Abnormal populations and functions of natural killer cells in patients with myelodysplastic syndromes

Harnessing the power of memory-like NK cells to fight cancer

Natural killer (NK) cells possess the innate ability to eliminate cancerous cells effectively. Their crucial role in immunosurveillance has been widely recognized and exploited for therapeutic intervention. Despite the fast-acting nature of NK cells, NK adoptive cell transfer lacks favorable response in some patients. Patient NK cells often display diminished phenotype in preventing cancer progression resulting in poor prognosis. Tumor microenvironment plays a significant role in causing the downfall of NK cells in patients. The release of inhibitory factors by tumor microenvironment hinders normal function of NK cells against tumor. To overcome this challenge, therapeutic strategies such as cytokine stimulation and genetic manipulation are being investigated to improve NK tumor-killing capacity. One of the promising approaches includes generation of more competent NK cells via ex vivo cytokines activation and proliferation. Cytokine-induced ML-NK demonstrated phenotypic alterations such as enhanced expression of activating receptors which help elevate their antitumor response. Previous preclinical studies showed enhanced cytotoxicity and IFNγ production in ML-NK cells compared to normal NK cells against malignant cells. Similar effects are shown in clinical studies in which MK-NK demonstrated encouraging results in treating hematological cancer. However, there is still a lack of in-depth studies using ML-NK in treating different types of tumors and cancers. With convincing preliminary response, this cell-based approach could be used to complement other therapeutic modalities to achieve better clinical outcomes.

Combined flow cytometry natural killer immunophenotyping and KIR/HLA-C genotyping reveal remarkable differences in acute myeloid leukemia patients, but suggest an overall impairment of the natural killer response

Introduction

Natural killer (NK) cells are key anti-tumor effectors of the innate immunity. Phenotypic differences allow us to discriminate in between three functional stages of maturation, named immature, mature and hypermature that are distinctive in terms of receptor expression, cytokine secretion, cytotoxic properties and organ trafficking. NKs display an impressive repertoire of highly polymorphic germline encoded receptors that can be either activating, triggering the effector's function, or inhibitory, limiting the immune response. In our study, we have investigated peripheral blood NK cells of acute myeloid leukemia (AML) patients.

Methods

The Killer Immunoglobulin-like receptors (KIRs) and the HLA-C genotypes were assessed, as HLA-C molecules are cognate antigens for inhibitory KIRs.

Results

The AA mainly inhibitory KIR haplotype was found in a higher proportion in AML, while a striking low frequency of the 2DS3 characterized the mainly activating Bx haplotype. Flow cytometry immunophenotyping evidenced a lower overall count of NK cells in AML versus healthy controls, with lower percentages of the immature and mature subpopulations, but with a markedly increase of the hypermature NKs. The analysis of the KIR2DL1, KIR2DL2, KIR2DL3, KIR3DL1, and NKG2A inhibitory receptors surface expression revealed a remarkable heterogeneity. However, an overall trend for a higher expression in AML patients could be noticed in all maturation subpopulations. Some of the AML patients with complex karyotypes or displaying a FLT3 gene mutation proved to be extreme outliers in terms of NK cells percentages or inhibitory receptors expression.

Discussion

We conclude that while the genetic background investigation in AML offers important pieces of information regarding susceptibility to disease or prognosis, it is flow cytometry that is able to offer details of finesse in terms of NK numbers and phenotypes, necessary for an adequate individual evaluation of these patients.

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.

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.

Natural Killer Cell Subpopulations and Inhibitory Receptor Dynamics in Myelodysplastic Syndromes and Acute Myeloid Leukemia

Natural killer (NK) cells are key innate immunity effectors that play a major role in malignant cell destruction. Based on expression patterns of CD16, CD56, CD57, and CD94, three distinct NK cell maturation stages have been described, which differ in terms of cytokine secretion, tissue migration, and the ability to kill target cells. Our study addressed NK cell maturation in bone marrow under three conditions: a normal developmental environment, during pre-leukemic state (myelodysplastic syndrome, MDS), and during leukemic transformation (acute myeloblastic leukemia, AML). In this study, we used a new tool to perform multicolor flow cytometry data analysis, based on principal component analysis, which allowed the unsupervised, accurate discrimination of immature, mature, and hypermature NK subpopulations. An impaired NK/T cell distribution was observed in the MDS bone marrow microenvironment compared with the normal and AML settings, and a phenotypic shift from the mature to the immature state was observed in NK cells under both the MDS and AML conditions. Furthermore, an impaired NK cell antitumor response, resulting in changes in NK cell receptor expression (CD159a, CD158a, CD158b, and CD158e1), was observed under MDS and AML conditions compared with the normal condition. The results of this study provide evidence for the failure of this arm of the immune response during the pathogenesis of myeloid malignancies. NK cell subpopulations display a heterogeneous and discordant dynamic on the spectrum between normal and pathological conditions. MDS does not appear to be a simple, intermediate stage but rather serves as a decisive step for the mounting of an efficient or ineffective immune response, leading to either the removal of the tumor cells or to malignancy.

