NK Cell Functional Impairment after Allogeneic Hematopoietic Stem Cell Transplantation Is Associated with Reduced Levels of T-bet and Eomesodermin

Elotuzumab Enhances CD16-Independent NK Cell-Mediated Cytotoxicity against Myeloma Cells by Upregulating Several NK Cell-Enhancing Genes

Multiple myeloma (MM) is an intractable hematological malignancy caused by abnormalities in plasma cells. Combination therapy using antibodies and natural killer (NK) effectors, which are innate immune cells with safe and potent antitumor activity, is a promising approach for cancer immunotherapy and can enhance antitumor effects. Elotuzumab (Elo) is an immune-stimulatory antibody that targets the signaling lymphocytic activation molecule family 7 (SLAMF7) expressed on the surface of MM and NK cells. We confirmed that Elo strongly promoted NK cell-mediated antibody-dependent cellular cytotoxicity (ADCC) against SLAMF7-positive MM cells in a CD16-dependent NK cell line, and also activated expanded NK cells derived from peripheral blood mononuclear cells of healthy donors and patients with MM in the present study. However, the antitumor effects and genes involved in the direct promotion of NK cell-mediated activation using Elo in CD16-independent NK cells are not clearly known. In this study, we demonstrated that Elo pretreatment significantly enhanced CD16-independent NK cell-mediated cytotoxicity in both SLAMF7-positive MM.1S and SLAMF7-negative K562, U266, and RPMI 8226 tumor cells. Upon direct simulation of CD16-independent NK cells with Elo, increased levels of CD107a degranulation and IFN-γ secretion were observed along with the upregulation of granzyme B, TNF-α, and IL-1α gene expression. The enhanced NK cell function could also be attributed to the increased expression of the transcription factors T-BET and EOMES. Furthermore, the augmentation of the antitumor effects of CD16-independent NK cells upon pretreatment with Elo enhanced the expression of CRTAM, TNFRSF9, EAT-2, and FOXP3 genes and reduced the expression of HSPA6. Our results suggest that Elo directly promotes the cytotoxic function of CD16-independent NK cells against target cells, which is associated with the upregulation of the expression of several NK cell-enhancing genes.

Reconstitution of Natural Killer cells after allogeneic hematopoietic stem cell transplantation is facilitated by Huiyang-Guben decoction through activating the Smad7/Stat3 signal pathway

Natural Killer (NK) cell is the first batch of re-constructed cell populations after allogeneic hematopoietic stem cell transplantation (allo-HSCT), and its delayed reconstitution inevitably causes poor outcome. The traditional Chinese medicine Huiyang-Guben decoction (HYGB) has been clinically used in patients undergoing allo-HSCT, but its effect on NK cell reconstruction is still unclear. 40 patients with allo-HSCT therapy were randomly divided into the control group and the HYGB group, and were given oral administration of normal saline or HYGB for 4 weeks before allo-HSCT, respectively. NK cells were cultured and treated with transforming growth factor β (TGF-β) and HYGB in vitro, and cell viability, cell apoptosis, and the function of NK cells were evaluated. Functional verification experiments were performed by knocking down signal transduction molecule 7 (Smad7) in NK cells before TGF-β and HYGB treatment. Clinical data suggested that HYGB intervention decreased the incidence of acute graft-versus-host disease after allo-HSCT, and increased the proportion of NK cell population. Meanwhile, HYGB improved cell viability, restrained apoptotic cell death, and enhanced cell killing activity of NK cells in patients with allo-HSCT. Notably, we found that HYGB significantly increased the expression level of Smad7 and the phosphorylation level of signal transducer and activator of transcription 3 (Stat3) in NK cells from patients with allo-HSCT. Moreover, HYGB alleviated TGF-β-induced NK cell impairment and re-activated the Smad7/Stat3 signaling in vitro, while silencing Smad7 reversed the protective effect of HYGB on TGF-β-treated NK cells. HYGB promotes NK cell reconstruction and improves NK cell function after allo-HSCT through activating the Smad7/Stat3 signaling pathway.

The Role of NK Cells and Their Exosomes in Graft Versus Host Disease and Graft Versus Leukemia

Natural killer (NK) cells are one of the innate immune cells that play an important role in preventing and controlling tumors and viral diseases, but their role in hematopoietic stem cell transplantation (HCT) is not yet fully understood. However, according to some research, these cells can prevent infections and tumor relapse without causing graft versus host disease (GVHD). In addition to NK cells, several studies are about the anti-leukemia effects of NK cell-derived exosomes that can highlight their roles in graft-versus-leukemia (GVL). In this paper, we intend to investigate the results of various articles on the role of NK cells in allogeneic hematopoietic cell transplantation and also their exosomes in GVL. Also, we have discussed the antiviral effects of these cells in post-HCT cytomegalovirus infection.

