Natural killer cell-based immunotherapy in cancer: current insights and future prospects

Natural killer cells in cancer immunotherapy

Natural killer (NK) cells, as innate lymphocytes, possess cytotoxic capabilities and engage target cells through a repertoire of activating and inhibitory receptors. Particularly, natural killer group 2, member D (NKG2D) receptor on NK cells recognizes stress-induced ligands-the MHC class I chain-related molecules A and B (MICA/B) presented on tumor cells and is key to trigger the cytolytic response of NK cells. However, tumors have developed sophisticated strategies to evade NK cell surveillance, which lead to failure of tumor immunotherapy. In this paper, we summarized these immune escaping strategies, including the downregulation of ligands for activating receptors, upregulation of ligands for inhibitory receptors, secretion of immunosuppressive compounds, and the development of apoptosis resistance. Then, we focus on recent advancements in NK cell immune therapies, which include engaging activating NK cell receptors, upregulating NKG2D ligand MICA/B expression, blocking inhibitory NK cell receptors, adoptive NK cell therapy, chimeric antigen receptor (CAR)-engineered NK cells (CAR-NK), and NKG2D CAR-T cells, especially several vaccines targeting MICA/B. This review will inspire the research in NK cell biology in tumor and provide significant hope for improving cancer treatment outcomes by harnessing the potent cytotoxic activity of NK cells.

Immune signature and therapeutic approach of natural killer cell in chronic liver disease and hepatocellular carcinoma

Natural killer (NK) cells are one of the key members of innate immunity that predominantly reside in the liver, potentiating immune responses against viral infections or malignant tumors. It has been reported that changes in cell numbers and function of NK cells are associated with the development and progression of chronic liver diseases (CLDs) including non-alcoholic fatty liver disease, alcoholic liver disease, and chronic viral hepatitis. Also, it is known that the crosstalk between NK cells and hepatic stellate cells plays an important role in liver fibrosis and cirrhosis. In particular, the impaired functions of NK cells observed in CLDs consequently contribute to occurrence and progression of hepatocellular carcinoma (HCC). Chronic infections by hepatitis B or C viruses counteract the anti-tumor immunity of the host by producing the sheddases. Soluble major histocompatibility complex class I polypeptide-related sequence A (sMICA), released from the cell surfaces by sheddases, disrupts the interaction and affects the function of NK cells. Recently, the MICA/B-NK stimulatory receptor NK group 2 member D (NKG2D) axis has been extensively studied in HCC. HCC patients with low membrane-bound MICA or high sMICA concentration have been associated with poor prognosis. Therefore, reversing the sMICA-mediated downregulation of NKG2D has been proposed as an attractive strategy to enhance both innate and adaptive immune responses against HCC. This review aims to summarize recent studies on NK cell immune signatures and its roles in CLD and hepatocellular carcinogenesis and discusses the therapeutic approaches of MICA/B-NKG2D-based or NK cell-based immunotherapy for HCC.

The Opioid Growth Factor in Growth Regulation and Immune Responses in Cancer

It has become apparent that endogenous opioids act not only as neurotransmitters and neuromodulators, but have multiple functions in the body. Activation of the opioid system by opiate drugs is associated with a risk of cancer development through direct stimulation of tumor cell proliferation and through immunosuppression. In contrast, the endogenous peptide opioid [Met5]-enkephalin, now commonly referred to as Opioid Growth Factor (OGF), negatively regulates cell proliferation in a wide number of cells during development, homeostasis, and neoplasia. This action is mediated through the opioid growth factor receptor, originally designated the zeta (ζ) opioid receptor. Further, contrary to the traditional notion of opiates as immunosuppressive, endogenous OGF has been shown to possess a number of positive immunomodulatory properties and may provide a beneficial effect in cancer by augmenting the activity of cells involved in both innate and acquired immunity. Taken together, the evidence supports consideration of opioid peptides such as OGF as new strategies for cancer therapy.

Oridonin enhances cytotoxic activity of natural killer cells against lung cancer

BACKGROUND

Oridonin is a Chinese herbal medicine exhibiting anti-tumor properties; however, its immune modulation capacity has yet to be elucidated. Our objective in this study was to determine whether oridonin enhances the anti-tumor activity of natural killer (NK) cells against lung cancer cells.

METHODS

LDH-releasing assays were used to investigate the effects of oridonin on NK-92MI cell activity against lung cancer cells. Flow cytometry and real-time PCR were used to examine the effects of oridonin on degranulation markers, cytotoxic factors, activating receptors on NK-92MI cells, and ligands in lung cancer cells. Western blot analysis provided insight into the mechanisms underlying the observed effects.

RESULTS

Oridonin enhanced the cytotoxic effects of NK-92MI cells against A549 lung cancer cells. This effect involved upregulating the expression of the degranulation marker CD107a and IFN-γ as well as activating receptors on NK cells and their ligand MICA/B. Oridonin also inhibited STAT3 phosphorylation in A549 cells and NK-92MI cells. A lung cancer mouse model confirmed the anti-tumor effects of oridonin and NK-92MI cells, wherein both treatments alone suppressed tumor growth. Oridonin was also shown to have a synergistic effect on the anti-tumor activity of NK-92MI cells.

CONCLUSIONS

The ability of oridonin to enhance the cytotoxic effects of NK cells indicates its potential as a novel therapeutic agent for the treatment of lung cancer.

The effects of KIR2DL4 stimulated NK-92 cells on the apoptotic pathways of HER2 + /HER-breast cancer cells

Natural killer (NK) cells are immune cells that have attracted significant attention due to their cytotoxic properties. They are believed to be highly effective in cancer therapy. In this study, anti-KIR2DL4 (Killer cell Immunoglobulin like Receptor, 2 Ig Domains and Long cytoplasmic tail 4) was used to stimulate the NK-92 activator receptor to increase their cytotoxicity on breast cancer cell lines. Unstimulated and stimulated NK-92 cells (sNK-92) were cocultured with breast cancer (MCF-7 and SK-BR-3) and normal breast (MCF-12A) cell lines at 1:1, 1:5, and 1:10 (Target:Effector) ratios. The most effective cell cytotoxicity ratio (1:10) was used in the immunostaining and western blot assays to evaluate apoptosis pathway proteins. The sNK-92 cells showed higher cytotoxic activity on breast cancer cells than NK-92 cells. sNK-92 cells had a selective significant cytotoxicity effect on MCF-7 and SK-BR-3 cells but not MCF-12A cells. While sNK-92 cells were effective at all cell concentrations, they were most effective at a 1:10 ratio. Immunostaining and western blots showed significantly higher BAX, caspase 3, and caspase 9 protein levels in all breast cancer cell groups cocultured with sNK-92 than with NK-92 cells. NK-92 cells stimulated with KIR2DL4 showed elevated cytotoxic activity. The cytotoxic activity of sNK-92 cells on breast cancer cells is via apoptosis pathways. However, their effect on normal breast cells is limited. While the obtained data contains only basic information, additional clinical studies are needed to provide a basis for a new treatment model.

