Abstract
Purpose of Review
Tyrosine kinase inhibitors (TKIs) are very successful for the treatment of chronic myeloid leukaemia (CML) but are not curative in most patients due to persistence of TKI-resistant leukaemia stem cells (LSCs). The bone marrow immune microenvironment (BME) provides protection to the LSC through multidimensional interactions, driving therapy resistance, and highlighting the need to circumvent these protective niches therapeutically. This review updates the evidence for interactions between CML cells and the immune microenvironment with a view to identifying targetable therapeutic vulnerabilities and describes what is known about the role of immune regulation in treatment-free remission (TFR).
Recent Findings
Intracellular signalling downstream of the chemotactic CXCL12-CXCR4 axis, responsible for disrupted homing in CML, has been elucidated in LSCs, highlighting novel therapeutic opportunities. In addition, LSCs expressing CXCL12-cleaving surface protein CD26 were highly correlated with CML burden, building on existing evidence. Newer findings implicate the adhesion molecule CD44 in TKI resistance, while JAK/STAT-mediated resistance to TKIs may occur downstream of extrinsic signalling in the BME. Exosomal BME-LSC cross-communication has also been explored. Finally, further detail on the phenotypes of natural killer (NK) cells putatively involved in maintaining successful TFR has been published, and NK-based immunotherapies are discussed.
Summary
Recent studies highlight and build on our understanding of the BME in CML persistence and TKI resistance, pinpointing therapeutically vulnerable interactions. Repurposing existing drugs and/or the development of novel inhibitors targeting these relationships may help to overcome these issues in TKI-resistant CML and be used as adjuvant therapy for sustained TFR.
Similar content being viewed by others
Avoid common mistakes on your manuscript.
Introduction
Differentiated blood cells of all lineages are derived from rare and multipotent hematopoietic stem cells (HSCs) which exist in a quiescent state. HSCs differentiate ‘asymmetrically’ by simultaneously self-renewing and producing a distinct, more differentiated progeny cell. Progressive differentiation of hematopoietic stem and progenitor cells (HSPCs) to more lineage-committed progeny is accompanied by a loss of self-renewal in a tightly-regulated continuum, which eventually leads to a complement of differentiated blood cells. This topic is reviewed elsewhere [1].
The bone marrow (BM) is permeated by endothelium-lined vascular tissue which enables trafficking of mature blood progeny via permeable sinusoids [2]. The surrounding BM immune microenvironment (BME) is sparsely populated with mesenchymal stem/stromal cells (MSCs) which are characterised by immunophenotype, secretion profile, and localisation. Perivascular MSCs, periarteriolar MSCs, and perisinusoidal MSCs can be defined by surface Nestin expression (Nes+), neuron/glia antigen 2 (NG2), or leptin receptor (LepR) expression, respectively [3]. MSCs are heterogeneous and multipotent [4], giving rise to ‘niche’ BMEs which can support hematopoietic cells distinctly. For example, the arteriolar niche (containing NG2+ pericytes) is a more favourable environment for long-term quiescent HSCs than the sinusoidal niche (containing LepR+ stromal cells), which facilitates differentiation [5]. MSCs can also modulate extrinsic immune cell responses, such as aiding suppressive regulatory T cell (Treg) generation while suppressing effector CD4+ T cells [6].
Numerous soluble factors maintain and regulate hematopoiesis within the BME. The chemokine CXCL12 binds to HSCs via surface receptor CXCR4, and this relationship is key to HSC maintenance [7, 8]. Three-dimensional imaging has also identified widespread distribution of CXCL12-abundant reticular (CAR) cells throughout the BM [9•]. HSC function can be modulated by sinusoidal endothelium-derived pleiotrophin [10] and vascular endothelium-derived E-selectin [11]. In addition, there are other cellular regulators of hematopoiesis in the BME, including macrophages (via CD82) [12] and megakaryocytes (via CXCL4 and TGF-β signalling) [13, 14]. Finally, reactive oxygen species (ROS) at the sinusoidal niche help to drive HSPCs towards differentiation and trafficking into the circulation [2]. HSCs may also interact with the bone-oriented endosteal niche [15]. A schematic representation of selected BM niches is shown in Fig. 1A, providing the context for exploring the BME in chronic myeloid leukaemia (CML) leukemogenesis.
CML is a clonal malignancy which arises due to chromosomal translocation and the fusion of the BCR and ABL1 genes. The resulting BCR::ABL1 fusion protein drives aberrant oncogenic signalling, expansion of malignant clones and clinical sequelae [16]. CML is usually diagnosed in the chronic phase (CP-CML), which can be managed long-term using BCR::ABL1-antagonising tyrosine kinase inhibitors (TKIs). A proportion of CP-CML may develop resistance to therapy or progress to blast phase (BP-CML), characterised by an acute condition, higher circulating blasts, and poor survival [17].
CML blasts are derived from a BCR::ABL1+ cell of origin termed a ‘leukaemia stem cell’ (LSC) due to its quiescence and self-renewal capacity [18, 19], akin to an HSC. LSCs are known to be resistant to TKIs through BCR::ABL1-independent mechanisms [20], and so can persist after successful TKI-induced remission, acting as a reservoir for CML relapse. Despite an improved understanding of LSC biology, they remain elusive and hard to target.
The mainstay of treatment for CP-CML involves BCR::ABL1-specific TKIs, and patients may be treated with multiple TKIs sequentially in order to attain/maintain a response. This review aims to update on the knowledge around the CML LSC, leukemic progeny, and the BME, in the context of therapeutic targeting, resistance, and treatment-free remission (TFR).
CXCL12-CXCR4 Axis
The CXCL12-CXCR4 axis can sustain LSCs in addition to HSCs. In a CML mouse engraftment model, Cxcl12 deletion in MSCs and CAR cells led to increased LSC cycling and TKI sensitivity, suggesting that stromal-derived Cxcl12 drives quiescence and TKI resistance. However, both undifferentiated LSC and progeny numbers increased, indicating that LSC self-renewal capacity was independent of Cxcl12 [21]. An earlier study demonstrated the formation of dense MSC/leukaemia progenitor clusters within the BM was also Cxcl12-driven [22], indicating that leukemic cells home towards a Cxcl12-rich niche.
Overexpression of the CXCL12 receptor CXCR4 in CML cells confers enhanced proliferative capacity and nilotinib resistance in vitro [23]. Chemotherapy resistance in K562 CML cells has also been associated with CXCR4 upregulation in addition to PI3K/AKT pathway activation and NF-κB nuclear translocation, highlighting an important signalling axis [24]. AKT phosphorylation downstream of CXCR4 activity has been described in K562 cells elsewhere [25].
In addition, the BCR::ABL1 target LASP1 was identified as an interactor of CXCR4 [23], in which low LASP1 activity/expression may contribute to the CXCR4-driven survival advantage of CML cells [26]. Butt et al. postulated that constitutive LASP1 phosphorylation by active BCR::ABL1 prevents CXCR4 stabilisation by LASP1, limiting CXCL12-CXCR4 signalling, and favouring cellular trafficking of CML cells from the BM into the periphery [27]. It has also been suggested that LASP1 is an intermediate player in CXCR4-AKT signalling [27].
Plerixafor is the only CXCR4 inhibitor in clinical use for autologous stem cell transplant (SCT), for which it aids peripheral mobilisation of CD34+ cells [28]. Plerixafor has not been evaluated clinically in CML. In relapsed acute myeloid leukaemia (AML), a phase I trial using Plerixafor demonstrated efficacy in overcoming stromal-leukaemia protection against targeted therapy, by mobilising CD34+CD38− leukaemia cells to the periphery [29].
A similar strategy has been explored in CML using other agents. In vivo inhibition of CXCL12 in CML using a targeted RNA oligonucleotide (NOX-A12/olaptesed pegol) was synergistic with TKI, suggesting that enhanced CML mobilisation out of the BME sensitised these cells to BCR::ABL1 inhibition [30]. NOX-A12 has since shown an acceptable clinical safety profile in other cancers [31] and may be suitable for clinical development in CML.
CD26
Disruption of the CXCL12-CXCR4 BM homing mechanism in leukemic cells has been partially attributed to activity of the surface enzyme dipeptidylpeptidase-IV (DDPIV/CD26) on LSCs. CD26 is expressed on CML LSCs as identified by the ability of BCR::ABL1+CD34+CD38−CD26+ LSCs to repopulate immunocompromised mice with CML, compared with CD26− cells. The engraftment of CD26+ LSC was more diffuse in the BM which has been attributed to CD26-mediated CXCL12 cleavage and disruption to chemotactic behaviour [32]. The difference in engraftment of short-term- (ST-) and long-term (LT)-HSCs has been partially attributed to CD26 activity [33].