4-1BB and cytokines trigger human NK, γδ T, and CD8+ T cell proliferation and activation, but are not required for their effector functions

INTRODUCTION

This study was designed to compare the costimulatory molecules and cytokines required to trigger the proliferation and activation of natural killer (NK), γδ T, and CD8⁺ T cells, and gain in-depth insight into the mechanisms shifting tolerance to immunity.

METHODS

K562-derived artificial antigen-presenting cells (aAPCs); that is, K562 forced to express CD86 and 4-1BBL costimulatory receptors, in the presence of cytokines, were used to mimic dendritic cells (DCs) and provide signals to support the proliferation and activation of NK, γδ T, and CD8⁺ T cells.

RESULTS

Three signals are required to trigger optimal proliferation in MART-1-specific CD8⁺ T cells: activation of T-cell receptors (TCRs) by the major histocompatibility complex (MHC) I/peptide complexes (signal 1); 4-1BB engagement (signal 2); and IL-15 and IL-21 receptor co-signaling (signal 3). NK and γδ T cell proliferation also require three signals, but the precise nature of signal 1 involving cell-to-cell contact was not determined. Once they become effectors, only signal 1 determines the sensitivity or resistance of the target cells to cytolysis by killer lymphocytes. When freshly purified, none had effector functions, except the NK cells, which could be activated by CD16 engagement.

CONCLUSIONS

Therefore, lymphocytes committed to kill are produced as inactive precursors, and the license to kill is delivered by three signals, allowing for extensive proliferation and effector function acquisition. This data challenges the paradigm of anergy and supports the danger signal theory originally proposed by Polly Matzinger, which states that killer cells are tolerant by default, thereby protecting the mammalian body from autoimmunity.

Human pegivirus-1 replication influences NK cell reconstitution after allogeneic haematopoietic stem cell transplantation

Introduction

Human pegivirus-1 (HPgV-1) is a so-called commensal virus for which no known associated organ disease has been found to date. Yet, it affects immune-reconstitution as previously studied in the HIV population, in whom active co-infection with HPgV-1 can modulate T and NK cell activation and differentiation leading to a protective effect against the evolution of the disease. Little is known on the effect of HPgV-1 on immune-reconstitution in allogeneic hematopoietic stem cell transplant (allo-HSCT) recipients, a patient population in which we and others have previously reported high prevalence of HPgV-1 replication. The aim of this study was to compare the immune reconstitution after allo-HSCT among HPgV-1-viremic and HPgV-1-non-viremic patients.

Methods

Within a cohort study of 40 allo-HSCT patients, 20 allo-HSCT recipients positive in plasma sample for HPgV-1 by rRT-PCR during the first year (1, 3, 6, 12 months) after transplantation were matched with 20 allo-HSCT recipients negative for HPgV-1. T and NK cell reconstitution was monitored by flow cytometry in peripheral blood samples from allo-HSCT recipients at the same time points.

Results

We observed no significant difference in the absolute number and subsets proportions of CD4 and CD8 T cells between patient groups at any analysed timepoint. We observed a significantly higher absolute number of NK cells at 3 months among HPgV-1-viremic patients. Immunophenotypic analysis showed a significantly higher proportion of CD56^bright NK cells mirrored by a reduced percentage of CD56^dim NK cells in HPgV-1-positive patients during the first 6 months after allo-HSCT. At 6 months post-allo-HSCT, NK cell phenotype significantly differed depending on HPgV-1, HPgV-1-viremic patients displaying NK cells with lower CD16 and CD57 expression compared with HPgV-1-negative patients. In accordance with their less differentiated phenotype, we detected a significantly reduced expression of granzyme B in NK cells in HPgV-1-viremic patients at 6 months.

Discussion

Our study shows that HPgV-1-viremic allo-HSCT recipients displayed an impaired NK cell, but not T cell, immune-reconstitution compared with HPgV-1-non-viremic patients, revealing for the first time a potential association between replication of the non-pathogenic HPgV-1 virus and immunomodulation after allo-HSCT.

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.

