Natural killer-cell counts are associated with molecular relapse-free survival after imatinib discontinuation in chronic myeloid leukemia: the IMMUNOSTIM study

Tyrosine Kinase Inhibitor Discontinuation in Chronic Myeloid Leukemia: Strategies to Optimize Success and New Directions

PURPOSE OF REVIEW

The discovery that patients suffering from chronic myeloid leukemia who obtain deep and long-lasting molecular responses upon treatment with tyrosine kinase inhibitors may maintain their disease silent for many years after therapy discontinuation launched the era of treatment-free remission as a key management goal in clinical practice. The purpose of this review on treatment-free remission is to discuss clinical advances, highlight knowledge gaps, and describe areas of research.

RECENT FINDINGS

Patients in treatment-free remission are a minority, and it is believed that some may still retain a reservoir of leukemic stem cells; thus, whether they can be considered as truly cured is uncertain. Strengthening BCR::ABL1 inhibition increases deep molecular responses but is not sufficient to improve treatment-free remission, and we lack biomarkers to identify and specifically target residual cells with aggressive potential. Another level of complexity resides in the intra- and inter-patient clonal heterogeneity of minimal residual disease and characteristics of the bone marrow environment. Finding determinants of deep molecular responses achievement and elucidating varying biological mechanisms enabling either post-tyrosine kinase inhibitor chronic myeloid leukemia control or relapse may help develop innovative and safe therapies. In the light of the increasing prevalence of CML, targeting the residual leukemic stem cell pool is thought to be the key.

Kinetics of BCR::ABL1 transcript levels and molecular relapse after tyrosine kinase inhibitors discontinuation in chronic myeloid leukemia patients: preliminary results from the DES-CML study

Tyrosine kinase inhibitors (TKI) have revolutionized the treatment of patients with chronic myeloid leukemia. Patients who achieve sustained deep molecular response are eligible for treatment discontinuation. DES-CML is an ongoing, phase 2 multicentric discontinuation trial. Adult patients with CML in chronic phase with typical BCR::ABL1 transcripts, stable deep molecular response (MR4.5 IS) for two years, and no previous resistance were eligible. Patients underwent a phase of TKI dose de-escalation for six months before discontinuation. TKI was reintroduced at the previous dose if the patient lost major molecular response (MMR) at any time. This study aimed to assess the impact of BCR-ABL transcript kinetics during TKI de-escalation and discontinuation phases on treatment-free survival. So far, the study recruited 41 patients, and 38 patients discontinued therapy (4 were in the second discontinuation attempt). Eleven patients lost MMR, one during the de-escalation phase and ten after discontinuation. 24-month treatment-free survival was 66% (95% CI: 48-84%) in a median follow-up of 7 (1-30) months. No patient lost hematological response or had disease progression. A higher rate of molecular relapses occurred in patients with fluctuating BCR::ABL1 levels after the discontinuation phase (with loss of MR4.5, but no loss of MMR) (P=0.04, HR-4.86 (1.03-22.9) but not confirmed in the multivariate analysis. The longer duration of TKI treatment (P=0.03, HR-1.02, 95%CI - 1.00-1.04) and MMR (P=0.004, HR-0.95, 95%CI - 0.92-098) were independent factors of a lower relapse rate.

High Level of CD8+PD-1+ Cells in Patients with Chronic Myeloid Leukemia Who Experienced Loss of MMR after Imatinib Discontinuation

Treatment-free remission (TFR) is achieved in approximately half of chronic myeloid leukemia (CML) patients treated with tyrosine kinase inhibitors. The mechanisms responsible for TFR maintenance remain elusive. This study aimed to identify immune markers responsible for the control of residual CML cells early in the TFR (at 3 months), which may be the key to achieving long-term TFR and relapse-free survival (RFS) after discontinuation of imatinib. Our study included 63 CML patients after imatinib discontinuation, in whom comprehensive analysis of changes in the immune system was performed by flow cytometry, and changes in the BCR::ABL1 transcript levels were assessed by RQ-PCR and ddPCR. We demonstrated a significant increase in the percentage of CD8+PD-1+ cells in patients losing TFR. The level of CD8+PD-1+ cells is inversely related to the duration of treatment and incidence of deep molecular response (DMR) before discontinuation. Analysis of the ROC curve showed that the percentage of CD8+PD-1+ cells may be a significant factor in early molecular recurrence. Interestingly, at 3 months of TFR, patients with the e13a2 transcript had a significantly higher proportion of the PD-1-expressing immune cells compared to patients with the e14a2. Our results suggest the important involvement of CD8+PD-1+ cells in the success of TFR and may help in identifying a group of patients who could successfully discontinue imatinib.

Second Treatment-Free Remission Attempt in Patients with Chronic Myeloid Leukemia

Long-term survival outcomes of patients with chronic myeloid leukemia in the chronic phase are now similar to those of the general population, following the introduction of ABL1 tyrosine kinase inhibitors (TKIs). Approximately 40% to 80% of patients with chronic myeloid leukemia successfully achieved treatment-free remission after the first attempt of TKI discontinuation (TFR1), after achieving a durable deep molecular response. However, the possibility of achieving treatment-free remission after a second attempt of TKI discontinuation (TFR2) remains unclear. Therefore, we reviewed current TFR2 studies to clarify the feasibility of achieving TFR2. We identified 5 TFR2 clinical trials and 2 real-world reports. TFR2 attempt may be feasible after retreatment with imatinib, nilotinib, or dasatinib. Patients who have achieved MR4.0 or deeper durable molecular remission are eligible to enter the TFR2 phase. Imatinib is well tolerated and can be administered for consolidative treatment before the TFR2 attempt, whereas drug-related adverse effects of nilotinib or dasatinib affect their tolerability and might lead to discontinuation. Late onset relapse (> 1 year or > 2 year) was often reported, thus careful monitoring is needed.

How to improve treatment-free remission eligibility in chronic myeloid leukaemia?

The achievement of treatment-free remission (TFR) has become a significant clinical end-point in the management of patients with chronic myeloid leukaemia (CML), providing an opportunity to discontinue therapy with tyrosine kinase inhibitors (TKIs) while maintaining deep molecular response (DMR). Early studies, such as the French STIM trial, have demonstrated that a portion of patients can maintain DMR after treatment cessation, with rates ranging from 40% to 50%, and most relapses occurring within the first 6 months. Key prognostic factors for successful TFR, including treatment duration, duration of DMR, risk scores, and transcript type, have been identified. Optimal patient selection for TFR remains a challenge, but recent research provides insights into potential strategies to increase TFR eligibility. Evidence suggests that early intervention switching to achieve optimal response, treatment combinations, proactive switch in the case of absence of DMR, dose-optimization and induction-maintenance approach can improve molecular responses and, consequently, enhance TFR eligibility. In this review, we report and discuss all the potential therapeutic strategies that may enhance eligibility for a first attempt at TFR, with a particular emphasis on potential future approaches.

Single-cell analysis of immune recognition in chronic myeloid leukemia patients following tyrosine kinase inhibitor discontinuation

Immunological control of residual leukemia cells is thought to occur in patients with chronic myeloid leukemia (CML) that maintain treatment-free remission (TFR) following tyrosine kinase inhibitor (TKI) discontinuation. To study this, we analyzed 55 single-cell RNA and T cell receptor (TCR) sequenced samples (scRNA+TCRαβ-seq) from patients with CML (n = 13, N = 25), other cancers (n = 28), and healthy (n = 7). The high number and active phenotype of natural killer (NK) cells in CML separated them from healthy and other cancers. Most NK cells in CML belonged to the active CD56dim cluster with high expression of GZMA/B, PRF1, CCL3/4, and IFNG, with interactions with leukemic cells via inhibitory LGALS9-TIM3 and PVR-TIGIT interactions. Accordingly, upregulation of LGALS9 was observed in CML target cells and TIM3 in NK cells when co-cultured together. Additionally, we created a classifier to identify TCRs targeting leukemia-associated antigen PR1 and quantified anti-PR1 T cells in 90 CML and 786 healthy TCRβ-sequenced samples. Anti-PR1 T cells were more prevalent in CML, enriched in bone marrow samples, and enriched in the mature, cytotoxic CD8 + TEMRA cluster, especially in a patient maintaining TFR. Our results highlight the role of NK cells and anti-PR1 T cells in anti-leukemic immune responses in CML.

In-depth characterization of NK cell markers from CML patients who discontinued tyrosine kinase inhibitor therapy

Introduction

Treatment-free remission (TFR) in patients with chronic myeloid leukemia in chronic phase is considered a safe option if suitable molecular monitoring is available. However, the question arises as to which factors can contribute to the maintenance of TFR, and immunologic surveillance of the remaining leukemic cells is believed to be one of them. Argentina Stop Trial is an open-label, single-arm, multicenter trial assessing TFR after tyrosine kinase inhibitors interruption, that after more than 4 years showed a successful TFR rate of 63%.

