related apoptosis-inducing ligand (TRAIL) on NK cells, while activated NK cell receptors were not affected. RIG-I-induced membrane-bound TRAIL initiated death-receptor-pathway-mediated apoptosis not only in allogeneic but also in autologous human leukocyte antigen (HLA) class I-positive and HLA class I-negative melanoma cells. These results identify the direct activation of RIG-I in NK cells as a novel mechanism for how RIG-I can trigger enhanced NK cell killing of tumor cells, underscoring the potential of RIG-I activation for tumor immunotherapy.     

Bortezomib and depsipeptide sensitize tumors to tumor necrosis factor-related apoptosis-inducing ligand: a novel method to potentiate natural killer cell tumor cytotoxicity

The proteasome inhibitor, bortezomib, and the histone deacetylase inhibitor, depsipeptide (FK228), up-regulate tumor death receptors. Therefore, we investigated whether pretreatment of malignant cells with these agents would potentiate natural killer (NK)-mediated tumor killing. NK cells isolated from healthy donors and patients with cancer were expanded in vitro and then tested for cytotoxicity against tumor cell lines before and after exposure to bortezomib or depsipeptide. In 11 of 13 (85%) renal cell carcinoma cell lines and in 16 of 37 (43%) other cancer cell lines, exposure to these drugs significantly increased NK cell-mediated tumor lysis compared with untreated tumor controls (P < 0.001). Furthermore, NK cells expanded from patients with metastatic renal cell carcinoma were significantly more cytotoxic against autologous tumor cells when pretreated with either bortezomib or depsipeptide compared with untreated tumors. Tumors sensitized to NK cell cytotoxicity showed a significant increase in surface expression of DR5 [tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-R2; P < 0.05]; in contrast, surface expression of MHC class I, MIC-A/B, DR4 (TRAIL-R1), and Fas (CD95) did not change. The enhanced susceptibility to NK cell killing was completely abolished by blocking TRAIL on NK cells, and partially abolished by blocking DR5 on tumor cells. These findings show that drug-induced sensitization to TRAIL could be used as a novel strategy to potentiate the anticancer effects of adoptively infused NK cells in patients with cancer.     

Interferon-α and its effects on cancer cell apoptosis

Interferon (IFN)-α is a cytokine that exhibits a wide range of biological activities and is used in various cancer treatments. It regulates numerous genes that serve roles in antiviral, antiproliferative and proapoptotic activities. For decades, one of the main aspects of clinical oncology has been the development of anticancer therapeutics that promote the effective elimination of cancer cells via apoptosis. However, the updated available information concerning IFN-α-induced cancer cell apoptosis needs to be assembled, so as to provide an improved theoretical reference for the basic scientific research and clinical treatment of malignant tumors. Therefore, the present review focuses on the potential effects of IFN-α in inducing cancer cell apoptosis. The biological characteristics of IFN-α, the apoptotic signaling pathways and molecular mechanisms of apoptosis caused by IFN-α are discussed in different types of cancer cells. The present review provided a comprehensive understanding of the effects of IFN-α on cancer cell apoptosis, which will aid in developing more efficient strategies to effectively control the progression of certain cancers.     

Macrophages inhibit human osteosarcoma cell growth after activation with the bacterial cell wall derivative liposomal muramyl tripeptide in combination with interferon-γ

Background

In osteosarcoma, the presence of tumor-infiltrating macrophages positively correlates with patient survival in contrast to the negative effect of tumor-associated macrophages in patients with other tumors. Liposome-encapsulated muramyl tripeptide (L-MTP-PE) has been introduced in the treatment of osteosarcoma patients, which may enhance the potential anti-tumor activity of macrophages. Direct anti-tumor activity of human macrophages against human osteosarcoma cells has not been described so far. Hence, we assessed osteosarcoma cell growth after co-culture with human macrophages.