T-BET and EOMES Accelerate and Enhance Functional Differentiation of Human Natural Killer Cells

T-bet and Eomes are transcription factors that are known to be important in maturation and function of murine natural killer (NK) cells. Reduced T-BET and EOMES expression results in dysfunctional NK cells and failure to control tumor growth. In contrast to mice, the current knowledge on the role of T-BET and EOMES in human NK cells is rudimentary. Here, we ectopically expressed either T-BET or EOMES in human hematopoietic progenitor cells. Combined transcriptome, chromatin accessibility and protein expression analyses revealed that T-BET or EOMES epigenetically represses hematopoietic stem cell quiescence and non-NK lineage differentiation genes, while activating an NK cell-specific transcriptome and thereby drastically accelerating NK cell differentiation. In this model, the effects of T-BET and EOMES are largely overlapping, yet EOMES shows a superior role in early NK cell maturation and induces faster NK receptor and enhanced CD16 expression. T-BET particularly controls transcription of terminal maturation markers and epigenetically controls strong induction of KIR expression. Finally, NK cells generated upon T-BET or EOMES overexpression display improved functionality, including increased IFN-γ production and killing, and especially EOMES overexpression NK cells have enhanced antibody-dependent cellular cytotoxicity. Our findings reveal novel insights on the regulatory role of T-BET and EOMES in human NK cell maturation and function, which is essential to further understand human NK cell biology and to optimize adoptive NK cell therapies.

TIGIT+ TIM-3+ NK cells are correlated with NK cell exhaustion and disease progression in patients with hepatitis B virus‑related hepatocellular carcinoma

The prognosis of hepatocellular carcinoma (HCC) is extremely poor, of which hepatitis B virus-related hepatocellular carcinoma (HBV-HCC) accounts for the majority in China. Immune checkpoint inhibitors have become an effective immunotherapy method for the treatment of HCC, but they are mainly used for T cells. NK cells play a vital role as the first line of defense against tumors. Therefore, we explored the characteristic expression pattern of immune checkpoints on NK cells of HBV-HCC patients. We analyzed the correlation between the co-expression of TIGIT and TIM-3 and the clinical progress of patients with HBV-HCC. The co-expression of TIGIT and TIM-3 on NK cells is elevated in patients with HBV-HCC. TIGIT⁺TIM-3⁺NK cells showed exhausted phenotypic characteristics and displayed dysfunction manifested as weakened killing function, reduced cytokine production, and proliferation function. TIGIT⁺TIM-3⁺NK cells participate in NK cells function exhaustion and are closely related to the disease progression of patients with HBV-HCC, suggesting a new target for future immunotherapy.

Phase I Trial of N-803, an IL15 Receptor Agonist, with Rituximab in Patients with Indolent Non-Hodgkin Lymphoma

PURPOSE

N-803 is an IL15 receptor superagonist complex, designed to optimize in vivo persistence and trans-presentation, thereby activating and expanding natural killer (NK) cells and CD8⁺ T cells. Monoclonal antibodies (mAbs) direct Fc receptor-bearing immune cells, including NK cells, to recognize and eliminate cancer targets. The ability of IL15R agonists to enhance tumor-targeting mAbs in patients has not been reported previously.

PATIENTS AND METHODS

Relapsed/refractory patients with indolent non-Hodgkin lymphoma were treated with rituximab and intravenous or subcutaneous N-803 on an open-label, dose-escalation phase I study using a 3+3 design (NCT02384954). Primary endpoint was maximum tolerated dose. Immune correlates were performed using multidimensional analysis via mass cytometry and cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq) which simultaneously measures protein and single-cell RNA expression.

RESULTS

This immunotherapy combination was safe and well tolerated and resulted in durable clinical responses including in rituximab-refractory patients. Subcutaneous N-803 plus rituximab induced sustained proliferation, expansion, and activation of peripheral blood NK cells and CD8 T cells, with increased NK cell and T cells present 8 weeks following last N-803 treatment. CITE-seq revealed a therapy-altered NK cell molecular program, including enhancement of AP-1 transcription factor. Furthermore, the monocyte transcriptional program was remodeled with enhanced MHC expression and antigen-presentation genes.

CONCLUSIONS

N-803 combines with mAbs to enhance tumor targeting in patients, and warrants further investigation in combination with immunotherapies.