Inhibitory receptors for HLA class I as immune checkpoints for natural killer cell-mediated antibody-dependent cellular cytotoxicity in cancer immunotherapy

Natural killer (NK) cells mediate potent anti-tumor responses, which makes them attractive targets for immunotherapy. The anti-tumor response of endogenous- or allogeneic NK cells can be enhanced through clinically available monoclonal antibodies that mediate antibody-dependent cellular cytotoxicity (ADCC). NK cell activation is regulated by interaction of inhibitory receptors with classical- and non-classical human leukocyte antigens (HLA) class I molecules. Inhibitory receptors of the killer immunoglobulin-like receptor (KIR) family interact with HLA-A, -B or -C epitopes, while NKG2A interacts with the non-classical HLA-E molecule. Both types of inhibitory interactions may influence the strength of the ADCC response. In the present review, we provide an overview of the effect of inhibitory KIRs and NKG2A on NK cell-mediated ADCC, which highlights the rationale for combination strategies with ADCC triggering antibodies and interference with the NK cell relevant inhibitory immune checkpoints, such as KIR and NKG2A.

Exploring the effect of polyamines on NK cell function in colorectal cancer process based on glycolysis

Natural killer (NK) cells are lymphocytes with important anti-tumour functions. Cellular metabolism is dynamically regulated in NK cells and strongly influences their responses. Myc is a key regulator of immune cell activity and function, but little is known about how Myc controls NK cell activation and function. In this study, we found that c-Myc is involved in the regulation of NK cell immune activity. In the development of colon cancer, the energy generation disorder of tumor cells promotes the plunder of polyamines of NK cells by tumor cells, resulting in the inhibition of NK cell c-Myc. After inhibition of c-Myc, glycolysis of NK cells was impaired, resulting in decreased killing activity. There are three main types of polyamines: putrescine (Put), spermidine (Spd) and spermine (Spm). We found that the NK cells could reverse the inhibition state of c-Myc and glycolysis energy supply disorder and recover the killing activity of NK cells after giving certain spermidine. These results suggest that polyamine content and glycolysis supply under the regulation of c-Myc play a crucial role in the immune activity of NK cells.

Multifaceted characterization of the biological and transcriptomic signatures of natural killer cells derived from cord blood and placental blood

Background

Perinatal blood including umbilical cord blood and placental blood are splendid sources for allogeneic NK cell generation with high cytotoxicity of combating pathogenic microorganism and malignant tumor. Despite the generation of NK cells from the aforementioned perinatal blood, yet the systematical and detailed information of the biological and transcriptomic signatures of UC-NKs and P-NKs before large-scale clinical applications in disease remodeling is still largely obscure.

Methods

Herein, we took advantage of the “3IL”-based strategy for high-efficient generation of NK cells from umbilical cord blood and placental blood (UC-NKs and P-NKs), respectively. On the one hand, we conducted flow cytometry (FCM) assay and coculture to evaluate the subpopulations, cellular vitality and cytotoxic activity of the aforementioned NK cells. On the other hand, with the aid of RNA-SEQ and multiple bioinformatics analyses, we further dissected the potential diversities of UC-NKs and P-NKs from the perspectives of transcriptomes.

Results

On the basis of the “3IL” strategy, high-efficient NKs were generated from mononuclear cells (MNCs) in perinatal blood. P-NKs revealed comparable ex vivo expansion but preferable activation and cytotoxicity upon K562 cells over UC-NKs. Both of the two NKs showed diversity in cellular vitality and transcriptome including apoptotic cells, cell cycle, gene expression profiling and the accompanied multifaceted biological processes.

Conclusions

Our data revealed the multifaceted similarities and differences of UC-NKs and P-NKs both at the cellular and molecular levels. Our findings supply new references for allogeneic NK cell-based immunotherapy in regenerative medicine and will benefit the further exploration for illuminating the underlying mechanism as well.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-022-02697-6.

Oral Papillomatosis: Its Relation with Human Papilloma Virus Infection and Local Immunity—An Update

Oral papilloma lesions may appear as a result of HPV infection, or not, and only special molecular methods could differentiate them. Low-risk and high-risk HPV types could induce oral HPV papillomatosis with different natural evolution, clearance and persistence mechanisms. The pathogenic mechanisms are based on the crosstalk between the oral epithelial and immune cells and this very efficient virus. HPV acts as a direct inducer in the process of transforming a benign lesion into a malignant one, the cancerization process being also debated in this paper. According to the degree of malignity, three types of papillomatous lesions can be described in the oral cavity: benign lesions, potential malign disorders and malignant lesions. The precise molecular diagnostic is important to identify the presence of various virus types and also the virus products responsible for its oncogenicity. An accurate diagnostic of oral papilloma can be established through a good knowledge of etiological and epidemiological factors, clinical examination and laboratory tests. This review intends to update the pathogenic mechanisms driving the macroscopic and histological features of oral papillomatosis having HPV infection as the main etiological factor, focusing on its interreference in the local immunity. In the absence of an accurate molecular diagnostic and knowledge of local immunological conditions, the therapeutic strategy could be difficult to decide.

Crosstalk between angiogenesis and immune regulation in the tumor microenvironment

Cancer creates a complex tumor microenvironment (TME) composed of immune cells, stromal cells, blood vessels, and various other cellular and extracellular elements. It is essential for the development of anti-cancer combination therapies to understand and overcome this high heterogeneity and complexity as well as the dynamic interactions between them within the TME. Recent treatment strategies incorporating immune-checkpoint inhibitors and anti-angiogenic agents have brought many changes and advances in clinical cancer treatment. However, there are still challenges for immune suppressive tumors, which are characterized by a lack of T cell infiltration and treatment resistance. In this review, we will investigate the crosstalk between immunity and angiogenesis in the TME. In addition, we will look at strategies designed to enhance anti-cancer immunity, to convert “immune suppressive tumors” into “immune activating tumors,” and the mechanisms by which these strategies enhance effector immune cell infiltration.

Modulation of intrinsic inhibitory checkpoints using nano-carriers to unleash NK cell activity

Natural killer (NK) cells provide a powerful weapon mediating immune defense against viral infections, tumor growth, and metastatic spread. NK cells demonstrate great potential for cancer immunotherapy; they can rapidly and directly kill cancer cells in the absence of MHC-dependent antigen presentation and can initiate a robust immune response in the tumor microenvironment (TME). Nevertheless, current NK cell-based immunotherapies have several drawbacks, such as the requirement for ex vivo expansion of modified NK cells, and low transduction efficiency. Furthermore, to date, no clinical trial has demonstrated a significant benefit for NK-based therapies in patients with advanced solid tumors, mainly due to the suppressive TME. To overcome current obstacles in NK cell-based immunotherapies, we describe here a non-viral lipid nanoparticle-based delivery system that encapsulates small interfering RNAs (siRNAs) to gene silence the key intrinsic inhibitory NK cell molecules, SHP-1, Cbl-b, and c-Cbl. The nanoparticles (NPs) target NK cells in vivo, silence inhibitory checkpoint signaling molecules, and unleash NK cell activity to eliminate tumors. Thus, the novel NP-based system developed here may serve as a powerful tool for future NK cell-based therapeutic approaches.

The Advantages and Challenges of Anticancer Dendritic Cell Vaccines and NK Cells in Adoptive Cell Immunotherapy

In the last decade, an impressive advance was achieved in adoptive cell therapy (ACT), which has improved therapeutic potential and significant value in promising cancer treatment for patients. The ACT is based on the cell transfer of dendritic cells (DCs) and/or immune effector cells. DCs are often used as vaccine carriers or antigen-presenting cells (APCs) to prime naive T cells ex vivo or in vivo. Cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells are used as major tool effector cells for ACT. Despite the fact that NK cell immunotherapy is highly effective and promising against many cancer types, there are still some limitations, including insignificant infiltration, adverse conditions of the microenvironment, the immunosuppressive cellular populations, and the low cytotoxic activity in solid tumors. To overcome these difficulties, novel methods of NK cell isolation, expansion, and stimulation of cytotoxic activity should be designed. In this review, we discuss the basic characteristics of DC vaccines and NK cells as potential adoptive cell preparations in cancer therapy.