Methods

Monocyte-derived M1-like and M2-like macrophages were polarized with LPS + IFN-γ, L-MTP-PE +/− IFN-γ or IL-10 and incubated with osteosarcoma cells. Two days later, viable tumor cell numbers were analyzed. Antibody-dependent effects were investigated using the therapeutic anti-EGFR antibody cetuximab.

Results

M1-like macrophages inhibited osteosarcoma cell growth when activated with LPS + IFN-γ. Likewise, stimulation of M1-like macrophages with liposomal muramyl tripeptide (L-MTP-PE) inhibited tumor growth, but only when combined with IFN-γ. Addition of the tumor-reactive anti-EGFR antibody cetuximab did not further improve the anti-tumor activity of activated M1-like macrophages. The inhibition was mediated by supernatants of activated M1-like macrophages, containing TNF-α and IL-1β. However, specific blockage of these cytokines, nitric oxide or reactive oxygen species did not inhibit the anti-tumor effect, suggesting the involvement of other soluble factors released upon macrophage activation. While LPS + IFN-γ–activated M2-like macrophages had low anti-tumor activity, IL-10–polarized M2-like macrophages were able to reduce osteosarcoma cell growth in the presence of the anti-EGFR cetuximab involving antibody-dependent tumor cell phagocytosis.

Conclusion

This study demonstrates that human macrophages can be induced to exert direct anti-tumor activity against osteosarcoma cells. Our observation that the induction of macrophage anti-tumor activity by L-MTP-PE required IFN-γ may be of relevance for the optimization of L-MTP-PE therapy in osteosarcoma patients.     

Resistance to Cytarabine Induces the Up-regulation of NKG2D Ligands and Enhances Natural Killer Cell Lysis of Leukemic Cells

Prolonged treatment of leukemic cells with chemotherapeutic agents frequently results in development of drug resistance. Moreover, selection of drug-resistant cell populations may be associated with changes in malignant properties such as proliferation rate, invasiveness, and immunogenicity. In the present study, the sensitivity of cytarabine (1-β-d-arabinofuranosylcytosine, araC)-resistant and parental human leukemic cell lines (T-lymphoid H9 and acute T-lymphoblastic leukemia Molt-4) to natural killer (NK) cell-mediated killing was investigated. The results obtained demonstrate that araC-resistant H9 and Molt-4 (H9^rARAC¹⁰⁰ and Molt-4^rARAC¹⁰⁰) cell lines are more sensitive to NK cell-mediated lysis than their respective parental cell lines. This increased sensitivity was associated with a higher surface expression of ligands for the NK cell-activating receptor NKG2D, notably UL16 binding protein-2 (ULBP-2) and ULBP-3 in H9^rARAC¹⁰⁰ and Molt-4^rARAC¹⁰⁰ cell lines. Blocking ULBP-2 and ULBP-3 or NKG2D with monoclonal antibody completely abrogated NK cell lysis. Constitutive phosphorylated extracellular signal-regulated kinase (ERK) but not pAKT was higher in araC-resistant cells than in parental cell lines. Inhibition of ERK using ERK inhibitor PD98059 decreased both ULBP-2/ULBP-3 expression and NK cell cytotoxicity. Furthermore, overexpression of constitutively active ERK in H9 parental cells resulted in increased ULBP-2/ULBP-3 expression and enhanced NK cell lysis. These results demonstrate that increased sensitivity of araC-resistant leukemic cells to NK cell lysis is caused by higher NKG2D ligand expression, resulting from more active ERK signaling pathway.     