Methods

In this context, we set up an immunological study by flow cytometry in order to analyze specific NK cell subsets from peripheral blood patient samples both at the time of discontinuation as well as during the subsequent months.

Results

At the time of discontinuation, patients show a mature NK cell phenotype, probably associated to TKI treatment. However, 3 months after discontinuation, significant changes in several NK cell receptors occurred. Patients with a higher proportion of CD56dim NK and PD-1+ NK cells showed better chances of survival. More interestingly, non-relapsing patients also presented a subpopulation of NK cells with features associated with the expansion after cytomegalovirus infection (expression of CD57+NKG2C+), and higher proportion of NKp30 and NKp46 natural cytotoxicity receptors, which resulted in greater degranulation and associated with better survival (p<0.0001).

Discussion

This NK cell subset could have a protective role in patients who do not relapse, thus further characterization could be useful for patients in sustained deep molecular response.

Immune modulation in chronic myeloid leukaemia patients treated with nilotinib and interferon-alpha

The addition of interferon to tyrosine kinase inhibitors (TKIs), to improve deep molecular response (DMR) and potentially treatment-free remission (TFR) rates in chronic-phase chronic myeloid leukaemia (CP-CML) patients is under active investigation. However, the immunobiology of this combination is poorly understood. We performed a comprehensive longitudinal assessment of immunological changes in CML patients treated with nilotinib and interferon-alpha (IFN-α) within the ALLG CML11 trial (n = 12) or nilotinib alone (n = 17). We demonstrate that nilotinib+IFN transiently reduced absolute counts of natural killer (NK) cells, compared with nilotinib alone. Furthermore, CD16+ -cytolytic and CD57+ CD62L- -mature NK cells were transiently reduced during IFN therapy, without affecting NK-cell function. IFN transiently increased cytotoxic T-lymphocyte (CTL) responses to leukaemia-associated antigens (LAAs) proteinase-3, BMI-1 and PRAME; and had no effect on regulatory T cells, or myeloid-derived suppressor cells. Patients on nilotinib+IFN who achieved MR4.5 by 12 months had a significantly higher proportion of NK cells expressing NKp46, NKp30 and NKG2D compared with patients not achieving this milestone. This difference was not observed in the nilotinib-alone group. The addition of IFN to nilotinib drives an increase in NK-activating receptors, CTLs responding to LAAs and results in transient immune modulation, which may influence earlier DMR, and its effect on long-term outcomes warrants further investigation.

Peripheral lymphocyte subsets as predicting factors for molecular recurrence after imatinib discontinuation in a phase 2 imatinib discontinuation trial in patients with chronic myeloid leukemia

INTRODUCTION

Treatment-free remission (TFR) is successful in half of the patients with chronic myeloid leukemia who discontinue Imatinib (IM) after sustained molecular response.

METHODS

In a prospective trial, we used pioglitazone for 3 months before stopping IM in 30 patients. Percentages of peripheral blood lymphocyte subsets were assessed before and after treatment. The relation of these data with duration of IM treatment and TRF were examined.

RESULTS

The median time of IM treatment was 117.6 months. After discontinuation, 11 patients had molecular recurrence after 5.2 months (2.4 - 30). The observation time for those remaining in TFR was 46 (26 - 56) months. The independent factors for the maintenance of TFR were the duration of IM treatment and the percentage of double-positive T cells at IM stop.

CONCLUSION

A longer treatment with imatinib was associated with a longer TFR after discontinuation. Pioglitazone could act as an immunomodulator, increasing DP T cells which may contribute to prevent relapse.

Case report: Long-term voluntary Tyrosine Kinase Inhibitor (TKI) discontinuation in chronic myeloid leukemia (CML): Molecular evidence of an immune surveillance

The classical natural history of chronic myeloid leukemia (CML) has been drastically modified by the introduction of tyrosine kinase inhibitor (TKI) therapies. TKI discontinuation is currently possible in patients in deep molecular responses, using strict recommendations of molecular follow-up due to risk of molecular relapse, especially during the first 6 months. We report here the case of a patient who voluntarily interrupted her TKI therapy. She remained in deep molecular remission (MR4) for 18 months followed by detection of a molecular relapse at +20 months. Despite this relapse, she declined therapy until the occurrence of the hematological relapse (+ 4 years and 10 months). Retrospective sequential transcriptome experiments and a single-cell transcriptome RNA-seq analysis were performed. They revealed a molecular network focusing on several genes involved in both activation and inhibition of NK-T cell activity. Interestingly, the single-cell transcriptome analysis showed the presence of cells expressing NKG7, a gene involved in granule exocytosis and highly involved in anti-tumor immunity. Single cells expressing as granzyme H, cathepsin-W, and granulysin were also identified. The study of this case suggests that CML was controlled for a long period of time, potentially via an immune surveillance phenomenon. The role of NKG7 expression in the occurrence of treatment-free remissions (TFR) should be evaluated in future studies.

Immunomodulatory Activity of the Tyrosine Kinase Inhibitor Dasatinib to Elicit NK Cytotoxicity against Cancer, HIV Infection and Aging

Tyrosine kinase inhibitors (TKIs) have been extensively used as a treatment for chronic myeloid leukemia (CML). Dasatinib is a broad-spectrum TKI with off-target effects that give it an immunomodulatory capacity resulting in increased innate immune responses against cancerous cells and viral infected cells. Several studies reported that dasatinib expanded memory-like natural killer (NK) cells and γδ T cells that have been related with increased control of CML after treatment withdrawal. In the HIV infection setting, these innate cells are associated with virus control and protection, suggesting that dasatinib could have a potential role in improving both the CML and HIV outcomes. Moreover, dasatinib could also directly induce apoptosis of senescence cells, being a new potential senolytic drug. Here, we review in depth the current knowledge of virological and immunogenetic factors associated with the development of powerful cytotoxic responses associated with this drug. Besides, we will discuss the potential therapeutic role against CML, HIV infection and aging.

Prevalence of the BCR/ABL fusion gene and T cell stimulation capacity of dendritic cells in chronic myelogenous leukemia

Dendritic cell (DC) vaccines are promising for immunotherapy, and their production using CD34⁺ hematopoietic stem cells (HPSCs) from patients with chronic myelogenous leukemia (CML) and healthy donors is well established. However, the generation of CD1a⁺CD14^- DCs and their functional properties in patients with CML remain elusive. Here, we aimed to study the biology of DCs generated from CD34^-/low HPSCs and evaluate the status of their BCR/ABL translocation, ability to stimulate T cells, and capacity of endocytosis compared to DCs derived from CD34⁺ HPSCs from both patients with CML and healthy donors. CD1a⁺CD14^- DCs were generated from CD34^-/low HPSCs and evaluated morphologically and functionally. CD34⁺ cells are frequently selected for transplantation and the entire CD34^-/low HPSC fraction is wasted. Here, we anticipated the CD34^- HPSC subset to constitute an invaluable source for acquiring DCs for immunotherapy. CD34⁺ and CD34^- HPSCs were sorted from the bone marrow samples of CML patients and healthy donors and differentiated ex vivo in a similar way. DCs from CD34^-Lin^- and CD34⁺Lin^- HPSCs expressed comparable surface markers (CD80, CD83, CD86, HLA-DR, CD40, and CD54). Functional analysis revealed that DCs acquired from both subsets retained a potent allogeneic T cell stimulatory capacity and an efficient phagocytic ability and showed a similar BCR/ABL translocation status. In conclusion, DCs were successfully differentiated from the CD34^-Lin^- cell subset and showed potent functional capacities, indicating their potential for application in immunotherapy and basic research.

Chronic Myeloid Leukemia, from Pathophysiology to Treatment-Free Remission: A Narrative Literature Review

Chronic myeloid leukemia (CML) is one of the most common leukemias occurring in the adult population. The course of CML is divided into three phases: the chronic phase, the acceleration phase, and the blast phase. Pathophysiology of CML revolves around Philadelphia chromosome that constitutively activate tyrosine kinase through BCR-ABL1 oncoprotein. In the era of tyrosine kinase inhibitors (TKIs), CML patients now have a similar life expectancy to people without CML, and it is now very rare for CML patients to progress to the blast phase. Only a small proportion of CML patients have resistance to TKI, caused by BCR-ABL1 point mutations. CML patients with TKI resistance should be treated with second or third generation TKI, depending on the BCR-ABL1 mutation. Recently, many studies have shown that it is possible for CML patients who achieve a long-term deep molecular response to stop TKIs treatment and maintain remission. This review aimed to provide an overview of CML, including its pathophysiology, clinical manifestations, the role of stem cells, CML treatments, and treatment-free remission.