Nanobody-Engineered Natural Killer Cell Conjugates for Solid Tumor Adoptive Immunotherapy

Cancer immunotherapy based on natural killer (NK) cells is demonstrated to be a promising strategy. However, NK cells are deficient in ligands that target specific tumors, resulting in limited antitumor efficacy. Here, a glycoengineering approach to imitate the chimeric antigen receptor strategy and decorate NK cells with nanobodies to promote NK-based immunotherapy in solid tumors is proposed. Nanobody 7D12, which specifically recognizes the human epidermal growth factor receptor (EGFR) that is overexpressed on many solid tumors, is coupled to the chemically synthesized DBCO-PEG₄ -GGG-NH₂ by sortase A-mediated ligation to generate DBCO-7D12. The NK92MI cells bearing azide groups are then equipped with DBCO-7D12 via bioorthogonal click chemistry. The resultant 7D12-NK92MI cells exhibit high specificity and affinity for EGFR-overexpressing tumor cells in vitro and in vivo by the 7D12-EGFR interaction, causing increased cytokine secretion to more effectively kill EGFR-positive tumor cells, but not EGFR-negative cancer cells. Importantly, the 7D12-NK92MI cells also show a wide anticancer spectrum and extensive tumor penetration. Furthermore, mouse experiments reveal that 7D12-NK92MI treatment achieves excellent therapeutic efficacy and outstanding safety. The authors' works provide a cell modification strategy using specific protein ligands without genetic manipulation and present a potential novel method for cancer-targeted immunotherapy by NK cells.

Exploring natural killer cell immunology as a therapeutic strategy in lung cancer

Cytotoxic immune cells are key in the control of tumor development and progression. Natural killer (NK) cells are the cytotoxic arm of the innate immune system with the capability to kill tumor cells and surveil tumor cell dissemination. As such, the interest in harnessing NK cells in tumor control is increasing in many solid tumor types, including lung cancer. Here, we review the pre-clinical models used to unveil the role of NK cells in immunosurveillance of solid tumors and highlight measures to enhance NK cell activity. Importantly, the development of NK immunotherapy is rapidly evolving. Enhancing the NK cell response can be achieved using two broad modalities: enhancing endogenous NK cell activity, or performing adoptive transfer of pre-activated NK cells to patients. Numerous clinical trials are evaluating the efficacy of NK cell immunotherapy in isolation or in combination with standard treatments, with encouraging initial results. Pre-clinical studies and early phase clinical trials suggest that patients with solid tumors, including lung cancer, have the potential to benefit from recent developments in NK cell immunotherapy.

Interrupted crosstalk between natural killer cells and anti-epidermal growth factor receptor: a possible role in hepatocellular carcinoma treatment failure

Hepatocellular carcinoma (HCC) is a major health problem worldwide. Most patients are diagnosed for the first time at late stages; this leads to a very poor prognosis. It is challenging to discover strategies for treatment at these advanced stages. Recently, monoclonal antibodies (mAbs) targeting specific cellular signaling pathways in HCC have been developed. Unfortunately, they still have a low survival rate, and some of them failed clinically to produce effective responses even if they showed very good results against HCC in preclinical studies. This review focuses on and discusses the possible causes for the failure of mAbs, precisely anti-Epidermal Growth Factor Receptor (EGFR) mAb and the crosstalk between this mAb and patients' NK cells.

New insights into the role of NK cells in cancer immunotherapy

Repetitive infusions of ex vivo expanded NK cells induced antitumor T-cell responses in a metastatic lung cancer mouse model. These were further potentiated by Treg depletion. Thus the combination of NK cell-based immunotherapy with other treatment modalities in the direction of adaptive response enhancement might promote long lasting antitumor immunity.

Ocular side effects of novel anti-cancer biological therapies

To examine the ocular side effects of selected biological anti-cancer therapies and the ocular and systemic prognosis of patients receiving them. We retrospectively reviewed all medical records of patients who received biological anti-cancer treatment from 1/2012 to 12/2017 and who were treated at our ocular oncology service. The following data was retrieved: primary malignancy, metastasis, type of biological therapy, ocular side effects, ophthalmic treatment, non-ocular side effects, and ocular and systemic disease prognoses. Twenty-two patients received biological therapies and reported ocular side effects. Eighteen patients (81.8%) had bilateral ocular side effects, including uveitis (40.9%), dry eye (22.7%), and central serous retinopathy (22.7%). One patient (4.5%) had central retinal artery occlusion (CRAO), and one patient (4.5%) had branch retinal vein occlusion (BRVO). At the end of follow-up, 6 patients (27.27%) had resolution of the ocular disease, 13 patients (59.09%) had stable ocular disease, and 3 patients (13.64%) had progression of the ocular disease. Visual acuity improved significantly at the end of follow-up compared to initial values. Eighteen patients (81.8%) were alive at study closure. Biological therapies can cause a wide range of ocular side effects ranging from dry eye symptoms to severe pathologies that may cause ocular morbidity and vision loss, such as uveitis, CRAO and BRVO. All patients receiving biological treatments should be screened by ophthalmologists before treatment, re-screened every 4–6 months during treatment, and again at the end of treatment. Patients on biological treatment who have ocular complaints should be urgently referred to ocular consultation for early identification and early intervention.

IL-2 and Anti-TGF-β Promote NK Cell Reconstitution and Anti-tumor Effects after Syngeneic Hematopoietic Stem Cell Transplantation

Simple Summary

Hematopoietic stem cell transplantation (HSCT) causes early immune deficiency and susceptibility to both opportunistic infections and cancer relapse. In this study, using a mouse model where donor cells can be tracked over time, we have observed that the combination of IL-2 (a cytokine which activates the immune system) combined with the blockade of TGF-β (a cytokine which suppresses the immune system) increased immune recovery and resulted in greater anti-tumor efficacy. The combination of IL-2 and anti-TGF-β accelerated NK cell and myeloid cell reconstitution after HSCT.

Abstract

The failure of autologous hematopoietic stem cell transplantation (HSCT) has been associated with a profound immunodeficiency that follows shortly after treatment, which renders patients susceptible to opportunistic infections and/or cancer relapse. Thus, given the additional immunosuppressive pathways involved in immune evasion in cancer, strategies that induce a faster reconstitution of key immune effector cells are needed. Natural killer (NK) cells mediate potent anti-tumor effector functions and are the first immune cells to repopulate after HSCT. TGF-β is a potent immunosuppressive cytokine that can impede both the development and function of immune cells. Here, we evaluated the use of an immunotherapeutic regimen that combines low dose of IL-2, an NK cell stimulatory signal, with TGF-β neutralization, in order to accelerate NK cell reconstitution following congenic HSCT in mice by providing stimulatory signals yet also abrogating inhibitory ones. This therapy led to a marked expansion of NK cells and accelerated NK cell maturation. Following HSCT, mature NK cells from the treated recipients displayed an activated phenotype and enhanced anti-tumor responses both in vitro and in vivo. No overt toxicities or adverse effects were observed in the treated recipients. However, these stimulatory effects on NK cell recovery were predicated upon continuous treatment as cessation of treatment led to return to baseline levels and to no improvement of overall immune recovery when assessed at later time-points, indicating strict regulatory control of the NK cell compartment. Overall, this study still demonstrates that therapies that combine positive and negative signals can be plausible strategies to accelerate NK cell reconstitution following HSCT and augment anti-tumor efficacy.