Trastuzumab upregulates programmed death ligand-1 expression through interaction with NK cells in gastric cancer

Background The predictive significance of programmed death ligand 1 (PD-L1) for programmed death 1 (PD-1) inhibitors remains unclear in gastric cancer (GC) due to the dynamic alteration by treatments. We aimed to elucidate the effects of trastuzumab (Tmab) on PD-L1 expression in GC.Methods PD-L1 expression was evaluated by multicolour flow cytometry analysis after co-culturing GG cell lines and immune cells with Tmab. IFN-γ in the co-culture experiments was quantified. Immunohistochemistry (IHC) for PD-L1 expression using clinical samples was also performed to confirm PD-L1 alteration by Tmab.Results PD-L1 expression was significantly upregulated by Tmab in HER2-amplified GC cell lines co-cultured with peripheral blood mononuclear cells (PBMCs). PD-L1 upregulation by Tmab was also observed in the GC cells co-cultured with NK cells in time-dependent manner, but not with monocytes. IFN-γ concentration in conditioned media from co-cultured PBMCs and NK cells with Tmab was significantly higher and anti-IFN-γ significantly suppress the Tmab-induced PD-L1 upregulation. IHC also suggested PD-L1 upregulation after Tmab treatment.Conclusions Tmab can upregulate PD-L1 expression on GC cells through interaction with NK cells. These results suggest clinical implications in the assessment of the predictive significance of PD-L1 expression for PD-1 inhibitors.Subject terms: Gastric cancer, Cancer immunotherapy     

脐血来源的DC增强NK和NKT细胞对白血病细胞的杀伤作用

目的:探讨脐血来源的树突状细胞(DC)增强自然杀伤(NK)细胞和自然杀伤性T(NKT)细胞对白血病细胞杀伤作用的影响机制.方法:提取脐带血单个核细胞(PBMC),体外诱导培养DC、NK和NKT淋巴细胞.以人髓性白血病K-562细胞作为靶细胞,检测NK、NKT、NK+DC和NKT+DC对靶细胞的杀伤效应.检测共培养上清液...     

Dasatinib and interferon alpha synergistically induce pyroptosis-like cell death in philadelphia chromosome positive acute lymphoblastic leukemia

Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ALL) is a high-risk disease subtype with a dismal prognosis. Inhibiting BCR-ABL kinase alone is insufficient to eradicate Ph+ALL clones, and alternative BCR-ABL-dependent and -independent pathways need to be targeted as an effective strategy. Our study revealed that the combination of dasatinib and interferon-α showed synergistic activity against Ph+ALL, inducing mitochondrial dysfunction and causing necrosis-like cell lysis. Mechanistic studies showed that the induced cell death was caspase-3-independent. Canonical necroptosis signals, such as RIP1 and MLKL, were not activated; instead, the pyroptosis executor Gasdermin D was upregulated expression and activated. The expression levels of extracellular ATP and IL-1β were also upregulated, both of which are markers of pyroptotic cell death. In a murine Ph+ALL model, the dual drug treatment prolonged the survival of tumor-bearing mice. More importantly, we incorporated the dual drugs to maintenance therapy in 39 patients who were unfit for allogeneic stem cell transplantation (allo-HSCT). The median follow-up was 28.5 months, the 4-year disease-free survival and overall survival rates were 52.2% and 65.2%, respectively. Our data suggest that the combination of dasatinib and interferon-α has potential synergistic activity against Ph+ALL and shows promise as a maintenance therapy for Ph+ALL patients who are unfit for allo-HSCT.     

Anti-4-1BB antibody-based combination therapy augments antitumor immunity by enhancing CD11c+CD8+ T cells in renal cell carcinoma

To improve the potential treatment strategies of incurable renal cell carcinoma (RCC), which is highly resistant to chemotherapy and radiotherapy, the present study established a combination therapy with immunostimulatory factor (ISTF) and anti-4-1BB monoclonal antibodies (mAbs) to augment the antitumor response in a murine RCC model. ISTF isolated from Actinobacillus actinomycetemcomitans stimulates macrophages, dendritic cells and B cells to produce IL-6, TNF-α, nitric oxide and major histocompatibility complex class II expression. 4-1BB (CD137) is expressed in activated immune cells, including activated T cells, and is a promising target for cancer immunotherapy. The administration of anti-4-1BB mAbs promoted antitumor immunity via enhancing CD11c⁺CD8⁺ T cells. The CD11c⁺CD8⁺ T cells were characterized by high killing activity and IFN-γ-producing ability, representing a phenotype of active effector cytotoxic T lymphocytes. The present study showed that combination therapy with ISTF and anti-4-1BB mAbs promoted partial tumor regression with established RCC, but monotherapy with ISTF or anti-4-1BB mAbs did not. These effects were speculated to be caused by the increase in CD11c⁺CD8⁺ T cells in the spleen and tumor, and IFN-γ production. These insights into the effector mechanisms of the combination of ISTF and anti-4-1BB mAbs may be useful for targeting incurable RCC.     