Identification of peripheral blood (PB) CD34+CD38−CD26+ cells was found to be diagnostic for CML in patients with a suspicious leukocytosis [34], supporting previous evidence and highlighting CD26 as a CML LSC biomarker. This has been confirmed by a prospective clinical study in which CD26 stratified suspected haematological malignancies into CML and non-CML [35].
CD34+CD38−CD26+ PB cells were correlated with BCR::ABL1 transcript in early CP-CML [36]. In contrast, interim analyses of the PROSPECTIVE FLOWERS study revealed that PB BCR::ABL1+ measurement was not associated with CD26+ LSC levels after initiation of TKI therapy, although CD26+ LSC levels at diagnosis could predict subsequent responses to TKIs [37]. The correlation of CD26+ LSC numbers in the PB and BM [38] may reflect their disrupted BM-homing ability, but also support its utility as a predictive biomarker.
Gliptins antagonise CD26 enzymatic activity and are clinically used in resistant diabetes mellitus, due to the catalytic action of CD26 on incretins. Gliptins can also impair CD26-mediated stromal interactions in vitro [32]. Pre-exposure of CD26+ LSC to vildagliptin was limited their engraftment in mice [32], although another study found no effect of vildagliptin on CML engraftment (± imatinib) when mice were treated in vivo [39]. However, this latter model selected only CD34+ cells and there may have been sub-optimal targeting of CD26 LSCs at this vildagliptin dose in vivo. There may also be inter-species differences between murine and human stroma.
In addition to gliptins, CD26 enzymatic activity was effectively blocked in HSCs by the small molecule inhibitor diprotin A in in vivo models of the hematopoietic system [33], but is not utilised clinically. Additionally, use of CD26-targeting immunoliposomes loaded with the BCL-2 inhibitor venetoclax showed promising anti-LSC effects in vitro [40], and may worthy of further exploration in vivo.
CXCR2 Signalling and TNF-α
An in vivo study demonstrated the upregulation of Cxcl1 on murine stromal cells (akin to human perivascular MSCs) in CML, with upregulation of LSC Cxcr2, the Cxcl1 receptor. This interaction maintained self-renewal in LSCs, but not HSCs, and was mediated by TNF-α signalling [41]. In humans, IL-8/CXCL8 binds to CXCR2 and is the equivalent to murine Cxcl1. The differential dependence of HSCs and LSCs on IL-8 signalling may provide a therapeutic window in CML. In AML, the blockade of IL-8 binding to CXCR2 using a novel experimental inhibitor (NCI34255) led to a reversal of therapy resistance [42], highlighting a means of therapeutically targeting IL-8/CXCR2 signalling in CML.
Monoclonal antibody (mAb) targeting of TNF-α with infliximab enhanced the effect of TKIs against LSCs, although IFN-γ-modulating effects of infliximab may be contributing to the observed effects [43]. Alternatively, CXCR2 signalling in CML may function via mTOR and c-Myc [44], identifying other therapeutic possibilities.
Adhesion Mechanisms
Evidence suggests that LSC quiescence is induced/maintained by LSC CD44 binding to vascular E-selectin, increasing therapy resistance. Godavarthy et al. elucidated that CD44 is negatively regulated transcriptionally by SCL/TAL1 within BCR::ABL1+ LSCs and that imatinib led to CD44 upregulation by SCL/TAL1 [45]. Baykal-Kӧse et al. demonstrated that CML cells upregulate CD44 to adapt phenotypically to TKI-induced stress [46]. Using a CML murine engraftment model, combined E-selectin inhibitor GMI-1217 (uproleselan) and imatinib led to improved survival and reduced BM endothelial adherence, compared to imatinib alone, supporting the hypothesis that E-selectin mediated adhesion by CML LSCs (via CD44) is an imatinib resistance mechanism [45]. A phase I/II trial of GMI-1217 in relapsed/refractory AML (NCT02306291) demonstrated an acceptable safety profile and promising efficacy, in combination with chemotherapy [47]. A phase III trial of GMI-1217 in a similar context is ongoing (NCT03616470) [48], which may support the clinical development of GMI-1217 for CML. E-selectin antagonist GMI-1070 was clinically safe in a phase III trial for sickle cell disease [49] but has not been trialled in hematologic malignancies. Other in vitro evidence suggests that CD44 mediates resistance to imatinib downstream of AF1q — a putative BCR::ABL1-independent oncogene [50].
Plant-derived verbascoside can block CD44 dimerisation [51], and it was shown to induce apoptosis in a model of CML, possibly by mediating p38-MAPK/JNK and Caspase-3 signalling, although the role of CD44 was not explored here [52]. CD44 is highly expressed within normal, CML and AML CD34+CD38+ and CD34+CD38− BM cells [53•], likely making it unsuitable as a CML LSC biomarker and a cancer-specific therapeutic target, but downstream signalling may be targetable.
Previous reports suggested CML LSCs were more dependent on L-selectin (CD62L) for BM homing and disease engraftment [54]. Soluble CD62L is elevated in CP-CML patients and reduced following imatinib treatment [55], suggesting it may have value as a marker of treatment response. In addition, soluble and T cell expression of CD62L may predict responses to TKIs in CML [56], indicating this marker may be more related to T cell responses than the CML cells themselves. Plasma levels of soluble adhesion molecule VCAM-1 (CD106) may also reflect responses to TKI [57].
IL1RAP and CD36
Landberg et al. have described the expression of LSC markers IL1RAP and CD36 which can separate BCR::ABL1+ from BCR::ABL1− populations and predict responses to TKI [58, 59]. IL1RAP is, as part of the IL-1 receptor (IL-1R) complex, responsive to cytokines such as IL-1β and IL-33 and may function via NFκB, as shown in K562 cells [60]. It is also expressed on BM MSCs. In vivo data have shown that chimeric antigen receptor T (CAR-T) cells targeting IL1RAP may be a viable option to eliminate MRD/LSCs and ‘cure’ CML [61].
IL1RAP+ LSCs can be separated into two subsets by CD36 expression [59]. CD36 is a fatty acid transporter which, in HSCs, has been shown to permit entry to the cell cycle in situations of emergency haematopoiesis (e.g., during infection) [62]. Previous evidence has suggested that CD36+ CML LSCs mediate chemoresistance via increased fatty acid oxidation, and home to adipose tissue niches within the BM [63]. Other preliminary data suggests that CD36 may not be essential for healthy hematopoietic cells [64], highlighting another potential therapeutic window.
CD93
Kinstrie et al. identified a novel population of primitive Lin−CD34+CD38−CD90+ LSCs expressing the transmembrane receptor CD93 which persisted in CML patients despite extended TKI treatment [65••]. Elsewhere, CD93 expression was found on CML LSCs, co-expressed with such markers as CD25 and IL1RAP, but also on some HSC populations [53•]. However, Riether et al. demonstrated that although both LSCs and normal HSCs expressed CD93, it was only required for self-renewal capacity in LSCs. In addition, the clinically-approved anti-sickness drug metoclopramide was found to inhibit CD93 and downstream signalling, therefore blocking LSC activity in vivo [66•]. This has not yet been evaluated clinically in CML.
Exosomal Crosstalk
Exosomes are cell-derived lipid nanoparticles containing genomic material which are involved in cell–cell communication. BCR::ABL1-containing exosomes can be detected in CP-CML patient plasma [67] and their release from CML cells can stimulate pro-survival signalling from BM MSCs [68]. CML cells can remodel the BME to facilitate a leukaemia-favourable niche using exosomes. For example, micro-RNA (miRNA) exosomal transfer to BM MSCs by CML cells was shown to inhibit the normal osteogenic function of these MSCs [69]. In the reverse direction, MSC-derived exosomes can promote CML cell survival and TKI resistance, putatively through cell extrinsic means (e.g., enhanced angiogenesis around the niche) [70]. Exosomal membrane proteins linked to TKI resistance, such as CD36, have been identified in CML and may represent candidate biomarkers for further development [71].
Exosomal communication can also impact on other immune populations within the BME. Ex vivo exposure of cord blood T cells to CML-derived exosomes led to upregulation of the exhaustion marker PD-1, which can be bound by its ligand PD-L1 to inhibit T cell activation. In addition, skewing towards a Treg phenotype was observed in this model [72], suggesting exosome-induced alteration of T cells favours immunosuppressive phenotypes which are permissive of CML leukemogenesis. Similarly, CML-derived exosomes can increase levels of anti-inflammatory IL-10 and immune cell-blocking ROS in the BME, in addition to skewing macrophages away from anti-tumour phenotypes [73].
