Elevated frequencies of CD4⁺ CD25⁺ CD127lo regulatory T cells is associated to poor prognosis in patients with acute myeloid leukemia

Single-cell sequencing unveils T-cell characteristic in acute myeloid leukemia

Acute myeloid leukemia (AML) presents as a remarkably heterogeneous disease, and the intricate role of various T cell subtypes, including T helper (Th) cells and regulatory T (Treg) cells, in immune dysregulation and the promotion of leukemia cell proliferation and survival is not yet fully understood. In this study, we conducted a comparative analysis of transcriptome profiles in T cells derived from bone marrow samples of three leukemia patients, both before and after treatment, as well as from a relapse sample. This analysis was facilitated through the utilization of single-cell RNA sequencing. The T cell population was subcategorized into CD4 + T cells and CD8 + T cells. Intriguingly, the composition of CD8 + T cells exhibited a relatively stable pattern before and after treatment, while a substantial difference in composition was observed in CD4 + T cells, notably in Th17 and Treg cell populations. Pseudotime trajectory analysis of CD4 + T cell clusters provided further insights into the augmented transition between Th17-like and Treg cells in AML. This transition was characterized by changes in the expression of key genes, including STAT3, CCR6, IL23R, FOXP3, and CTLA4, along their developmental path. An increased cell-to-cell interaction between AML blast cells and all types of T cells appeared to contribute to the restoration of normal T cell proportions. Notably, the LGALS9-CD45 and LGALS9-CD44 pathways emerged as pivotal interactions between blast cells and Treg cells. Our findings unveil an imbalanced differentiation pattern in CD4 + T cells and elucidate the immunosuppressive profiles linked to leukemia cells, thereby enhancing our understanding of CD4 + T cell functionality in the context of AML.

The KIR2DL family serves as prognostic biomarkers and correlates with immune infiltrates in acute myeloid leukaemia

Acute myeloid leukaemia (AML) is a prevalent haematological malignancy in which various immune and stromal cells in the bone marrow microenvironment have instrumental roles and substantially influence its progression. KIR2DL is a member of the immunoglobulin-like receptor family and a natural killer (NK) cell surface-specific receptor. However, its impact on immune infiltration regarding AML has not been addressed. We aimed to explore molecular markers associated with the immune microenvironment and prognosis of AML with a particular focus on KIR2DL family members. Analysis of data from The Cancer Genome Atlas and Genotype-Tissue Expression databases revealed that KIR2DL1, KIR2DL3 and KIR2DL4 expression were significantly upregulated in AML and associated with decreased overall survival (OS). Moreover, univariate Cox analysis implicated KIR2DL genes as independent prognostic markers of OS. Functional enrichment analysis revealed that KIR2DL genes were associated with immune cells, the immune microenvironment and NK cell-mediated cytotoxicity. Additionally, immune infiltration analyses revealed that KIR2DL upregulation was associated with stronger immune infiltration. Finally, we performed drug sensitivity profiling of KIR2DL genes using the Cellminer database. Collectively, our findings suggest that KIR2DL1, KIR2DL3 and KIR2DL4 have critical roles in AML and may represent novel biomarker genes for disease prognosis and immune infiltration.

Utilizing exosomes as sparking clinical biomarkers and therapeutic response in acute myeloid leukemia

Acute myeloid leukemia (AML) is a malignant clonal tumor originating from immature myeloid hematopoietic cells in the bone marrow with rapid progression and poor prognosis. Therefore, an in-depth exploration of the pathogenesis of AML can provide new ideas for the treatment of AML. In recent years, it has been found that exosomes play an important role in the pathogenesis of AML. Exosomes are membrane-bound extracellular vesicles (EVs) that transfer signaling molecules and have attracted a large amount of attention, which are key mediators of intercellular communication. Extracellular vesicles not only affect AML cells and normal hematopoietic cells but also have an impact on the bone marrow microenvironment and immune escape, thereby promoting the progression of AML and leading to refractory relapse. It is worth noting that exosomes and the various molecules they contain are expected to become the new markers for disease monitoring and prognosis of AML, and may also function as drug carriers and vaccines to enhance the treatment of leukemia. In this review, we mainly summarize to reveal the role of exosomes in AML pathogenesis, which helps us elucidate the application of exosomes in AML diagnosis and treatment.

Understanding the interaction between leukaemia stem cells and their microenvironment to improve therapeutic approaches

Although chemotherapeutic regimens can eliminate blasts in leukaemia patients, such therapies are associated with toxicity and often fail to eliminate all malignant cells resulting in disease relapse. Disease relapse has been attributed to the persistence of leukaemia cells in the bone marrow (BM) with the capacity to recapitulate disease; these cells are often referred to as leukaemia stem cells (LSCs). Although LSCs have distinct characteristics in terms of pathobiology and immunophenotype, they are still regulated by their interactions with the surrounding microenvironment. Thus, understanding the interaction between LSCs and their microenvironment is critical to identify effective therapies. To this end, there are numerous efforts to develop models to study such interactions. In this review, we will focus on the reciprocal interactions between LSCs and their milieu in the BM. Furthermore, we will highlight relevant therapies targeting these interactions and discuss some of the promising in vitro models designed to mimic such relationship. LINKED ARTICLES: This article is part of a themed issue on Cancer Microenvironment and Pharmacological Interventions. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.2/issuetoc.

CD200/CD200R: Bidirectional Role in Cancer Progression and Immunotherapy

As an immune checkpoint molecule, CD200 serves a foundational role in regulating immune homeostasis and promoting self-tolerance. While CD200 expression occurs in various immune cell subsets and normal tissues, its aberrant expression patterns in hematologic malignancies and solid tumors have been linked to immune evasion and cancer progression under pathological conditions, particularly through interactions with its cognate receptor, CD200R. Through this CD200/CD200R signaling pathway, CD200 exerts its immunosuppressive effects by inhibiting natural killer (NK) cell activation, cytotoxic T cell functions, and M1-polarized macrophage activity, while also facilitating expansion of myeloid-derived suppressor cells (MDSCs) and Tregs. Moreover, CD200/CD200R expression has been linked to epithelial-to-mesenchymal transition and distant metastasis, further illustrating its role in cancer progression. Conversely, CD200 has also been shown to exert anti-tumor effects in certain cancer types, such as breast carcinoma and melanoma, indicating that CD200 may exert bidirectional effects on cancer progression depending on the specific tumor microenvironment (TME). Regardless, modulating the CD200/CD200R axis has garnered clinical interest as a potential immunotherapeutic strategy for cancer therapy, as demonstrated by early-phase clinical trials. However, further research is necessary to fully understand the complex interactions of CD200 in the tumor microenvironment and to optimize its therapeutic potential in cancer immunotherapy.

Granulocyte-Macrophage-Colony-Stimulating-Factor Combined with Prostaglandin E1 Create Dendritic Cells of Leukemic Origin from AML Patients' Whole Blood and Whole Bone Marrow That Mediate Antileukemic Processes after Mixed Lymphocyte Culture