A Systematic Review on Second Treatment-Free Remission (TFR) Attempt in Chronic Myeloid Leukemia (CML): Can it be Applied in Clinical Practice?

The prognosis and life expectancy of chronic myeloid leukemia (CML) patients have improved significantly with the launch of first tyrosine kinase inhibitor (TKI), imatinib. Maintaining at least one major molecular response in CML patients without the use of TKI is known as treatment-free remission (TFR). The safety of the first TFR (TFR1) effort has been reported by numerous studies. However, some patients relapse during TFR1. A second TFR (TFR2) can be tried again in those patients. This systematic review aims to evaluate individual patient characteristics for a TFR2, factors predicting successful TFR2, monitoring, consequences of the cessation of TKI, and studies about TFR2. We identified 5 studies related TFR2. The results showed that the first failed TKI discontinuation attempt is not an indicator of a second TKI discontinuation failure. TKIs could safely and successfully be discontinued for a second time in chronic phase CML patients despite a TFR1 failure. The most important factors for estimating TFR2 success are the speed of molecular relapse and the TKI-free duration after the first TKI discontinuation attempt. New trends in the management of CML patients are reducing the side effects of treatment, lessening the financial burden, and improving the quality of life of patients as CML has developed into a manageable chronic disease rather than an aggressive cancer. Although there are many studies and guidelines on TFR1, there are few studies on TFR2 and predictive factors. More data is still needed regarding TFR2 attempt in patients with CML.

Extracellular Vesicles and Their Roles in the Tumor Immune Microenvironment

Tumor cells actively incorporate molecules (e.g., proteins, lipids, RNA) into particles named extracellular vesicles (EVs). Several groups have demonstrated that EVs can be transferred to target (recipient) cells, making EVs an important means of intercellular communication. Indeed, EVs are able to modulate the functions of target cells by reprogramming signaling pathways. In a cancer context, EVs promote the formation of a supportive tumor microenvironment (TME) and (pre)metastatic niches. Recent studies have revealed that immune cells, tumor cells and their secretome, including EVs, promote changes in the TME and immunosuppressive functions of immune cells (e.g., natural killer, dendritic cells, T and B cells, monocytes, macrophages) that allow tumor cells to establish and propagate. Despite the growing knowledge on EVs and on their roles in cancer and as modulators of the immune response/escape, the translation into clinical practice remains in its early stages, hence requiring improved translational research in the EVs field. Here, we comprehensively review the current knowledge and most recent research on the roles of EVs in tumor immune evasion and immunosuppression in both solid tumors and hematological malignancies. We also highlight the clinical utility of EV-mediated immunosuppression targeting and EV-engineering. Importantly, we discuss the controversial role of EVs in cancer biology, current limitations and future perspectives to further the EV knowledge into clinical practice.

Expansions of tumor-reactive Vdelta1 gamma-delta T cells in newly diagnosed patients with chronic myeloid leukemia

Recent studies have underscored the importance of gamma-delta (γδ) T cells in mediating potent MHC-unrestricted cytotoxicity in numerous malignancies. Here, we analyzed Vδ1 and Vδ2 γδ T cell subsets in newly diagnosed chronic myeloid leukemia (CML) patients (n = 40) who had initiated tyrosine kinase inhibitor (TKI) therapy including imatinib (n = 22), nilotinib (n = 14) and dasatinib (n = 4). Patient peripheral blood samples were analyzed at diagnosis and monitored prospectively at 3, 6, 12 and 18 months post-TKI. γδ T cells isolated from healthy donors and CML patients were used against K562, LAMA-84 and KYO-1 cell lines and against primary CML cells in cytotoxicity assays. We found large expansions of Vδ1 and Vδ2 T cells in patients at diagnosis compared to age-matched healthy donors (n = 40) (p < 0.0001). The γδ T cell reconstitution in patients on imatinib and also on nilotinib showed significant reductions of Vδ1 T cell and Vδ2 T cell absolute counts at 3 months compared to diagnosis. Importantly, Vδ1 and Vδ2 T absolute cell counts remained at normal levels from 3 months throughout the follow-up. Next, we observed susceptibility to specific lysis of primary CML tumor cells by Vδ1 T cells from healthy donors. Furthermore, we determined inherent cytotoxic reactivity by autologous patients’ Vδ1 T lymphocytes against primary CML tumor cells. Finally, the TCR clonality profiles showed in CML patients mostly polyclonal repertoires regardless of the TKI. Our results provide further evidence into γδ T cell antileukemia immunity in CML that might be beneficial for long-term disease control and treatment outcome.

De-escalation or discontinuation of tyrosine kinase inhibitor in patients with chronic myeloid leukemia: A multicentral, open-label, prospective trial in China

Background: Long-term treatment-free remission (TFR) represents a new goal for chronic myeloid leukemia (CML). Optimizing dose of tyrosine kinase inhibitors (TKIs) in the CML treatment maybe a new challenge to maintain effective and improving patients' quality of life. We hypothesized that administration of low-dose TKIs does not compromise major molecular response (MMR) in patients with CML who have a deep molecular response (DMR). Methods: We did an open-label, randomized trial at eight hospitals in China. Eligible CML-CP patients (aged 18-70 years) had shown continuous response to TKI more than 5 years and maintained MR4.5 (BCR-ABLIS ≤ 0.0032%) in recent 18 months. Patients were randomly assigned (1:1) to the TKI de-escalation group or the discontinuation group. Randomization was done with permuted blocks (block size four) and implemented through an interactive web-based randomization system. Recurrence was defined as the single sample with real time Quantitative PCR (RT-qPCR) measurement greater than 0.1% (MMR). The primary endpoint was 12-month MMR rate in patients who received de-escalation or discontinuation of TKIs. This study was registered at ClinicalTrials.gov (NCT04143087). Results: Around 125 patients were enrolled between October 23, 2019 and October 31, 2020, 62 patients received dose de-escalation of TKIs, while 63 patients in the discontinuation group. In the de-escalation group, molecular recurrence-free survival at 12 months was 88.32% (95% CI 79%-98%), whereas molecular recurrence-free survival in the discontinuation group at 12 months was 59.98% (95% CI 47-73). No progressions occurred at the data cut-off date. All 29 recurrence cases restart TKI treatment returned to MMR. Cytolytic NK cells as a proportion of lymphocyte cells were significantly increased from baseline after 6 months whether in the de-escalation or TKIs cessation group (P = 0.048, 0.001, respectively); compared with the relapsing patients, Tregs proportion was decreased (P = 0.003), and higher proportion of NK cells were found in non-relapsing patients whether in TKI de-escalation or discontinuation group (P = 0.011, 0.007, respectively). We also found that the de-escalation group showed better disease-specific HRQOL in regards to its impact on emotional functioning, fatigue, pain, and financial difficulties. Conclusion: With 88.32% MMR in 12-months follow-up after de-escalation TKIs' treatment, dose-halving could become a new treatment paradigm for CML patients who with DMR under continuing maintenance therapy with TKIs.

Molecular Changes in Chronic Myeloid Leukemia During Tyrosine Kinase Inhibitors Treatment. Focus on Immunological Pathways

Introduction

The aim of our research was to investigate changes in the molecular background of the immune response in the chronic phase (CP) of chronic myeloid leukaemia (CML) during treatment with tyrosine kinase inhibitors (TKIs).

Methods

Global gene and miRNA expression profiles were assessed using genome-wide RNA and miRNA microarray technology in bone marrow mononuclear cells. Fifty-one patients were recruited, and bone marrow samples were taken at diagnosis before treatment with TKIs and after 3, 6, and 12 months of treatment with TKIs. The largest number of upregulated genes was observed when the 0-month group (time of diagnosis) was compared to the 3-month group; 1774 genes were significantly upregulated, and 390 genes were significantly downregulated.

Discussion

Upregulated biological processes according to gene ontology (GO) classification involved basic cellular processes such as cell division, cell cycle, cell-cell adhesion, protein transport, mitotic nuclear division, apoptosis, and DNA replication. Differentially expressed miRNAs were annotated using GO classification to several immunity-related processes, including the T cell receptor signalling pathway, T cell costimulation, immune response, and inflammatory response. TKI therapy exerts a significant impact on cellular cycle processes and T-cell activation, which was proven at the molecular level.

