Large-scale ex vivo expansion and characterization of natural killer cells for clinical applications

Chimeric antigen receptor-natural killer cells: Novel insight into immunotherapy for solid tumors (Review)

The chimeric antigen receptor (CAR) is an artificially modified fusion protein consisting of an extracellular antigen-binding domain, transmembrane domain and intracellular signalling domain. CAR-T therapy has demonstrated remarkable clinical efficacy in hematological malignancies. However, cytokine release syndrome and other side effects have hindered its application in solid tumors. CAR-natural killer (NK) cells have attracted broad attention due to their safety in clinical applications, their mechanism in recognising cancer cells and the abundance of its clinical specimens. Preclinical and clinical trials of human primary NK cells and NK-92 cell lines demonstrated that CAR-NK cells are able to fight haematological malignancies and solid tumors. However, the implication of CAR-NK cell therapy also has certain challenges, including the expansion and activation of primary NK cells in vitro, selection of CAR targets, survival time of CAR-NK cells in vivo, storage and transportation of NK cells, and efficiency of NK cell transduction. This review focuses on the latest progress of CAR-NK cells in the treatment of solid tumors.

NKp30 - A prospective target for new cancer immunotherapy strategies

Natural killer (NK) cells are an important arm of the innate immune system. They constitutively express the NKp30 receptor. NKp30-mediated responses are triggered by the binding of specific ligands e.g. tumour cell-derived B7-H6 and involve the secretion of cytotoxic mediators including TNF-α, IFN-γ, perforins and granzymes. The latter two constitute a target cell-directed response that is critical in the process of immunosurveillance. The structure of NKp30 is presented, focusing on the ligand-binding site, on the ligand-induced structural changes and on the experimental data available correlating structure and binding affinity. The translation of NKp30 structural changes to disease progression is also reviewed. NKp30 role in immunotherapy has been explored in chimeric antigen receptor T-cell (CAR-T) therapy. However, antibodies or small ligands targeting NKp30 have not yet been developed. The data reviewed herein unveil the key structural aspects that must be considered for drug design in order to develop novel immunotherapy approaches.

CAR-NK cells: A promising cellular immunotherapy for cancer

Natural Killer (NK) cells and CD8⁺ cytotoxic T cells are two types of immune cells that can kill target cells through similar cytotoxic mechanisms. With the remarkable success of chimeric antigen receptor (CAR)-engineered T (CAR-T) cells for treating haematological malignancies, there is a rapid growing interest in developing CAR-engineered NK (CAR-NK) cells for cancer therapy. Compared to CAR-T cells, CAR-NK cells could offer some significant advantages, including: (1) better safety, such as a lack or minimal cytokine release syndrome and neurotoxicity in autologous setting and graft-versus-host disease in allogenic setting, (2) multiple mechanisms for activating cytotoxic activity, and (3) high feasibility for 'off-the-shelf' manufacturing. CAR-NK cells could be engineered to target diverse antigens, enhance proliferation and persistence in vivo, increase infiltration into solid tumours, overcome resistant tumour microenvironment, and ultimately achieve an effective anti-tumour response. In this review, we focus on recent progress in genetic engineering and clinical application of CAR-NK cells, and discuss current challenges and future promise of CAR-NK cells as a novel cellular immunotherapy in cancer.

Engineering the Bridge between Innate and Adaptive Immunity for Cancer Immunotherapy: Focus on γδ T and NK Cells

Most studies on genetic engineering technologies for cancer immunotherapy based on allogeneic donors have focused on adaptive immunity. However, the main limitation of such approaches is that they can lead to severe graft-versus-host disease (GvHD). An alternative approach would bolster innate immunity by relying on the natural tropism of some subsets of the innate immune system, such as γδ T and natural killer (NK) cells, for the tumor microenvironment and their ability to kill in a major histocompatibility complex (MHC)-independent manner. γδ T and NK cells have the unique ability to bridge innate and adaptive immunity while responding to a broad range of tumors. Considering these properties, γδ T and NK cells represent ideal sources for developing allogeneic cell therapies. Recently, significant efforts have been made to exploit the intrinsic anti-tumor capacity of these cells for treating hematologic and solid malignancies using genetic engineering approaches such as chimeric antigen receptor (CAR) and T cell receptor (TCR). Here, we review over 30 studies on these two approaches that use γδ T and NK cells in adoptive cell therapy (ACT) for treating cancer. Based on those studies, we propose several promising strategies to optimize the clinical translation of these approaches.