Unraveling the Role of Innate Lymphoid Cells in AcuteMyeloid Leukemia

Simple Summary

Acute myeloid leukemia (AML) is an aggressive form of cancer found in the blood and bone marrow with poor survival rates. Patients with AML are known to have many defects in their immune system which render immune cells unable to detect and/or kill cancer cells. Natural Killer (NK) cells are innate immune effector cells responsible for surveying the body to eliminate cancer cells as well as alert other immune cells to help clear the cancer cells. NK cells have developmental and functional defects in AML patients. While advances have been made to understand these NK cell defects in the setting of AML, the role of other closely related and recently discovered members of the innate lymphoid cell (ILC) family is much less clear. The ILC family is comprised of NK cells, ILC1s, ILC2s, and ILC3s, and due in part to their recent discovery, non-NK ILCs are just now beginning to be investigated in the setting of AML. By better understanding how AML alters the normal function of these cell types, and how the alteration regulates AML growth, we may be able to target and tailor new forms of therapy for patients.

Abstract

Over the past 50 years, few therapeutic advances have been made in treating acute myeloid leukemia (AML), an aggressive form of blood cancer, despite vast improvements in our ability to classify the disease. Emerging evidence suggests the immune system is important in controlling AML progression and in determining prognosis. Natural killer (NK) cells are important cytotoxic effector cells of the innate lymphoid cell (ILC) family that have been shown to have potent anti-leukemic functions. Recent studies are now revealing impairment or dysregulation of other ILCs in various types of cancers, including AML, which limits the effectiveness of NK cells in controlling cancer progression. NK cell development and function are inhibited in AML patients, which results in worse clinical outcomes; however, the specific roles of other ILC populations in AML are just now beginning to be unraveled. In this review, we summarize what is known about the role of ILC populations in AML.

Impact of Bone Marrow Natural Killer Cells (NK); Soluble TNF-α and IL-32 Levels in Myelodysplastic Syndrome Patients

Background:

Myelodysplastic syndromes (MDS) are complex clonal hemopoietic progenitor cell disorders that result from the evolution of aberrant clones which lead to leukemia. Disorders of the immune system serve important functions in the pathophysiology and progression of this disorder. This study aimed to assess the bone marrow natural killer cells percentage as well as soluble TNF-α and sIL-32 concentration levels in MDS patients.

Methods:

Bone marrow samples were obtained from 34 MDS; 12 MDS-AML and 10 controls. The percentage of total NK cells and mature NK cells were determined by flowcytometry. Bone Marrow soluble TNF-α and sIL-32 concentration levels were measured by ELISA.

Results:

The percentage of total NK and mature NK cells were significantly lower in MDS patients as compared to controls (P<0.001). The NK cells percentages were significantly related to MDS severity scores being lowest in high score followed by intermediate score and then low score (P<0.001). Moreover; the bone marrow sTNF-α and sIL-32 levels were higher in AML-MDS group; followed by MDS group then the control group and the differences are statistically significant (P<0.001 for both).

Conclusion:

The reduction in NK cells might have a role in AML evolution on the top of MDS. Likewise, the bone marrow sTNF-α; and sIL32 might have a role in MDS cytopenia.

Natural Killer Cells in Myeloid Malignancies: Immune Surveillance, NK Cell Dysfunction, and Pharmacological Opportunities to Bolster the Endogenous NK Cells

Natural killer (NK) cells are large granular lymphocytes involved in our defense against certain virus-infected and malignant cells. In contrast to T cells, NK cells elicit rapid anti-tumor responses based on signals from activating and inhibitory cell surface receptors. They also lyse target cells via antibody-dependent cellular cytotoxicity, a critical mode of action of several therapeutic antibodies used to treat cancer. A body of evidence shows that NK cells can exhibit potent anti-tumor activity against chronic myeloid leukemia (CML), acute myeloid leukemia (AML), and myelodysplastic syndromes (MDS). However, disease-associated mechanisms often restrain the proper functions of endogenous NK cells, leading to inadequate tumor control and risk for disease progression. Although allogeneic NK cells can prevent leukemia relapse in certain settings of stem cell transplantation, not all patients are eligible for this type of therapy. Moreover, remissions induced by adoptively infused NK cells are only transient and require subsequent therapy to maintain durable responses. Hence, new strategies are needed to trigger full and durable anti-leukemia responses by NK cells in patients with myeloid malignancies. To achieve this, we need to better understand the interplay between the malignant cells, their microenvironment, and the NK cells. This review focuses on mechanisms that are involved in suppressing NK cells in patients with myeloid leukemia and MDS, and means to restore their full anti-tumor potential. It also discusses novel molecular targets and approaches, such as bi- and tri-specific antibodies and immune checkpoint inhibitors, to redirect and/or unleash the NK cells against the leukemic cells.