The Spliceosome: A New Therapeutic Target in Chronic Myeloid Leukaemia

Simple Summary

RNA splicing factors are frequently altered in cancer and have been found mutated or deregulated in myeloid malignancies, justifying the growing interest in new therapeutic strategies. We recently showed that the DNA methylation alterations of CD34⁺CD15⁻ chronic myeloid leukaemia (CML) cells affect alternative splicing genes, suggesting that spliceosome actors might be altered in chronic-phase (CP)-CML. We investigated the expression of 12 splicing genes in primary CP-CML CD34⁺ cells at diagnosis (n = 15). We found that CP-CML CD34⁺ cells had a distinct splicing signature profile, suggesting: (i) a spliceosome deregulation from the diagnosis time and (ii) an intraclonal heterogeneity. In vitro incubation of a spliceosome-targeted drug (TG003) showed that CP-CML CD34⁺ cells are spliceosome dependent; moreover, with the combination of TKI, the two drugs showing an additive effect while sparing healthy donors cells. Our results suggest that the spliceosome may be a new potential target for the treatment of CML.

Abstract

RNA splicing factors are frequently altered in cancer and can act as both oncoproteins and tumour suppressors. They have been found mutated or deregulated, justifying the growing interest in the targeting of splicing catalysis, splicing regulatory proteins, and/or specific, key altered splicing events. We recently showed that the DNA methylation alterations of CD34⁺CD15⁻ chronic myeloid leukaemia (CML) cells affect, among others, alternative splicing genes, suggesting that spliceosome actors might be altered in chronic-phase (CP)-CML. We investigated the expression of 12 spliceosome genes known to be oncogenes or tumour suppressor genes in primary CP-CML CD34⁺ cells at diagnosis (n = 15). We found that CP-CML CD34⁺ cells had a distinct splicing signature profile as compared with healthy donor CD34⁺ cells or whole CP-CML cells, suggesting: (i) a spliceosome deregulation from the diagnosis time and (ii) an intraclonal heterogeneity. We could identify three profile types, but there was no relationship with a patient’s characteristics. By incubating cells with TKI and/or a spliceosome-targeted drug (TG003), we showed that CP-CML CD34⁺ cells are both BCR::ABL and spliceosome dependent, with the combination of the two drugs showing an additive effect while sparing healthy donors cells. Our results suggest that the spliceosome may be a new potential target for the treatment of CML.

Immunomodulatory Effects of IFNα on T and NK Cells in Chronic Myeloid Leukemia Patients in Deep Molecular Response Preparing for Treatment Discontinuation

A deep and stable molecular response (DMR) is a prerequisite for a successful treatment-free remission (TFR) in chronic myeloid leukemia (CML). In order to better identify and analyze potential candidates of successful TFR, we examined the phenotypic and functional host immune compartment in DMR patients who had received TKI treatment only (TKI-only) or had been previously treated with interferon-alpha (IFNα + TKI) or had received IFNα treatment only (IFNα-only). The T/NK-cell subset distribution, NK- and T-cell cytokine production, activation and maturation markers were measured in 44 patients in DMR treated with IFNα only (9), with IFNα + TKI (11) and with TKI-only (24). IFNα + TKI and TKI-only groups were eligible to TKI discontinuation according to the NCCN and ESMO guidelines (stable MR4 for more than two years). In IFNα-treated patients, we documented an increased number of lymphocytes capable of producing IFNγ and TNFα compared to the TKI-only group. In INFα + TKI patients, the percentage of NKG2C expression and its mean fluorescence intensity were significantly higher compared to the TKI-only group and to the INFα-only group in the CD56dim/CD16+ NK cell subsets (INFα + TKI vs. TKI-only p = 0.041, p = 0.037; INFα + TKI vs. INFα-only p = 0.03, p = 0.033, respectively). Furthermore, in INFα-only treated patients, we observed an increase of NKp46 MFI in the CD56bright/CD16- NK cell subset that becomes significant compared to the INFα + TKI group (p = 0.008). Our data indicate that a previous exposure to IFNα substantially and persistently modified the immune system of CML patients in memory T lymphocytes, differentiated NKG2C+ “long-lived” NK cells responses, even years after the last IFNα contact.

Altered distribution and function of NK-cell subsets lead to impaired tumor surveillance in JAK2V617F myeloproliferative neoplasms

In cancer, tumor cells and their neoplastic microenvironment can sculpt the immunogenic phenotype of a developing tumor. In this context, natural killer (NK) cells are subtypes of lymphocytes of the innate immune system recognized for their potential to eliminate neoplastic cells, not only through direct cytolytic activity but also by favoring the development of an adaptive antitumor immune response. Even though the protective effect against leukemia due to NK-cell alloreactivity mediated by the absence of the KIR-ligand has already been shown, and some data on the role of NK cells in myeloproliferative neoplasms (MPN) has been explored, their mechanisms of immune escape have not been fully investigated. It is still unclear whether NK cells can affect the biology of BCR-ABL1-negative MPN and which mechanisms are involved in the control of leukemic stem cell expansion. Aiming to investigate the potential contribution of NK cells to the pathogenesis of MPN, we characterized the frequency, receptor expression, maturation profile, and function of NK cells from a conditional Jak2V617F murine transgenic model, which faithfully resembles the main clinical and laboratory characteristics of human polycythemia vera, and MPN patients. Immunophenotypic analysis was performed to characterize NK frequency, their subtypes, and receptor expression in both mutated and wild-type samples. We observed a higher frequency of total NK cells in JAK2V617F mutated MPN and a maturation arrest that resulted in low-numbered mature CD11b⁺ NK cells and increased immature secretory CD27⁺ cells in both human and murine mutated samples. In agreement, inhibitory receptors were more expressed in MPN. NK cells from Jak2V617F mice presented a lower potential for proliferation and activation than wild-type NK cells. Colonies generated by murine hematopoietic stem cells (HSC) after mutated or wild-type NK co-culture exposure demonstrated that NK cells from Jak2V617F mice were deficient in regulating differentiation and clonogenic capacity. In conclusion, our findings suggest that NK cells have an immature profile with deficient cytotoxicity that may lead to impaired tumor surveillance in MPN. These data provide a new perspective on the behavior of NK cells in the context of myeloid malignancies and can contribute to the development of new therapeutic strategies, targeting onco-inflammatory pathways that can potentially control transformed HSCs.

IFN-α with dasatinib broadens the immune repertoire in patients with chronic-phase chronic myeloid leukemia

In chronic myeloid leukemia (CML), combination therapies with tyrosine kinase inhibitors (TKIs) aim to improve the achievement of deep molecular remission that would allow therapy discontinuation. IFN-α is one promising candidate, as it has long-lasting effects on both malignant and immune cells. In connection with a multicenter clinical trial combining dasatinib with IFN-α in 40 patients with chronic-phase CML (NordCML007, NCT01725204), we performed immune monitoring with single-cell RNA and T cell receptor (TCR) sequencing (n = 4, 12 samples), bulk TCRβ sequencing (n = 13, 26 samples), flow cytometry (n = 40, 106 samples), cytokine analyses (n = 17, 80 samples), and ex vivo functional studies (n = 39, 80 samples). Dasatinib drove the immune repertoire toward terminally differentiated NK and CD8⁺ T cells with dampened functional capabilities. Patients with dasatinib-associated pleural effusions had increased numbers of CD8⁺ recently activated effector memory T (Temra) cells. In vitro, dasatinib prevented CD3-induced cell death by blocking TCR signaling. The addition of IFN-α reversed the terminally differentiated phenotypes and increased the number of costimulatory intercellular interactions and the number of unique putative epitope-specific TCR clusters. In vitro IFN-α had costimulatory effects on TCR signaling. Our work supports the combination of IFN-α with TKI therapy, as IFN-α broadens the immune repertoire and restores immunological function.

Tyrosine Kinase Inhibitor discontinuation in Chronic Myeloid Leukemia: eligibility criteria and predictors of success

TKI discontinuation proved to be safe and feasible in patients with CML with deep and durable molecular responses, introducing an additional treatment goal for these patients beyond overall survival. However, treatment interruption is a safe procedure only with appropriate patient selection and monitoring. Clinical and biological factors associated with better outcomes do not yet offer a precise stratification of patients according to their risk of relapse. This article aims at reviewing the leading studies present in the field in order to define eligibility criteria for discontinuation and predictors of success.

Natural killer cells: the next wave in cancer immunotherapy

Immunotherapies focusing on rejuvenating T cell activities, like PD-1/PD-L1 and CTLA-4 blockade, have unprecedentedly revolutionized the landscape of cancer treatment. Yet a previously underexplored component of the immune system - natural killer (NK) cell, is coming to the forefront of immunotherapeutic attempts. In this review, we discuss the contributions of NK cells in the success of current immunotherapies, provide an overview of the current preclinical and clinical strategies at harnessing NK cells for cancer treatment, and highlight that NK cell-mediated therapies emerge as a major target in the next wave of cancer immunotherapy.