T Cell Exhaustion
The concept of T cell exhaustion refers to the impairment of T cell effector function which often arises during malignancy due to chronic antigen exposure, although definitions vary [74]. T cell expression of exhaustion markers such as PD-1 [75], TIM-3, and LAG-3 [76] have been demonstrated to reflect the leukaemia burden in patients, and decrease during effective responses to TKI therapy. In addition, immunosuppressive Tregs have been shown to reflect leukaemia burden [76]. As such, reversal of leukaemia-induced T cell exhaustion may be a therapeutic opportunity. Inhibition of TIM-3 ± PD-1 or LAG-3 has been described as effective against solid tumours and there is particular interest into applying these in AML [77]. There is an ongoing phase III trial in chronic myelomonocytic leukaemia (CMML) — a rare disease which is related, but distinct, to CML — investigating the efficacy of anti-TIM-3 antibody sabstolimab on overall survival.
Modulating PD-1/PD-L1 Signalling
PD-1/PD-L1 signalling is a known mechanism of T cell suppression. PD-1 (CD279) is typically expressed by T and B cells, while its ligand PD-L1 is expressed on a wide number of cell types, and often on tumour cells as a means of immune escape [78].
PD-L1-carrying exosomes derived from BM MSCs transfer to tumour cells of varying phenotype in vivo [79], demonstrating a mechanism by which MSCs can encourage immune escape by oncogenic cells. CML cells may also influence innate immune populations such that they express higher levels of PD-L1 [80], potentially as a mechanism of T-cell anti-tumour suppression.
Inhibition of the PD-1/PD-L1 axis is established as an anti-leukemic strategy. There is an ongoing trial investigating the safety and efficacy of combined anti-PD-1 antibody pembrolizumab with TKIs in CP-CML [81•]. Other means of inhibition may counteract PD-L1 activity. BRD4 degradation was found to reduce PD-L1 upregulation on CML LSCs, which is attributed to both inhibition of IFN-γ-mediated upregulation and because the PDL1 gene is a target of BRD4 [82]. Pharmacological inhibition of inflammatory mediators IRAK1 and IRAK4 may also reduce PD-L1 expression on CML LSCs [83].
Hypoxia and PI3K
Chronic hypoxia within the BME has been well-studied in the context of AML LSC pathogenesis. CML cells are sensitive to hypoxia [84], and the critical regulator of hypoxia responses, hypoxia-inducible factor 1α (HIF1α), is essential for CML LSC survival in the BME [85]. Recent evidence demonstrated that BP-CML cells displayed an altered balance of available ROS and antioxidant species in the cell — or redox balance — due to a perturbed synergism between HIF1α and opposing Notch1 [86]. Metabolic rewiring of LSCs in response to the unique BME conditions, such as chronic hypoxia, modulates the cells’ responses to therapy and offers myriad of therapeutic targeting opportunities; this topic is covered elsewhere [87].
Inhibition of the PI3 kinase (PI3K) pathway may be effective against the LSC-BME interactome, particularly the hypoxic context. Oxidative stress induced by hypoxia was shown to be mitigated by adaptive PI3K signalling in ex vivo murine BM-MSCs, downstream of leukaemia initiating factor (LIF) [88], highlighting niche-targeting opportunities.
Simultaneous inhibition of PI3K (± mTOR) signalling with copanlisib (or BEZ235, respectively) was shown to effectively block osteoblast proliferation and prevent osteoblast-mediated resistance to TKIs in CML LSCs [89]. While this suggests that PI3K is important to LSC-extrinsic means of TKI resistance, other evidence has shown that CML cell intrinsic BCR::ABL1 signalling via the PI3K/AKT/mTOR axis also drives TKI resistance/cell survival, via other players including epidermal growth factor receptor kinase substrate 8 (EPS8) [90] and c-Myc [91]. A clinical trial of copanlisib in acute relapsed/refractory leukaemias (but not CML) was well tolerated at lower doses [92].
Inhibition of Janus Kinases
JAK/STAT signalling is an intracellular regulator of hematopoietic cell function [93] and has been explored as a therapeutic target within TKI-resistant CML. The JAK1/2 inhibitor ruxolitinib is clinically approved for myeloproliferative neoplasms and was shown to effectively impair repopulation of immunodeficient mice by self-renewing CML HSPCs, attributed to JAK/STAT5 inhibition primarily [94]. JAK2 inhibition with ruxolitinib could also impair CML cell immune evasion by preventing the BCR::ABL1-independent MHC-II downregulation that has been observed in CML HSPCs [95]. Zhang et al. demonstrated in vivo that BM-MSC-derived Il-7 was a mechanism of BCR::ABL1-independent JAK1/STAT5-mediated TKI resistance in CML cell lines [96]. These data underpin the rationale for combined TKI and JAK inhibition to overcome therapy resistance.
Combination therapy of ruxolitinib and nilotinib was explored in a recent phase I trial which reported promising efficacy of the combination [97], although another ruxolitinib/TKI combination trial in CML (NCT01751425) was stopped early due to lack of efficacy (data not published). Trials targeting the BME in CML are summarised in Table 1, and a schematic representation of targeting opportunities in the BME is shown in Fig. 1B.
Other Secreted Factors
Other secreted factors within the BME have more recently been highlighted in CML pathogenesis. Himburg et al. found that pleiotrophin, which is normally produced by BM-MSCs, is upregulated in CML HSPCs downstream of BCR::ABL1 induction in vivo and leads to cell self-maintenance, independently of MSCs [98]. Successful inhibitors of pleiotrophin have not been described in recent years. Separately, a cytokine screen of CML patient samples identified myostatin propeptide (MSTNpp) to significantly stimulate CD34+CD38low proliferation in vitro, independently of its known ligand myostatin. In addition, MSTNpp plasma levels were found to be the same in CML and non-CML patients, suggesting unsuitability as a biomarker, although it could be investigated as a therapeutic target. This study also identified soluble CD14 (Scd14), IL-21, IL-13 variant (IL-13v), and CCL28 as important for CML CD34+CD38low expansion [99] and should be investigated further. A summary of putative and established biomarkers for CML are summarised in Table 2.
Treatment-Free Remission
CP-CML patients on TKIs who achieve prolonged deep molecular remission (DMR; BCR::ABL1 transcript ≤ 0.01% on the International Scale [IS]) can attempt to stop TKIs permanently without relapse, termed ‘treatment-free remission’ (TFR). Long-term TFR rates of up to 70% have been reported clinically [104]. However, only a minority of patients achieve DMR and hence can attempt TFR. Hypotheses as to why only some patients sustain TFR often focus on the anti-leukemic role of the host immune system, particularly within the BME.
Some evidence has focused on natural killer (NK) cell populations in TFR. A recent study found that TFR could be predicted by expression of NK receptors NKG2A and NKG2D, which enable stronger priming of NK cells for cytotoxic responses [105]. This is in agreement with another recent study [106] but contrasts others, which either found no differences in NKG2A/NKG2D expression comparing TFR vs. relapsing patients [107] or that elevated NK cells were associated with relapse [108]. Single-cell analyses have shown NK cells in TFR patients display a more activated phenotype than healthy controls, suggesting the importance of cytotoxic NK responses in controlling BCR::ABL1+ residual cells [109••].
Many of these studies assessed PB NK cells which may not capture any differential phenotype of BME-derived NK cells. In CML patient BM, but not PB, a terminally mature CD57+ subset was significantly higher than in healthy controls, indicating a possible role for BME influences on the differentiation status of these NK cells in CML specifically [110]. This is reflective of previous observations made in PB [75]; however, the importance of CD57.+ NK cells to TFR is unclear. The use of expanded NK cell immunotherapy to eliminate MRD in CML is being explored clinically [111] and may represent an option for adjuvant therapy in patients attempting TFR. Other novel NK-based therapeutics include anti-leukemic mAbs which induce targeted NK antibody-mediated responses and CAR-NK cell therapy, neither of which is described for CML, but for other malignancies, as reviewed by Allison et al. [112]
IFN-α as an Adjuvant Therapy
Interferon alpha (IFN-α) was a mainstay of treatment for CP-CML prior to the introduction of TKIs into standard practice [113]. Combination therapy of IFN-α and TKIs has recently garnered interest as a means of achieving DMR more rapidly than TKIs alone (discussed by Talpaz et al. [114]). Some evidence suggests IFN-α could be combined with later generation TKIs for the effective treatment of BP-CML [115].
Limited evidence suggests IFN-α is an effective adjuvant for sustained TFR with short TKI duration, although one-third of patients did not tolerate IFN-α side effects in this study [116]. In another study, CML patients with DMR who took IFN-α were also more likely to stay in TFR at 18 months post-TKI cessation, although the rate of TFR in the non-IFN-α group was considerably lower than reported in other trials [117], suggesting some differences in the cohort/methodologies to other TFR trials.