Although several (chemotherapeutic) protocols to treat acute myeloid leukemia (AML) are available, high rates of relapses in successfully treated patients occur. Strategies to stabilize remissions are greatly needed. The combination of the (clinically approved) immune-modulatory compounds Granulocyte-Macrophage-Colony-Stimulating-Factor (GM-CSF) and Prostaglandine E1 (PGE-1) (Kit-M) converts myeloid blasts into dendritic cells of leukemic origin (DCleu). After stimulation with DCleu ex vivo, leukemia-specific antileukemic immune cells are activated. Therefore, Kit-M treatment may be an attractive immunotherapeutic tool to treat patients with myeloid leukemia. Kit-M-mediated antileukemic effects on whole bone marrow (WBM) were evaluated and compared to whole blood (WB) to evaluate the potential effects of Kit-M on both compartments. WB and WBM samples from 17 AML patients at first diagnosis, in persisting disease and at relapse after allogeneic stem cell transplantation (SCT) were treated in parallel with Kit-M to generate DC/DCleu. Untreated samples served as controls. After a mixed lymphocyte culture enriched with patients' T cells (MLC), the leukemia-specific antileukemic effects were assessed through the degranulation- (CD107a+ T cells), the intracellular IFNγ production- and the cytotoxicity fluorolysis assay. Quantification of cell subtypes was performed via flow cytometry. In both WB and WBM significantly higher frequencies of (mature) DCleu were generated without induction of blast proliferation in Kit-M-treated samples compared to control. After MLC with Kit-M-treated vs. not pretreated WB or WBM, frequencies of (leukemia-specific) immunoreactive cells (e.g., non-naive, effector-, memory-, CD3+β7+ T cells, NK- cells) were (significantly) increased, whereas leukemia-specific regulatory T cells (Treg, CD152+ T cells) were (significantly) decreased. The cytotoxicity fluorolysis assay showed a significantly improved blast lysis in Kit-M-treated WB and WBM compared to control. A parallel comparison of WB and WBM samples revealed no significant differences in frequencies of DCleu, (leukemia-specific) immunoreactive cells and achieved antileukemic processes. Kit-M was shown to have comparable effects on WB and WBM samples regarding the generation of DCleu and activation of (antileukemic) immune cells after MLC. This was true for samples before or after SCT. In summary, a potential Kit-M in vivo treatment could lead to antileukemic effects in WB as well as WBM in vivo and to stabilization of the disease or remission in patients before or after SCT. A clinical trial is currently being planned.

Relapse of acute myeloid leukemia after allogeneic stem cell transplantation: immune escape mechanisms and current implications for therapy

Acute myeloid leukemia (AML) is a heterogeneous disease characterized by the expansion of immature myeloid cells in the bone marrow (BM) and peripheral blood (PB) resulting in failure of normal hematopoiesis and life-threating cytopenia. Allogeneic hematopoietic stem cell transplantation (allo-HCT) is an established therapy with curative potential. Nevertheless, post-transplant relapse is common and associated with poor prognosis, representing the major cause of death after allo-HCT. The occurrence of relapse after initially successful allo-HCT indicates that the donor immune system is first able to control the leukemia, which at a later stage develops evasion strategies to escape from immune surveillance. In this review we first provide a comprehensive overview of current knowledge regarding immune escape in AML after allo-HCT, including dysregulated HLA, alterations in immune checkpoints and changes leading to an immunosuppressive tumor microenvironment. In the second part, we draw the line from bench to bedside and elucidate to what extend immune escape mechanisms of relapsed AML are yet exploited in treatment strategies. Finally, we give an outlook how new emerging technologies could help to improve the therapy for these patients, and elucidate potential new treatment options.

Targeting apoptosis dysregulation in myeloid malignancies - The promise of a therapeutic revolution

In recent years, the therapeutic landscape of myeloid malignancies has been completely revolutionized by the introduction of several new drugs, targeting molecular alterations or pathways crucial for leukemia cells survival. Particularly, many agents targeting apoptosis have been investigated in both pre-clinical and clinical studies. For instance, venetoclax, a pro-apoptotic agent active on BCL-2 signaling, has been successfully used in the treatment of acute myeloid leukemia (AML). The impressive results achieved in this context have made the apoptotic pathway an attractive target also in other myeloid neoplasms, translating the experience of AML. Therefore, several drugs are now under investigation either as single or in combination strategies, due to their synergistic efficacy and capacity to overcome resistance. In this paper, we will review the mechanisms of apoptosis and the specific drugs currently used and under investigation for the treatment of myeloid neoplasia, identifying critical research necessities for the upcoming years.

Phase 2 study of PD-1 blockade following autologous transplantation for patients with AML ineligible for allogeneic transplant

Allogeneic transplant remains the best postremission therapy for patients with nonfavorable risk acute myeloid leukemia (AML). However, some patients are ineligible because of psychosocial barriers, such as lack of appropriate caregiver support. We hypothesized that immune checkpoint inhibition after autologous transplant might represent effective postremission therapy in such patients. We conducted a phase 2 study of autologous transplantation followed by administration of pembrolizumab (8 cycles starting day +1). Twenty patients with nonfavorable AML in complete remission were treated (median age, 64 years; CR1, 80%); 55% were non-White and adverse-risk AML was present in 40%. Treatment was well tolerated, with only 1 nonrelapse death. Immune-related adverse events occurred in 9 patients. After a median follow-up of 80 months, 14 patients remain alive, with 10 patients in continuous remission. The estimated 2-year LFS was 48.4%, which met the primary end point of 2-year LFS >25%; the 2-year overall survival (OS), nonrelapse mortality, and cumulative incidences of relapse were 68%, 5%, and 46%, respectively. In comparison with a propensity score-matched cohort group of patients with AML receiving allogeneic transplant, the 3-year OS was similar (73% vs 76%). Patients in the study had inferior LFS (51% vs 75%) but superior postrelapse survival (45% vs 14%). In conclusion, programmed cell death protein-1 blockade after autologous transplant is a safe and effective alternative postremission strategy in patients with nonfavorable risk AML who are ineligible for allogeneic transplant, a context in which there is significant unmet need. This trial was registered at www.clinicaltrials.gov as #NCT02771197.

Unveiling T cell evasion mechanisms to immune checkpoint inhibitors in acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous and aggressive hematologic malignancy that is associated with a high relapse rate and poor prognosis. Despite advances in immunotherapies in solid tumors and other hematologic malignancies, AML has been particularly difficult to treat with immunotherapies, as their efficacy is limited by the ability of leukemic cells to evade T cell recognition. In this review, we discuss the common mechanisms of T cell evasion in AML: (1) increased expression of immune checkpoint molecules; (2) downregulation of antigen presentation molecules; (3) induction of T cell exhaustion; and (4) creation of an immunosuppressive environment through the increased frequency of regulatory T cells. We also review the clinical investigation of immune checkpoint inhibitors (ICIs) in AML. We discuss the limitations of ICIs, particularly in the context of T cell evasion mechanisms in AML, and we describe emerging strategies to overcome T cell evasion, including combination therapies. Finally, we provide an outlook on the future directions of immunotherapy research in AML, highlighting the need for a more comprehensive understanding of the complex interplay between AML cells and the immune system.

The role of bone marrow microenvironment (BMM) cells in acute myeloid leukemia (AML) progression: immune checkpoints, metabolic checkpoints, and signaling pathways

Acute myeloid leukemia (AML) comprises a multifarious and heterogeneous array of illnesses characterized by the anomalous proliferation of myeloid cells in the bone marrow microenvironment (BMM). The BMM plays a pivotal role in promoting AML progression, angiogenesis, and metastasis. The immune checkpoints (ICs) and metabolic processes are the key players in this process. In this review, we delineate the metabolic and immune checkpoint characteristics of the AML BMM, with a focus on the roles of BMM cells e.g. tumor-associated macrophages, natural killer cells, dendritic cells, metabolic profiles and related signaling pathways. We also discuss the signaling pathways stimulated in AML cells by BMM factors that lead to AML progression. We then delve into the roles of immune checkpoints in AML angiogenesis, metastasis, and cell proliferation, including co-stimulatory and inhibitory ICs. Lastly, we discuss the potential therapeutic approaches and future directions for AML treatment, emphasizing the potential of targeting metabolic and immune checkpoints in AML BMM as prognostic and therapeutic targets. In conclusion, the modulation of these processes through the use of directed drugs opens up new promising avenues in combating AML. Thereby, a comprehensive elucidation of the significance of these AML BMM cells' metabolic and immune checkpoints and signaling pathways on leukemic cells can be undertaken in the future investigations. Additionally, these checkpoints and cells should be considered plausible multi-targeted therapies for AML in combination with other conventional treatments in AML. Video Abstract.

Divergent CD4+ T-cell profiles are associated with anti-HLA alloimmunization status in platelet-transfused AML patients

Introduction

Acute myeloid leukemia (AML) is one of the commonest hematologic disorders. Due to the high frequency of disease- or treatment-related thrombocytopenia, AML requires treatment with multiple platelet transfusions, which can trigger a humoral response directed against platelets. Some, but not all, AML patients develop an anti-HLA immune response after multiple transfusions. We therefore hypothesized that different immune activation profiles might be associated with anti-HLA alloimmunization status.

