Ex Vivo Expanded and Activated Natural Killer Cells Prolong the Overall Survival of Mice with Glioblastoma-like Cell-Derived Tumors

Antitumor Effects of Intravenous Natural Killer Cell Infusion in an Orthotopic Glioblastoma Xenograft Murine Model and Gene Expression Profile Analysis

Despite standard multimodality treatment, containing maximum safety resection, temozolomide, radiotherapy, and a tumor-treating field, patients with glioblastoma (GBM) present with a dismal prognosis. Natural killer cell (NKC)-based immunotherapy would play a critical role in GBM treatment. We have previously reported highly activated and ex vivo expanded NK cells derived from human peripheral blood, which exhibited anti-tumor effect against GBM cells. Here, we performed preclinical evaluation of the NK cells using an in vivo orthotopic xenograft model, the U87MG cell-derived brain tumor in NOD/Shi-scid, IL-2RɤKO (NOG) mouse. In the orthotopic xenograft model, the retro-orbital venous injection of NK cells prolonged overall survival of the NOG mouse, indirectly indicating the growth-inhibition effect of NK cells. In addition, we comprehensively summarized the differentially expressed genes, especially focusing on the expression of the NKC-activating receptors' ligands, inhibitory receptors' ligands, chemokines, and chemokine receptors, between murine brain tumor treated with NKCs and with no agents, by using microarray. Furthermore, we also performed differentially expressed gene analysis between an internal and external brain tumor in the orthotopic xenograft model. Our findings could provide pivotal information for the NK-cell-based immunotherapy for patients with GBM.

ROS regulation in gliomas: implications for treatment strategies

Gliomas are one of the most common primary malignant tumours of the central nervous system (CNS), of which glioblastomas (GBMs) are the most common and destructive type. The glioma tumour microenvironment (TME) has unique characteristics, such as hypoxia, the blood-brain barrier (BBB), reactive oxygen species (ROS) and tumour neovascularization. Therefore, the traditional treatment effect is limited. As cellular oxidative metabolites, ROS not only promote the occurrence and development of gliomas but also affect immune cells in the immune microenvironment. In contrast, either too high or too low ROS levels are detrimental to the survival of glioma cells, which indicates the threshold of ROS. Therefore, an in-depth understanding of the mechanisms of ROS production and scavenging, the threshold of ROS, and the role of ROS in the glioma TME can provide new methods and strategies for glioma treatment. Current methods to increase ROS include photodynamic therapy (PDT), sonodynamic therapy (SDT), and chemodynamic therapy (CDT), etc., and methods to eliminate ROS include the ingestion of antioxidants. Increasing/scavenging ROS is potentially applicable treatment, and further studies will help to provide more effective strategies for glioma treatment.

An efficient feeder-free and chemically-defined expansion strategy for highly purified natural killer cells derived from human cord blood

Introduction

Natural killer cells (NKCs) are immune cells that can attack cancer cells through the direct recognition of ligands without prior sensitization. Cord blood-derived NKCs (CBNKCs) represent a promising tool for allogenic NKC-based cancer immunotherapy. Efficient NKC expansion and decreased T cell inclusion are crucial for the success of allogeneic NKC-based immunotherapy without inducing graft-versus-host reactions. We previously established an efficient ex vivo expansion system consisting of highly purified-NKCs derived from human peripheral blood. Herein, we evaluated the performance of the NKC expansion system using CB and characterized the expanded populations.

Methods

Frozen CB mononuclear cells (CBMCs), with T cells removed, were cultured with recombinant human interleukin (rhIL)-18 and rhIL-2 under conditions where anti-NKp46 and anti-CD16 antibodies were immobilized. Following 7, 14, and 21 days of expansion, the purity, fold-expansion rates of NKCs, and the expression levels of NK activating and inhibitory receptors were assessed. The ability of these NKCs to inhibit the growth of T98G, a glioblastoma (GBM) cell line sensitive to NK activity, was also examined.

Results

All expanded T cell-depleted CBMCs were included in over 80%, 98%, and 99% of CD3^-CD56⁺ NKCs at 7, 14, and 21 days of expansion, respectively. The NK activating receptors LFA-1, NKG2D, DNAM-1, NKp30, NKp44, NKp46, FcγRIII and NK inhibitory receptors TIM-3, TIGIT, TACTILE, NKG2A were expressed on the expanded-CBNKCs. Two out of three of the expanded-CBNKCs weakly expressed PD-1, yet gradually expressed PD-1 according to expansion period. One of the three expanded CBNKCs almost lacked PD-1 expression during the expansion period. LAG-3 expression was variable among donors, and no consistent changes were identified during the expansion period. All of the expanded CBNKCs elicited distinct cytotoxicity-mediated growth inhibition on T98G cells. The level of cytotoxicity was gradually decreased based on the prolonged expansion period.