A serum-free protocol for the ex vivo expansion of Cytokine-Induced Killer cells using gas-permeable static culture flasks

Cytokine-Induced (CIK) cells represent an attractive approach for cell-based immunotherapy, as they show several advantages compared with other strategies. Here we describe an original serum-free protocol for CIK cell expansion that employs G-Rex devices and compare the resulting growth, viability, phenotypic profile and cytotoxic activity with conventional culture in tissue flasks. CIK cells were obtained from buffy coats, seeded in parallel in G-Rex and tissue flasks, and stimulated with clinical-grade IFN-γ, anti-CD3 antibody and IL-2. G-Rex led to large numbers of CIK cells, with a minimal need for technical interventions, thus reducing the time and costs of culture manipulation. CIK cells generated in G-Rex showed a less differentiated phenotype, with a significantly higher expression of naive-associated markers such as CD62L, CD45RA and CCR7, which correlates with a remarkable expansion potential in culture and could lead to longer persistence and a more sustained anti-tumor response in vivo. The described procedure can be easily translated to large-scale production under Good Manufacturing Practice. Overall, this protocol has strong advantages over existing procedures, as it allows easier, time-saving and cost-effective production of CIK effector cells, fostering their clinical application.

Detection of response to tumor microenvironment-targeted cellular immunotherapy using nano-radiomics

Immunotherapies, including cell-based therapies, targeting the tumor microenvironment (TME) result in variable and delayed responses. Thus, it has been difficult to gauge the efficacy of TME-directed therapies early after administration. We investigated a nano-radiomics approach (quantitative analysis of nanoparticle contrast-enhanced three-dimensional images) for detection of tumor response to cellular immunotherapy directed against myeloid-derived suppressor cells (MDSCs), a key component of TME. Animals bearing human MDSC-containing solid tumor xenografts received treatment with MDSC-targeting human natural killer (NK) cells and underwent nanoparticle contrast-enhanced computed tomography (CT) imaging. Whereas conventional CT-derived tumor metrics were unable to differentiate NK cell immunotherapy tumors from untreated tumors, nano-radiomics revealed texture-based features capable of differentiating treatment groups. Our study shows that TME-directed cellular immunotherapy causes subtle changes not effectively gauged by conventional imaging metrics but revealed by nano-radiomics. Our work provides a method for noninvasive assessment of TME-directed immunotherapy potentially applicable to numerous solid tumors.

Analysis of ex vivo expanded and activated clinical-grade human NK cells after cryopreservation

BACKGROUND AIMS

Several methods to expand and activate (EA) NK cells ex vivo have been developed for the treatment of relapsed or refractory cancers. Infusion of fresh NK cells is generally preferred to the infusion of cryopreserved/thawed (C/T) NK cells because of concern that cryopreservation diminishes NK cell activity. However, there has been little head-to-head comparison of the functionality of fresh versus C/T NK cell products.

METHODS

We evaluated activity of fresh and C/T EA NK cells generated by interleukin (IL)-15, IL-2 and CD137L expansion.

RESULTS

Analysis of C/T NK cell products demonstrated decreased recovery of viable CD56⁺ cells, but the proportion of NK cells in the C/T EA NK cell product did not decrease compared with the fresh EA NK cell product. Fresh and C/T EA NK cells demonstrated increased granzyme B compared with NK cells pre-expansion, but only fresh EA NK cells showed increased NKG2D. Compared with fresh EA NK cells, cytotoxic ability of C/T EA NK cells was reduced, but C/T EA NK cells remained potently cytotoxic against tumor cells via both antibody-independent and antibody-dependent mechanisms within 4 h post-thaw. Fresh EA NK cells generated high levels of gamma interferon (IFN-γ), which was abrogated by JAK1/JAK2 inhibition with ruxolitinib, but C/T EA NK cells showed lower IFN-γ unaffected by JAK1/JAK2 inhibition.