Characterization of Surface Receptor Expression and Cytotoxicity of Human NK Cells and NK Cell Subsets in Overweight and Obese Humans

Obesity is associated with an increased risk for several cancer types and an altered phenotype and functionality of natural killer (NK) cells. This study aimed to investigate the association of overweight and obesity with NK cell functions and receptor expression profiles in humans. Therefore, peripheral blood mononuclear cells were isolated from normal weight, overweight, and obese healthy blood donors. In depth analysis of immune cell populations and 23 different surface markers, including NK cell receptors, NK-cell-related markers as well as functional intracellular markers on total NK cells and NK subgroups were performed by multicolor flow cytometry. The data revealed a decreased expression of the activating NK cell receptors KIR2DS4 and NKp46 as well as an increased expression of the inhibitory NK cell receptors NKG2A and Siglec-7 in overweight and obese compared to normal weight individuals. Additionally, the expression of the adhesion molecule CD62L and the maturation and differentiation marker CD27 was downregulated in NK cells of overweight and obese subjects. Furthermore, the cytotoxicity of NK cells against colorectal cancer cells was decreased in overweight and obese subjects. Investigations on underlying killing mechanisms demonstrated a reduced TRAIL expression on NK cells of obese subjects suggesting an impaired death receptor pathway in obesity. The present study gives new insights into an impaired functionality and phenotype of NK cells and NK cell subsets in overweight and obesity. These phenotypic alterations and dysfunction of NK cells might be an explanation for the increased cancer risk in obesity.

A Flow Cytometry-Based Whole Blood Natural Killer Cell Cytotoxicity Assay Using Overnight Cytokine Activation

Background: Measurement of natural killer (NK) cell function has important clinical utility in several diseases. Although the flow cytometry (FC)-based 4-h NK cytotoxicity assay using peripheral blood mononuclear cells (PBMCs) in the clinical laboratory has been used for this purpose, this assay requires large amounts of blood and a rapid PBMC isolation step. Here, we developed an FC-based overnight NK cytotoxicity assay using whole blood (WB), and applied it to patients with liver diseases.

Methods: Peripheral blood of healthy volunteers (n = 28) and patients with liver diseases, including hepatocellular carcinoma (n = 19) and liver cirrhosis (n = 7), was analyzed for complete blood count, absolute NK cell count, and NK cell activity (NKA). NKA was evaluated in three assay types: an FC-based overnight WB NK cytotoxicity assay using carboxyfluorescein diacetate succinimidyl ester-labeled K562 cells in the presence of various cytokine combinations [including interleukin (IL)-2, IL-18, and IL-21], an FC-based 4-h PBMC NK cytotoxicity assay, and an FC-based CD107a degranulation assay using WB and PBMCs.

Results: Optimal cytokine combinations for NK cell activation in WB were determined (IL-2/IL-18, IL-2/IL-21, and IL-2/IL-18/IL-21). A good correlation was observed between WB and PBMC NK cytotoxicity assays; absolute NK cell counts were better correlated with the WB NK cytotoxicity assay than with the PBMC NK cytotoxicity assay. This WB NK cytotoxicity assay showed that patients with liver diseases had significantly lower NK cytotoxicity than healthy volunteers, under stimulation with various cytokines (p < 0.001).

Conclusion: The proposed FC-based overnight WB NK cytotoxicity assay correlates well with the conventional 4-h PBMC NK cytotoxicity assay, demonstrating future potential as a supportive assay for clinical laboratory research and observational studies.

Application of In Vivo Imaging Techniques for Monitoring Natural Killer Cell Migration and Tumor Infiltration

In recent years, the use of natural killer (NK) cell-based immunotherapy has shown promise against various cancer types. To some extent therapeutic potential of NK cell-based immunotherapy depends on migration of NK cells towards tumors in animal models or human subjects and subsequent infiltration. Constant improvement in the pharmacological and therapeutic properties of NK cells is driving the performance and use of NK cell-based immunotherapies. In this review, we summarize the molecular imaging techniques used in monitoring the migration and infiltration of NK cells in vivo at preclinical and clinical levels. A review of pros and cons of each molecular imaging modality is done. Finally, we provide our perception of the usefulness of molecular imaging approaches for in vivo monitoring of NK cells in preclinical and clinical scenarios.

Establishment and Preclinical Therapy of Patient-derived Hepatocellular Carcinoma Xenograft Model

Hepatocellular carcinoma (HCC) is a world-wide health problem. Poor and delayed diagnoses as well as high recurrence rate resulting in high mortality rate. In this study, we established a patient-derived xenograft (PDX) model from HCC patient, and continuously maintained with subcutaneous passage more than 20 times. This HCC PDX tumor exhibited the same histological characteristics with the HCC patient and could be used to verify therapeutic effect of liver cancer. We further evaluated this PDX model by experimental chemotherapy, demonstrating that this HCC PDX model was sensitive to sorafenib treatment. Further, the potential of natural killer cell-based immunotherapy for HCC was tested using this model. We found that NK92 cells effectively suppressed the tumor growth in vivo and prolonged the survival time of HCC-bearing PDX mice. This study indicates that HCC PDX model is a good platform to testify the efficacy of preclinical chemotherapy and immunotherapy.

Tumor immune microenvironment modulation-based drug delivery strategies for cancer immunotherapy

The past years have witnessed promising clinical feedback for anti-cancer immunotherapies, which have become one of the hot research topics; however, they are limited by poor delivery kinetics, narrow patient response profiles, and systemic side effects. To the best of our knowledge, the development of cancer is highly associated with the immune system, especially the tumor immune microenvironment (TIME). Based on the comprehensive understanding of the complexity and diversity of TIME, drug delivery strategies focused on the modulation of TIME can be of great significance for directing and improving cancer immunotherapy. This review highlights the TIME modulation in cancer immunotherapy and summarizes the versatile TIME modulation-based cancer immunotherapeutic strategies, medicative principles and accessory biotechniques for further clinical transformation. Remarkably, the recent advances of cancer immunotherapeutic drug delivery systems and future prospects of TIME modulation-based drug delivery systems for much more controlled and precise cancer immunotherapy will be emphatically discussed.

Preservation of cell-based immunotherapies for clinical trials

In the unique supply chain of cellular therapies, preservation is important to keep the cell product viable. Many factors in cryopreservation affect the outcome of a cell therapy: (i) formulation and introduction of a freezing medium, (ii) cooling rate, (iii) storage conditions, (iv) thawing conditions and (v) post-thaw processing. This article surveys clinical trials of cellular immunotherapy that used cryopreserved regulatory, chimeric antigen receptor or gamma delta T cells, dendritic cells or natural killer (NK) cells. Several observations are summarized from the given information. The aforementioned cell types have been similarly frozen in media containing 5-10% dimethyl sulfoxide (DMSO) with plasma, serum or human serum albumin. Two common freezing methods are an insulated freezing container such as Nalgene Mr. Frosty and a controlled-rate freezer at a cooling rate of -1°C/min. Water baths at approximately 37°C have been commonly used for thawing. Post-thaw processing of cryopreserved cells varied greatly: some studies infused the cells immediately upon thawing; some diluted the cells in a carrier solution of varying formulation before infusion; some washed cells to remove cryoprotective agents; and others re-cultured cells to recover cell viability or functionality lost due to cryopreservation. Emerging approaches to preserving cellular immunotherapies are also described. DMSO-free formulations of the freezing media have demonstrated improved preservation of cell viability in T lymphocytes and of cytotoxic function in natural killer cells. Saccharides are a common type of molecule used as an alternative cryoprotective agent to DMSO. Improving methods of preservation will be critical to growth in the clinical use of cellular immunotherapies.