Patients attempting TFR (in DMR) who had been treated with both IFN-α and TKIs prior to discontinuation showed a stronger memory-like phenotype in the NK cell compartment (defined by NKG2C+) and a Th1-skewed T cell response [118•]. Proportions of CD56bright NK cells were reported to increase in patients attempting TFR who also received IFN-α therapy after TKI discontinuation, as opposed to those who did not [119]. It seems counterintuitive that CD56bright NK cells, which are weakly cytolytic, are elevated in patients who sustain TFR, based on previous assumptions about the anti-tumour role of cytotoxic NK cells. Another study found that CML patients co-treated with IFN-α and TKI had higher PB populations of immune cells typically seen as ‘immunosuppressive’ including CD56bright NK cells and granulocytic myeloid-derived suppressor cells (Gr-MDSCs) [120], which again conflicts with the idea that IFN-α enhances sustained TFR. Further characterisation of immune function in TFR is required to complement these studies.
Conclusion
While TKIs continue to be effective for long-term management of CP-CML, the achievement of sustained DMR is a challenge for many patients. Additionally, a shift in focus to maintaining long-term TFR stresses the need to eliminate MRD and the BCR::ABL1+ LSC in CML. Newer evidence highlights the protective role of BM niches towards the LSC and the complex immune microenvironment(s) which facilitate TKI resistance, therefore identifying novel therapeutic vulnerabilities. Ongoing clinical investigation explores the feasibility of some approaches in CML and other haematological malignancies which manipulate the BME. Overall, bringing modern CML therapy beyond TKIs alone, increasing the number of patients that can attempt and successfully maintain TFR.
Data Availability
There is no research data within this article for which availability is required.
Abbreviations
- BM:
-
Bone marrow
- BME:
-
Bone marrow microenvironment
- BP-CML:
-
Blast phase chronic myeloid leukaemia
- CAR:
-
CXCL12-abundant reticular
- CML:
-
Chronic myeloid leukaemia
- CMML:
-
Chronic myelomonocytic leukaemia
- CP-CML:
-
Chronic phase chronic myeloid leukaemia
- DMR:
-
Deep molecular remission
- DPPIV:
-
Dipeptidylpeptidase-IV
- Gr-MDSC:
-
Granulocytic myeloid-derived suppressor cell
- HIF1α:
-
Hypoxia-inducible factor 1α
- HSC:
-
Hematopoietic stem cell
- HSPC:
-
Hematopoietic stem and progenitor cell
- IL-1R:
-
IL-1 receptor
- ILK:
-
Integrin-linked kinase
- IS:
-
International scale
- LepR:
-
Leptin receptor
- LIF:
-
Leukaemia initiating factor
- LSC:
-
Leukaemia stem cell
- LT-HSC:
-
Long-term hematopoietic stem cell
- mAb:
-
Monoclonal antibody
- MSC:
-
mesenchymal stem/stromal cell
- MSTNpp:
-
myostatin propeptide
- N-cad:
-
N-cadherin
- Nes:
-
nestin
- NG2:
-
neuron/glia antigen 2
- NK:
-
natural killer
- PB:
-
peripheral blood
- PI3K:
-
PI3 kinase
- qRT-PCR:
-
quantitative real-time PCR
- ROS:
-
reactive oxygen species
- ST-HSC:
-
short-term hematopoietic stem cell
- TFR:
-
treatment-free remission
- TKI:
-
tyrosine kinase inhibitor
- Treg:
-
regulatory T cell
References
Papers of particular interest, published recently, have been highlighted as: • Of importance •• Of major importance
Laurenti E, Göttgens B. From haematopoietic stem cells to complex differentiation landscapes. Nature. 2018;553(7689):418–26. https://doi.org/10.1038/nature25022.
Itkin T, Gur-Cohen S, Spencer JA, Schajnovitz A, Ramasamy SK, Kusumbe AP, et al. Distinct bone marrow blood vessels differentially regulate haematopoiesis. Nature. 2016;532(7599):323–8. https://doi.org/10.1038/nature17624.
Asada N, Kunisaki Y, Pierce H, Wang Z, Fernandez NF, Birbrair A, et al. Differential cytokine contributions of perivascular haematopoietic stem cell niches. Nat Cell Biol. 2017;19(3):214–23. https://doi.org/10.1038/ncb3475.
Zhao M, Tao F, Venkatraman A, Li Z, Smith SE, Unruh J, et al. N-Cadherin-expressing bone and marrow stromal progenitor cells maintain reserve hematopoietic stem cells. Cell Rep. 2019;26(3):652-69.e6. https://doi.org/10.1016/j.celrep.2018.12.093.
Kunisaki Y, Bruns I, Scheiermann C, Ahmed J, Pinho S, Zhang D, et al. Arteriolar niches maintain haematopoietic stem cell quiescence. Nature. 2013;502(7473):637–43. https://doi.org/10.1038/nature12612.
Luz-Crawford P, Kurte M, Bravo-Alegría J, Contreras R, Nova-Lamperti E, Tejedor G, et al. Mesenchymal stem cells generate a CD4+CD25+Foxp3+ regulatory T cell population during the differentiation process of Th1 and Th17 cells. Stem Cell Res Ther. 2013;4(3):65. https://doi.org/10.1186/scrt216.
Sugiyama T, Kohara H, Noda M, Nagasawa T. Maintenance of the hematopoietic stem cell pool by CXCL12-CXCR4 chemokine signaling in bone marrow stromal cell niches. Immunity. 2006;25(6):977–88. https://doi.org/10.1016/j.immuni.2006.10.016.
Zhang Y, Dépond M, He L, Foudi A, Kwarteng EO, Lauret E, et al. CXCR4/CXCL12 axis counteracts hematopoietic stem cell exhaustion through selective protection against oxidative stress. Sci Rep. 2016;6(1):37827. https://doi.org/10.1038/srep37827.
Gomariz A, Helbling PM, Isringhausen S, Suessbier U, Becker A, Boss A, et al. Quantitative spatial analysis of haematopoiesis-regulating stromal cells in the bone marrow microenvironment by 3D microscopy. Nat Commun. 2018;9(1):2532. https://doi.org/10.1038/s41467-018-04770-z This applies state-of-the-art technology to capture the spatial resolution of the BME.
Himburg HA, Termini CM, Schlussel L, Kan J, Li M, Zhao L, et al. Distinct bone marrow sources of pleiotrophin control hematopoietic stem cell maintenance and regeneration. Cell Stem Cell. 2018;23(3):370-81.e5. https://doi.org/10.1016/j.stem.2018.07.003.
Winkler IG, Barbier V, Nowlan B, Jacobsen RN, Forristal CE, Patton JT, et al. Vascular niche E-selectin regulates hematopoietic stem cell dormancy, self renewal and chemoresistance. Nat Med. 2012;18(11):1651–7. https://doi.org/10.1038/nm.2969.
Hur J, Choi J-I, Lee H, Nham P, Kim T-W, Chae C-W, et al. CD82/KAI1 maintains the dormancy of long-term hematopoietic stem cells through interaction with DARC-expressing macrophages. Cell Stem Cell. 2016;18(4):508–21. https://doi.org/10.1016/j.stem.2016.01.013.
Bruns I, Lucas D, Pinho S, Ahmed J, Lambert MP, Kunisaki Y, et al. Megakaryocytes regulate hematopoietic stem cell quiescence through CXCL4 secretion. Nat Med. 2014;20(11):1315–20. https://doi.org/10.1038/nm.3707.
Zhao M, Perry JM, Marshall H, Venkatraman A, Qian P, He XC, et al. Megakaryocytes maintain homeostatic quiescence and promote post-injury regeneration of hematopoietic stem cells. Nat Med. 2014;20(11):1321–6. https://doi.org/10.1038/nm.3706.
Kajiume T, Kawahara Y, Yuge L, Kobayashi M. Osteoblastic adherence regulates hematopoietic stem cell self-renewal and differentiation: a conceptional in vitro and in vivo study. Stem Cell Investig. 2021;8:21. https://doi.org/10.21037/sci-2021-019.
Ren R. Mechanisms of BCR–ABL in the pathogenesis of chronic myelogenous leukaemia. Nat Rev Cancer. 2005;5(3):172–83. https://doi.org/10.1038/nrc1567.
Apperley JF. Chronic myeloid leukaemia. Lancet. 2015;385(9976):1447–59. https://doi.org/10.1016/s0140-6736(13)62120-0.
Holyoake T, Jiang X, Eaves C, Eaves A. Isolation of a highly quiescent subpopulation of primitive leukemic cells in chronic myeloid leukemia. Blood. 1999;94(6):2056–64.
Holyoake TL, Vetrie D. The chronic myeloid leukemia stem cell: stemming the tide of persistence. Blood. 2017;129(12):1595–606. https://doi.org/10.1182/blood-2016-09-696013.