DISCUSSION

Usage of C/T EA NK cells may be an option to provide serial "boost" NK cell infusions from a single apheresis to maximize NK cell persistence and potentially improve NK-induced responses to refractory cancer.

Genome engineering of induced pluripotent stem cells to manufacture natural killer cell therapies

Natural killer (NK) cells play a crucial role in host immunity by detecting cells that downregulate MHC class I presentation and upregulate stress ligands, as commonly seen in cancers. Current NK therapies using primary NK cells are prone to manufacturing issues related to expansion and storage. Alternative cell sources utilizing immortalized NK cell lines require irradiation and are dependent on systemic IL-2 administration, which has been associated with adverse effects. In contrast, NK cells differentiated from induced pluripotent stem cells (iPSC-NK cells) offer an off-the-shelf alternative that may overcome these bottlenecks. The development of a serum-free and feeder-free differentiation protocol allows for the manufacturing of clinically adaptable iPSC-NK cells that are equally as effective as primary NK cells and the NK-92 cell line for many indications. Moreover, genetic modifications targeting NK-mediated antibody-dependent cellular cytotoxicity capabilities, cytotoxicity, and checkpoint inhibitors may increase the therapeutic potential of iPSC-NK products. This review will highlight the current sources for NK therapies and their respective constraints, discuss recent developments in the manufacturing and genetic engineering of iPSC-NK cells, and provide an overview of ongoing clinical trials using NK cells.

Streamlined production of genetically modified T cells with activation, transduction and expansion in closed-system G-Rex bioreactors

BACKGROUND

Gas Permeable Rapid Expansion (G-Rex) bioreactors have been shown to efficiently expand immune cells intended for therapeutic use, but do not address the complexity of the viral transduction step required for many engineered T-cell products. Here we demonstrate a novel method for transduction of activated T cells with Vectofusin-1 reagent. Transduction is accomplished in suspension, in G-Rex bioreactors. The simplified transduction step is integrated into a streamlined process that uses a single bioreactor with limited operator intervention.

METHODS

Peripheral blood mononuclear cells (PBMCs) from healthy donors were thawed, washed and activated with soluble anti-CD3 and anti-CD28 antibodies either in cell culture bags or in G-Rex bioreactors. Cells were cultured in TexMACS GMP medium with interleukin (IL)-7 and IL-15 and transduced with RetroNectin in bags or Vectorfusin-1 in the G-Rex. Total viable cell number, fold expansion, viability, transduction efficiency, phenotype and function were compared between the two processes.

RESULTS

The simplified process uses a single vessel from activation through harvest and achieves 56% transduction with 29-fold expansion in 11 days. The cells generated in the simplified process do not differ from cells produced in the conventional bag-based process functionally or phenotypically.

DISCUSSION

This study demonstrates that T cells can be transduced in suspension. Further, the conventional method of generating engineered T cells in bags for clinical use can be streamlined to a much simpler, less-expensive process without compromising the quality or function of the cell product.

Nanoparticle-Mediated Intracellular Protection of Natural Killer Cells Avoids Cryoinjury and Retains Potent Antitumor Functions

The ability of natural killer (NK) cells to mediate potent antitumor immunity in clinical adoptive transfer settings relies, in large part, on their ability to retain cytotoxic function following cryopreservation. To avoid potential systemic toxicities associated with infusions of NK cells into patients in the presence of dimethylsulfoxide (DMSO), interest in alternative cryoprotective agents (CPAs) with improved safety profiles has grown. Despite the development of various sugars, amino acids, polyols, and polyampholytes as cryoprotectants, their ability to promote protection from intracellular cryodamage is limited because they mostly act outside of the cell. Though ways to shuttle cryoprotectants intracellularly exist, NK cells' high aversity to manipulation and freezing has meant they are highly understudied as targets for the development of new cryopreservation approaches. Here, the first example of a safe and efficient platform for the intracellular delivery of non-DMSO CPAs to NK cells is presented. Biocompatible chitosan-based nanoparticles are engineered to mediate the efficient DMSO-free cryopreservation of NK cells. NK cells cryopreserved in this way retain potent cytotoxic, degranulation, and cytokine production functions against tumor targets. This not only represents the first example of delivering nanoparticles to NK cells, but illustrates the clinical potential in manufacturing safer allogeneic adoptive immunotherapies "off the shelf."