Chronic myeloid leukaemia patients at diagnosis and resistant to tyrosine kinase inhibitor therapy display exhausted T-cell phenotype

The search for novel targets in chronic myeloid leukaemia (CML) is ongoing, to improve treatment efficacy in refractory disease and increase eligibility for tyrosine kinase inhibitor (TKI) discontinuation. Increased frequency of Tregs and effector Tregs was evident at diagnosis, together with increased expression of T‐cell exhaustion markers, including in regulatory T cells at diagnosis and in patients with refractory disease. Plasma analysis revealed significantly increased levels of cytokines including tumour necrosis factor (TNF)‐a and interleukin (IL)‐6 at diagnosis, in keeping with a pro‐inflammatory state prior to treatment. We hence demonstrate T‐cell exhaustion and a pro‐inflammatory state at diagnosis in CML, likely secondary to leukaemia‐associated antigenic overload associated with increased disease burden.

The prognostic role of NKG2A expression for patients with chronic myeloid leukemia after treatment discontinuation

This study aims to evaluate the possibility of tyrosine kinase inhibitors (TKIs) discontinuation in chronic myeloid leukemia (CML) patients who obtained sustained deep molecular response (DMR) and to explore the prognostic role of NK cells in treatment-free remission (TFR). Sixty CML patients who discontinued TKI treatment were enrolled, and we also investigated the immune profiles in 27 CML patients after TKI cessation. Of the 60 patients, the estimated TFR rate was 60.8% [95% CI: 49.5-74.8%] at 12 months. Patients who had longer TKI duration, major molecular response, and DMR maintenance time had a significantly higher TFR rate. And a higher percentage of NKG2A⁺NK cells and NKG2A⁺CD56^brightCD16^-NK cells were independent prognostic factors of TFR in multivariate analysis. These results indicate the practicality of the cessation of TKIs and patients with stable NK cell counts accompanied by higher cytotoxicity and increased killing capacity are more inclined to get sustained treatment-free survival.

Kinetics of early and late molecular recurrences after first-line imatinib cessation in chronic myeloid leukemia: updated results from the STIM2 trial

Discontinuation of tyrosine kinase inhibitors in chronic phase chronic myeloid leukemia is feasible in clinical practice based on recently published international recommendations. Nevertheless, factors predictive of molecular recurrence have not been fully elucidated and long-term follow-up of patients enrolled in clinical studies are required in order to update knowledge on discontinuation attempts particularly in terms of the safety and durability of treatment-free remission (TFR). In the current study, we updated results from the STIM2 study in the light of the consensual criterion of molecular recurrence reported in different international recommendations. Among the 199 patients included in the perprotocol study, 108 patients lost a major molecular response. With a median follow-up of 40.8 months (5.5-111 months), the probability of treatment-free remission was 43.4% [36.3-50.4] at 5 years, 40.9% [32.8-47.3] at 7 years and 34.5% [25.6- 43.3] at 9 years. Molecular recurrence occurred between 0 to 6 months, 6 to 24 months and after 24 months in 75 patients (69%), 15 patients (14%) and 18 patients (17%), respectively. Notably, the kinetics of molecular recurrence differed significantly between these three subgroups with a median time from loss of MR4 (BCR::ABL1 IS≤0.01%) to loss of major molecular response of 1, 7 and 22 months, respectively. Predictive factors of molecular recurrence differed according to the time of occurrence of the molecular recurrence. Durations of imatinib treatment and deep molecular response as well as BCR::ABL1/ABL1 levels at cessation of tyrosine kinase inhibitor treatment, as quantified by reverse transcriptase droplet digital polymerase chain reaction, are involved in molecular recurrence occurring up to 24 months but not beyond. (ClinicalTrial. gov Identifier NCT#0134373).

Treatment-Free Remission in Chronic Myeloid Leukemia Patients Treated With Low-Dose TKIs: A Feasible Option Also in the Real-Life. A Campus CML Study

Treatment-free remission (TFR) has become a primary therapeutic goal in CML and is also considered feasible by international guidelines. TKIs dose reduction is often used in real-life practice to reduce adverse events, although its impact on TFR is still a matter of debate. This study aimed to explore the attitude of Italian hematologists towards prescribing TKIs at reduced doses and its impact on TFR. In September 2020, a questionnaire was sent to 54 hematology centers in Italy participating to the Campus CML network. For each patient, data on the main disease characteristics were collected. Most of the hematologists involved (64.4%) believed that low-dose TKIs should not influence TFR. Indeed, this approach was offered to 194 patients. At the time of TFR, all but 3 patients had already achieved a DMR, with a median duration of 61.0 months. After a median follow-up of 29.2 months, 138 (71.1%) patients were still in TFR. Interestingly, TFR outcome was not impaired by any of the variables examined, including sex, risk scores, BCR-ABL1 transcript types, previous interferon, type and number of TKIs used before treatment cessation, degree of DMR or median duration of TKIs therapy. On the contrary, TFR was significantly better after dose reduction due to AEs; furthermore, patients with a longer DMR duration showed a trend towards prolonged TFR. This survey indicates that low-dose TKI treatment is an important reality. While one third of Italian hematologists still had some uncertainties on TFR feasibility after using reduced doses of TKIs outside of clinical trials, TFR has often been considered a safe option even in patients treated with low-dose TKIs in the real-life setting. It should be noted that only 28.9% of our cases had a molecular recurrence, less than reported during standard dose treatment. Consequently, TFR is not impaired using low-dose TKIs.

Discontinuation of Tyrosine Kinase Inhibitors in Patients with Chronic Myeloid Leukemia: a Review of the Biological Factors Associated with Treatment-Free Remission

Purpose of Review

Clinical factors alone do not enable us to differentiate which patients will maintain treatment-free remission (TFR) from those who are likely to relapse. Thus, patient-specific factors must also play a role. This review will update the reader on the most recent studies presenting biological factors that can help predict tyrosine kinase inhibitor (TKI) discontinuation success.

Recent Findings

Cellular and molecular factors with a suggested role in TFR include immune factors and leukemic stem cell (LSC) persistence; the BCR::ABL1 transcript type, halving time, and BCR::ABL1 DNA and RNA positivity; as well as other molecular factors such as somatic mutations, RNA expression, and telomere length.

Summary

Our review presents several biomarkers with predictive value for TFR but also highlights areas of unmet need. Future discontinuation guidelines will likely include biological factors for the personalization of TFR prediction. However, it will be important that such advances do not prevent more patients from making a TKI discontinuation attempt.

Emerging concepts for assessing and predicting treatment-free remission in chronic myeloid leukemia patients

INTRODUCTION

In chronic myeloid leukemia (CML) patients who have reached a deep and sustained reduction of residual disease can attempt a discontinuation. The 'treatment-free remission' (TFR) has become a real long-term endpoint for 30-40% of chronic phase patients.

AREAS COVERED

In this review, we focus our attention on possible prognostic features who can predict the success of tyrosine kinase inhibitors discontinuation and how we can assess the minimal residual disease (MRD) during the TFR phase. Broad research was made on Medline, Embase and archives from EHA and ASH congresses.

EXPERT OPINION

Median duration of TKI therapy and of deep molecular response are the main prognostic factors identified in most trials and real-life experiences on discontinuation. Immunological pathways have been proposed as possible control on successful TFR as also early molecular response dynamics. Appropriate molecular monitoring by RQ-PCR in the TFR phase has been proposed by several international recommendations and digital droplet PCR (ddPCR) seems to have a possible role in the future for a better identification of candidate to this possible therapeutic strategy.

Regulatory T Cell as a Biomarker of Treatment-Free Remission in Patients with Chronic Myeloid Leukemia

Treatment-free remission (TFR) has become a therapeutic goal in chronic myeloid leukemia (CML), and approximately half of the patients with chronic phase-CML (CML-CP) with deep molecular remission (DMR) by tyrosine-kinase inhibitors (TKIs) have achieved TFR. However, the mechanism of continuous TFR is still unclear, as there are "fluctuate" patients who have BCR-ABL-positive leukemia cells but do not observe obvious relapse. We focused on the immune response and conducted an immune analysis using clinical samples from the imatinib discontinuation study, JALSG-STIM213. The results showed that, in the group that maintained TFR for 3 years, changes in regulatory T (Treg) cells were observed early after stopping imatinib treatment. The effector Treg (eTreg) cells increased transiently at 1 month after stopping imatinib and then returned to baseline at 3 months after stopping imatinib treatment. There was no difference in the Treg phenotype, and CD8+ T cells in the TFR group were relatively activated. High concentrations of imatinib before stopping were negatively correlated with eTreg cells after stopping imatinib. These data suggest immunological involvement in the maintenance of the TFR, and that Treg cells after stopping imatinib might be a biomarker for TFR. Furthermore, high imatinib exposure may have a negative immunological impact on the continuous TFR.