Methods

We tested this hypothesis, by analyzing CD4+ T lymphocyte (TL) subsets and their immune control molecules in flow cytometry and single-cell multi-omics.

Results

A comparison of immunological status between anti-HLA alloimmunized and non-alloimmunized AML patients identified differences in the phenotype and function of CD4+ TLs. CD4+ TLs from alloimmunized patients displayed features of immune activation, with higher levels of CD40 and OX40 than the cells of healthy donors. However, the most notable differences were observed in non-alloimmunized patients. These patients had lower levels of CD40 and OX40 than alloimmunized patients and higher levels of PD1. Moreover, the Treg compartment of non-alloimmunized patients was larger and more functional than that in alloimmunized patients. These results were supported by a multi-omics analysis of immune response molecules in conventional CD4+ TLs, Tfh circulating cells, and Tregs.

Discussion

Our results thus reveal divergent CD4+ TL characteristics correlated with anti-HLA alloimmunization status in transfused AML patients. These differences, characterizing CD4+ TLs independently of any specific antigen, should be taken into account when considering the immune responses of patients to infections, vaccinations, or transplantations.

IL-8 in bone marrow and peripheral blood of patients with B-cell acute lymphoblastic leukemia is associated with high regulatory T cell counts, degree of tumor infiltration and expression of CXCR1 in blasts

INTRODUCTION

Regulatory T cells (Treg cells) in a tumor environment and the expression of forkhead box P3 (FOXP3) in tumor cells have been associated with a poor prognosis. There are few studies evaluating Treg cells and FOXP3 in B-cell acute lymphoblastic leukemia (B-cell ALL). This study aimed to evaluate the frequencies of Treg cells in bone marrow (BM) and peripheral blood (PB) of patients with B-cell ALL and to determine their associations with the circulating cytokine profile and the expression of CXCR1 (IL-8 receptor) in Treg cells, as well as to compare FOXP3 expression in blasts of patients with B-cell ALL and normal lymphoid precursors.

METHODS

Samples of BM and PB from patients with B-cell ALL and healthy controls were studied. Treg cells, cytokines, FOXP3 and CXCR1 were evaluated using flow cytometry and analyzed.

RESULTS

A total of 20 patients with B-cell ALL and 10 healthy controls were included. In B-cell ALL patients, Treg cell frequencies increased significantly, with higher percentages in the PB. Absolute Treg cell counts were associated with absolute blast counts in the BM and PB and with an IL-8 concentration. The IL-8 and IL-6 levels were associated with the CXCR1 expression in PB Treg cells. In addition, a greater expression of FOXP3 was observed in leukemic blasts than in normal lymphoid precursors.

CONCLUSIONS

These results suggest that the presence of Treg cells and cytokines in the tumor environment may correspond to mechanisms to evade the immune response. For that reason, it would be important to monitor these parameters in B-cell ALL to establish their effect on the disease prognosis.

Checkpoint Inhibitors in Acute Myeloid Leukemia

The prognosis of acute myeloid leukemia (AML) remains unsatisfactory. Among the reasons for the poor response to therapy and high incidence of relapse, there is tumor cell immune escape, as AML blasts can negatively influence various components of the immune system, mostly weakening T-cells. Since leukemic cells can dysregulate immune checkpoints (ICs), receptor-based signal transductors that lead to the negative regulation of T-cells and, eventually, to immune surveillance escape, the inhibition of ICs is a promising therapeutic strategy and has led to the development of so-called immune checkpoint inhibitors (ICIs). ICIs, in combination with conventional chemotherapy, hypomethylating agents or targeted therapies, are being increasingly tested in cases of AML, but the results reported are often conflicting. Here, we review the main issues concerning the immune system in AML, the main pathways leading to immune escape and the results obtained from clinical trials of ICIs, alone or in combination, in newly diagnosed or relapsed/refractory AML.

Immune cell proportions correlate with clinicogenomic features and ex vivo drug responses in acute myeloid leukemia

Introduction

The implementation of small-molecule and immunotherapies in acute myeloid leukemia (AML) has been challenging due to genetic and epigenetic variability amongst patients. There are many potential mechanisms by which immune cells could influence small-molecule or immunotherapy responses, yet, this area remains understudied.

Methods

Here we performed cell type enrichment analysis from over 560 AML patient bone marrow and peripheral blood samples from the Beat AML dataset to describe the functional immune landscape of AML.

Results

We identify multiple cell types that significantly correlate with AML clinical and genetic features, and we also observe significant correlations of immune cell proportions with ex vivo small-molecule and immunotherapy responses. Additionally, we generated a signature of terminally exhausted T cells (Tex) and identified AML with high monocytic proportions as strongly correlating with increased proportions of these immunosuppressive T cells.

Discussion

Our work, which is accessible through a new "Cell Type" module in our visualization platform (Vizome; http://vizome.org/), can be leveraged to investigate potential contributions of different immune cells on many facets of the biology of AML.

Effect of changes in lymphocyte subsets at diagnosis in acute myeloid leukemia on prognosis: association with complete remission rates and relapse free survivals

We prospectively investigated whether the characteristics of lymphocyte subsets at diagnosis in acute myeloid leukemia (AML) patients are different from healthy controls and affect treatment outcomes. A total of 91 AML patients classified into 3 genetic risk subgroups (favorable/intermediate/poor) according to 2022 NCCN guidelines were enrolled. We measured lymphocyte subsets by flow cytometry with peripheral blood samples at diagnosis and compared results with healthy controls. Influences of lymphocyte subsets on complete remission (CR) rates and survivals were also evaluated. AML patients had significantly lower numbers and proportions of CD56dimCD16+ natural killer (NK) cells, central memory T cells, and regulatory T cells than healthy controls. Higher proportion of helper/inducer T cells, CD4+CD31+ naïve T cells, and decreased proportion of NK cells significantly increased CR rates in 65 non-promyelocytic leukemia patients (P = 0.034, 0.027, and 0.019, respectively), and it was also significant in multivariable analysis with age/risk adjusted (P = 0.014, 0.016, and 0.045, respectively). NK cells < 4.8% of lymphocytes demonstrated significantly shorter relapse free survivals (RFS) in both univariate and multivariate analyses with risk adjusted (P = 0.006 and 0.037, respectively). AML patients showed significant lower numbers of CD56dimCD16+ NK cells, central memory T cells, and regulatory T cells than healthy controls at diagnosis. Higher proportion of helper/inducer T cells and CD4+CD31+ naïve T cells and decreased proportion of NK cells at diagnosis were independent factor of increasing probability of CR, and proportion of NK cells < 4.8% at diagnosis had adverse impact in RFS.

NK cell defects: implication in acute myeloid leukemia

Acute Myeloid Leukemia (AML) is a complex disease with rapid progression and poor/unsatisfactory outcomes. In the past few years, the focus has been on developing newer therapies for AML; however, relapse remains a significant problem. Natural Killer cells have strong anti-tumor potential against AML. This NK-mediated cytotoxicity is often restricted by cellular defects caused by disease-associated mechanisms, which can lead to disease progression. A stark feature of AML is the low/no expression of the cognate HLA ligands for the activating KIR receptors, due to which these tumor cells evade NK-mediated lysis. Recently, different Natural Killer cell therapies have been implicated in treating AML, such as the adoptive NK cell transfer, Chimeric antigen receptor-modified NK (CAR-NK) cell therapy, antibodies, cytokine, and drug treatment. However, the data available is scarce, and the outcomes vary between different transplant settings and different types of leukemia. Moreover, remission achieved by some of these therapies is only for a short time. In this mini-review, we will discuss the role of NK cell defects in AML progression, particularly the expression of different cell surface markers, the available NK cell therapies, and the results from various preclinical and clinical trials.