Magnetic Nanoparticles Attached to the NK Cell Surface for Tumor Targeting in Adoptive Transfer Therapies Does Not Affect Cellular Effector Functions

Adoptive cell transfer therapy is currently one of the most promising approaches for cancer treatment. This therapy has some limitations, however, such as the dispersion of in vivo-administered cells, causing only a small proportion to reach the tumor. Nanotechnological approaches could offer a solution for this drawback, as they can increase cell retention and accumulation in a region of interest. In particular, strategies employing magnetic nanoparticles (MNPs) to improve targeting of adoptively transferred T or NK cells have been explored in mice. In vivo magnetic retention is reported using the human NK cell line NK-92MI transfected with MNPs. Primary NK cells are nonetheless highly resistant to transfection, and thus we explore in here the possibility of attaching the MNPs to the NK cell surface to overcome this issue, and examine whether this association would affect NK effector functions. We assessed the attachment of MNPs coated with different polymers to the NK cell surface, and found that APS-MNP attached more efficiently to the NK-92MI cell surface. In association with MNPs, these cells preserved their main functions, exhibiting a continued capacity to degranulate, conjugate with and lyse target cells, produce IFN-γ, and respond to chemotactic signals. MNP-loaded NK-92MI cells were also retained in an in vitro capillary flow system by applying an EMF. A similar analysis was carried out in primary NK cells, isolated from mice, and expanded in vitro. These primary murine NK cells also maintained their functionality intact after MNP treatment and were successfully retained in vitro. This work therefore provides further support for using MNPs in combination with EMFs to favor specific retention of functional NK cells in a region of interest, which may prove beneficial to adoptive cell-therapy protocols.

Cryopreserved Human Natural Killer Cells Exhibit Potent Antitumor Efficacy against Orthotopic Pancreatic Cancer through Efficient Tumor-Homing and Cytolytic Ability (Running Title: Cryopreserved NK Cells Exhibit Antitumor Effect)

Pancreatic cancer is known to be highly aggressive, and desmoplasia-induced accumulation of extracellular matrix (ECM), which is a hallmark of many pancreatic cancers, severely restricts the therapeutic efficacy of both immunotherapeutics and conventional chemotherapeutics due to the ECM functioning as a major physical barrier against permeation and penetration. In the case of cell-based immunotherapeutics, there are several other bottlenecks preventing translation into clinical use due to their biological nature; for example, poor availability of cell therapeutic in a readily usable form due to difficulties in production, handling, shipping, and storage. To address these challenges, we have isolated allogeneic natural killer (NK) cells from healthy donors and expanded them in vitro to generate cryopreserved stocks. These cryopreserved NK cells were thawed to evaluate their therapeutic efficacy against desmoplastic pancreatic tumors, ultimately aiming to develop a readily accessible and mass-producible off-the-shelf cell-based immunotherapeutic. The cultured NK cells post-thawing retained highly pure populations of activated NK cells that expressed various activating receptors and a chemokine receptor. Furthermore, systemic administration of NK cells induced greater in vivo tumor growth suppression when compared with gemcitabine, which is the standard chemotherapeutic used for pancreatic cancer treatment. The potent antitumor effect of NK cells was mediated by efficient tumor-homing ability and infiltration into desmoplastic tumor tissues. Moreover, the infiltration of NK cells led to strong induction of apoptosis, elevated expression of the antitumor cytokine interferon (IFN)-γ, and inhibited expression of the immunosuppressive transforming growth factor (TGF)-β in tumor tissues. Expanded and cryopreserved NK cells are strong candidates for future cell-mediated systemic immunotherapy against pancreatic cancer.

Characterization of human natural killer cells for therapeutic use

As a part of the innate immune system, natural killer (NK) cells are cytotoxic lymphocytes that can exert cytotoxic activity against infected or transformed cells. Furthermore, due to their expression of a functional Fc receptor, they have also been eluded as a major effector fraction in antibody-dependent cellular cytotoxicity. These characteristics have led to multiple efforts to use them for adoptive immunotherapy against various malignancies.  There are now at least 70 clinical trials testing the safety and efficacy of NK cell products around the world in early-phase clinical trials. NK cells are also being tested in the context of tumor retargeting via chimeric antigen receptors, other genetic modification strategies, as well as tumor-specific activation strategies such as bispecific engagers with or without cytokine stimulations. One advantage of the use of NK cells for adoptive immunotherapy is their potential to overcome HLA barriers. This has led to a plethora of sources, such as cord blood hematopoietic stem cells and induced pluripotent stem cells, which can generate comparatively high cytotoxic NK cells to peripheral blood counterparts. However, the variety of the sources has led to a heterogeneity in the characterization of the final infusion product. Therefore, in this review, we will discuss a comparative assessment strategy, from characterization of NK cells at collection to final product release by various phenotypic and functional assays, in an effort to predict potency of the cellular product.

Functional Assessment for Clinical Use of Serum-Free Adapted NK-92 Cells

Natural killer (NK) cells stand out as promising candidates for cellular immunotherapy due to their capacity to kill malignant cells. However, the therapeutic use of NK cells is often dependent on cell expansion and activation with considerable amounts of serum and exogenous cytokines. We aimed to develop an expansion protocol for NK-92 cells in an effort to generate a cost-efficient, xeno-free, clinical grade manufactured master cell line for therapeutic applications. By making functional assays with NK-92 cells cultured under serum-free conditions (NK-92_SF) and comparing to serum-supplemented NK-92 cells (NK-92_S) we did not observe significant alterations in the viability, proliferation, receptor expression levels, or in perforin and granzyme levels. Interestingly, even though NK-92_SF cells displayed decreased degranulation and cytotoxicity against tumor cells in vitro, the degranulation capacity was recovered after overnight incubation with 20% serum in the medium. Moreover, lentiviral vector-based genetic modification efficiency of NK-92_SF cells was comparable with NK-92_S cells. The application of similar strategies can be useful in reducing the costs of manufacturing cells for clinical use and can help us understand and implement strategies towards chemically defined expansion and genetic modification protocols.

Magnetic delivery of Fe3O4@polydopamine nanoparticle-loaded natural killer cells suggest a promising anticancer treatment

Natural killer (NK)-cell-based immunotherapy has been reported to have promising prospects in the treatment of non-small cell lung cancer, one of the most common malignancies in the world. It has been proven that higher the NK cell infiltration into the tumor, the better is the curative effect. Therefore, it would be beneficial to develop a method that increases NK cell recruitment and infiltration into the tumor site. The purpose of this study was to establish an immune-cell delivery system for clear lung cancer cells based on magnetic nanoparticle (NP)-labeled NK cells that can be accumulated at the tumor site by placing a tiny external magnetic device inside animals. We developed superparamagnetic iron oxide NPs consisting of a magnetic Fe3O4 core and a shell of polydopamine (PDA) for magnetic targeting therapy. Fe3O4@PDA NPs possess favorable physiological stability and biocompatibility that facilitate their active uptake by NK cells. The biology of NK cells was not affected by the presence of NPs. In vitro and in vivo studies showed that Fe3O4@PDA NP-labeled NK cells significantly inhibited tumor growth and reduced the expression of Ki-67 and increased the apoptosis of A549 cancer cells. H&E staining showed Fe3O4@PDA NP-labeled NK cells, under a magnetic field, had higher intra-tumoral iron density and increased accumulation of CD56+ NK cells. Our results suggest that Fe3O4@PDA NPs are a promising magnetic nanomaterial that can manipulate immune cells, thereby inhibiting tumor growth.