Conclusions

Our established feeder-free expansion system yielded large scale highly purified and cytotoxic NKCs derived from human CB. The system provides a stable supply of clinical grade off-the-shelf NKCs and may be feasible for allogeneic NKC-based immunotherapy for cancers, including GBM.

Cytokines impact natural killer cell phenotype and functionality against glioblastoma in vitro

Objective

Natural killer (NK) cells are a part of the innate immune system and first-line defense against cancer. Since they possess natural mechanisms to recognize and kill tumor cells, NK cells are considered as a potential option for an off-the-shelf allogeneic cell-based immunotherapy. Here, our objective was to identify the optimal cytokine-based, feeder-free, activation and expansion protocol for cytotoxic NK cells against glioblastoma in vitro.

Methods

NK cells were enriched from human peripheral blood and expanded for 16 days with different activation and cytokine combinations. The expansion conditions were evaluated based on NK cell viability, functionality, expansion rate and purity. The cytotoxicity and degranulation of the expanded NK cells were measured in vitro from co‑cultures with the glioma cell lines U‑87 MG, U‑87 MG EGFR vIII, LN-229, U-118 and DK-MG. The best expansion protocols were selected from ultimately 39 different conditions: three magnetic cell‑selection steps (Depletion of CD3+ cells, enrichment of CD56+ cells, and depletion of CD3+ cells followed by enrichment of CD56+ cells); four activation protocols (continuous, pre-activation, re-activation, and boost); and four cytokine combinations (IL-2/15, IL‑21/15, IL‑27/18/15 and IL-12/18/15).

Results

The expansion rates varied between 2-50-fold, depending on the donor and the expansion conditions. The best expansion rate and purity were gained with sequential selection (Depletion of CD3+ cells and enrichment of CD56+ cells) from the starting material and pre-activation with IL‑12/18/15 cytokines, which are known to produce cytokine-induced memory-like NK cells. The cytotoxicity of these memory-like NK cells was enhanced with re-activation, diminishing the donor variation. The most cytotoxic NK cells were produced when cells were boosted at the end of the expansion with IL-12/18/15 or IL-21/15.

Conclusion

According to our findings the ex vivo proliferation capacity and functionality of NK cells is affected by multiple factors, such as the donor, composition of starting material, cytokine combination and the activation protocol. The cytokines modified the NK cells' phenotype and functionality, which was evident in their reactivity against the glioma cell lines. To our knowledge, this is the first comprehensive comparative study performed to this extent, and these findings could be used for upscaling clinical NK cell manufacturing.

Therapeutic Anti-KIR Antibody of 1-7F9 Attenuates the Antitumor Effects of Expanded and Activated Human Primary Natural Killer Cells on In Vitro Glioblastoma-like Cells and Orthotopic Tumors Derived Therefrom

Glioblastoma (GBM) is the leading malignant intracranial tumor, where prognosis for which has remained extremely poor for two decades. Immunotherapy has recently drawn attention as a cancer treatment, including for GBM. Natural killer (NK) cells are immune cells that attack cancer cells directly and produce antitumor immunity-related cytokines. The adoptive transfer of expanded and activated NK cells is expected to be a promising GBM immunotherapy. We previously established an efficient expansion method that produced highly purified, activated primary human NK cells, which we designated genuine induced NK cells (GiNKs). The GiNKs demonstrated antitumor effects in vitro and in vivo, which were less affected by blockade of the inhibitory checkpoint receptor programmed death 1 (PD-1). In the present study, we assessed the antitumor effects of GiNKs, both alone and combined with an antibody targeting killer Ig-like receptor 2DLs (KIR2DL1 and DL2/3, both inhibitory checkpoint receptors of NK cells) in vitro and in vivo with U87MG GBM-like cells and the T98G GBM cell line. Impedance-based real-time cell growth assays and apoptosis detection assays revealed that the GiNKs exhibited growth inhibitory effects on U87MG and T98G cells by inducing apoptosis. KIR2DL1 blockade attenuated the growth inhibition of the cell lines in vitro. The intracranial administration of GiNKs prolonged the overall survival of the U87MG-derived orthotopic xenograft brain tumor model. The KIR2DL1 blockade did not enhance the antitumor effects; rather, it attenuated it in the same manner as in the in vitro experiment. GiNK immunotherapy directly administered to the brain could be a promising immunotherapeutic alternative for patients with GBM. Furthermore, KIR2DL1 blockade appeared to require caution when used concomitantly with GiNKs.

Natural Killer Cells and Immunotherapy

Natural killer (NK) cells are innate immune cells that demonstrate cytolytic activity against tumor cells, virus-infected cells and other physiologically stressed cells, such as senescent cells [...].