Immunogenic Cell Death in Hematological Malignancy Therapy

Although the curative effect of hematological malignancies has been improved in recent years, relapse or drug resistance of hematological malignancies will eventually recur. Furthermore, the microenvironment disorder is an important mechanism in the pathogenesis of hematological malignancies. Immunogenic cell death (ICD) is a unique mechanism of regulated cell death (RCD) that triggers an intact antigen-specific adaptive immune response by firing a set of danger signals or damage-associated molecular patterns (DAMPs), which is an immunotherapeutic modality with the potential for the treatment of hematological malignancies. This review summarizes the existing knowledge about the induction of ICD in hematological malignancies and the current research on combining ICD inducers with other treatment strategies for hematological malignancies.

BET inhibitors rescue anti-PD1 resistance by enhancing TCF7 accessibility in leukemia-derived terminally exhausted CD8+ T cells

Many acute myeloid leukemia (AML) patients exhibit hallmarks of immune exhaustion, such as increased myeloid-derived suppressor cells, suppressive regulatory T cells and dysfunctional T cells. Similarly, we have identified the same immune-related features, including exhausted CD8+ T cells (TEx) in a mouse model of AML. Here we show that inhibitors that target bromodomain and extra-terminal domain (BET) proteins affect tumor-intrinsic factors but also rescue T cell exhaustion and ICB resistance. Ex vivo treatment of cells from AML mice and AML patients with BET inhibitors (BETi) reversed CD8+ T cell exhaustion by restoring proliferative capacity and expansion of the more functional precursor-exhausted T cells. This reversal was enhanced by combined BETi and anti-PD1 treatment. BETi synergized with anti-PD1 in vivo, resulting in the reduction of circulating leukemia cells, enrichment of CD8+ T cells in the bone marrow, and increase in expression of Tcf7, Slamf6, and Cxcr5 in CD8+ T cells. Finally, we profiled the epigenomes of in vivo JQ1-treated AML-derived CD8+ T cells by single-cell ATAC-seq and found that JQ1 increases Tcf7 accessibility specifically in Tex cells, suggesting that BETi likely acts mechanistically by relieving repression of progenitor programs in Tex CD8+ T cells and maintaining a pool of anti-PD1 responsive CD8+ T cells.

A Phase I Trial of Allogeneic γδ T Lymphocytes From Haploidentical Donors in Patients With Refractory or Relapsed Acute Myeloid Leukemia

Introduction We report the results of a phase I clinical trial NCT03790072 of an adoptive transfer of γδ T lymphocytes from haploidentical donors in patients with refractory/relapsed acute myeloid leukemia after lymphodepletion regimen. Patients and methods Healthy donor mononuclear cells collected by leukapheresis were consistently expanded to generate products of 10⁹ to 10¹⁰ γδ T cells. Seven patients received donor-derived T cell product at doses of 10⁶/kg (n = 3), 10⁷/kg (n = 3), and 10⁸/kg (n = 1). Results Four patients had bone marrow evaluation at day 28. One patient had a complete remission, one was classified as morphologic leukemia-free state, one had stable disease and one had no evidence of response. In one patient, there was evidence of disease control with repeat infusions up to 100 days after first dosing. There were no treatment-related serious adverse events or treatment-related Common Terminology Criteria for Adverse Events grade 3 or greater toxicities at any dose level. Allogeneic Vγ9Vδ2 T cell infusion was shown to be safe and feasible up to a cell dose of 10⁸/kg. Discussion In agreement with previously published studies, the infusion of allogeneic Vγ9Vδ2 cells was safe. The contribution of lymphodepleting chemotherapy to responses seen cannot be ruled out. Main limitation of the study is the low number of patients and interruption due to COVID-19 pandemic. Conclusion These positive Phase 1 results support progression to phase II clinical trials.

Cuproptosis-related lncRNA signature for prognostic prediction in patients with acute myeloid leukemia

BACKGROUND

Long non-coding RNAs (lncRNAs) have been reported to have a crucial impact on the pathogenesis of acute myeloid leukemia (AML). Cuproptosis, a copper-triggered modality of mitochondrial cell death, might serve as a promising therapeutic target for cancer treatment and clinical outcome prediction. Nevertheless, the role of cuproptosis-related lncRNAs in AML is not fully understood.

METHODS

The RNA sequencing data and demographic characteristics of AML patients were downloaded from The Cancer Genome Atlas database. Pearson correlation analysis, the least absolute shrinkage and selection operator algorithm, and univariable and multivariable Cox regression analyses were applied to identify the cuproptosis-related lncRNA signature and determine its feasibility for AML prognosis prediction. The performance of the proposed signature was evaluated via Kaplan-Meier survival analysis, receiver operating characteristic curves, and principal component analysis. Functional analysis was implemented to uncover the potential prognostic mechanisms. Additionally, quantitative real-time PCR (qRT-PCR) was employed to validate the expression of the prognostic lncRNAs in AML samples.

RESULTS

A signature consisting of seven cuproptosis-related lncRNAs (namely NFE4, LINC00989, LINC02062, AC006460.2, AL353796.1, PSMB8-AS1, and AC000120.1) was proposed. Multivariable cox regression analysis revealed that the proposed signature was an independent prognostic factor for AML. Notably, the nomogram based on this signature showed excellent accuracy in predicting the 1-, 3-, and 5-year survival (area under curve = 0.846, 0.801, and 0.895, respectively). Functional analysis results suggested the existence of a significant association between the prognostic signature and immune-related pathways. The expression pattern of the lncRNAs was validated in AML samples.

CONCLUSION

Collectively, we constructed a prediction model based on seven cuproptosis-related lncRNAs for AML prognosis. The obtained risk score may reveal the immunotherapy response in patients with this disease.

Blasts in context: the impact of the immune environment on acute myeloid leukemia prognosis and treatment

Acute myeloid leukemia (AML) is a cancer that originates from the bone marrow (BM). Under physiological conditions, the bone marrow supports the homeostasis of immune cells and hosts memory lymphoid cells. In this review, we summarize our present understanding of the role of the immune microenvironment on healthy bone marrow and on the development of AML, with a focus on T cells and other lymphoid cells. The types and function of different immune cells involved in the AML microenvironment as well as their putative role in the onset of disease and response to treatment are presented. We also describe how the immune context predicts the response to immunotherapy in AML and how these therapies modulate the immune status of the bone marrow. Finally, we focus on allogeneic stem cell transplantation and summarize the current understanding of the immune environment in the post-transplant bone marrow, the factors associated with immune escape and relevant strategies to prevent and treat relapse.

The potential role of the thymus in immunotherapies for acute myeloid leukemia

Understanding the factors which shape T-lymphocyte immunity is critical for the development and application of future immunotherapeutic strategies in treating hematological malignancies. The thymus, a specialized central lymphoid organ, plays important roles in generating a diverse T lymphocyte repertoire during the infantile and juvenile stages of humans. However, age-associated thymic involution and diseases or treatment associated injury result in a decline in its continuous role in the maintenance of T cell-mediated anti-tumor/virus immunity. Acute myeloid leukemia (AML) is an aggressive hematologic malignancy that mainly affects older adults, and the disease's progression is known to consist of an impaired immune surveillance including a reduction in naïve T cell output, a restriction in T cell receptor repertoire, and an increase in frequencies of regulatory T cells. As one of the most successful immunotherapies thus far developed for malignancy, T-cell-based adoptive cell therapies could be essential for the development of a durable effective treatment to eliminate residue leukemic cells (blasts) and prevent AML relapse. Thus, a detailed cellular and molecular landscape of how the adult thymus functions within the context of the AML microenvironment will provide new insights into both the immune-related pathogenesis and the regeneration of a functional immune system against leukemia in AML patients. Herein, we review the available evidence supporting the potential correlation between thymic dysfunction and T-lymphocyte impairment with the ontogeny of AML (II-VI). We then discuss how the thymus could impact current and future therapeutic approaches in AML (VII). Finally, we review various strategies to rejuvenate thymic function to improve the precision and efficacy of cancer immunotherapy (VIII).