Natural killer cell-based immunotherapy: From transplantation toward targeting cancer stem cells

Natural killer (NK) cells are key players of the innate immune system. NK cells provide protection against infectious pathogens and malignancies in cell. This characteristic may be attributable to their intrinsic diverse potentialities and also their cooperation with adaptive immune lymphocytes, known as B and T cells. The growth, recurrence, and metastasis of cancer cells, and the failure of cytoreductive therapies against cancer cells are due to the small population of intratumor stem-like cells, called cancer stem cells (CSCs). Furthermore, NK cells can efficiently eradicate heterogeneous tumor cells after a long-term treatment. Therefore, NK cell-based therapy is a promising strategy to target and break CSC-associated resistance to anticancer drugs treatment. In this review, we have presented an overview of the emerging knowledge of the characteristics, diversities, and mechanism-driven immune surveillance of human NK cells and advances in NK cell-based immunotherapies. Finally, we will discuss how these cells can be applied to introduce the next generation of vaccine- and immune-based approaches to prevent drug resistance.

Pharmacologically upregulated carcinoembryonic antigen-expression enhances the cytolytic activity of genetically-modified chimeric antigen receptor NK-92MI against colorectal cancer cells

BACKGROUND

The natural killer cell line, NK-92MI, is cytotoxic against various types of cancer. The aim of this study was to develop chimeric antigen receptor-modified (CAR) NK-92MI cells targeting carcinoembryonic antigen-expressing (CEA) tumours and increase killing efficacy by pharmacologically modifying CEA-expression.

RESULT

We generated anti-CEA-CAR NK-92MI cells by retroviral vector transduction. This genetically-modified cell line recognised and lysed high CEA-expressing tumour cell lines (LS174T) at 47.54 ± 12.60% and moderate CEA-expressing tumour cell lines (WiDr) at 31.14 ± 16.92% at a 5:1 effector: target (E/T) ratio. The cell line did not lyse low CEA-expressing tumour cells (HCT116) as they did their parental cells (NK-92MI cells). The histone deacetylase-inhibitor (HDAC) sodium butyrate (NaB) and the methylation-inhibitor 5-azacytidine (5-AZA), as epigenetic modifiers, induced CEA-expression in HCT116 and WiDr cells. Although the IC₅₀ of 5 fluorouracil (5-FU) increased, both cell lines showed collateral sensitivity to anti-CEA-CAR NK-92MI cells. The cytolytic function of anti-CEA-CAR NK-92MI cells was increased from 22.99 ± 2.04% of lysis background to 69.20 ± 11.92% after NaB treatment, and 69.70 ± 9.93% after 5-AZA treatment, at a 10:1 E/T ratio in HCT116 cells. The WiDr cells showed similar trend, from 22.99 ± 4.01% of lysis background to 70.69 ± 10.19% after NaB treatment, and 59.44 ± 10.92% after 5-AZA treatment, at a 10:1 E/T ratio.

CONCLUSIONS

This data indicates that the effector-ability of anti-CEA-CAR NK-92MI increased in a CEA-dependent manner. The combination of epigenetic-modifiers like HDAC-inhibitors, methylation-inhibitors, and adoptive-transfer of ex vivo-expanded allogeneic-NK cells may be clinically applicable to patients with in 5-FU resistant condition.

hIL-15-gene modified human natural killer cells (NKL-IL15) exhibit anti-human leukemia functions

PURPOSE

Natural killer (NK) cells can kill transformed cells and represent anti-tumor activities for improving the immunotherapy of cancer. In previous works, we established human interleukin-15 (hIL-15) gene-modified NKL cells (NKL-IL15) and demonstrated their efficiency against human hepatocarcinoma cells (HCCs) in vitro and in vivo. To further assess the applicability of NKL-IL15 cells in adoptive cellular immunotherapy for human leukemia, here we report their natural cytotoxicity against leukemia in vitro and in vivo.

METHODS

Flow cytometry, ELISA and MTT methods were performed for molecular expression, cell proliferation and cytotoxicity assays. Leukemia xenograft NOD/SCID mice were established by subcutaneous injection with K562 cells, and then treated with irradiated NKL cells.

RESULTS

We found NKL-IL15 cells displayed a significant high cytolysis activity against both human leukemia cell lines and primary leukemia cells from patients, accompanied with up-regulated expression of molecules related to NK cell cytotoxicity such as perforin, granzyme B and NKp80. Moreover, cytokines secreted by NKL-IL15 cells, including TNF-α and IFN-γ, could induce the expression of NKG2D ligands on target cells, which increased the susceptibility of leukemia cells to NK cell-mediated cytolysis. Encouragingly, NKL-IL15 cells significantly inhibited the growth of leukemia cells in xenografted NOD/SCID mice and prolonged the survival of tumor-bearing mice dramatically. Furthermore, NKL-IL15 cells displayed stimulatory effects on hPBMCs, indicating the immunesuppressive status of leukemia patients could be improved by NKL-IL15 cell treatment.

CONCLUSIONS

These results provided evidence that IL-15 gene-modification could augment NK cell-mediated anti-human leukemia function, which would improve primary NK cell-based immunotherapy for leukemia in future.

Ex vivo expansion of human peripheral blood natural killer cells and cytotoxic T lymphocytes from lung cancer patients

Lung cancer is the most common type of cancer with the highest cancer-associated mortality rates worldwide, as well as in Vietnam. Numerous studies have demonstrated that higher numbers and higher rate of activity of infiltrating natural killer (NK) cells and cytotoxic T lymphocytes (CTLs) in the tumor are closely correlated with positive prognosis, tumor size decrease and longer survival of lung cancer patients. In the present study, the effectiveness of BINKIT^® kit in the ex vivo expansion of NK cells and CTLs in the peripheral blood of 7 patients aged between 30 and 84 years with metastatic lung cancer was evaluated. After 21 days of culture, the average number of CTLs (CD3⁺CD8⁺) increased by 742.3-fold in the CTL culture, accounting for 72.2% of the cultured cell population, and the mean cell viability was 95.7%. In the NK cell culture, the average number of NK cells (CD3^-CD56⁺) increased by 637.5-fold, accounting for 84.3% of the cultured cell population, with an average viability of 94.7%. The percentage of active NK cells (CD3^-CD56⁺ bright) was 82.1%, which increased by 408.9-fold. Notably, a close correlation was identified between the numbers of cytokine-induced killer (CD3⁺CD56⁺) and NK (CD3^-CD56⁺) cells in the NK cell culture (P<0.05). In the two culture conditions (namely NK cell and CTL cultures), no clear correlation was identified between the rate of initial immune cells in the peripheral blood and the corresponding number following ex vivo expansion (P>0.05). These results revealed that the method of expansion and activation of NK cells and CTLs from peripheral blood was successfully applied using BINKIT, and reached the requirements for clinical applications in cancer treatment in Vietnam.

A possible mechanism of impaired NK cytotoxicity in cancer patients: Down-regulation of DAP10 by TGF-β1

Aims and background

Elevated TGF-β1 secretion and down-modulation of NKG2D underlies impaired NK cytotoxicity in cancer patients. However, the molecular mechanism of immunosuppression by TGF-β1 is not yet clarified.

Methods

IL-2-activated human NK cells were cultured with TGF-β1. Protein levels of NKG2D and DAP10 were examined by FACS or immunoblot analyses. Real-time RT-PCR was performed to quantify the transcription levels. MAPK inhibitors were used to investigate intracellular signaling.