Corbin AS, Agarwal A, Loriaux M, Cortes J, Deininger MW, Druker BJ. Human chronic myeloid leukemia stem cells are insensitive to imatinib despite inhibition of BCR-ABL activity. J Clin Invest. 2011;121(1):396–409. https://doi.org/10.1172/jci35721.
Agarwal P, Isringhausen S, Li H, Paterson AJ, He J, Gomariz Á, et al. Mesenchymal niche-specific expression of Cxcl12 controls quiescence of treatment-resistant leukemia stem cells. Cell Stem Cell. 2019;24(5):769-84.e6. https://doi.org/10.1016/j.stem.2019.02.018.
Agarwal P, Isringhausen S, Li H, Paterson AJ, He J, Nagasawa T, et al. Role of CXCL12-expressing mesenchymal stromal cell niches in maintaining treatment-resistant leukemia stem cells. Blood. 2018;132:1291. https://doi.org/10.1182/blood-2018-99-117762.
Frietsch JJ, Kastner C, Grunewald TG, Schweigel H, Nollau P, Ziermann J, et al. LASP1 is a novel BCR-ABL substrate and a phosphorylation-dependent binding partner of CRKL in chronic myeloid leukemia. Oncotarget. 2014;5(14):5257–71. https://doi.org/10.18632/oncotarget.2072.
Wang Y, Miao H, Li W, Yao J, Sun Y, Li Z, et al. CXCL12/CXCR4 axis confers adriamycin resistance to human chronic myelogenous leukemia and oroxylin A improves the sensitivity of K562/ADM cells. Biochem Pharmacol. 2014;90(3):212–25. https://doi.org/10.1016/j.bcp.2014.05.007.
Liu P, Ma D, Yu Z, Zhe N, Ren M, Wang P, et al. Overexpression of heme oxygenase-1 in bone marrow stromal cells promotes microenvironment-mediated imatinib resistance in chronic myeloid leukemia. Biomed Pharmacother. 2017;91:21–30. https://doi.org/10.1016/j.biopha.2017.04.076.
Herrmann AB, Müller ML, Orth MF, Müller JP, Zernecke A, Hochhaus A, et al. Knockout of LASP1 in CXCR4 expressing CML cells promotes cell persistence, proliferation and TKI resistance. J Cell Mol Med. 2020;24(5):2942–55. https://doi.org/10.1111/jcmm.14910.
Butt E, Stempfle K, Lister L, Wolf F, Kraft M, Herrmann AB, et al. Phosphorylation-dependent differences in CXCR4-LASP1-AKT1 interaction between breast cancer and chronic myeloid leukemia. Cells. 2020;9(2). https://doi.org/10.3390/cells9020444.
De Clercq E. Mozobil® (Plerixafor, AMD3100), 10 years after its approval by the US Food and Drug Administration. Antivir Chem Chemother. 2019;27:2040206619829382. https://doi.org/10.1177/2040206619829382.
Borthakur G, Zeng Z, Cortes JE, Chen HC, Huang X, Konopleva M, et al. Phase 1 study of combinatorial sorafenib, G-CSF, and plerixafor treatment in relapsed/refractory, FLT3-ITD-mutated acute myelogenous leukemia patients. Am J Hematol. 2020;95(11):1296–303. https://doi.org/10.1002/ajh.25943.
Weisberg EL, Sattler M, Azab AK, Eulberg D, Kruschinski A, Manley PW, et al. Inhibition of SDF-1-induced migration of oncogene-driven myeloid leukemia by the L-RNA aptamer (Spiegelmer), NOX-A12, and potentiation of tyrosine kinase inhibition. Oncotarget; Vol 8, No 66. 2017.
Halama N, Prüfer U, Froemming A, Beyer D, Eulberg D, Jungnelius JU, et al. 613P - Phase I/II study with CXCL12 inhibitor NOX-A12 and pembrolizumab in patients with microsatellite-stable, metastatic colorectal or pancreatic cancer. Annals of Oncology. 2019;30:v231. https://doi.org/10.1093/annonc/mdz246.090.
Herrmann H, Sadovnik I, Cerny-Reiterer S, Rülicke T, Stefanzl G, Willmann M, et al. Dipeptidylpeptidase IV (CD26) defines leukemic stem cells (LSC) in chronic myeloid leukemia. Blood. 2014;123(25):3951–62. https://doi.org/10.1182/blood-2013-10-536078.
Al-Amoodi AS, Li Y, Al-Ghuneim A, Allehaibi H, Isaioglou I, Esau LE, et al. Refining the migration and engraftment of short-term and long-term HSCs by enhancing homing-specific adhesion mechanisms. Blood Adv. 2022;6(15):4373–91. https://doi.org/10.1182/bloodadvances.2022007465.
Raspadori D, Pacelli P, Sicuranza A, Abruzzese E, Iurlo A, Cattaneo D, et al. Flow cytometry assessment of CD26(+) leukemic stem cells in peripheral blood: a simple and rapid new diagnostic tool for chronic myeloid leukemia. Cytometry B Clin Cytom. 2019;96(4):294–9. https://doi.org/10.1002/cyto.b.21764.
Rahman K, Singh MK, Chandra D, Gupta R, Sarkar MK, Gupta P, et al. CD26 expression on circulating CD34+/CD38- progenitor population is a specific and reliable tool for the rapid flow cytometric diagnosis of chronic myeloid leukemia—a single-center validation study. Int J Lab Hematol. 2022;44(3):524–30. https://doi.org/10.1111/ijlh.13826.
Ebian HF, Abdelnabi AM, Abdelazem AS, Khamis T, Fawzy HM, Hussein S. Peripheral blood CD26 positive leukemic stem cells as a possible diagnostic and prognostic marker in chronic myeloid leukemia. Leuk Res Rep. 2022;17:100321. https://doi.org/10.1016/j.lrr.2022.100321.
Bocchia M, Sicuranza A, Pacelli P, Iurlo A, Abruzzese E, Galimberti S, et al. Peripheral blood CD26+ leukemia stem cells monitoring in chronic myeloid leukemia patients from diagnosis to response to TKIs: interim results of a multicenter prospective study (PROSPECTIVE FLOWERS). Blood. 2020;136(Supplement 1):45–6. https://doi.org/10.1182/blood-2020-139306.
Sharma P, Sachdeva MUS, Naseem S, Sreedharanunni S, Das R, Malhotra P, et al. Identification of peripheral blood CD26+ leukemic stem cells has a potential role in the rapid diagnosis of chronic myeloid leukemia. Int J Lab Hematol. 2022;44(3):518–23. https://doi.org/10.1111/ijlh.13807.
Willmann M, Sadovnik I, Eisenwort G, Entner M, Bernthaler T, Stefanzl G, et al. Evaluation of cooperative antileukemic effects of nilotinib and vildagliptin in Ph(+) chronic myeloid leukemia. Exp Hematol. 2018;57:50-9.e6. https://doi.org/10.1016/j.exphem.2017.09.012.
Houshmand M, Garello F, Stefania R, Gaidano V, Cignetti A, Spinelli M, et al. Targeting chronic myeloid leukemia stem/progenitor cells using Venetoclax-loaded immunoliposome. Cancers (Basel). 2021;13(6). https://doi.org/10.3390/cancers13061311.
Agarwal P, Li H, Choi K, Hueneman K, He J, Welner RS, et al. TNF-α-induced alterations in stromal progenitors enhance leukemic stem cell growth via CXCR2 signaling. Cell Rep. 2021;36(2):109386. https://doi.org/10.1016/j.celrep.2021.109386.
Vijay V, Miller R, Vue GS, Pezeshkian MB, Maywood M, Ast AM, et al. Interleukin-8 blockade prevents activated endothelial cell mediated proliferation and chemoresistance of acute myeloid leukemia. Leuk Res. 2019;84:106180. https://doi.org/10.1016/j.leukres.2019.106180.
Herrmann O, Kuepper MK, Bütow M, Costa IG, Appelmann I, Beier F, et al. Infliximab therapy together with tyrosine kinase inhibition targets leukemic stem cells in chronic myeloid leukemia. BMC Cancer. 2019;19(1):658. https://doi.org/10.1186/s12885-019-5871-2.
Kim JH, Lee SJ, Kang KW, Lee BH, Park Y, Kim BS. CXCR2, a novel target to overcome tyrosine kinase inhibitor resistance in chronic myelogenous leukemia cells. Biochem Pharmacol. 2021;190:114658. https://doi.org/10.1016/j.bcp.2021.114658.
Godavarthy PS, Herkt S, Hayduk N, Weissenberger E, Manavski Y, Lucas T, et al. The vascular bone marrow niche influences outcome in chronic myeloid leukemia. Blood. 2018;132:3846. https://doi.org/10.1182/blood-2018-99-112398.