Multidimensional Analyses of Donor Memory-Like NK Cells Reveal New Associations with Response after Adoptive Immunotherapy for Leukemia

Natural killer (NK) cells are an emerging cancer cellular therapy and potent mediators of antitumor immunity. Cytokine-induced memory-like (ML) NK cellular therapy is safe and induces remissions in patients with acute myeloid leukemia (AML). However, the dynamic changes in phenotype that occur after NK-cell transfer that affect patient outcomes remain unclear. Here, we report comprehensive multidimensional correlates from ML NK cell-treated patients with AML using mass cytometry. These data identify a unique in vivo differentiated ML NK-cell phenotype distinct from conventional NK cells. Moreover, the inhibitory receptor NKG2A is a dominant, transcriptionally induced checkpoint important for ML, but not conventional NK-cell responses to cancer. The frequency of CD8α⁺ donor NK cells is negatively associated with AML patient outcomes after ML NK therapy. Thus, elucidating the multidimensional dynamics of donor ML NK cells in vivo revealed critical factors important for clinical response, and new avenues to enhance NK-cell therapeutics. SIGNIFICANCE: Mass cytometry reveals an in vivo memory-like NK-cell phenotype, where NKG2A is a dominant checkpoint, and CD8α is associated with treatment failure after ML NK-cell therapy. These findings identify multiple avenues for optimizing ML NK-cell immunotherapy for cancer and define mechanisms important for ML NK-cell function.This article is highlighted in the In This Issue feature, p. 1775.

Cytotoxicity of Donor Natural Killer Cells to Allo-Reactive T Cells Are Related With Acute Graft-vs.-Host-Disease Following Allogeneic Stem Cell Transplantation

Objectives: The mechanism and immunoregulatory role of human natural killer (NK) cells in acute graft-vs.-host-disease (aGVHD) remains unclear. This study quantitatively analyzed the cytotoxicity of donor NK cells toward allo-reactive T cells, and investigated their relationship with acute GVHD (aGVHD).

Methods: We evaluated NK dose, subgroup, and receptor expression in allografts from 98 patients who underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT). A CD107a degranulating assay was used as a quantitative detection method for the cytotoxic function of donor NK cells to allo-reactive T cells. In antibody-blocking assay, NK cells were pre-treated with anti-DNAM-1(CD226), anti-NKG2D, anti-NKP46, or anti-NKG-2A monoclonal antibodies (mAbs) before the degranulating assay.

Results: NK cells in allografts effectively inhibited auto-T cell proliferation following alloantigen stimulation, selectively killing alloantigen activated T cells. NKG2A⁻ NK cell subgroups showed higher levels of CD107a degranulation toward activated T cells, when compared with NKG2A⁻ subgroups. Blocking NKG2D or CD226 (DNAM-1) led to significant reductions in degranulation, whereas NKG2A block resulted in increased NK degranulation. Donor NK cells in the aGVHD group expressed lower levels of NKG2D and CD226, higher levels of NKG2A, and showed higher CD107a degranulation levels when compared with NK cells in the non-aGVHD group. Using univariate analysis, higher NK degranulation activities in allografts (CD107a^high) were correlated with a decreased risk in grade I–IV aGVHD (hazard risk [HR] = 0.294; P < 0.0001), grade III–IV aGVHD (HR = 0.102; P < 0.0001), and relapse (HR = 0.157; P = 0.015), and improved overall survival (HR = 0.355; P = 0.028) after allo-HSCT. Multivariate analyses showed that higher NK degranulation activities (CD107a^high) in allografts were independent risk factors for grades, I–IV aGVHD (HR = 0.357; P = 0.002), and grades III–IV aGVHD (HR = 0.13; P = 0.009).

Conclusions: These findings reveal that the degranulation activity of NK in allografts toward allo-activated T cells was associated with the occurrence and the severity of aGVHD, after allogeneic stem cell transplantation. This suggested that cytotoxicity of donor NK cells to allo-reactive T cells have important roles in aGVHD regulation.

Human Term Pregnancy Decidual NK Cells Generate Distinct Cytotoxic Responses

Decidual NK cells (dNK) are the main lymphocyte population in early pregnancy decidual mucosa. Although dNK decrease during pregnancy, they remain present in decidual tissues at term. First trimester dNK facilitate trophoblast invasion, provide protection against infections, and were shown to have many differences in their expression of NKRs, cytokines, and cytolytic capacity compared with peripheral blood NK cells (pNK). However, only limited data are available on the phenotype and function of term pregnancy dNK. In this study, dNK from human term pregnancy decidua basalis and decidua parietalis tissues were compared with pNK and first trimester dNK. Profound differences were found, including: 1) term pregnancy dNK have an increased degranulation response to K562 and PMA/ionomycin but lower capacity to respond to human CMV-infected cells; 2) term pregnancy dNK are not skewed toward recognition of HLA-C, as was previously shown for first trimester dNK; and 3) protein and gene expression profiles identified multiple differences between pNK, first trimester, and term pregnancy dNK, suggesting term pregnancy dNK are a distinct type of NK cells. Understanding the role of dNK throughout pregnancy is of high clinical relevance for studies aiming to prevent placental inflammatory disorders as well as maternal-to-fetal transmission of pathogens.