Inflammatory Cytokines Shape an Altered Immune Response During Myeloid Malignancies

The immune microenvironment is a critical driver and regulator of leukemic progression and hematological disease. Recent investigations have demonstrated that multiple immune components play a central role in regulating hematopoiesis, and dysfunction at the immune cell level significantly contributes to neoplastic disease. Immune cells are acutely sensitive to remodeling by leukemic inflammatory cytokine exposure. Importantly, immune cells are the principal cytokine producers in the hematopoietic system, representing an untapped frontier for clinical interventions. Due to a proinflammatory cytokine environment, dysregulation of immune cell states is a hallmark of hematological disease and neoplasia. Malignant immune adaptations have profound effects on leukemic blast proliferation, disease propagation, and drug-resistance. Conversely, targeting the immune landscape to restore hematopoietic function and limit leukemic expansion may have significant therapeutic value. Despite the fundamental role of the immune microenvironment during the initiation, progression, and treatment response of hematological disease, a detailed examination of how leukemic cytokines alter immune cells to permit, promote, or inhibit leukemia growth is lacking. Here we outline an immune-based model of leukemic transformation and highlight how the profound effect of immune alterations on the trajectory of malignancy. The focus of this review is to summarize current knowledge about the impacts of pro- and anti-inflammatory cytokines on immune cells subsets, their modes of action, and immunotherapeutic approaches with the potential to improve clinical outcomes for patients suffering from hematological myeloid malignancies.

A randomized, phase II trial of adjuvant immunotherapy with durable TKI-free survival in patients with chronic phase CML

PURPOSE

Chronic myeloid leukemia (CP-CML) patients can achieve undetectable minimal residual disease (UMRD) and discontinue tyrosine kinase inhibitors (TKIs). Cellular immunity plays an important role in CML disease control. We conducted a randomized, non-blinded phase II trial of adjuvant immunotherapy with TKIs to facilitate TKI discontinuation.

METHODS

TKI-treated patients with CP-CML were randomized to receive the K562/GM-CSF vaccine (vaccine) OR Interferon-α + Sargramostim (IFN). If UMRD was achieved, then all treatment was stopped. Patients who did not achieve UMRD within one year, had a molecular relapse, or discontinued therapy for toxicity could crossover.

RESULTS

Thirty-four patients were randomized to IFN (n = 18) or vaccine (n = 16), and 21 patients crossed over (IFN⟶vaccine: n = 9, vaccine⟶IFN, n = 12). TKIs at enrollment included imatinib (n = 31), nilotinib (n = 2), and dasatinib (n = 1). No patients discontinued vaccine due to side effects, while 33 % of IFN-treated patients discontinued treatment. More patients randomized to IFN (47.4 %, 95 % CI: 16.7-66.7 %) versus vaccine (25.0 %, 95 % CI: 0.5-43.5 %) achieved UMRD within one year. Seven patients randomized to IFN discontinued treatment with 28.6 % (95 % CI: 8.9-92.2 %) sustaining treatment-free remission (TFR) at 1 year, while three patients randomized to vaccine discontinued treatment with none sustaining TFR. Including crossover, there was a cumulative discontinuation success rate of 36.4 % (95 % CI: 16.6 %-79.5 %) after adjuvant IFN. Patients who sustained TFR received a median of 29 months of imatinib prior to discontinuation.

CONCLUSION

Adjuvant IFN led to durable TFRs with limited prior TKI exposure with comparable success to prior discontinuation trials, but many patients stopped IFN early.

Treatment-Free Remission in Chronic Myeloid Leukemia and New Approaches by Targeting Leukemia Stem Cells

The therapeutic landscape for chronic myeloid leukemia (CML) has improved significantly with the approval of tyrosine kinase inhibitors (TKIs) for therapeutic use. Most patients with optimal responses to TKIs can have a normal life expectancy. Treatment-free remission (TFR) after discontinuing TKI has increasingly become a new goal for CML treatment. However, TKI only "control" CML, and relapse after discontinuation has become a key factor hindering patient access to attempt TFR. In this study, we reviewed studies on TKI discontinuation, including both first and second-generation TKI. We also reviewed predictors of relapse, new monitoring methods, and strategies targeting leukemic stem cells.

Compromised anti-tumor-immune features of myeloid cell components in chronic myeloid leukemia patients

Chronic myeloid leukemia (CML) is a form of myeloproliferative neoplasm caused by the oncogenic tyrosine kinase BCR-ABL. Although tyrosine kinase inhibitors have dramatically improved the prognosis of patients with CML, several problems such as resistance and recurrence still exist. Immunological control may contribute to solving these problems, and it is important to understand why CML patients fail to spontaneously develop anti-tumor immunity. Here, we show that differentiation of conventional dendritic cells (cDCs), which are vital for anti-tumor immunity, is restricted from an early stage of hematopoiesis in CML. In addition, we found that monocytes and basophils, which are increased in CML patients, express high levels of PD-L1, an immune checkpoint molecule that inhibits T cell responses. Moreover, RNA-sequencing analysis revealed that basophils express genes related to poor prognosis in CML. Our data suggest that BCR-ABL not only disrupts the “accelerator” (i.e., cDCs) but also applies the “brake” (i.e., monocytes and basophils) of anti-tumor immunity, compromising the defense against CML cells.

NK Cells in Myeloproliferative Neoplasms (MPN)

Simple Summary

NK cells are important innate immune effectors that contribute substantially to tumor control, however the role of NK cells in haematological cancers is not as well understood. The aim of this review is to highlight the importance of the role of NK cells in the management of Ph+ Myeloproliferative Neoplasms, and emphasize the need and possible benefits of a more in-depth investigation into their role in classical MPNs and show potential strategies to harness the anti-tumoral capacities of NK cells.

Abstract

Myeloproliferative neoplasms (MPNs) comprise a heterogenous group of hematologic neoplasms which are divided into Philadelphia positive (Ph+), and Philadelphia negative (Ph−) or classical MPNs. A variety of immunological factors including inflammatory, as well as immunomodulatory processes, closely interact with the disease phenotypes in MPNs. NK cells are important innate immune effectors and substantially contribute to tumor control. Changes to the absolute and proportionate numbers of NK cell, as well as phenotypical and functional alterations are seen in MPNs. In addition to the disease itself, a variety of therapeutic options in MPNs may modify NK cell characteristics. Reports of suppressive effects of MPN treatment strategies on NK cell activity have led to intensive investigations into the respective compounds, to elucidate the possible negative effects of MPN therapy on control of the leukemic clones. We hereby review the available literature on NK cells in Ph+ and Ph− MPNs and summarize today’s knowledge on disease-related alterations in this cell compartment with particular focus on known therapy-associated changes. Furthermore, we critically evaluate conflicting data with possible implications for future projects. We also aim to highlight the relevance of full NK cell functionality for disease control in MPNs and the importance of considering specific changes related to therapy in order to avoid suppressive effects on immune surveillance.

Novel developments in chronic myeloid leukaemia

PURPOSE OF REVIEW

Despite unprecedented challenges during the preceding year, there have been a wide range of significant advances in the field of chronic myeloid leukaemia. In this review article we highlight papers reporting on some of the most important developments over the last year, both with regards to the clinical management of patients with chronic myeloid leukaemia, as well as studies that help to increase our understanding of the pathophysiology of the disease. We have performed a PubMed search to identify important papers and abstracts listed over the last year and have included additional papers published prior to this, where relevant, to provide context.

RECENT FINDINGS

We comment on novel biomarkers for treatment free remission as well as recent results from second generation Tyrosine Kinase Inhibitor (TKI) discontinuation studies. We discuss new techniques that are being used to assess TKI resistance as well as reviewing novel and emerging approaches to the management of resistant patients, including the use of combination therapies.

SUMMARY

This review highlights some of the most important research to have been reported over the last year in the field of chronic myeloid leukaemia, encompassing emerging diagnostic techniques, biomarkers and novel therapeutic options.

Treatment-Free Remission-A New Aim in the Treatment of Chronic Myeloid Leukemia

Tyrosine kinases inhibitors (TKIs) revolutionized chronic myeloid leukemia (CML) treatment for many years, prolonging patients' life expectancy to be comparable to age-matched healthy individuals. According to the latest the European LeukemiaNet (ELN) recommendations, CML treatment aims to achieve long-term remission without treatment (TFR), which is feasible in more than 40% of patients. Nearly all molecular relapses occur during the first 6 months after TKI withdrawal and do not progress to clinical relapse. The mechanisms that are responsible for CML relapses remain unexplained. It is suggested that maintaining TFR is not directly related to the total disposing of the gene transcript BCR-ABL1, but it might be a result of the restoration of the immune surveillance in CML. The importance of the involvement of immunocompetent cells in the period of TKI withdrawal is also emphasized by the presence of specific symptoms in some patients with "withdrawal syndrome". The goal of this review is to analyze data from studies regarding TFRs in order to characterize the elements of the immune system of patients that might prevent CML molecular relapse. The role of modern droplet digital polymerase chain reaction (ddPCR) and next-generation sequencing (NGS) in better identification of low levels of BCR-ABL1 transcripts was also taken into consideration for refining the eligibility criteria to stop TKI therapy.