Results

TGF-β1 down-regulated total and surface NKG2D, which was partially dependent on transcriptional regulation. TGF-β1 treatment of human NK cells resulted in significant changes in both transcriptional and translational levels of DAP10. Moreover, treatment with bafilomycin A1 or folimycin restored total NKG2D levels in TGF-β1-treated NK cells. The impaired NKG2D down-modulation by TGF-β1 was not associated with activation of the MAPK signaling pathway.

Conclusions

TGF-β1 down-modulates surface NKG2D expression by controlling the transcriptional and translational levels of DAP10.

Molecular Imaging: A Useful Tool for the Development of Natural Killer Cell-Based Immunotherapies

Molecular imaging is a relatively new discipline that allows visualization, characterization, and measurement of the biological processes in living subjects, including humans, at a cellular and molecular level. The interaction between cancer cells and natural killer (NK) cells is complex and incompletely understood. Despite our limited knowledge, progress in the search for immune cell therapies against cancer could be significantly improved by dynamic and non-invasive visualization and tracking of immune cells and by visualization of the response of cancer cells to therapies in preclinical and clinical studies. Molecular imaging is an essential tool for these studies, and a multimodal molecular imaging approach can be applied to monitor immune cells in vivo, for instance, to visualize therapeutic effects. In this review, we discuss the usefulness of NK cells in cancer therapies and the preclinical and clinical usefulness of molecular imaging in NK cell-based therapies. Furthermore, we discuss different molecular imaging modalities for use with NK cell-based therapies, and their preclinical and clinical applications in animal and human subjects. Molecular imaging has contributed to the development of NK cell-based therapies against cancers in animal models and to the refinement of current cell-based cancer immunotherapies. Developing sensitive and reproducible non-invasive molecular imaging technologies for in vivo NK cell monitoring and for real-time assessment of therapeutic effects will accelerate the development of NK cell therapies.

A Listeria-derived polypeptide promotes in vivo activation of NK cells for antitumor therapy

Immunotherapies have shown promise in treatment of cancer, but more potent and targeted therapies are needed. Natural killer (NK) cells are lymphocytes with innate ability to recognize and lyse tumor cells. When activated, they also produce type II interferon (IFNγ) to orchestrate the activity of other immune cells. Strategies to elicit NK cell activation in vivo have potential usefulness in anti-tumor immunotherapies. Here, we report on a strategy to stimulate NK cell activation and anti-tumor activity in mice with established B16.F10 murine melanomas. We and others previously observed that NK cells are rapidly activated during infection by pathogens such as the bacterium Listeria monocytogenes (Lm). A secreted Lm virulence protein, p60, and a fragment of p60 termed L1S were previously shown to stimulate innate immune responses and promote NK cell activation. We purified recombinant L1S and characterized its activity in cell culture studies. Recombinant L1S protein was also observed to promote accumulation and robust NK cell activation in the lungs when given via intratracheal instillation to control and tumor-bearing mice. Importantly, therapeutic administration of a single L1S dose was found to significantly reduce the number and area of "metastatic" tumor nodules on the lungs of mice with established B16.F10 murine melanomas. Depletion studies showed that these antitumor effects were dependent on NK cells and IFNγ. These data provide proof of concept that administration of a single immune-modulating microbial polypeptide can be used to therapeutically boost NK cell in vivo activation and promote anti-tumor responses.

Chimeric Antigen Receptor-Engineered NK-92 Cells: An Off-the-Shelf Cellular Therapeutic for Targeted Elimination of Cancer Cells and Induction of Protective Antitumor Immunity

Significant progress has been made in recent years toward realizing the potential of natural killer (NK) cells for cancer immunotherapy. NK cells can respond rapidly to transformed and stressed cells and have the intrinsic potential to extravasate and reach their targets in almost all body tissues. In addition to donor-derived primary NK cells, also the established NK cell line NK-92 is being developed for adoptive immunotherapy, and general safety of infusion of irradiated NK-92 cells has been established in phase I clinical trials with clinical responses observed in some of the cancer patients treated. To enhance their therapeutic utility, NK-92 cells have been modified to express chimeric antigen receptors (CARs) composed of a tumor-specific single chain fragment variable antibody fragment fused via hinge and transmembrane regions to intracellular signaling moieties such as CD3ζ or composite signaling domains containing a costimulatory protein together with CD3ζ. CAR-mediated activation of NK cells then bypasses inhibitory signals and overcomes NK resistance of tumor cells. In contrast to primary NK cells, CAR-engineered NK-92 cell lines suitable for clinical development can be established from molecularly and functionally well-characterized single cell clones following good manufacturing practice-compliant procedures. In preclinical in vitro and in vivo models, potent antitumor activity of NK-92 variants targeted to differentiation antigens expressed by hematologic malignancies, and overexpressed or mutated self-antigens associated with solid tumors has been found, encouraging further development of CAR-engineered NK-92 cells. Importantly, in syngeneic mouse tumor models, induction of endogenous antitumor immunity after treatment with CAR-expressing NK-92 cells has been demonstrated, resulting in cures and long-lasting immunological memory protecting against tumor rechallenge at distant sites. Here, we summarize the current status and future prospects of CAR-engineered NK-92 cells as off-the-shelf cellular therapeutics, with special emphasis on ErbB2 (HER2)-specific NK-92 cells that are approaching clinical application.

Modeling Natural Killer Cell Targeted Immunotherapies

Animal models have extensively contributed to our understanding of human immunobiology and to uncover the underlying pathological mechanisms occurring in the development of diseases. However, mouse models do not reproduce the genetic and molecular complexity inherent in human disease conditions. Human immune system (HIS) mouse models that are susceptible to human pathogens and can recapitulate human hematopoiesis and tumor immunobiology provide one means to bridge the interspecies gap. Natural killer cells are the founding member of the innate lymphoid cell family. They exert a rapid and strong immune response against tumor and pathogen-infected cells. Their antitumor features have long been exploited for therapeutic purposes in the context of cancer. In this review, we detail the development of highly immunodeficient mouse strains and the models currently used in cancer research. We summarize the latest improvements in adoptive natural killer (NK) cell therapies and the development of novel NK cell sources. Finally, we discuss the advantages of HIS mice to study the interactions between human NK cells and human cancers and to develop new therapeutic strategies.

Adoptive natural killer cell therapy is effective in reducing pulmonary metastasis of Ewing sarcoma

The survival of patients with metastatic or relapsed Ewing sarcoma (ES) remains dismal despite intensification of combination chemotherapy and radiotherapy, precipitating the need for novel alternative therapies with minimal side effects. Natural killer (NK) cells are promising additions to the field of cellular immunotherapy. Adoptive NK cell therapy has shown encouraging results in hematological malignancies. Despite these initial promising successes, however, NK cell therapy for solid tumors remains to be investigated using in vivo tumor models. The purpose of this study is to evaluate the efficacy of ex vivo expanded human NK cells in controlling primary and metastatic ES tumor growth in vitro and in vivo. Using membrane-bound IL-21 containing K562 (K562-mbIL-21) expansion platform, we were able to obtain sufficient numbers of expanded NK (eNK) cells that display favorable activation phenotypes and inflammatory cytokine secretion, along with a strong in vitro cytotoxic effect against ES. Furthermore, eNK therapy significantly decreased lung metastasis without any significant therapeutic effect in limiting primary tumor growth in an in vivo xenograft model. Our data demonstrate that eNK may be effective against pulmonary metastatic ES, but challenges remain to direct proper trafficking and augmenting the cytotoxic function of eNK to target primary tumor sites.