Resistance of infant leukemia with MLL rearrangement to tumor necrosis factor-related apoptosis-inducing ligand: a possible mechanism for poor sensitivity to antitumor immunity.

Malignant cells generally acquire some immune escape mechanisms for clonal expansion. Immune escape mechanisms also contribute to the failure of graft-versus-leukemia (GVL) effect after allogeneic hematopoietic stem cell transplantation (allo-SCT). Infant leukemias with mixed-lineage leukemia (MLL) rearrangement have a remarkably short latency, and GVL effect after allo-SCT has not been clearly evidenced in these leukemias. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)- and FasL-mediated cytotoxic pathways play important roles in cytotoxic T-lymphocyte- and natural killer cell-mediated antitumor immunity and optimal GVL activity. We investigated the in vitro sensitivity of MLL-rearranged acute lymphoblastic leukemia (ALL) and acute myeloblastic leukemia (AML) cells to TRAIL- and FasL-mediated cytotoxicity. Most of cell lines and primary leukemia cells were highly resistant to TRAIL primarily owing to low cell-surface expression of death receptors in ALL and simultaneous expression of decoy receptors in AML. Nearly half of cell lines and majority of primary leukemia cells showed low sensitivity to FasL. These results suggest that resistance to death-inducing ligands, particularly to TRAIL, could be one of the mechanisms for a rapid clonal expansion and a poor sensitivity to the GVL effect in infant leukemias with MLL rearrangement.     

Interferon-alpha-2b induces autophagy in hepatocellular carcinoma cells through Beclin1 pathway

Objective

To determine whether Interferon-alpha-2b (IFN-α2b) can modulate the autophagic response in hepatocellular carcinoma cells.

Methods

Hepatocellular carcinoma cells were treated with IFN-α2b. Autophagy was assessed by acridine orange staining, GFP-LC3 dotted assay, transmission electron microscopy and immunoblotting.

Results

Acridine orange staining showed that IFN-α2b triggered the accumulation of acidic vesicular and autolysosomes in HepG2 cells. The acridine orange HepG2 cell ratios were (4.3±1.0)%, (6.9±1.4)%, and (13.1±2.3)%, respectively, after treatment with 100, 1,000, and 10,000 IU/mL IFN-α2b for 48 h. A markedly punctate pattern was observed in HepG2 cells treated with 10,000 IU/mL IFN-α2b for 48 h, but only diffuse and weakly fluorescent GFP-LC3 puncta was observed in control cells. HepG2 cells treated with 10,000 IU/mL IFN-α2b for 48 h developed autophagosome-like characteristics, including single- or double-membrane vacuoles containing intact and degraded cellular debris. The Beclin1 and LC3-II protein expression was up-regulated by IFN-α2b treatment.

Conclusion

Autophagy can be induced in a dose-dependent manner by treatment with IFN-α2b in HepG2 cells, and the Beclin1 signaling pathway was stimulated by IFN-α2b.KEYWORDS : Interferon-alpha-2b (IFN-α2b), autophagy, acridine orange, Beclin1, transmission electron microscopy     

PD-1hiTIM-3+ T cells associate with and predict leukemia relapse in AML patients post allogeneic stem cell transplantation