Early BCR-ABL1 kinetics are predictive of subsequent achievement of treatment-free remission in chronic myeloid leukemia

With treatment-free remission (TFR) rapidly becoming the ultimate goal of therapy in chronic myeloid leukemia (CML), there is a need to develop strategies to maximize sustained TFR by improving our understanding of its key determinants. Chronic-phase CML patients attempting TFR were evaluated to identify the impact of multiple variables on the probability of sustained TFR. Early molecular response dynamics were included as a predictive variable, assessed by calculating the patient-specific halving time of BCR-ABL1 after commencing tyrosine kinase inhibitor (TKI) therapy. Overall, 115 patients attempted TFR and had ≥12 months of follow-up. The probability of sustained TFR, defined as remaining in major molecular response off TKI therapy for 12 months, was 55%. The time taken for the BCR-ABL1 value to halve was the strongest independent predictor of sustained TFR: 80% in patients with a halving time of <9.35 days (first quartile) compared with only 4% if the halving time was >21.85 days (last quartile) (P < .001). The e14a2 BCR-ABL1 transcript type and duration of TKI exposure before attempting TFR were also independent predictors of sustained TFR. However, the BCR-ABL1 value measured at 3 months of TKI was not an independent predictor of sustained TFR. A more rapid initial BCR-ABL1 decline after commencing TKI also correlated with an increased likelihood of achieving TFR eligibility. The association between sustained TFR and the time taken for BCR-ABL1 to halve after commencing TKI was validated using an independent dataset. These data support the critical importance of the initial kinetics of BCR-ABL1 decline for long-term outcomes.

Profiles of NK cell subsets are associated with successful tyrosine kinase inhibitor discontinuation in chronic myeloid leukemia and changes following interferon treatment

Recent studies have shown that approximately 50% of patients with chronic myeloid leukemia (CML) receiving tyrosine kinase inhibitor (TKI) therapy with a sustained deep molecular response (DMR) (BCR-ABL1^IS ≤ 0.01%) can achieve treatment-free remission (TFR, stopping TKI without relapse) and that prior interferon (IFN)-α therapy and higher NK cell counts at and after TKI discontinuation are associated with TFR. We recently reported that post-TKI discontinuation of IFN-α therapy could prevent molecular relapse (MR, BCR-ABL1^IS > 0.1%). Here, we evaluated whether NK cells are associated with MR and investigated the effects of post-TKI discontinuation IFN-α therapy on lymphocyte subsets. A total of 34 patients measuring blood lymphocyte subclasses were included. In the 22 patients who did not receive IFN-α therapy, at 1 month after TKI discontinuation, the nonrelapsed patients showed a significantly higher proportion and count of NK cells than the relapsed patients. In particular, the proportion and count of CD56dim NK cells were significantly higher in the nonrelapsed patients than in the relapsed patients. In the 12 patients who received IFN-α therapy, the level of CD56bright NK cells increased significantly after 3 and 6 months of IFN-α therapy. In summary, NK cells, in particular CD56dim NK cells, were associated with MR after TKI discontinuation in patients with CML. Additionally, IFN-α therapy gradually increased the level of CD56bright NK cells in patients with CML.

Understanding and Monitoring Chronic Myeloid Leukemia Blast Crisis: How to Better Manage Patients

Chronic myeloid leukemia (CML) is triggered primarily by the t(9;22) (q34.13; q11.23) translocation. This reciprocal chromosomal translocation leads to the formation of the BCR-ABL fusion gene. Patients in the chronic phase (CP) experience a good curative effect with tyrosine kinase inhibitors. However, cases are treatment refractory, with a dismal prognosis, when the disease has progressed to the accelerated phase (AP) or blast phase (BP). Until now, few reports have provided a comprehensive description of the mechanisms involved at different molecular levels. Indeed, the underlying pathogenesis of CML evolution comprises genetic aberrations, chromosomal translocations (except for the Philadelphia chromosome), telomere biology, and epigenetic anomalies. Herein, we provide knowledge of the biology responsible for blast transformation of CML at several levels, such as genetics, telomere biology, and epigenetic anomalies. Because of the limited treatment options available and poor outcomes, only the therapeutic response is monitored regularly, which involves BCR-ABL transcript level assessment and immunologic surveillance, with the optimal treatment strategy for patients in CP adapted to evaluate disease recurrence or progression. Overall, selecting optimal treatment endpoints to predict survival and successful TFR improves the quality of life of patients. Thus, identifying risk factors and developing risk-adapted therapeutic options may contribute to a better outcome for advanced-phase patients.

Optimizing NK Cell-Based Immunotherapy in Myeloid Leukemia: Abrogating an Immunosuppressive Microenvironment

Natural killer (NK) cells are prominent cytotoxic and cytokine-producing components of the innate immune system representing crucial effector cells in cancer immunotherapy. Presently, various NK cell-based immunotherapies have contributed to the substantial improvement in the reconstitution of NK cells against advanced-staged and high-risk AML. Various NK cell sources, including haploidentical NK cells, adaptive NK cells, umbilical cord blood NK cells, stem cell-derived NK cells, chimeric antigen receptor NK cells, cytokine-induced memory-like NK cells, and NK cell lines have been identified. Devising innovative approaches to improve the generation of therapeutic NK cells from the aforementioned sources is likely to enhance NK cell expansion and activation, stimulate ex vivo and in vivo persistence of NK cells and improve conventional treatment response of myeloid leukemia. The tumor-promoting properties of the tumor microenvironment and downmodulation of NK cellular metabolic activity in solid tumors and hematological malignancies constitute a significant impediment in enhancing the anti-tumor effects of NK cells. In this review, we discuss the current NK cell sources, highlight ongoing interventions in enhancing NK cell function, and outline novel strategies to circumvent immunosuppressive factors in the tumor microenvironment to improve the efficacy of NK cell-based immunotherapy and expand their future success in treating myeloid leukemia.

Subsequent attempt tyrosine kinase inhibitor discontinuation in patients with chronic myeloid leukemia; a single institute experience

Discontinuation of tyrosine kinase inhibitors (TKIs) is now a feasible therapeutic goal for patients with chronic phase chronic myeloid leukemia (CML-CP). Whereas approximately half of patients experience molecular relapse, after resuming with any TKI; the majority re-achieve a deep molecular response (DMR). It is unclear whether such patients who re-achieve a durable DMR can discontinue TKI safely again. Here, we retrospectively assessed first, second, and third attempts to stop TKIs in patients with CML-CP. At the first attempt, 28 out of a total of 53 patients achieved sustained treatment-free remission (TFR; 53.4%; 95% confidence interval [CI], 39.0%-65.9%). Subsequently, 10 of 25 patients attempted a second TKI discontinuation, and in all cases, this was after receiving second-generation TKIs. Four of 10 patients successfully achieved TFR (37.5%; 95% CI, 9.9%-65.9%). All patients who relapsed at the second TKI discontinuation attempt were re-administered TKIs, and soon achieved at least a major molecular remission. All six second relapse patients had a loss of MR^4.5 at 3 months after TKI discontinuation. These findings suggest that second and third attempts to successfully stop TKI treatment are feasible in patients with CML-CP.

Late molecular recurrences in patients with chronic myeloid leukemia experiencing treatment-free remission

Treatment-free remission (TFR) is an opportunity for patients with chronic myeloid leukemia (CML). Reported cumulative incidence curves of molecular recurrence (MRec) arbor a 2-phase shape with mainly early events, but also some late events (late MRec [LMRec]). Having discontinued our first patient in 2004, we have access to a prolonged follow-up, enabling us to characterize these late events. Over 15 years, 128 patients from our institution were registered in the Stop Imatinib (STIM; A Study for Tyrosine Kinase Inhibitors Discontinuation [A-STIM]) trial. MRec was defined by the loss of major molecular response (BCR-ABL1IS >0.1%). At the first TFR attempt, patients had been taking a tyrosine kinase inhibitor for a median of 7.1 years and in BCR-ABL1IS ≤0.01% (MR4) for a median of 4 years. The median follow-up of patients in TFR was 6.5 years. The TFR rate was estimated to be 45.6% after 7 years. For 9/65 (14%) patients experiencing MRec, recurrence occurred after 2 years in TFR (median, 3.6 years). The residual rate of MRec after 2 years was estimated to be 18%. The probability of remaining in TFR was 65.4% for patients having experienced fluctuations of their minimal residual disease (MRD) (at least 2 consecutive measurements BCR-ABL1IS >0.0032% or loss of MR4), whereas it was 100% for those with stable MRD (P = .003). After 2 years in TFR, we observed an 18% residual rate of LMRec. These late events represent 14% of all MRec and occur in patients with fluctuating MRD measurements. A long-term molecular follow-up therefore remains mandatory for CML patients in TFR. The A-STIM study was registered at www.clinicaltrials.gov as #NCT02897245.