Bone Marrow Microenvironment as a Source of New Drug Targets for the Treatment of Acute Myeloid Leukaemia

Acute myeloid leukaemia (AML) is a heterogeneous disease with one of the worst survival rates of all cancers. The bone marrow microenvironment is increasingly being recognised as an important mediator of AML chemoresistance and relapse, supporting leukaemia stem cell survival through interactions among stromal, haematopoietic progenitor and leukaemic cells. Traditional therapies targeting leukaemic cells have failed to improve long term survival rates, and as such, the bone marrow niche has become a promising new source of potential therapeutic targets, particularly for relapsed and refractory AML. This review briefly discusses the role of the bone marrow microenvironment in AML development and progression, and as a source of novel therapeutic targets for AML. The main focus of this review is on drugs that modulate/target this bone marrow microenvironment and have been examined in in vivo models or clinically.

A Novel Defined Pyroptosis-Related Gene Signature for the Prognosis of Acute Myeloid Leukemia

Pyroptosis is an inflammatory form of programmed necrotic cell death, but its potential prognostic value in acute myeloid leukemia (AML) remains unclear. On the basis of available AML data from TCGA and TARGET databases, a 10-gene signature model was constructed to effectively predict AML prognosis by performing LASSO Cox regression analysis, which showed that patients with a low-risk score had a significantly better prognosis than that of the high-risk group, and receiver operator characteristic (ROC) analysis achieved superior performance in the prognostic model. The model was further well-verified in an external GEO cohort. Multivariable Cox regression analysis showed that, in addition to age, the risk score was an independent poor survival factor for AML patients, and a nomogram model was constructed with high accuracy. Moreover, the high-risk group generally had higher cytolytic activity and increased levels of infiltrating immune cells, including tumor-infiltrating lymphocytes (TILs) and regulatory T cells (Tregs), which could be related to the expression of immune checkpoint genes. Additionally, low-risk AML patients may have a better response from traditional chemotherapeutic drugs. In conclusion, a pyroptosis-related gene signature can independently predict the prognosis of AML patients with sufficient predictive power, and pyroptosis plays an important role in the immune microenvironment of AML, which may be used to develop a new effective therapeutic method for AML in the future.

Regulation of hematopoietic and leukemia stem cells by regulatory T cells

Adult bone marrow (BM) hematopoietic stem cells (HSCs) are maintained in a quiescent state and sustain the continuous production of all types of blood cells. HSCs reside in a specialized microenvironment the so-called HSC niche, which equally promotes HSC self-renewal and differentiation to ensure the integrity of the HSC pool throughout life and to replenish hematopoietic cells after acute injury, infection or anemia. The processes of HSC self-renewal and differentiation are tightly controlled and are in great part regulated through cellular interactions with classical (e.g. mesenchymal stromal cells) and non-classical niche cells (e.g. immune cells). In myeloid leukemia, some of these regulatory mechanisms that evolved to maintain HSCs, to protect them from exhaustion and immune destruction and to minimize the risk of malignant transformation are hijacked/disrupted by leukemia stem cells (LSCs), the malignant counterpart of HSCs, to promote disease progression as well as resistance to therapy and immune control. CD4⁺ regulatory T cells (Tregs) are substantially enriched in the BM compared to other secondary lymphoid organs and are crucially involved in the establishment of an immune privileged niche to maintain HSC quiescence and to protect HSC integrity. In leukemia, Tregs frequencies in the BM even increase. Studies in mice and humans identified the accumulation of Tregs as a major immune-regulatory mechanism. As cure of leukemia implies the elimination of LSCs, the understanding of these immune-regulatory processes may be of particular importance for the development of future treatments of leukemia as targeting major immune escape mechanisms which revolutionized the treatment of solid tumors such as the blockade of the inhibitory checkpoint receptor programmed cell death protein 1 (PD-1) seems less efficacious in the treatment of leukemia. This review will summarize recent findings on the mechanisms by which Tregs regulate stem cells and adaptive immune cells in the BM during homeostasis and in leukemia.

The prognostic marker FLVCR2 associated with tumor progression and immune infiltration for acute myeloid leukemia

Acute myeloid leukemia (AML) is one of the most common hematopoietic malignancies in adults. The tumor microenvironment (TME) has a critical effect on AML occurrence, recurrence, and progression. The gene feline leukemia virus subgroup C cellular receptor family member 2 (FLVCR2) belongs to the major facilitator superfamily of transporter protein members, which is primarily involved in transporting small molecules. The potential role of FLVCR2 in the TME in AML has not been investigated. To clarify the expression and role of FLVCR2 in AML, we analyzed the Gene Expression Omnibus and The Cancer Genome Atlas databases and found that FLVCR2 mRNA expression significantly increased among patients with AML. Furthermore, based on an analysis of the Gene Expression Profiling Interactive Analysis database, FLVCR2 upregulation predicted dismal overall survival of patients with AML. Our validation analysis revealed the significant upregulation of FLVCR2 within the bone marrow of AML relative to healthy controls by western blotting and qPCR assays. Gene set enrichment analysis was conducted to explore FLVCR2’s related mechanism in AML. We found that high FLVCR2 expression was related to infiltration degrees of immune cells and immune scores among AML cases, indicating that FLVCR2 possibly had a crucial effect on AML progression through the immune response. Specifically, FLVCR2 upregulation was negatively related to the immune infiltration degrees of activated natural killer cells, activated memory CD4+ T cells, activated dendritic cells, and CD8+ T cells using CIBERSORT analysis. According to the in vitro research, FLVCR2 silencing suppressed AML cell growth and promoted their apoptosis. This study provides insights into FLVCR2’s effect on tumor immunity, indicating that it might serve as an independent prognostic biomarker and was related to immune infiltration within AML.

Enhanced stimulation of antigen-specific immune responses against nucleophosmin 1 mutated acute myeloid leukaemia by an anti-programmed death 1 antibody

Nucleophosmin1 (NPM1) is one of the most commonly mutated genes in AML and is often associated with a favourable prognosis. Immune responses play an increasing role in AML treatment decisions; however, the role of immune checkpoint inhibition is still not clear. To address this, we investigated specific immune responses against NPM1, and three other leukaemia-associated antigens (LAA), PRAME, Wilms' tumour 1 and RHAMM in AML patients. We investigated T cell responses against leukaemic progenitor/stem cells (LPC/LSC) using colony-forming immunoassays and flow cytometry. We examined whether immune checkpoint inhibition with the anti-programmed death 1 antibody increases the immune response against stem cell-like cells, comparing cells from NPM1 mutated and NPM1 wild-type AML patients. We found that the anti-PD-1 antibody, nivolumab, increases LAA stimulated cytotoxic T lymphocytes and the cytotoxic effect against LPC/LSC. The effect was strongest against NPM1^mut cells when the immunogenic epitope was derived from the mutated region of NPM1 and these effects were enhanced through the addition of anti-PD-1. The data suggest that patients with NPM1 mutated AML could be treated with the immune checkpoint inhibitor anti-PD-1 and that this treatment combined with NPM1-mutation specific directed immunotherapy could be even more effective for this unique group of patients.

Targeting the Tumor Microenvironment in Acute Myeloid Leukemia: The Future of Immunotherapy and Natural Products

The tumor microenvironment (TME) plays an essential role in the development, proliferation, and survival of leukemic blasts in acute myeloid leukemia (AML). Within the bone marrow and peripheral blood, various phenotypically and functionally altered cells in the TME provide critical signals to suppress the anti-tumor immune response, allowing tumor cells to evade elimination. Thus, unraveling the complex interplay between AML and its microenvironment may have important clinical implications and are essential to directing the development of novel targeted therapies. This review summarizes recent advancements in our understanding of the AML TME and its ramifications on current immunotherapeutic strategies. We further review the role of natural products in modulating the TME to enhance response to immunotherapy.

Microenvironmental Features Driving Immune Evasion in Myelodysplastic Syndromes and Acute Myeloid Leukemia

Bone marrow, besides the known functions of hematopoiesis, is an active organ of the immune system, functioning as a sanctuary for several mature immune cells. Moreover, evidence suggests that hematopoietic stem cells (the bone marrow’s functional unit) are capable of directly sensing and responding to an array of exogenous stimuli. This chronic immune stimulation is harmful to normal hematopoietic stem cells, while essential for the propagation of myeloid diseases, which show a dysregulated immune microenvironment. The bone marrow microenvironment in myelodysplastic syndromes (MDS) is characterized by chronic inflammatory activity and immune dysfunction, that drive excessive cellular death and through immune evasion assist in cancer cell expansion. Acute myeloid leukemia (AML) is another example of immune response failure, with features that augment immune evasion and suppression. In this review, we will outline some of the functions of the bone marrow with immunological significance and describe the alterations in the immune landscape of MDS and AML that drive disease progression.