Indirect Impact of PD-1/PD-L1 Blockade on a Murine Model of NK Cell Exhaustion

The induction of exhaustion on effector immune cells is an important limiting factor for cancer immunotherapy efficacy as these cells undergo a hierarchical loss of proliferation and cytolytic activity due to chronic stimulation. Targeting PD-1 has shown unprecedented clinical benefits for many cancers, which have been attributed to the prevention of immune suppression and exhaustion with enhanced anti-tumor responses. In this study, we sought to evaluate the role of the PD-1/PD-L1 pathway in murine natural killer (NK) cell activation, function, and exhaustion. In an in vivo IL-2-dependent exhaustion mouse model, neutralization of the PD-1/PD-L1 pathway improved NK cell activation after chronic stimulation when compared to control-treated mice. These cells displayed higher proliferative capabilities and enhanced granzyme B production. However, the blockade of these molecules during long-term in vitro IL-2 stimulation did not alter the progression of NK cell exhaustion (NCE), suggesting an indirect involvement of PD-1/PD-L1 on NCE. Given the expansion of CD8 T cells and regulatory T cells (Tregs) observed upon acute and chronic stimulation with IL-2, either of these two populations could influence NK cell homeostasis after PD-L1/PD-1 therapy. Importantly, CD8 T cell activation and functional phenotype were indeed enhanced by PD-1/PD-L1 therapy, particularly with anti-PD-1 treatment that resulted in the highest upregulation of CD25 during chronic stimulation and granted an advantage for IL-2 over NK cells. These results indicate a competition for resources between NK and CD8 T cells that arguably delays the onset of NCE rather than improving its activation during chronic stimulation. Supporting this notion, the depletion of CD8 T cells reversed the benefits of PD-1 therapy on chronically stimulated NK cells. These data suggest a bystander effect of anti-PD1 on NK cells, resulting from the global competition that exists between NK and CD8 T cells for IL-2 as a key regulator of these cells' activation. Thus, achieving an equilibrium between these immune cells might be important to accomplish long-term efficacy during anti-PD-1/IL-2 therapy.

Regulation of murine NK cell exhaustion through the activation of the DNA damage repair pathway

NK cell exhaustion (NCE) due to sustained proliferation results in impaired NK cell function with loss of cytokine production and lytic activity. Using murine models of chronic NK cell stimulation, we have identified a phenotypic signature of NCE characterized by up-regulation of the terminal differentiation marker KLRG1 and by down-regulation of eomesodermin and the activating receptor NKG2D. Chronic stimulation of mice lacking NKG2D resulted in minimized NCE compared to control mice, thus identifying NKG2D as a crucial mediator of NCE. NKG2D internalization and downregulations on NK cells has been previously observed in the presence of tumor cells with high expression of NKG2D ligands (NKG2DL) due to the activation of the DNA damage repair pathways. Interestingly, our study revealed that during NK cell activation there is an increase of MULT1, and NKG2DL, that correlates with an induction of DNA damage. Treatment with the ATM DNA damage repair pathway inhibitor KU55933 (KU) during activation reduced NCE by improving expression of activation markers and genes involved in cell survival, by sustaining NKG2D expression and by preserving cell functionality. Importantly, NK cells expanded ex vivo in the presence of KU displayed increased anti-tumor efficacy in both NKG2D-dependent and -independent mouse models. Collectively, these data demonstrate that NCE is caused by DNA damage and regulated, at least in part, by NKG2D. Further, the prevention of NCE is a promising strategy to improve NK cell-based immunotherapy.

Loss of Canonical Notch Signaling Affects Multiple Steps in NK Cell Development in Mice

Within the hematopoietic system, the Notch pathway is critical for promoting thymic T cell development and suppressing the B and myeloid lineage fates; however, its impact on NK lymphopoiesis is less understood. To study the role of Notch during NK cell development in vivo, we investigated different NK cell compartments and function in Rbp-Jk^fl/flVav-Cre^tg/+ mice, in which Rbp-Jk, the major transcriptional effector of canonical Notch signaling, was specifically deleted in all hematopoietic cells. Peripheral conventional cytotoxic NK cells in Rbp-Jk-deleted mice were significantly reduced and had an activated phenotype. Furthermore, the pool of early NK cell progenitors in the bone marrow was decreased, whereas immature NK cells were increased, leading to a block in NK cell maturation. These changes were cell intrinsic as the hematopoietic chimeras generated after transplantation of Rbp-Jk-deficient bone marrow cells had the same NK cell phenotype as the Rbp-Jk-deleted donor mice, whereas the wild-type competitors did not. The expression of several crucial NK cell regulatory pathways was significantly altered after Rbp-Jk deletion. Together, these results demonstrate the involvement of canonical Notch signaling in regulation of multiple stages of NK cell development.