Prognosis of leukemia relapse post allogeneic stem cell transplantation (alloSCT) is poor and effective new treatments are urgently needed. T cells are pivotal in eradicating leukemia through a graft versus leukemia (GVL) effect and leukemia relapse is considered a failure of GVL. T-cell exhaustion is a state of T-cell dysfunction mediated by inhibitory molecules including programmed cell death protein 1 (PD-1) and T-cell immunoglobulin domain and mucin domain 3 (TIM-3). To evaluate whether T-cell exhaustion and inhibitory pathways are involved in leukemia relapse post alloSCT, we performed phenotypic and functional studies on T cells from peripheral blood of acute myeloid leukemia patients receiving alloSCT. Here we report that PD-1^hiTIM-3⁺ cells are strongly associated with leukemia relapse post transplantation. Consistent with exhaustion, PD-1^hiTIM-3⁺ T cells are functionally deficient manifested by reduced production of interleukin 2 (IL-2), tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ). In addition, these cells demonstrate a phenotype consistent with exhausted antigen-experienced T cells by losing T_N and T_EMRA subsets. Importantly, increase of PD-1^hiTIM-3⁺ cells occurs before clinical diagnosis of leukemia relapse, suggesting their predictive value. Results of our study provide an early diagnostic approach and a therapeutic target for leukemia relapse post transplantation.     

Differential modulation of natural killer cell cytotoxicity by 17β-estradiol and prolactin through the NKG2D/NKG2DL axis in cervical cancer cells

Natural killer (NK) cells play a crucial role in cervical cancer (CC). As estrogens and prolactin (PRL) have been reported to be involved in CC, the present study attempted to elucidate the effects of both hormones on NK cells in CC. For this purpose, NKL cells, as well as CC-derived cell lines (HeLa, SiHa and C33A) and non-tumorigenic keratinocytes (HaCaT cells) were stimulated with 17β-estradiol (E2; 10 nM), PRL (200 ng/ml), or both (E2 and PRL) for 48 h. The expression of hormone receptors (estrogen receptor α and β, G protein-coupled estrogen receptor 1 and PRL receptor) and NK cell activating receptors [natural killer group 2D (NKG2D), natural cytotoxicity triggering receptor 3, natural cytotoxicity triggering receptor 2 and natural cytotoxicity triggering receptor 1] were measured using western blot analysis and flow cytometry, respectively. In the HeLa, SiHa, C33A and HaCaT cells stimulated with the hormones, the expression of NKG2D ligands [MHC class I polypeptide-related sequence A/B (MICA/B)] on the membrane and the soluble form of MICA was evaluated using flow cytometry and ELISA. Cytotoxicity assay was performed using GFP-transfected K562 cells as target cells. E2 reduced NKL cell-mediated cytotoxicity, while PRL exerted the opposite effect. NKL cells expressed different hormone receptor forms, of which PRL only induced a decrease in NKG2D expression compared to the untreated control NKL cells. PRL increased MICA/B expression in HeLa cells and E2 and PRL reversed this effect. However, in SiHa cells, the concurrent incubation with the two hormones decreased MICA/B expression. E2 and PRL, either alone or in combination, decreased soluble MICA secretion in all CC cell lines, while E2 solely increased soluble MICA secretion in SiHa cells. On the whole, the present study provides evidence that E2 and PRL mediate the mechanisms through which NK and CC cells mediate a cytotoxic response and these have an antagonistic effect on NK cell-mediated cytotoxicity.     

Targeting leukemic stem cells by breaking their dormancy

Transient or long‐term quiescence, the latter referred to as dormancy are fundamental features of at least some adult stem cells. The status of dormancy is likely a critical mechanism for the observed resistance of normal HSCs and leukemic stem cells (LSCs) to anti‐proliferative chemotherapy. Recent studies have revealed cytokines such as Interferon‐alpha (IFNα) and G‐CSF as well as arsenic trioxide (As2O3) to be efficient agents for promoting cycling of dormant HSCs and LSCs. Most interestingly, such cell cycle activated stem cells become exquisitely sensitive to killing by different chemotherapeutic agents, suggesting that dormant LSCs in patients may be targeted by a sequential two‐step protocol involving an initial activation by IFNα, G‐CSF or As2O3, followed by targeted chemotherapy.