Current progress in NK cell biology and NK cell-based cancer immunotherapy

A better understanding of the complex interactions between the immune system and tumour cells from different origins has opened the possibility to design novel procedures of antitumoral immunotherapy. One of these novel approaches is based on the use of autologous or allogeneic natural killer (NK) cells to treat cancer. In the last decade, different strategies to activate NK cells and their use in adoptive NK cell-based therapy have been established. Although NK cells are often considered as a uniform cell population, several phenotypic and functionally distinct NK cells subsets exist in healthy individuals, that are differentially affected by ageing or by apparently innocuous viruses such as cytomegalovirus (CMV). In addition, further alterations in the expression of activating and inhibitory receptors are found in NK cells from cancer patients, likely because of their interaction with tumour cells. Thus, NK cells represent a promising strategy for adoptive immunotherapy of cancer already tested in phase 1/2 clinical trials. However, the existence of NK cell subpopulations expressing different patterns of activating and inhibitory receptors and different functional capacities, that can be found to be altered not only in cancer patients but also in healthy individuals stratified by age or CMV infection, makes necessary a personalized definition of the procedures used in the selection, expansion, and activation of the relevant NK cell subsets to be successfully used in NK cell-based immunotherapy.

NK Cell-Based Immunotherapy in Renal Cell Carcinoma

Natural killer (NK) cells are cytotoxic lymphocytes that are able to kill tumor cells without prior sensitization. It has been shown that NK cells play a pivotal role in a variety of cancers, highlighting their relevance in tumor immunosurveillance. NK cell infiltration has been reported in renal cell carcinoma (RCC), the most frequent kidney cancer in adults, and their presence has been associated with patients’ survival. However, the role of NK cells in this disease is not yet fully understood. In this review, we summarize the biology of NK cells and the mechanisms through which they are able to recognize and kill tumor cells. Furthermore, we discuss the role that NK cells play in renal cell carcinoma, and review current strategies that are being used to boost and exploit their cytotoxic capabilities.

Study protocol for a phase II, multicentre, prospective, non-randomised clinical trial to assess the safety and efficacy of infusing allogeneic activated and expanded natural killer cells as consolidation therapy for paediatric acute myeloblastic leukaemia

INTRODUCTION

Acute myeloblastic leukaemia (AML) constitutes the second most common haematological malignancy in the paediatric population. Current treatment regimens are based on the administration of polychemotherapy, combining high doses of cytarabine with anthracyclines and topoisomerase inhibitors. Allogeneic haematopoietic stem cell transplantation (HSCT) is an option for high-risk patients with AML (and for intermediate-risk patients if a sibling donor is available). With this strategy, AML survival has increased substantially; however, it has remained stagnant at approximately 60%, with relapse being the principal culprit. The predominant role of the immune system and natural killer (NK) cells in controlling paediatric AML has gained importance within the context of HSCT. In this protocol, we propose incorporating this cell therapy as an adjuvant treatment through the infusion of activated and expanded haploidentical NK (NKAE) cells in paediatric patients with AML who are in cytological remission after completing consolidation therapy, and with no indication for HSCT.

METHODS AND ANALYSIS

Patients up to 30 years of age, diagnosed with AML, in their first cytological remission, who have completed both the induction and the consolidation phases of chemotherapy and do not meet the criteria for allogeneic HSCT are eligible. The patients will receive two doses of NKAE cells once a week, using a GMP K562-mbIL15-41BBL stimulus from a haploidentical donor and interleukin 2 subcutaneously. The patients will then be followed up for 36 months to assess the primary endpoint, which is the probability of relapse after NK cell infusion.

ETHICS AND DISSEMINATION

This clinical trial was approved by the Clinical Research Ethics Committee of La Paz University Hospital and The Spanish Agency of Medicines and Medical Devices. Findings will be disseminated through peer-reviewed publications, conference presentations and community reporting.

TRIAL REGISTRATION NUMBER

EudraCT code: 2015-001901-15, ClinicalTrials.gov Identifier: NCT02763475.