Genome-wide analyses and functional profiling of human NK cell lines

Natural killer (NK) cell lines, including YTS, NK92, NK3.3, and NKL, represent excellent models for the study of human natural killer cells. While phenotypic and functional differences between these cell lines have been reported, a multi-parametric study, encompassing genomic, phenotypic, and functional assays, has not been performed. Here, using a combination of techniques including microarray and copy number analyses, flow cytometry, and functional assays, we provide in-depth genetic, functional, and phenotypic comparison of YTS, NK92, NK3.3, and NKL cell lines. Specifically, we found that while the cell lines shared similarities in enrichment of growth and survival pathways, they had differential expression of 557 genes, including genes related to NK cell development, survival, and function. In addition, we provide genetic and phenotypic analyses that demonstrate distinct developmental origins of NK92, YTS, and NKL cell lines. Specifically, NK92 has a phenotype associated with the CD56^bright NK cell subset, while both YTS and NKL appear more CD56^dim-like. Finally, by classifying cell lines based on their lytic potential, we identified genes differentially expressed between NK cell lines with high and low lytic function. Taken together, these data provide the first comprehensive genetic, phenotypic, and functional analyses of these commonly used NK cell lines and provides deeper understanding into their origins and function. This will ultimately improve their use as models for human NK cell biology.

Comparison of Phenotypic and Functional Characteristics Between Canine Non-B, Non-T Natural Killer Lymphocytes and CD3+CD5dimCD21- Cytotoxic Large Granular Lymphocytes

Natural killer (NK) cells play a pivotal role in the immune response against infections and malignant transformation, and adopted transfer of NK cells is thought to be a promising therapeutic approach for cancer patients. Previous reports describing the phenotypic features of canine NK cells have produced inconsistent results. Canine NK cells are still defined as non-B and non-T (CD3⁻CD21⁻) large granular lymphocytes. However, a few reports have demonstrated that canine NK cells share the phenotypic characteristics of T lymphocytes, and that CD3⁺CD5^dimCD21⁻ lymphocytes are putative canine NK cells. Based on our previous reports, we hypothesized that phenotypic modulation could occur between these two populations during activation. In this study, we investigated the phenotypic and functional differences between CD3⁺CD5^dimCD21⁻ (cytotoxic large granular lymphocytes) and CD3⁻CD5⁻CD21⁻ NK lymphocytes before and after culture of peripheral blood mononuclear cells isolated from normal dogs. The results of this study show that CD3⁺CD5^dimCD21⁻ lymphocytes can be differentiated into non-B, non-T NK (CD3⁻CD5⁻CD21⁻TCRαβ⁻TCRγδ⁻GranzymeB⁺) lymphocytes through phenotypic modulation in response to cytokine stimulation. In vitro studies of purified CD3⁺CD5^dimCD21⁻ cells showed that CD3⁻CD5⁻CD21⁻ cells are derived from CD3⁺CD5^dimCD21⁻ cells through phenotypic modulation. CD3⁺CD5^dimCD21⁻ cells share more NK cell functional characteristics compared with CD3⁻CD5⁻CD21⁻ cells, including the expression of T-box transcription factors (Eomes, T-bet), the production of granzyme B and interferon-γ, and the expression of NK cell-related molecular receptors such as NKG2D and NKp30. In conclusion, the results of this study suggest that CD3⁺CD5^dimCD21⁻ and CD3⁻CD5⁻CD21⁻ cells both contain a subset of putative NK cells, and the difference between the two populations may be due to the degree of maturation.

Long-term maintenance of peripheral blood derived human NK cells in a novel human IL-15- transgenic NOG mouse

We generated a novel mouse strain expressing transgenic human interleukin-15 (IL-15) using the severe immunodeficient NOD/Shi-scid-IL-2Rγ^null (NOG) mouse genetic background (NOG-IL-15 Tg). Human natural killer (NK) cells, purified from the peripheral blood (hu-PB-NK) of normal healthy donors, proliferated when transferred into NOG-IL-15 Tg mice. In addition, the cell number increased, and the hu-PB-NK cells persisted for 3 months without signs of xenogeneic graft versus host diseases (xGVHD). These in vivo-expanded hu-PB-NK cells maintained the original expression patterns of various surface antigens, including NK receptors and killer cell immunoglobulin-like receptor (KIR) molecules. They also contained significant amounts of granzyme A and perforin. Inoculation of K562 leukemia cells into hu-PB-NK-transplanted NOG-IL-15 Tg mice resulted in significant suppression of tumor growth compared with non-transplanted mice. Furthermore, NOG-IL-15 Tg mice allowed for engraftment of in vitro-expanded NK cells prepared for clinical cell therapy. These cells exerted antibody-dependent cell-mediated cytotoxicity (ADCC) on Her2-positive gastric cancer cells in the presence of therapeutic anti-Her2 antibody, and subsequently suppressed tumor growth. Our results collectively suggest that the NOG-IL-15 Tg mice are a useful model for studying human NK biology and evaluating human NK cell-mediated in vivo cytotoxicity.