The Smac Mimetic BV6 Improves NK Cell-Mediated Killing of Rhabdomyosarcoma Cells by Simultaneously Targeting Tumor and Effector Cells

Rhabdomyosarcoma (RMS), the most common cancer of connective tissues in pediatrics, is often resistant to conventional therapies. One underlying mechanism of this resistance is the overexpression of Inhibitor of Apoptosis (IAP) proteins, leading to a dysfunctional cell death program within tumor cells. Smac mimetics (SM) are small molecules that can reactivate the cell death program by antagonizing IAP proteins and thereby compensating their overexpression. Here, we report that SM sensitize two RMS cell lines (RD and RH30) toward natural killer (NK) cell-mediated killing on the one hand, and increase the cytotoxic potential of NK cells on the other. The SM-induced sensitization of RH30 cells toward NK cell-mediated killing is significantly reduced through blocking tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) on NK cells prior to coculture. In addition, the presence of zVAD.fmk, a pancaspase inhibitor, rescues tumor cells from the increase in killing, indicating an apoptosis-dependent cell death. On the NK cell side, the presence of SM in addition to IL-2 during the ex vivo expansion leads to an increase in their cytotoxic activity against RH30 cells. This effect is mainly TNFα-dependent and partially mediated by NK cell activation, which is associated with transcriptional upregulation of NF-κB target genes such as IκBα and RelB. Taken together, our findings implicate that SM represent a novel double-hit strategy, sensitizing tumor and activating NK cells with one single drug.

Ex vivo expansion of CD3depleted cord blood-MNCs in the presence of bone marrow stromal cells; an appropriate strategy to provide functional NK cells applicable for cellular therapy

Considering umbilical cord blood (UCB) as a rich source of hematopoietic stem cells, we introduced a cost-effective approach to expand CD3^depleted UCB-MNCs into functional NK cells. CD3^depleted UCB-MNCs were expanded in the presence or absence of a feeder [bone marrow stem cells (BMSCs) or osteoblasts], with or without cytokines and their differentiation into NK cells was determined by flow cytometry. NK cell function was quantified by LAMP-1/CD107a expression, TNF-α/IFN-γ release, and LDH release/PI staining in targets. Higher expansion of NK cells was observed after two weeks in the presence of BMSCs and cytokines (104±15) compared to osteoblasts and cytokines (84±29, p<0.05). On day 14, CD3^depleted UCB-MNCs in the presence of BMSCs and cytokines showed lower expression of CD3, CD19, CD14, CD15 and CD69 as well as higher expression of CD2 and CD7, which were suggestive of cell differentiation into mature NK cell lineage. Strong cytotoxicity of expanded cells was also identified with higher LDH release and PI% in targets. Significant upregulation of LAMP-1 with decreased release of IFN-γ and TNF-α from effectors were observed. We demonstrate an effective expansion of UCB-NK cells that maintained their functional capabilities applicable for cellular therapies.

Natural killer cell subsets and receptor expression in peripheral blood mononuclear cells of a healthy Korean population: Reference range, influence of age and sex, and correlation between NK cell receptors and cytotoxicity

BACKGROUND

The purpose of this study was to identify CD56^bright and CD56^dim natural killer (NK) cell subsets and analyze their receptors expression in a healthy Korean population, and to determine whether receptor expression correlates with age, sex, and cytotoxicity.

MATERIALS AND METHODS

We performed multicolor flow cytometry assays to analyze the expression of various NK cell receptors (CD16, NKG2A, NKG2C, NKG2D, CD57, DNAM-1, CD8a, CD62L, NKp30, and NKp46) on both CD3^-/CD56^dim and CD3^-/CD56^bright NK cells in whole-blood samples from 122 healthy donors. The expression of these receptors was compared according to age (<30years, n=22, 30-60years, n=73 and >60years, n=27) and gender (male, n=61, female, n=61). NK cell cytotoxicity assays were performed with peripheral blood mononuclear cells (PBMCs) from 18 individuals. The results were compared to the expression levels of NKp30 and NKp46 receptors.

RESULTS

A normal reference range for NK cell receptor expression in two NK cell subsets was established. NKp46 and NKG2D expression gradually decreased with age (p<0.01 and p<0.05, respectively) whereas NK cell proportion and numbers, frequencies of CD56^dim cells, and CD57 expression increased with age (p<0.01 in all cases). Men showed greater NK cell proportion and numbers, frequencies of CD56^dim cells, and CD57 expression compared to those of women (p<0.05 and p<0.001; p<0.01 and p<0.01, respectively). Notably, the expression of NKp46 was negatively correlated with NK cell frequency (r=-0.42, p<0.001). Furthermore, NK cell cytotoxicity was found to positively correlate with NCR expression (p=0.02), but not NK cell proportion (p=0.80).

CONCLUSION

We have established a profile of NK cell surface receptors for a Korean population, and revealed that age and gender have an effect on the expression of NK cell receptors in the population. Our data might explain why neither NK cell numbers nor proportions correlate with NK cell cytotoxicity.

Trends and advances in tumor immunology and lung cancer immunotherapy

Among several types of tumor, lung cancer is considered one of the most fatal and still the main cause of cancer-related deaths. Although chemotherapeutic agents can improve survival and quality of life compared with symptomatic treatment, cancers usually still progress after chemotherapy and are often aggravated by serious side effects. In the last few years there has been a growing interest in immunotherapy for lung cancer based on promising preliminary results in achieving meaningful and durable treatments responses with minimal manageable toxicity. This article is divided into two parts, the first part discusses the role of human immune system in controlling and eradicating cancer and the mechanisms of immune response evasion by tumor. The second part reviews the recent progress made in immunotherapy for lung cancer with results from trials evaluating therapeutic vaccines in addition to immune checkpoint blockade, specifically cytotoxic T lymphocyte associated protein 4, programmed death receptor 1 pathway, using monoclonal antibodies.

Intratumoral natural killer cells show reduced effector and cytolytic properties and control the differentiation of effector Th1 cells

Natural killer (NK) cells are known to have effector and cytolytic properties to kill virus infected or tumor cells spontaneously. Due to these properties, NK cells have been used as an adoptive cellular therapy to control tumor growth in various clinical trials but have shown limited clinical benefits. This indicates that our knowledge about phenotypic and functional differences in NK cells within the tumor microenvironment and secondary lymphoid tissues is incomplete. In this work, we report that B16F10 cell-induced melanoma recruits the CD11b⁺CD27⁺ subset of NK cells at a very early stage during tumor progression. These intratumoral NK cells showed increased expression of CD69, reduced inhibitory receptor KLRG1, and decreased proliferative ability. As compared to splenic NK cells, intratumoral NK cells showed decreased expression of activating receptors NKG2D, Ly49D and Ly49H; increased inhibitory receptors, NKG2A and Ly49A; decreased cytokines IFNγ and GM-CSF; decreased cytokine receptors IL-21R, IL-6Rα, and CD122 expression. Depletion of NK cells led to decrease peripheral as well as intratumoral effector CD4⁺T-bet⁺ cells (Th1), and increased tumor growth. Furthermore, purified NK cells showed increased differentiation of Th1 cells in an IFNγ-dependent manner. Anti-NKG2D in the culture promoted differentiation of effector Th1 cells. Collectively, these observations suggest that intratumoral NK cells possess several inhibitory functions that can be partly reversed by signaling through the NKG2D receptor or by cytokine stimulation, which then leads to increased differentiation of effector Th1 cells.