NK cells for cancer immunotherapy

Natural killer (NK) cells can swiftly kill multiple adjacent cells if these show surface markers associated with oncogenic transformation. This property, which is unique among immune cells, and their capacity to enhance antibody and T cell responses support a role for NK cells as anticancer agents. Although tumours may develop several mechanisms to resist attacks from endogenous NK cells, ex vivo activation, expansion and genetic modification of NK cells can greatly increase their antitumour activity and equip them to overcome resistance. Some of these methods have been translated into clinical-grade platforms and support clinical trials of NK cell infusions in patients with haematological malignancies or solid tumours, which have yielded encouraging results so far. The next generation of NK cell products will be engineered to enhance activating signals and proliferation, suppress inhibitory signals and promote their homing to tumours. These modifications promise to significantly increase their clinical activity. Finally, there is emerging evidence of increased NK cell-mediated tumour cell killing in the context of molecularly targeted therapies. These observations, in addition to the capacity of NK cells to magnify immune responses, suggest that NK cells are poised to become key components of multipronged therapeutic strategies for cancer.

Engineering of Natural Killer Cells for Clinical Application

The clinical success of chimeric antigen receptor-directed T cells in leukemia and lymphoma has boosted the interest in cellular therapy of cancer. It has been known for nearly half a century that a subset of lymphocytes called natural killer (NK) cells can recognize and kill cancer cells, but their clinical potential as therapeutics has not yet been fully explored. Progress in methods to expand and genetically modify human NK cells has resulted in technologies that allow the production of large numbers of highly potent cells with specific anticancer activity. Here, we describe clinically applicable protocols for NK cell engineering, including expansion of NK cells and genetic modification using electroporation of messenger RNA.

Methods and Process Optimization for Large-Scale CAR T Expansion Using the G-Rex Cell Culture Platform

The G-Rex cell culture platform is based on a gas-permeable membrane technology that provides numerous advantages over other systems. Conventional bioreactor platform technologies developed for large scale mammalian cell expansion are typically constrained by the mechanics of delivering oxygen to an expanding cell population. These systems often utilize complex mechanisms to enhance oxygen delivery, such as stirring, rocking, or perfusion, which adds to expense and increases their overall risk of failure. On the other hand, G-Rex gas-permeable membrane-based bioreactors provide a more physiologic environment and avoid the risk and cost associated with more complex systems. The result is a more robust, interacting cell population established through unlimited oxygen and nutrients that are available on demand. By removing the need to actively deliver oxygen, these bioreactors can hold larger medium volumes (more nutrients) which allows the cells to reach a maximum density without complexity or need for media exchange. This platform approach is scaled to meet the needs of research through commercial production with a direct, linear correlation between small and large devices. In the G-Rex platform, examples of cell expansion (9-14 day duration) include; CAR-T cells, which have atypical harvest density of 20-30 × 10⁶/cm² (or 2-3 × 10⁹ cells in a 100 cm² device); NK cells, which have a typical harvest density of 20-30 × 10⁶/cm² (or 2-3 × 10⁹ cells in a 100 cm² device) and numerous other cell types that proliferate without the need for intervention or complex processes normally associated with large scale culture. Here we describe the methods and concepts used to optimize expansion of various cell types in the static G-Rex bioreactor platform.

Adult peripheral blood and umbilical cord blood NK cells are good sources for effective CAR therapy against CD19 positive leukemic cells

Among hematological cancers, Acute Lymphoblastic Leukemia (ALL) and Chronic Lymphocytic Leukemia (CLL) are the most common leukemia in children and elderly people respectively. Some patients do not respond to chemotherapy treatments and it is necessary to complement it with immunotherapy-based treatments such as chimeric antigen receptor (CAR) therapy, which is one of the newest and more effective treatments against these cancers and B-cell lymphoma. Although complete remission results are promising, CAR T cell therapy presents still some risks for the patients, including cytokine release syndrome (CRS) and neurotoxicity. We proposed a different immune cell source for CAR therapy that might prevent these side effects while efficiently targeting malignant cells. NK cells from different sources are a promising vehicle for CAR therapy, as they do not cause graft versus host disease (GvHD) in allogenic therapies and they are prompt to attack cancer cells without prior sensitization. We studied the efficacy of NK cells from adult peripheral blood (AB) and umbilical cord blood (CB) against different target cells in order to determine the best source for CAR therapy. AB CAR-NK cells are slightly better at killing CD19 presenting target cells and CB NK cells are easier to stimulate and they have more stable number from donor to donor. We conclude that CAR-NK cells from both sources have their advantages to be an alternative and safer candidate for CAR therapy.