Natural Killer Cells in Graft-versus-Host-Disease after Allogeneic Hematopoietic Cell Transplantation

Allogeneic hematopoietic cell transplantation (HCT) is a well-established therapeutic modality effective for a variety of hematological malignancies but, unfortunately, is associated with significant morbidity and mortality related to cancer relapse as well as to transplant-related complications including graft-versus-host-disease (GvHD). Natural killer (NK) cells are the first donor-derived lymphocyte subset to recover after HCT, and their crucial role in protection against cancer relapse and infections is well established. Conversely, the role played by NK cells in GvHD is still controversial. Early studies suggested a participation of NK cells in GvHD induction or exacerbation. Subsequently, experimental evidence obtained in mice as well observational studies performed in humans led to a model in which NK cells play a regulatory role in GvHD by repressing alloreactive T cell responses. This widely accepted model has been recently challenged by clinical evidence indicating that NK cells can in some cases promote GvHD. In this review, we summarize available knowledge about the role of NK cells in GVHD pathogenesis. We review studies uncovering cellular mechanisms through which NK cells interact with other immune cell subsets during GvHD leading to a model in which NK cells naturally suppress GvHD through their cytotoxic ability to inhibit T cell activation unless exogenous hyperactivation lead them to produce proinflammatory cytokines that can conversely sustain T cell-mediated GvHD induction.

Effect of CMV and Aging on the Differential Expression of CD300a, CD161, T-bet, and Eomes on NK Cell Subsets

Natural killer (NK) cells are innate lymphoid cells involved in the defense against virus-infected cells and tumor cells. NK cell phenotype and function is affected with age and cytomegalovirus (CMV) latent infection. Aging affects the frequency and phenotype of NK cells, and CMV infection also contributes to these alterations. Thus, a reduction of CD56^bright NK cell subpopulation associated with age and an expansion of memory-like NK cells CD56^dimCD57⁺NKG2C⁺ probably related to CMV seropositivity have been described. NK cells express T-bet and Eomes transcription factors that are necessary for the development of NK cells. Here, we analyze the effect of age and CMV seropositivity on the expression of CD300a and CD161 inhibitory receptors, and T-bet and Eomes transcription factors in NK cell subsets defined by the expression of CD56 and CD57. CD300a is expressed by the majority of NK cells. CD56^bright NK cells express higher levels of CD300a than CD56^dim NK cells. An increase in the expression of CD300a was associated with age, whereas a decreased expression of CD161 in CD56^dim NK cells was associated with CMV seropositivity. In CD56^dim NK cells, an increased percentage of CD57⁺CD300a⁺ and a reduction in the percentage of CD161⁺CD300a⁺ cells were found to be associated with CMV seropositivity. Regarding T-bet and Eomes transcription factors, CMV seropositivity was associated with a decrease of T-bet^hi in CD56^dimCD57⁺ NK cells from young individuals, whereas Eomes expression was increased with CMV seropositivity in both CD56^bright and CD56^dimCD57^+/− (from middle age and young individuals, respectively) and was decreased with aging in all NK subsets from the three group of age. In conclusion, CMV infection and age induce significant changes in the expression of CD300a and CD161 in NK cell subsets defined by the expression of CD56 and CD57. T-bet and Eomes are differentially expressed on NK cell subsets, and their expression is affected by CMV latent infection and aging.