Baykal-Köse S, Acikgoz E, Yavuz AS, GönülGeyik Ö, Ateş H, Sezerman OU, et al. Adaptive phenotypic modulations lead to therapy resistance in chronic myeloid leukemia cells. PLoS One. 2020;15(2):e0229104. https://doi.org/10.1371/journal.pone.0229104.
DeAngelo DJ, Jonas BA, Liesveld JL, Bixby DL, Advani AS, Marlton P, et al. Phase 1/2 study of uproleselan added to chemotherapy in patients with relapsed or refractory acute myeloid leukemia. Blood. 2022;139(8):1135–46. https://doi.org/10.1182/blood.2021010721.
DeAngelo DJ, Erba HP, Jonas BA, O'Dwyer M, Marlton P, Huls GA, et al. A phase III trial to evaluate the efficacy of uproleselan (GMI-1271) with chemotherapy in patients with relapsed/refractory acute myeloid leukemia. Journal of Clinical Oncology. 2019;37(15_suppl):TPS7066-TPS. https://doi.org/10.1200/JCO.2019.37.15_suppl.TPS7066.
Dampier CD, Telen MJ, Wun T, Brown C, Desai PC, El Rassi F, et al. A randomized clinical trial of the efficacy and safety of Rivipansel for sickle cell vaso-occlusive crisis (VOC). Blood. 2022. https://doi.org/10.1182/blood.2022015797.
Li W, Ji M, Lu F, Pang Y, Dong X, Zhang J, et al. Novel AF1q/MLLT11 favorably affects imatinib resistance and cell survival in chronic myeloid leukemia. Cell Death Dis. 2018;9(9):855. https://doi.org/10.1038/s41419-018-0900-7.
Wang C, Wang Z, Chen C, Fu X, Wang J, Fei X, et al. A low MW inhibitor of CD44 dimerization for the treatment of glioblastoma. Br J Pharmacol. 2020;177(13):3009–23. https://doi.org/10.1111/bph.15030.
Akgun-Cagliyan G, Cort-Donmez A, Kilic-Toprak E, Altintas F. Verbascoside potentiates the effect of tyrosine kinase inhibitors on the induction of apoptosis and oxidative stress via the Abl-mediated MAPK signalling pathway in chronic myeloid leukaemia. Exp Ther Med. 2022;24(2):514. https://doi.org/10.3892/etm.2022.11441.
Herrmann H, Sadovnik I, Eisenwort G, Rülicke T, Blatt K, Herndlhofer S, et al. Delineation of target expression profiles in CD34+/CD38- and CD34+/CD38+ stem and progenitor cells in AML and CML. Blood Adv. 2020;4(20):5118-32https://doi.org/10.1182/bloodadvances.2020001742 This study integrates findings on multiple differing putative LSC surface markers including CD93, CD26, CD25, and IL1RAP.
Krause DS, Lazarides K, Lewis JB, von Andrian UH, Van Etten RA. Selectins and their ligands are required for homing and engraftment of BCR-ABL1+ leukemic stem cells in the bone marrow niche. Blood. 2014;123(9):1361–71. https://doi.org/10.1182/blood-2013-11-538694.
Elkholy MM, Fahmi MW, El-Haggar SM. Dynamic changes in the levels of sCD62L and SPARC in chronic myeloid leukaemia patients during imatinib treatment. J Clin Pharm Ther. 2022. https://doi.org/10.1111/jcpt.13759.
Sopper S, Mustjoki S, White D, Hughes T, Valent P, Burchert A, et al. Reduced CD62L expression on T cells and increased soluble CD62L levels predict molecular response to tyrosine kinase inhibitor therapy in early chronic-phase chronic myelogenous leukemia. J Clin Oncol. 2017;35(2):175–84. https://doi.org/10.1200/jco.2016.67.0893.
Abdel Hammed MR, Ahmed YA, Adam EN, Bakry R, Elnaggar MG. sVCAM-1, and TGFβ1 in chronic phase, chronic myeloid leukemia patients treated with tyrosine kinase inhibitors. Egypt J Immunol. 2022;29(4):163–73.
Landberg N, Hansen N, Askmyr M, Ågerstam H, Lassen C, Rissler M, et al. IL1RAP expression as a measure of leukemic stem cell burden at diagnosis of chronic myeloid leukemia predicts therapy outcome. Leukemia. 2016;30(1):255–8. https://doi.org/10.1038/leu.2015.135.
Landberg N, von Palffy S, Askmyr M, Lilljebjörn H, Sandén C, Rissler M, et al. CD36 defines primitive chronic myeloid leukemia cells less responsive to imatinib but vulnerable to antibody-based therapeutic targeting. Haematologica. 2018;103(3):447–55. https://doi.org/10.3324/haematol.2017.169946.
de Boer B, Sheveleva S, Apelt K, Vellenga E, Mulder AB, Huls G, et al. The IL1-IL1RAP axis plays an important role in the inflammatory leukemic niche that favors acute myeloid leukemia proliferation over normal hematopoiesis. Haematologica. 2020;106(12):3067–78. https://doi.org/10.3324/haematol.2020.254987.
Warda W, Larosa F, Neto Da Rocha M, Trad R, Deconinck E, Fajloun Z, et al. CML hematopoietic stem cells expressing IL1RAP can be targeted by chimeric antigen receptor-engineered T cells. Cancer Res. 2019;79(3):663–75. https://doi.org/10.1158/0008-5472.Can-18-1078.
Mistry JJ, Hellmich C, Moore JA, Jibril A, Macaulay I, Moreno-Gonzalez M, et al. Free fatty-acid transport via CD36 drives β-oxidation-mediated hematopoietic stem cell response to infection. Nat Commun. 2021;12(1):7130. https://doi.org/10.1038/s41467-021-27460-9.
Ye H, Adane B, Khan N, Sullivan T, Minhajuddin M, Gasparetto M, et al. Leukemic stem cells evade chemotherapy by metabolic adaptation to an adipose tissue niche. Cell Stem Cell. 2016;19(1):23–37. https://doi.org/10.1016/j.stem.2016.06.001.
Meng O, Zhao Y, Yaghmour G, Alachkar H. Gene expression patterns and functional characterization of CD36 in normal hematopoietic cells. Blood. 2021;138(Supplement 1):4293-. https://doi.org/10.1182/blood-2021-154188.
Kinstrie R, Horne GA, Morrison H, Irvine D, Munje C, Castañeda EG, et al. CD93 is expressed on chronic myeloid leukemia stem cells and identifies a quiescent population which persists after tyrosine kinase inhibitor therapy. Leukemia. 2020;34(6):1613-25https://doi.org/10.1038/s41375-019-0684-5 This study describes a highly novel CD93+ LSC population which could allow therapeutic targeting to overcome TKI resistance.
Riether C, Radpour R, Kallen NM, Bürgin DT, Bachmann C, Schürch CM, et al. Metoclopramide treatment blocks CD93-signaling-mediated self-renewal of chronic myeloid leukemia stem cells. Cell Reports. 2021;34(4). https://doi.org/10.1016/j.celrep.2020.108663. (This identifies a novel mechanism of targeting CD93+ LSCs.)
Bernardi S, Foroni C, Zanaglio C, Re F, Polverelli N, Turra A, et al. Feasibility of tumor-derived exosome enrichment in the onco-hematology leukemic model of chronic myeloid leukemia. Int J Mol Med. 2019;44(6):2133–44. https://doi.org/10.3892/ijmm.2019.4372.
Corrado C, Saieva L, Raimondo S, Santoro A, De Leo G, Alessandro R. Chronic myelogenous leukaemia exosomes modulate bone marrow microenvironment through activation of epidermal growth factor receptor. J Cell Mol Med. 2016;20(10):1829–39. https://doi.org/10.1111/jcmm.12873.
Gao X, Wan Z, Wei M, Dong Y, Zhao Y, Chen X, et al. Chronic myelogenous leukemia cells remodel the bone marrow niche via exosome-mediated transfer of miR-320. Theranostics. 2019;9(19):5642–56. https://doi.org/10.7150/thno.34813.
Zhang X, Yang Y, Yang Y, Chen H, Tu H, Li J. Exosomes from bone marrow microenvironment-derived mesenchymal stem cells affect CML cells growth and promote drug resistance to tyrosine kinase inhibitors. Stem Cells Int. 2020;2020:8890201. https://doi.org/10.1155/2020/8890201.
Hrdinova T, Toman O, Dresler J, Klimentova J, Salovska B, Pajer P, et al. Exosomes released by imatinib-resistant K562 cells contain specific membrane markers, IFITM3, CD146 and CD36 and increase the survival of imatinib-sensitive cells in the presence of imatinib. Int J Oncol. 2021;58(2):238–50. https://doi.org/10.3892/ijo.2020.5163.