Natural killer cells and acute myeloid leukemia: promises and challenges

Acute myeloid leukemia (AML) is considered as one of the most malignant conditions of the bone marrow. Over the past few decades, despite substantial progresses in the management of AML, relapse remission remains a major problem. Natural killer cells (NK cells) are known as a unique component of the innate immune system. Due to swift tumor detection, distinct cytotoxic action, and extensive immune interaction, NK cells have been used in various cancer settings for decades. It has been a growing knowledge of therapeutic magnitudes ranging from adoptive NK cell transfer to chimeric antigen receptor NK cells, aiming to achieve better therapeutic responses in patients with AML. In this article, the potentials of NK cells for treatment of AML are highlighted, and challenges for such therapeutic methods are discussed. In addition, the clinical application of NK cells, mainly in patients with AML, is pictured according to the existing evidence.

Immune-Based Therapeutic Interventions for Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is an aggressive, clonally heterogeneous, myeloid malignancy, with a 5-year overall survival of approximately 27%. It constitutes the most common acute leukemia in adults, with an incidence of 3-5 cases per 100,000 in the United States. Despite great advances in understanding the molecular mechanisms underpinning leukemogenesis, the past several decades had seen little change to the backbone of therapy, comprised of an anthracycline-based induction regimen for those who are fit enough to receive it, followed by risk-stratified post-remission therapy with consolidation cytarabine or allogeneic stem cell transplantation (allo-SCT). Allo-SCT is the most fundamental form of immunotherapy in which donor cytotoxic T and NK cells recognize and eradicate residual AML in the graft-versus-leukemia (GvL) effect. Building on that, several alternative or synergistic approaches to exploit both self and foreign immunity against AML have been developed. Checkpoint inhibitors, for example, CTLA-4 inhibitors, PD-1 inhibitors, and PD-L1 inhibitors block proteins found on T cells or cancer cells that stop the immune system from attacking the cancer cells. They have been used with limited success in both the AML relapsed/refractory (R/R) and post SCT settings. AML tumor mutational burden is low compared to solid tumors and thus, it is less likely to generate neoantigens and respond to antibody-mediated checkpoint blockade that has shown unprecedented results in solid tumors. Therefore, alternative therapeutic strategies that work independently of the T cell receptor (TCR) specificity have been developed. They include bispecific antibodies, which recruit T cells through CD3 engagement, and in AML have shown an overall response rate ranging between 14 and 30% in early phase trials. Chimeric Antigen Receptor (CAR) T cell therapy is a type of treatment in which T cells are genetically engineered to produce a recombinant receptor that redirects the specificity and function of T lymphocytes. However, lack of cell surface targets exclusively expressed on AML cells including Leukemic Stem Cells (LSCs) combined with clonal heterogeneity represents the biggest challenge in developing CAR therapy for AML. Antibody-Drug Conjugates (ADC) constitute the only FDA-approved immunotherapy to treat AML with Gemtuzumab Ozogamicin, a CD33-specific ADC used in CEBPα-mutated AML. The identification of additional cell surface targets is critical for the development of other ADC's potentially useful in the induction and maintenance regimens, given the ease at which these reagents can be generated and managed. Here, we will review those immune-based therapeutic interventions and highlight active areas of research investigations toward fulfillment of the great promise of immunotherapy to AML.

Immune-related gene signature predicts clinical outcomes and immunotherapy response in acute myeloid leukemia

Background

The immune response in the bone marrow microenvironment has implications for progression and prognosis in acute myeloid leukemia (AML). However, few immune‐related biomarkers for AML prognosis and immunotherapy response have been identified. We aimed to establish a predictive gene signature and to explore the determinants of prognosis in AML.

Methods

Immune‐related genes with clinical significance were screened by a weighted gene co‐expression network analysis. Seven immune‐related genes were used to establish a gene signature by a multivariate Cox regression analysis. Based on the signature, low‐ and high‐risk groups were compared with respect to the immune microenvironment, immune checkpoints, pathway activities, and mutation frequencies. The tumor immune dysfunction and exclusion (TIDE) method was used to predict the response to immune checkpoint blockade (ICB) therapy. The Connectivity Map database was used to explore small‐molecule drugs expected to treat high‐risk populations.

Results

A seven‐gene prognostic signature was used to classify patients into high‐ and low‐risk groups. Prognosis was poorer for patients in the former than in the latter. The high‐risk group displayed higher levels of immune checkpoint molecules (LAG3, PD‐1, CTLA4, PD‐L2, and PD‐L1), immune cell infiltration (dendritic cells, T helper 1, and gamma delta T), and somatic mutations (NPM1 and RUNX1). Moreover, hematopoietic stem cell/leukemia stem cell pathways were enriched in the high‐risk phenotype. Compared with that in the low‐risk group, the lower TIDE score for the high‐risk group implied that this group is more likely to benefit from ICB therapy. Finally, some drugs (FLT3 inhibitors and BCL inhibitors) targeting the expression profiles associated with the high‐risk group were generated using Connectivity Map.

Conclusion

The newly developed immune‐related gene signature is an effective biomarker for predicting prognosis in AML and provides a basis, from an immunological perspective, for the development of comprehensive therapeutic strategies.

Release of IFN-γ by acute myeloid leukemia cells remodels bone marrow immune microenvironment by inducing regulatory T cells

PURPOSE

The stromal and immune bone marrow (BM) landscape is emerging as a crucial determinant for acute myeloid leukemia (AML). Regulatory T cells (Tregs) are enriched in the AML microenvironment, but the underlying mechanisms are poorly elucidated. Here, we addressed the effect of IFN-γ released by AML cells in BM Tregs induction and its impact on AML prognosis.

EXPERIMENTAL DESIGN

BM aspirates from AML patients were subdivided according to IFNG expression. Gene expression profiles in INFGhigh and IFNGlow samples were compared by microarray and NanoString analysis and used to compute a prognostic index. The IFN-g release effect on the BM microenvironment was investigated in mesenchymal stromal cell (MSC)/AML cell co-cultures. In mice, AML cells silenced for IFN-γ expression were injected intrabone.

RESULTS

IFNGhigh AMLsamples showed an upregulation of inflammatory genes, usually correlated with a good prognosis in cancer. By contrast, in AML patients, high IFNG expression associated with poor overall survival. Notably, IFN-g release by AML cells positively correlated with a higher BM suppressive Tregs' frequency. In co-culture experiments, IFNGhigh AML cells modified MSC transcriptome by up-regulating IFN-γ-dependent genes related to Treg induction, including indoleamine 2,3-dioxygenase 1 (IDO1). IDO1 inhibitor abrogated the effect of IFN-γ release by AML cells on MSC-derived Treg induction. Invivo, the genetic ablation of IFN-γ production by AML cells reduced MSC IDO1 expression and Treg infiltration, hindering AML engraftment.

CONCLUSIONS

IFN-g release by AML cells induces an immune-regulatory program in MSCs and remodels BM immunological landscape toward Treg induction, contributing to an immunotolerant microenvironment.