Advances in NK cell therapy for brain tumors

Despite advances in treatment regimens that comprise surgery, chemotherapy, and radiation, outcome of many brain tumors remains dismal, more so when they recur. The proximity of brain tumors to delicate neural structures often precludes complete surgical resection. Toxicity and long-term side effects of systemic therapy remain a concern. Novel therapies are warranted. The field of NK cell-based cancer therapy has grown exponentially and currently constitutes a major area of immunotherapy innovation. This provides a new avenue for the treatment of cancerous lesions in the brain. In this review, we explore the mechanisms by which the brain tumor microenvironment suppresses NK cell mediated tumor control, and the methods being used to create NK cell products that subvert immune suppression. We discuss the pre-clinical studies evaluating NK cell-based immunotherapies that target several neuro-malignancies and highlight advances in molecular imaging of NK cells that allow monitoring of NK cell-based therapeutics. We review current and ongoing NK cell based clinical trials in neuro-oncology.

Natural Killer Cell-Based Immunotherapy against Glioblastoma

Glioblastoma (GBM) is the most aggressive and malignant primary brain tumor in adults. Despite multimodality treatment involving surgical resection, radiation therapy, chemotherapy, and tumor-treating fields, the median overall survival (OS) after diagnosis is approximately 2 years and the 5-year OS is poor. Considering the poor prognosis, novel treatment strategies are needed, such as immunotherapies, which include chimeric antigen receptor T-cell therapy, immune checkpoint inhibitors, vaccine therapy, and oncolytic virus therapy. However, these therapies have not achieved satisfactory outcomes. One reason for this is that these therapies are mainly based on activating T cells and controlling GBM progression. Natural killer (NK) cell-based immunotherapy involves the new feature of recognizing GBM via differing mechanisms from that of T cell-based immunotherapy. In this review, we focused on NK cell-based immunotherapy as a novel GBM treatment strategy.

Establishment of an efficient ex vivo expansion strategy for human natural killer cells stimulated by defined cytokine cocktail and antibodies against natural killer cell activating receptors

Introduction

Cell-based immunotherapy is categorized as a regenerative therapy under the Regenerative Medicine Safety Act in Japan. Natural killer (NK) cell-based immunotherapy is considered a promising strategy for treating cancer, including glioblastoma (GBM). We previously reported an expansion method for highly purified human peripheral blood-derived NK cells using a cytokine cocktail. Here, we aimed to establish a more efficient NK cell expansion method as compared to our previously reported method.

Methods

T cell-depleted human peripheral blood mononuclear cells (PBMCs) were isolated from three healthy volunteers. The depleted PBMCs were cultured in the presence of recombinant human interleukin (rhIL)-18 and high-dose rhIL-2 in anti-NKp46 and/or anti-CD16 antibody immobilization settings. After 14 days of expansion, the purity and expansion ratio of CD3-CD56+ NK cells were determined. The cytotoxicity-mediated growth inhibition of T98G cells (an NK activity-sensitive GBM cell line) was evaluated using a non-labeling, impedance-based real-time cell analyzer.

Results

Anti-NKp46 stimulation increased the NK cell purity and expansion ratio as compared to the non-antibody-stimulated population. Anti-CD16 stimulation weakly enhanced the NK cell expansion ratio of the non-antibody-stimulated population and enhanced the NK cell purity and expansion ratio of anti-NKp46-stimulated populations. All NK cell-containing populations tested distinctly inhibited T98G cell growth. These effects tended to be enhanced in an NK cell purity-dependent manner. In some cases, anti-CD16 stimulation decreased growth inhibition of T98G cell compared to other conditions despite the comparable NK cell purity.

Conclusions

We established a robust large-scale feeder-free expansion system for highly purified human NK cells using a defined cytokine cocktail and anti-NK cell activating receptor antibodies. The expansion system could be feasible for autologous or allogeneic NK cell-based immunotherapy of GBM. Moreover, it is easily controlled under Japanese law on regenerative medicine.

The War Is on: The Immune System against Glioblastoma—How Can NK Cells Drive This Battle?

Natural killer (NK) cells are innate lymphocytes that play an important role in immunosurveillance, acting alongside other immune cells in the response against various types of malignant tumors and the prevention of metastasis. Since their discovery in the 1970s, they have been thoroughly studied for their capacity to kill neoplastic cells without the need for previous sensitization, executing rapid and robust cytotoxic activity, but also helper functions. In agreement with this, NK cells are being exploited in many ways to treat cancer. The broad arsenal of NK-based therapies includes adoptive transfer of in vitro expanded and activated cells, genetically engineered cells to contain chimeric antigen receptors (CAR-NKs), in vivo stimulation of NK cells (by cytokine therapy, checkpoint blockade therapies, etc.), and tumor-specific antibody-guided NK cells, among others. In this article, we review pivotal aspects of NK cells’ biology and their contribution to immune responses against tumors, as well as providing a wide perspective on the many antineoplastic strategies using NK cells. Finally, we also discuss those approaches that have the potential to control glioblastoma—a disease that, currently, causes inevitable death, usually in a short time after diagnosis.