Jafarzadeh N, Gholampour MA, Alivand MR, Kavousi S, Arzi L, Rad F, et al. CML derived exosomes promote tumor favorable functional performance in T cells. BMC Cancer. 2021;21(1):1002. https://doi.org/10.1186/s12885-021-08734-3.
Jafarzadeh N, Safari Z, Pornour M, Amirizadeh N, Forouzandeh Moghadam M, Sadeghizadeh M. Alteration of cellular and immune-related properties of bone marrow mesenchymal stem cells and macrophages by K562 chronic myeloid leukemia cell derived exosomes. J Cell Physiol. 2019;234(4):3697–710. https://doi.org/10.1002/jcp.27142.
Blank CU, Haining WN, Held W, Hogan PG, Kallies A, Lugli E, et al. Defining ‘T cell exhaustion.’ Nat Rev Immunol. 2019;19(11):665–74. https://doi.org/10.1038/s41577-019-0221-9.
Hughes A, Clarson J, Tang C, Vidovic L, White DL, Hughes TP, et al. CML patients with deep molecular responses to TKI have restored immune effectors and decreased PD-1 and immune suppressors. Blood. 2017;129(9):1166–76. https://doi.org/10.1182/blood-2016-10-745992.
Harrington P, Dillon R, Radia D, McLornan D, Woodley C, Asirvatham S, et al. Chronic myeloid leukaemia patients at diagnosis and resistant to tyrosine kinase inhibitor therapy display exhausted T-cell phenotype. Br J Haematol. 2022;198(6):1011–5. https://doi.org/10.1111/bjh.18302.
Rezaei M, Tan J, Zeng C, Li Y, Ganjalikhani-Hakemi M. TIM-3 in leukemia; immune response and beyond. Front Oncol. 2021;11:753677. https://doi.org/10.3389/fonc.2021.753677.
Jiang X, Wang J, Deng X, Xiong F, Ge J, Xiang B, et al. Role of the tumor microenvironment in PD-L1/PD-1-mediated tumor immune escape. Mol Cancer. 2019;18(1):10. https://doi.org/10.1186/s12943-018-0928-4.
Sun Y, Guo J, Yu L, Guo T, Wang J, Wang X, et al. PD-L1+ exosomes from bone marrow-derived cells of tumor-bearing mice inhibit antitumor immunity. Cell Mol Immunol. 2021;18(10):2402–9. https://doi.org/10.1038/s41423-020-0487-7.
Harada I, Sasaki H, Murakami K, Nishiyama A, Nakabayashi J, Ichino M, et al. Compromised anti-tumor–immune features of myeloid cell components in chronic myeloid leukemia patients. Sci Rep. 2021;11(1):18046. https://doi.org/10.1038/s41598-021-97371-8.
Zeidan AM, Wang V, Radich JP, Bewersdorf JP, Bhatt VR, Sharon E, et al. Blast MRD CML 1 trial: blockade of PD-1 added to standard therapy to target measurable residual disease (MRD) in chronic myeloid leukemia (CML) — a phase II study of adding the anti-PD-1 pembrolizumab to tyrosine kinase inhibitors in patients with chronic myeloid leukemia and persistently detectable minimal residual disease: a trial of the ECOG-ACRIN Cancer Research Group (EA9171). Blood. 2020;136(Supplement 1):1-. https://doi.org/10.1182/blood-2020-137734. (This ongoing trial will provide key clinical information about PD-1/PD-L1 inhibition in CML.)
Peter B, Eisenwort G, Sadovnik I, Bauer K, Willmann M, Rülicke T, et al. BRD4 degradation blocks expression of MYC and multiple forms of stem cell resistance in Ph(+) chronic myeloid leukemia. Am J Hematol. 2022;97(9):1215–25. https://doi.org/10.1002/ajh.26650.
Tanaka Y, Takeda R, Fukushima T, Mikami K, Tsuchiya S, Tamura M, et al. Eliminating chronic myeloid leukemia stem cells by IRAK1/4 inhibitors. Nat Commun. 2022;13(1):271. https://doi.org/10.1038/s41467-021-27928-8.
Giuntoli S, Rovida E, Barbetti V, Cipolleschi MG, Olivotto M, Dello Sbarba P. Hypoxia suppresses BCR/Abl and selects imatinib-insensitive progenitors within clonal CML populations. Leukemia. 2006;20(7):1291–3. https://doi.org/10.1038/sj.leu.2404224.
Zhang H, Li H, Xi HS, Li S. HIF1α is required for survival maintenance of chronic myeloid leukemia stem cells. Blood. 2012;119(11):2595–607. https://doi.org/10.1182/blood-2011-10-387381.
Singh V, Singh R, Kushwaha R, Verma SP, Tripathi AK, Mahdi AA. The molecular role of HIF1α is elucidated in chronic myeloid leukemia. Front Oncol. 2022;12:912942. https://doi.org/10.3389/fonc.2022.912942.
Kumar R, Krause DS. Recent advances in understanding chronic myeloid leukemia: where do we stand? Fac Rev. 2021;10:35. https://doi.org/10.12703/r/10-35.
Liang Y, Zhou R, Liu X, You L, Chen C, Ye X, et al. Leukemia inhibitory factor facilitates self-renewal and differentiation and attenuates oxidative stress of BMSCs by activating PI3K/AKT signaling. Oxid Med Cell Longev. 2022;2022:5772509. https://doi.org/10.1155/2022/5772509.
Filik Y, Bauer K, Hadzijusufovic E, Haider P, Greiner G, Witzeneder N, et al. PI3-kinase inhibition as a strategy to suppress the leukemic stem cell niche in Ph+ chronic myeloid leukemia. Am J Cancer Res. 2021;11(12):6042–59.
Huang R, Liu H, Chen Y, He Y, Kang Q, Tu S, et al. EPS8 regulates proliferation, apoptosis and chemosensitivity in BCR-ABL positive cells via the BCR-ABL/PI3K/AKT/mTOR pathway. Oncol Rep. 2018;39(1):119–28. https://doi.org/10.3892/or.2017.6102.
Shiri Heris R, Safaroghli-Azar A, Yousefi A-M, Hamidpour M, Bashash D. Anti-leukemic effect of PI3K inhibition on chronic myeloid leukemia (CML) cells: shedding new light on the mitigating effect of c-Myc and autophagy on BKM120 cytotoxicity. Cell Biol Int. 2020;44(5):1212–23. https://doi.org/10.1002/cbin.11322.
Lang F, Wunderle L, Badura S, Schleyer E, Brüggemann M, Serve H, et al. A phase I study of a dual PI3-kinase/mTOR inhibitor BEZ235 in adult patients with relapsed or refractory acute leukemia. BMC Pharmacol Toxicol. 2020;21(1):70. https://doi.org/10.1186/s40360-020-00446-x.
Ward AC, Touw I, Yoshimura A. The Jak-Stat pathway in normal and perturbed hematopoiesis. Blood. 2000;95(1):19–29.
Gallipoli P, Cook A, Rhodes S, Hopcroft L, Wheadon H, Whetton AD, et al. JAK2/STAT5 inhibition by nilotinib with ruxolitinib contributes to the elimination of CML CD34+ cells in vitro and in vivo. Blood. 2014;124(9):1492–501. https://doi.org/10.1182/blood-2013-12-545640.
Tarafdar A, Hopcroft LE, Gallipoli P, Pellicano F, Cassels J, Hair A, et al. CML cells actively evade host immune surveillance through cytokine-mediated downregulation of MHC-II expression. Blood. 2017;129(2):199–208. https://doi.org/10.1182/blood-2016-09-742049.
Zhang X, Tu H, Yang Y, Jiang X, Hu X, Luo Q, et al. Bone marrow-derived mesenchymal stromal cells promote resistance to tyrosine kinase inhibitors in chronic myeloid leukemia via the IL-7/JAK1/STAT5 pathway. J Biol Chem. 2019;294(32):12167–79. https://doi.org/10.1074/jbc.RA119.008037.
Sweet K, Hazlehurst L, Sahakian E, Powers J, Nodzon L, Kayali F, et al. A phase I clinical trial of ruxolitinib in combination with nilotinib in chronic myeloid leukemia patients with molecular evidence of disease. Leuk Res. 2018;74:89–96. https://doi.org/10.1016/j.leukres.2018.10.002.
Himburg HA, Roos M, Fang T, Zhang Y, Termini CM, Schlussel L, et al. Chronic myeloid leukemia stem cells require cell-autonomous pleiotrophin signaling. J Clin Invest. 2020;130(1):315–28. https://doi.org/10.1172/jci129061.
von Palffy S, Landberg N, Sandén C, Zacharaki D, Shah M, Nakamichi N, et al. A high-content cytokine screen identifies myostatin propeptide as a positive regulator of primitive chronic myeloid leukemia cells. Haematologica. 2020;105(8):2095–104. https://doi.org/10.3324/haematol.2019.220434.