Targeting PD-1/PD-L1 pathway in myelodysplastic syndromes and acute myeloid leukemia

Myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) are clonal hematopoietic stem cell diseases arising from the bone marrow (BM), and approximately 30% of MDS eventually progress to AML, associated with increasingly aggressive neoplastic hematopoietic clones and poor survival. Dysregulated immune microenvironment has been recognized as a key pathogenic driver of MDS and AML, causing high rate of intramedullary apoptosis in lower-risk MDS to immunosuppression in higher-risk MDS and AML. Immune checkpoint molecules, including programmed cell death-1 (PD-1) and programmed cell death ligand-1 (PD-L1), play important roles in oncogenesis by maintaining an immunosuppressive tumor microenvironment. Recently, both molecules have been examined in MDS and AML. Abnormal inflammatory signaling, genetic and/or epigenetic alterations, interactions between cells, and treatment of patients all have been involved in dysregulating PD-1/PD-L1 signaling in these two diseases. Furthermore, with the PD-1/PD-L1 pathway activated in immune microenvironment, the milieu of BM shift to immunosuppressive, contributing to a clonal evolution of blasts. Nevertheless, numerous preclinical studies have suggested a potential response of patients to PD-1/PD-L1 blocker. Current clinical trials employing these drugs in MDS and AML have reported mixed clinical responses. In this paper, we focus on the recent preclinical advances of the PD-1/PD-L1 signaling in MDS and AML, and available and ongoing outcomes of PD-1/PD-L1 inhibitor in patients. We also discuss the novel PD-1/PD-L1 blocker-based immunotherapeutic strategies and challenges, including identifying reliable biomarkers, determining settings, and exploring optimal combination therapies.

Increased TOX expression concurrent with PD-1, Tim-3, and CD244 expression in T cells from patients with acute myeloid leukemia

BACKGROUND

T cell dysregulation is a common event in leukemia. Recent findings have indicated that aberrant expression of immune checkpoint proteins may be associated with disease relapse and progression in acute myeloid leukemia (AML). TOX, a transcription factor in the HMG-box protein superfamily, was found to be a potential target for immunotherapy not only in solid tumors but also in hematological malignancies. However, little is known about TOX expression and co-expression with immune checkpoint proteins or the exhausted phenotype in the T cell subsets in AML. Thus, in this study, we analyzed TOX expression and co-expression with PD-1, Tim-3, and CD244 in T cells.

METHODS

TOX expression and co-expression with PD-1, Tim-3, and CD244 in CD3+, CD4+, regulatory T (Treg), and CD8+ T cells were analyzed by multi-color fluorescent flow cytometry in peripheral blood (PB) and bone marrow (BM) samples from patients with de novo AML and AML in complete remission (CR) and healthy individuals (HIs).

RESULTS

A significantly increased percentage of TOX+CD3+, CD4+, and CD8+ T cells was found in PB from patients with de novo AML in comparison with HIs. Double-positive TOX+CD244+, TOX+PD-1+, and TOX+Tim-3+ T cells markedly increased in the CD3+, CD4+, and CD8+ T cell populations in de novo AML patients compared with HIs, and similar trends were demonstrated for TOX+Tim-3+CD3+/CD4+/CD8+ T cells in de novo AML compared with AML-CR patients. In addition, the number of TOX+, TOX+PD-1+, and TOX+Tim-3+Treg cells significantly increased in de novo AML patients compared with HIs, and TOX+PD-1+Treg cells were higher in de novo AML compared with AML-CR patients. Moreover, TOX positively correlated with Tim-3 expression in CD8+ and Treg cells, and a positive correlation between the expression of TOX+ CD4+ and CD244+CD4+ T cells was found. Furthermore, an increased percentage of TOX+Tim-3+ T cells in BM was also found in de novo AML patients compared with HIs.

CONCLUSIONS

Increased TOX concurrent with PD-1, Tim-3, and CD244 in T cells may contribute to T cell exhaustion and impair their function in AML. Such exhausted T cells may be partially revised when AML patients achieve CR after chemotherapy. TOX may be considered a potential target for reversing T cell exhaustion and improving T cell function in AML.

Regulatory T cells promote the stemness of leukemia stem cells through IL10 cytokine-related signaling pathway

Regulatory T cells (Tregs) could maintain the characteristics of stem cells and inhibit the differentiation of normal hematopoietic stem/progenitor cells. Recent studies have shown that Tregs, as an important component of acute myeloid leukemia (AML) microenvironments, can help AML cells to evade immune surveillance. However, their function in directly regulating the stemness of AML cells remains elusive. In this study, the increased stemness of AML cells promoted by Tregs was verified in vitro and in vivo. The cytokines released by Tregs were explored, the highly expressed anti-inflammatory cytokine IL10 was found, which could promote the stemness of AML cells through the activation of PI3K/AKT signal pathway. Moreover, disrupting the IL10/IL10R/PI3K/AKT signal in AML/ETO c-kit^mut (A/Ec) leukemia mice could prolong the mice survival and reduce the stemness of A/Ec leukemia cells. Finally, it was confirmed in patient samples that the proportion of Tregs to leukemia stem cells (LSCs) was positively correlated, and in CD34⁺ primary AML cells, the activation of PI3K/AKT was stronger in patients with high Tregs' infiltration. After rhIL10 treatment, primary AML cells showed increased activation of PI3K/AKT signaling. Therefore, blocking the interaction between Tregs and AML cells may be a new approach to target LSCs in AML treatment.

Catch me if you can: how AML and its niche escape immunotherapy

In spite of the remarkable progress in basic and preclinical studies of acute myeloid leukemia (AML), the five-year survival rate of AML patients remains poor, highlighting the urgent need for novel and synergistic therapies. Over the past decade, increased attention has been focused on identifying suitable immunotherapeutic strategies for AML, and in particular on targeting leukemic cells and their progenitors. However, recent studies have also underlined the important contribution of the leukemic microenvironment in facilitating tumor escape mechanisms leading to disease recurrence. Here, we describe the immunological features of the AML niche, with particular attention to the crosstalk between the AML blasts and the cellular components of the altered tumor microenvironment (TME) and the mechanisms of immune escape that hamper the therapeutic effects of the most advanced treatments. Considering the AML complexity, immunotherapy approaches may benefit from a rational combination of complementary strategies aimed at preventing escape mechanisms without increasing toxicity.

The Role of T Cell Immunotherapy in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a heterogeneous disease associated with various alterations in T cell phenotype and function leading to an abnormal cell population, ultimately leading to immune exhaustion. However, restoration of T cell function allows for the execution of cytotoxic mechanisms against leukemic cells in AML patients. Therefore, long-term disease control, which requires multiple therapeutic approaches, includes those aimed at the re-establishment of cytotoxic T cell activity. AML treatments that harness the power of T lymphocytes against tumor cells have rapidly evolved over the last 3 to 5 years through various stages of preclinical and clinical development. These include tissue-infiltrated lymphocytes (TILs), bispecific antibodies, immune checkpoint inhibitors (ICIs), chimeric antigen receptor T (CAR-T) cell therapy, and tumor-specific T cell receptor gene-transduced T (TCR-T) cells. In this review, these T cell-based immunotherapies and the potential of TILs as a novel antileukemic therapy will be discussed.

The Potential Advantage of Targeting Both PD-L1/PD-L2/PD-1 and IL-10-IL-10R Pathways in Acute Myeloid Leukemia

Tumor cells promote the suppression of host anti-tumor type 1 T cell responses by various mechanisms, including the upregulation of surface inhibitory molecules such as programmed death ligand (PD-L)-1, and the production of immunosuppressive cytokines such as interleukin-10 (IL-10). There are over 2000 trials investigating PD-L1 and/or its receptor programmed-death 1 (PD-1) blockade in cancer, leading to the approval of PD-1 or PD-L1 inhibitors in several types of solid cancers and in hematological malignancies. The available data suggest that the molecule PD-L1 on antigen-presenting cells suppresses type 1 T cell immune responses such as cytotoxicity, and that the cytokine IL-10, in addition to downregulating immune responses, increases the expression of inhibitory molecule PD-L1. We hypothesize that the manipulation of both the co-inhibitory network (with anti-PD-L1 blocking antibodies) and suppressor network (with anti-IL-10 blocking antibodies) is an attractive immunotherapeutic intervention for acute myeloid leukemia (AML) patients ineligible for standard treatment with chemotherapy and hematopoietic stem cell transplantation, and with less severe adverse reactions. The proposed combination of these two immunotherapies represents a new approach that can be readily translated into the clinic to improve the therapeutic efficacy of AML disease treatment.