Fewer Circulating Natural Killer Cells 28 Days After Double Cord Blood Transplantation Predicts Inferior Survival and IL-15 Response

Natural Killer (NK) cell immune reconstitution after double umbilical cord blood transplantation (dUCBT) is rapid and thought to be involved in graft vs. leukemia (GvL) reactions. To investigate the role of NK cell recovery on clinical outcomes, the absolute number of NK cells at Day 28 after dUCBT was determined and patients with low numbers of NK cells had inferior two year disease-free survival (hazard ratio 1.96; p=0.04). A detailed developmental and functional analysis of the recovering NK cells was performed to link NK recovery and patient survival. The proportion of NK cells in each developmental stage was similar for patients with low, medium, and high Day 28 NK cell numbers. As compared to healthy controls, patients post-transplant showed reduced NK functional responses upon K562 challenge (CD107a, IFN-γ, and TNFα); however, there were no differences based on Day 28 NK cell number. Patients with low NK numbers had 30% less STAT5 phosphorylation in response to exogenous IL-15 (p=0.04) and decreased Eomes expression (p=0.025) compared to patients with high NK numbers. Decreased STAT5 phosphorylation and Eomes expression may be indicative of reduced sensitivity to IL-15 in the low NK cell group. Incubation of patient samples with IL-15 superagonist (ALT803) increased cytotoxicity and cytokine production in all patient groups. Thus, clinical interventions, including administration of IL-15 early after transplantation may increase NK cell number and function and, in turn, improve transplantation outcomes.

Modulation of T-bet and Eomes during Maturation of Peripheral Blood NK Cells Does Not Depend on Licensing/Educating KIR

Peripheral natural killer (NK) cells upregulate T-bet and downregulate Eomes, the key transcription factors regulating NK cell maturation and function during the last maturation steps toward terminally differentiated effector cells. During this process, NK cells acquire killer immunoglobulin-like receptors (KIR) and effector functions, such as cytotoxicity and target cell-induced cytokine production. Inhibitory KIR are pivotal in the control of effector functions, but whether they also modulate T-bet/Eomes expression is unknown. We have measured T-bet/Eomes levels, KIR expression, and effector functions of maturing CD94^negCD56^dimNK cells using CD57 as surface marker for maturation. Our cohort consisted of 23 healthy blood donors (HBD) homozygous for the KIR A haplotype that contains only inhibitory KIR2DL1 (ligand HLA-C2), KIR2DL3 (ligand HLA-C1), and KIR3DL1 (ligand HLA-Bw4). We confirm that during maturation of NK cells, the number of KIR increases, levels of T-bet/Eomes are modulated, and that cells acquire effector functions, such as cytotoxicity (CD107) and target cell-induced cytokine production (TNF-α). Because maturation was associated with the increase of the number of KIR as well as with the modulation of T-bet/Eomes, the number of KIR correlated with the extent of T-bet/Eomes modulation. However, whether the KIR were triggered by their cognate HLA ligands or not had no impact on T-bet and Eomes expression, indicating that modulation of T-box transcription factors during NK cell maturation does not depend on signals conveyed by KIR. We discuss the relevance of this finding in the context of models of NK cell maturation while cautioning that results obtained in a perhaps quite heterogeneous cohort of HBD are not necessarily conclusive.

T-bet and Eomesodermin in NK Cell Development, Maturation, and Function

Recent reports give insights into the role of the T-box transcription factors, T-bet and Eomesodermin (Eomes), in NK cell biology. In this mini-review, we recapitulate the initial reports that delineate T-bet and Eomes as master regulators of NK cell development, maturation, and function. We discuss how T-bet and Eomes expression is regulated during NK cell development and peripheral maturation. Furthermore, we summarize the current literature on the role of T-bet and Eomes in the transcriptional regulation of NK cell function and review possible effects of T-box transcription factor anomalies during aging, infection, cancer, and after hematopoietic stem cell transplantation. We discuss how the current data argue in favor of a model of T-bet and Eomes synergy in transcriptional regulation of NK cell function and identify T-box transcription factors as potential targets for therapeutic interventions.

Functional Reconstitution of Natural Killer Cells in Allogeneic Hematopoietic Stem Cell Transplantation

Natural killer (NK) cells are the first lymphocyte population to reconstitute following allogeneic hematopoietic stem cell transplantation (HSCT) and are important in mediating immunity against both leukemia and pathogens. Although NK cell numbers generally reconstitute within a month, the acquisition of mature NK cell phenotype and full functional competency can take 6 months or more, and is influenced by graft composition, concurrent pharmacologic immunosuppression, graft-versus-host disease, and other clinical factors. In addition, cytomegalovirus infection and reactivation have a dominant effect on NK cell memory imprinting following allogeneic HSCT just as it does in healthy individuals. Our understanding of NK cell education and licensing has evolved in the years since the "missing self" hypothesis for NK-mediated graft-versus-leukemia effect was first put forward. For example, we now know that NK cell "re-education" can occur, and that unlicensed NK cells can be more protective than licensed NK cells in certain settings, thus raising new questions about how best to harness graft-versus-leukemia effect. Here, we review current understanding of the functional reconstitution of NK cells and NK cell education following allogeneic HSCT, highlighting a conceptual framework for future research.