Combination Therapies in Chronic Myeloid Leukemia for Potential Treatment-Free Remission: Focus on Leukemia Stem Cells and Immune Modulation

Although tyrosine Kinase Inhibitors (TKI) has revolutionized the treatment of chronic myeloid leukemia (CML), patients are not cured with the current therapy modalities. Also, the more recent goal of CML treatment is to induce successful treatment-free remission (TFR) among patients achieving durable deep molecular response (DMR). Together, it is necessary to develop novel, curative treatment strategies. With advancements in understanding the biology of CML, such as dormant Leukemic Stem Cells (LSCs) and impaired immune modulation, a number of agents are now under investigation. This review updates such agents that target LSCs, and together with TKIs, have the potential to eradicate CML. Moreover, we describe the developing immunotherapy for controlling CML.

Chronic Myeloid Leukemia: Modern therapies, current challenges and future directions

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm caused by a reciprocal translocation [t(9;22)(q34;q11.2)] that leads to the fusion of ABL1 gene sequences (9q34) downstream of BCR gene sequences (22q11) and is cytogenetically visible as Philadelphia chromosome (Ph). The resulting BCR/ABL1 chimeric protein is a constitutively active tyrosine kinase that activates multiple signaling pathways, which collectively lead to malignant transformation. During the early (chronic) phase of CML (CP-CML), the myeloid cell compartment is expanded, but differentiation is maintained. Without effective therapy, CP-CML invariably progresses to blast phase (BP-CML), an acute leukemia of myeloid or lymphoid phenotype. The development of BCR-AB1 tyrosine kinase inhibitors (TKIs) revolutionized the treatment of CML and ignited the start of a new era in oncology. With three generations of BCR/ABL1 TKIs approved today, the majority of CML patients enjoy long term remissions and near normal life expectancy. However, only a minority of patients maintain remission after TKI discontinuation, a status termed treatment free remission (TFR). Unfortunately, 5-10% of patients fail TKIs due to resistance and are at risk of progression to BP-CML, which is curable only with hematopoietic stem cell transplantation. Overcoming TKI resistance, improving the prognosis of BP-CML and improving the rates of TFR are areas of active research in CML.

Treatment-free remission and immunity in chronic myeloid leukemia

Chronic myeloid leukemia (CML) is caused by the reciprocal translocation t(9;22)(q34;q11), resulting in the BCR-ABL1 fusion gene. BCR-ABL1 tyrosine kinase inhibitors (TKIs) improve overall survival in patients with chronic phase CML (CML-CP). Approximately half of the patients who achieve a durable deep molecular response can achieve sustained treatment-free remission (TFR) after TKI discontinuation; thus TFR is now a therapeutic goal for most patients with CML-CP. Sensitive BCL-ABL1 transcript detection methods reveal that evidence of residual CML cells remains in patients who achieve sustained TFR, indicating that the host immune system protects against CML relapse. The human immune system is composed of innate and adaptive arms. Natural killer cells are major components of the innate immune system, while T cells are major components of the adaptive immune system. Myeloid-derived suppressor cells and regulatory T cells, both suppressors of the immune response, have important roles in the regulation of CML. Here, we review the current understanding of the immune response in CML, especially in TFR.

Natural Killer Cells and Anti-Cancer Therapies: Reciprocal Effects on Immune Function and Therapeutic Response

Simple Summary

Natural Killer (NK) cells are innate lymphocytes that play an important role in the immune response against cancer. Their activity is controlled by a balance of inhibitory and activating receptors, which in cancer can be skewed to favor their suppression in support of immune escape. It is therefore imperative to find ways to optimize their antitumor functionality. In this review, we explore and discuss how their activity influences, or even mediates, the efficacy of various anti-cancer therapies and, vice versa, how their activity can be affected by these therapies. Knowledge of the mechanisms underlying these observations could provide rationales for combining anti-cancer treatments with strategies enhancing NK cell function in order to improve their therapeutic efficacy.

Abstract

Natural Killer (NK) cells are innate immune cells with the unique ability to recognize and kill virus-infected and cancer cells without prior immune sensitization. Due to their expression of the Fc receptor CD16, effector NK cells can kill tumor cells through antibody-dependent cytotoxicity, making them relevant players in antibody-based cancer therapies. The role of NK cells in other approved and experimental anti-cancer therapies is more elusive. Here, we review the possible role of NK cells in the efficacy of various anti-tumor therapies, including radiotherapy, chemotherapy, and immunotherapy, as well as the impact of these therapies on NK cell function.

MR 4log and low levels of NK cells are associated with higher molecular relapse after imatinib discontinuation: Results of a prospective trial

BACKGROUND

Treatment-free survival (TFS) in chronic myeloid leukemia (CML) is a new goal. This prospective study aims to evaluate imatinib discontinuation's feasibility and safety in patients with deep molecular response MR4 (BCR-ABL1 < 0.01 % IS).

METHODS

Study was approved by the ethical committee and registered at Clinicaltrials.gov (NCT03239886). Incluision criteria were: age ≥ 18y, chronic phase, first-line imatinib for 36 months, MR4 for 12 months, no previous transplant or resistance. Imatinib was resumed when two samples confirmed the loss of MMR. The primary endpoint was molecular recurrence-free survival (MRFS) at 24 months. Lymphocyte subpopulations were counted in peripheral blood before discontinuation.

RESULTS

31 patients were included from Dec/2016 until Oct/2017. Median age was 54years, 58 % male, 58 % low Sokal, 65 % b3a2 transcripts, and 61 % were in MR4.5. Imatinib therapy's median time was 9.7y (3-14.9 y), median time of MR4 was 6.9y (1.6-10.3y). MRFS at 24 months was 55 % (95 % CI 39-75). Thirteen patients relapsed, 46 % after six months of discontinuation, and all patients recovered MMR. Median time to recover MMR was one month. MR4.5 was the only factor associated with MRFS. NK cells proportion at baseline was lower in patients with only MR4 who relapsed after discontinuation.

CONCLUSION

With a median duration of sustained MR4 above five years, as recommended by most TKI discontinuation guidelines, the TFS was similar to previous studies. Only MR4.5 was associated with lower risk of relapse. Further studies are needed to evaluate whether patients with only MR4 and low NK cell levels are suitable for discontinuation.

Improving outcomes in chronic myeloid leukemia through harnessing the immunological landscape

The quest for treatment-free remission (TFR) and deep molecular response (DMR) in chronic myeloid leukemia (CML) has been profoundly impacted by tyrosine kinase inhibitors (TKIs). Immunologic surveillance of residual leukemic cells is hypothesized to be one of the critical factors in successful TFR, with self-renewing leukemic stem cells implicated in relapse. Immunological characterization in CML may help to develop novel immunotherapies that specifically target residual leukemic cells upon TKI discontinuation to improve TFR rates. This review focuses on immune dysfunction in newly diagnosed CML patients, and the role that TKIs and other therapies have in restoring immune surveillance. Immune dysfunction and immunosurveillance in CML points towards several emerging areas in the key goals of DMR and TFR, including: (1) Aspects of innate immune system, in particular natural killer cells and the newly emerging target plasmacytoid dendritic cells. (2) The adaptive immune system, with promise shown in regard to leukemia-associated antigen vaccine-induced CD8 cytotoxic T-cells (CTL) responses, increased CTL expansion, and immune checkpoint inhibitors. (3) Immune suppressive myeloid-derived suppressor cells and T regulatory cells that are reduced in DMR and TFR. (4) Immunomodulator mesenchymal stromal cells that critically contribute to leukomogenesis through immunosuppressive properties and TKI- resistance. Therapeutic strategies that leverage existing immunological approaches include donor lymphocyte infusions, that continue to be used, often in combination with TKIs, in patients relapsing following allogeneic stem cell transplant. Furthermore, previous standards-of-care, including interferon-α, hold promise in attaining TFR in the post-TKI era. A deeper understanding of the immunological landscape in CML is therefore vital for both the development of novel and the repurposing of older therapies to improve TFR outcomes.