OMIP-080: 29-Color flow cytometry panel for comprehensive evaluation of NK and T cells reconstitution after hematopoietic stem cells transplantation

This 29-color panel was developed and optimized for the monitoring of NK cell and T cell reconstitution in peripheral blood of patients after HSCT. We considered major post-HSCT complications during the design, such as relapses, viral infections, and GvHD and identification of lymphocyte populations relevant to their resolution. The panel includes markers for all major NK cell and T cell subsets and analysis of their development and qualitative properties. In the NK cell compartment, we focus mainly on CD57 + NKG2C+ cells and the expression of activating (NKG2D, DNAM-1) and inhibitory receptors (NKG2A, TIGIT). Another priority is the characterization of T cell reconstitution; therefore, we included detection of CD4+ RTEs based on CD45RA, CD62L, CD95, and CD31 as a marker of thymus function. Besides that, we also analyze the emergence and properties of major T cell populations with a particular interest in CD8, Th1, ThCTL, and Treg subsets. Overall, the panel allows for comprehensive analysis of the reconstituting immune system and identification of potential markers of immune cell dysfunction.

Immunosuppression characterized by increased Treg cell and IL-10 levels in benzene-induced hematopoietic toxicity mouse model

Benzene is a typical hematopoietic toxic substance, that can cause serious blood and circulatory system diseases such as aplastic anemia, myelodysplastic syndrome and acute myeloid leukemia, but the immunological mechanism by which this occurs is not clear. T helper cells play a key role in regulating the immune balance in the body. In this study, benzene-induced hematopoietic toxicity BALB/c mice model was established, and changes in immune organs and T helper cell subsets (Th1, Th2, Th17 and Treg cells) were explored. At 28 days after subcutaneous injection of 150 mg/kg benzene, mice showed pancytopenia and obvious pathological damage to the bone marrow, spleen, and thymus. Flow cytometry revealed that the number of CD4⁺CD25⁺Foxp3⁺ Treg cells in the spleen increased significantly. The level of IL-10 in the spleen, serum, and bone marrow increased, while the levels of IL-17 in the spleen and serum decreased. Furthermore, the levels of CD4 and CD8 proteins in the spleen decreased. Immunofluorescence results showed that levels of Foxp3, a specific transcription factor that induced the differentiation of Treg cells, increased after exposure to benzene. Our results demonstrate that immunosuppression occurred in the benzene-induced hematopoietic toxicity model mice, and Treg cells and secreted IL-10 may play a key role in the process.

Emerging Bone Marrow Microenvironment-Driven Mechanisms of Drug Resistance in Acute Myeloid Leukemia: Tangle or Chance?

Simple Summary

Despite high rates of remission obtained with conventional chemotherapy, the persistence of leukemic cells after treatments, eventually exiting in disease relapse, remains the main challenge in acute myeloid leukemia (AML). Increasing evidence indicates that, besides AML cell mutations, stromal and immune cells, as leukemic microenvironment components, may protect AML cells from therapies. Here, we will recapitulate emerging bone marrow (BM) microenvironment-dependent mechanisms of therapy resistance. The understanding of these processes will help find new drug combinations and conceive novel and more effective treatments.

Abstract

Acute myeloid leukemia (AML) has been considered for a long time exclusively driven by critical mutations in hematopoietic stem cells. Recently, the contribution of further players, such as stromal and immune bone marrow (BM) microenvironment components, to AML onset and progression has been pointed out. In particular, mesenchymal stromal cells (MSCs) steadily remodel the leukemic niche, not only favoring leukemic cell growth and development but also tuning their responsiveness to treatments. The list of mechanisms driven by MSCs to promote a leukemia drug-resistant phenotype has progressively expanded. Moreover, the relative proportion and the activation status of immune cells in the BM leukemic microenvironment may vary by influencing their reactivity against leukemic cells. In that, the capacity of the stroma to re-program immune cells, thus promoting and/or hampering therapeutic efficacy, is emerging as a crucial aspect in AML biology, adding an extra layer of complexity. Current treatments for AML have mainly focused on eradicating leukemia cells, with little consideration for the leukemia-damaged BM niche. Increasing evidence on the contribution of stromal and immune cells in response to therapy underscores the need to hold the mutual interplay, which takes place in the BM. A careful dissection of these interactions will help provide novel applications for drugs already under experimentation and open a wide array of opportunities for new drug discovery.

MAIT cells numbers and frequencies in patients with acute myeloid leukemia at diagnosis: association with cytogenetic profile and gene mutations

Harnessing or monitoring immune cells is actually a major topic in pre-clinical and clinical studies in acute myeloid leukemia (AML). Mucosal-Associated Invariant T cells (MAIT) constitute one of the largest subset of innate-like, cytotoxic T cell subsets in humans. Despite some papers suggesting a role for MAIT cells in cancer, their specific involvement remains unclear, especially in myeloid malignancies. This prospective monocentric study included 216 patients with a newly diagnosed AML. Circulating MAIT cells were quantified by flow cytometry at diagnosis and during intensive chemotherapy. We observed that circulating MAIT cells show a specific decline in AML patients at diagnosis compared to healthy donors. Post-induction monitored patients presented with a drastic drop in MAIT cell numbers, with recovery after one month. We also found correlation between decrease in MAIT cells number and adverse cytogenetic profile. FLT3-ITD and IDH ½ mutations were associated with higher MAIT cell numbers. Patients with high level of activated MAIT cells are under-represented within patients with a favorable cytogenetic profile, and over-represented among patients with IDH1 mutations or bi-allelic CEBPA mutations. We show for the first time that circulating MAIT cells are affected in newly diagnosed AML patients, suggesting a link between MAIT cells and AML progression. Our work fosters new studies to deepen our knowledge about the role of MAIT cells in cancer.

Increase in polymorphonuclear myeloid-derived suppressor cells and regulatory T-cells in children with B-cell acute lymphoblastic leukemia

Our study aimed to evaluate the levels of MDSCs and Tregs in pediatric B-cell acute lymphoblastic leukemia (B-ALL), their relation to patients' clinical and laboratory features, and the impact of these cells on the induction response. This study included 31 pediatric B-ALL patients and 27 healthy controls. All patients were treated according to the protocols of the modified St. Jude Children's Research Hospital total therapy study XIIIB for ALL. Levels of MDSCs and Tregs were analyzed using flow cytometry. We observed a reduction in the levels of CD4 + T-cells and an increase in both the polymorphonuclear MDSCs (PMN-MDSCs) and Tregs. The frequencies of PMN-MDSCs and Tregs were directly related to the levels of peripheral and bone marrow blast cells and CD34 + cells. Complete postinduction remission was associated with reduced percentages of PMN-MDSCs and Tregs, with the level of PMN-MDCs in this subpopulation approaching that of healthy controls. PMN-MDSCs and Tregs jointly play a critical role in maintaining an immune-suppressive state suitable for B-ALL tumor progression. Thereby, they could be independent predictors of B-ALL progress, and finely targeting both PMN-MDSCs and Tregs may be a promising approach for the treatment of B-ALL.

Vaccine and Cell-based Therapeutic Approaches in Acute Myeloid Leukemia

Over the past decade, our increased understanding of the interactions between the immune system and cancer cells has led to paradigm shifts in the clinical management of solid and hematologic malignancies. The incorporation of immune-targeted strategies into the treatment landscape of acute myeloid leukemia (AML), however, has been challenging. While this is in part due to the inability of the immune system to mount an effective tumor-specific immunogenic response against the heterogeneous nature of AML, the decreased immunogenicity of AML cells also represents a major obstacle in the effort to design effective immunotherapeutic strategies. In fact, AML cells have been shown to employ sophisticated escape mechanisms to evade elimination, such as direct immunosuppression of natural killer cells and decreased surface receptor expression leading to impaired recognition by the immune system. Yet, cellular and humoral immune reactions against tumor-associated antigens (TAA) of acute leukemia cells have been reported and the success of allogeneic stem cell transplantation and monoclonal antibodies in the treatment of AML clearly provides proof that an immunotherapeutic approach is feasible in the management of this disease. This review discusses the recent progress and persisting challenges in cellular immunotherapy for patients with AML.