Zeidan AM, Al-Kali A, Borate U, Cluzeau T, DeZern AE, Esteve J, et al. Sabatolimab (MBG453) combination treatment regimens for patients (Pts) with higher-risk myelodysplastic syndromes (HR-MDS): the MDS studies in the stimulus immuno-myeloid clinical trial program. Blood. 2021;138(Supplement 1):4669-. https://doi.org/10.1182/blood-2021-145626.
Lee MY, Park CJ, Cho YU, You E, Jang S, Seol CA, et al. Differences in PD-1 expression on CD8+ T-cells in chronic myeloid leukemia patients according to disease phase and TKI medication. Cancer Immunol Immunother. 2020;69(11):2223–32. https://doi.org/10.1007/s00262-020-02617-5.
Li MY, Zhao C, Chen L, Yao FY, Zhong FM, Chen Y, et al. Quantitative proteomic analysis of plasma exosomes to identify the candidate biomarker of imatinib resistance in chronic myeloid leukemia patients. Front Oncol. 2021;11:779567. https://doi.org/10.3389/fonc.2021.779567.
Mohd Yacob A, Muhamad NA, Chang KM, Akmal Hisham H, Mat Yusoff Y, Ibrahim L. Hsa-miR-181a-5p, hsa-miR-182-5p, and hsa-miR-26a-5p as potential biomarkers for BCR-ABL1 among adult chronic myeloid leukemia treated with tyrosine kinase inhibitors at the molecular response. BMC Cancer. 2022;22(1):332. https://doi.org/10.1186/s12885-022-09396-5.
Clark RE, Polydoros F, Apperley JF, Milojkovic D, Rothwell K, Pocock C, et al. De-escalation of tyrosine kinase inhibitor therapy before complete treatment discontinuation in patients with chronic myeloid leukaemia (DESTINY): a non-randomised, phase 2 trial. The Lancet Haematology. 2019;6(7):e375–83. https://doi.org/10.1016/S2352-3026(19)30094-8.
Xu Z, Yin J, Sun Q, Hu J, Hong M, Qian S, et al. The prognostic role of NKG2A expression for patients with chronic myeloid leukemia after treatment discontinuation. Leuk Lymphoma. 2022:1–11. https://doi.org/10.1080/10428194.2022.2090549.
Vigón L, Luna A, Galán M, Rodríguez-Mora S, Fuertes D, Mateos E, et al. Identification of immunological parameters as predictive biomarkers of relapse in patients with chronic myeloid leukemia on treatment-free remission. Journal of Clinical Medicine. 2021;10(1). https://doi.org/10.3390/jcm10010042.
Ilander M, Olsson-Strömberg U, Schlums H, Guilhot J, Brück O, Lähteenmäki H, et al. Increased proportion of mature NK cells is associated with successful imatinib discontinuation in chronic myeloid leukemia. Leukemia. 2017;31(5):1108–16. https://doi.org/10.1038/leu.2016.360.
Kumagai T, Nakaseko C, Nishiwaki K, Yoshida C, Ohashi K, Takezako N, et al. Dasatinib cessation after deep molecular response exceeding 2 years and natural killer cell transition during dasatinib consolidation. Cancer Sci. 2018;109(1):182–92. https://doi.org/10.1111/cas.13430.
Yu G, Lu W, Chen X, Li Y, Long J, Zheng Z, et al. Single-cell RNA sequencing to explore composition of peripheral blood NK cells in patients with chronic myeloid leukemia in treatment-free remission. Leukemia & Lymphoma. 2022:1–12. https://doi.org/10.1080/10428194.2022.2086243. (This study builds on existing evidence on NK cells, which are important in TFR, at extremely high resolution, informing our understanding of their importance for CML remission/TFR.)
Yao D, Xu L, Liu L, Zeng X, Zhong J, Lai J, et al. Increased expression of TIGIT/CD57 in peripheral blood/bone marrow NK cells in patients with chronic myeloid leukemia. Biomed Res Int. 2020;2020:9531549. https://doi.org/10.1155/2020/9531549.
Rein LAM, Rizzieri DA. A phase I trial of incorporating natural killer (K-NK) cells for patients with chronic myeloid leukemia (CML) and molecular residual disease after tyrosine kinase inhibitor (TKI) therapy. Blood. 2020;136(Supplement 1):5-. https://doi.org/10.1182/blood-2020-142062.
Allison M, Mathews J, Gilliland T, Mathew SO. Natural killer cell-mediated immunotherapy for leukemia. Cancers (Basel). 2022;14(3). https://doi.org/10.3390/cancers14030843.
Silver RT, Woolf SH, Hehlmann R, Appelbaum FR, Anderson J, Bennett C, et al. An evidence-based analysis of the effect of busulfan, hydroxyurea, interferon, and allogeneic bone marrow transplantation in treating the chronic phase of chronic myeloid leukemia: developed for the American Society of Hematology: presented in part at the Education Session of the American Society of Hematology, December 5, 1998, Miami Beach. FL Blood. 1999;94(5):1517–36. https://doi.org/10.1182/blood.V94.5.1517.
Talpaz M, Mercer J, Hehlmann R. The interferon-alpha revival in CML. Ann Hematol. 2015;94(2):195–207. https://doi.org/10.1007/s00277-015-2326-y.
Hayashi K, Ikegame K, Takahashi N. The combination of interferon-alpha and ponatinib enables faster and deeper molecular responses in patient with de novo blast crisis of CML: Interferon-Alpha May Return as a CML Treatment. Case Rep Hematol. 2021;2021:5518727. https://doi.org/10.1155/2021/5518727.
Webster JA, Robinson TM, Blackford AL, Warlick E, Ferguson A, Borrello I, et al. A randomized, phase II trial of adjuvant immunotherapy with durable TKI-free survival in patients with chronic phase CML. Leukemia Research. 2021;111:106737. https://doi.org/10.1016/j.leukres.2021.106737.
Jun K, Ya-Zhen Q, Xiao-Su Z, Hong-Xia S, Yue-Yun L, Kai-Yan L, et al. Interferon-α may help prevent molecular relapse of chronic myeloid leukemia after the discontinuation of tyrosine kinase inhibitors. Ther Adv Hematol. 2021;12:2040620720986643. https://doi.org/10.1177/2040620720986643.
Puzzolo MC, Breccia M, Mariglia P, Colafigli G, Pepe S, Scalzulli E, et al. Immunomodulatory effects of IFNα on T and NK cells in chronic myeloid leukemia patients in deep molecular response preparing for treatment discontinuation. J Clin Med. 2022;11(19). https://doi.org/10.3390/jcm11195594. (This study is highly relevant to ongoing investigation into the role of NK cells in TFR.)
Kong J, Qin Y-z, Zhao X-S, Hou Y, Liu K-y, Huang X-j, et al. Profiles of NK cell subsets are associated with successful tyrosine kinase inhibitor discontinuation in chronic myeloid leukemia and changes following interferon treatment. Annals of Hematology. 2021;100(10):2557–66. https://doi.org/10.1007/s00277-021-04606-9.
Alves R, McArdle SEB, Vadakekolathu J, Gonçalves AC, Freitas-Tavares P, Pereira A, et al. Flow cytometry and targeted immune transcriptomics identify distinct profiles in patients with chronic myeloid leukemia receiving tyrosine kinase inhibitors with or without interferon-α. J Transl Med. 2020;18(1):2. https://doi.org/10.1186/s12967-019-02194-x.
Author information
Authors and Affiliations
Corresponding authors
Ethics declarations
Funding
SDP is funded by a Cancer Research UK Biomarker Award (CRCPJT\100006). Both SDP and MC are employees of the University of Glasgow.
All reported studies/experiments with human or animal subjects performed by the authors have been previously published and complied with all applicable ethical standards (including the Helsinki declaration and its amendments, institutional/national research committee standards, and international/national/institutional guidelines).
Conflict of Interest
SDP declares that he has no conflict of interest. MC has received research funding from Cyclacel and Incyte; is/has been an advisory board member for Astellas, Novartis, Incyte, Jazz Pharmaceuticals, Pfizer and Servier; and has received honoraria from Astellas, Novartis, Incyte, Pfizer, and Jazz Pharmaceuticals.
Human and Animal Rights and Informed Consent.
This article does not contain any studies with human or animal subjects performed by any of the authors.
Additional information
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
This article is part of the Topical Collection on Chronic Myeloid Leukemias.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
About this article
Cite this article
Patterson, S.D., Copland, M. The Bone Marrow Immune Microenvironment in CML: Treatment Responses, Treatment-Free Remission, and Therapeutic Vulnerabilities. Curr Hematol Malig Rep 18, 19–32 (2023). https://doi.org/10.1007/s11899-023-00688-6
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11899-023-00688-6