Antigen-independent killer cells prepared for adoptive immunotherapy: One source, divergent protocols, diverse nomenclature

Adoptive cell therapy (ACT) using tumor antigen-independent killer cells has been widely used in clinical trials of cancer treatment. Circumventing the need for identification of a particular tumor-associated antigen on tumor cells, the approach has opened possibilities for the extension of ACT immunotherapy to patients with a wide variety of cancer types. Namely, Natural Killer (NK), Lymphokine-activated Killer (LAK) cells and Cytokine-induced killer (CIK) cells are the most commonly used cell types in antigen-independent adoptive immunotherapy of cancer. They all originate from peripheral blood mononuclear cells and share several common features in their killing mechanisms. However, despite broad application in clinical settings, the boundaries between these cell types are not very clearly defined. The current study aims to review different aspects of these cell populations in terms of phenotypical characteristic and preparation media, to clarify how the boundaries are set.

Membrane bound IL-21 based NK cell feeder cells drive robust expansion and metabolic activation of NK cells

NK cell adoptive therapy is a promising cancer therapeutic approach, but there are significant challenges that limiting its feasibility and clinical efficacy. One difficulty is the paucity of clinical grade manufacturing platforms to support the large scale expansion of highly active NK cells. We created an NK cell feeder cell line termed 'NKF' through overexpressing membrane bound IL-21 that is capable of inducing robust and sustained proliferation (>10,000-fold expansion at 5 weeks) of highly cytotoxic NK cells. The expanded NK cells exhibit increased cytotoxic function against a panel of blood cancer and solid tumor cells as compared to IL-2-activated non-expanded NK cells. The NKF-expanded NK cells also demonstrate efficacy in mouse models of human sarcoma and T cell leukemia. Mechanistic studies revealed that membrane-bound IL-21 leads to an activation of a STAT3/c-Myc pathway and increased NK cell metabolism with a shift towards aerobic glycolysis. The NKF feeder cell line is a promising new platform that enables the large scale proliferation of highly active NK cells in support of large scale third party NK cell clinical studies that have been recently intiatied. These results also provide mechanistic insights into how membrane-bound IL-21 regulates NK cell expansion.

T-Cell Receptor Stimulation Enhances the Expansion and Function of CD19 Chimeric Antigen Receptor-Expressing T Cells

PURPOSE

Current protocols for CD19 chimeric antigen receptor-expressing T cells (CD19.CAR-T cells) require recipients to tolerate preinfusion cytoreductive chemotherapy, and the presence of sufficient target antigen on normal or malignant B cells.

PATIENTS AND METHODS

We investigated whether additional stimulation of CD19.CAR-T cells through their native receptors can substitute for cytoreductive chemotherapy, inducing expansion and functional persistence of CD19.CAR-T even in patients in remission of B-cell acute lymphocytic leukemia. We infused a low dose of CD19.CAR-modified virus-specific T cells (CD19.CAR-VST) without prior cytoreductive chemotherapy into 8 patients after allogeneic stem cell transplant.

RESULTS

Absent virus reactivation, we saw no CD19.CAR-VST expansion. In contrast, in patients with viral reactivation, up to 30,000-fold expansion of CD19.CAR-VSTs was observed, with depletion of CD19⁺ B cells. Five patients remain in remission at 42-60+ months.

CONCLUSIONS

Dual T-cell receptor and CAR stimulation can thus potentiate effector cell expansion and CAR-target cell killing, even when infusing low numbers of effector cells without cytoreduction.

Medulloblastoma rendered susceptible to NK-cell attack by TGFβ neutralization

BACKGROUND

Medulloblastoma (MB), the most common pediatric brain cancer, presents with a poor prognosis in a subset of patients with high risk disease, or at recurrence, where current therapies are ineffective. Cord blood (CB) natural killer (NK) cells may be promising off-the-shelf effector cells for immunotherapy due to their recognition of malignant cells without the need for a known target, ready availability from multiple banks, and their potential to expand exponentially. However, they are currently limited by immune suppressive cytokines secreted in the MB tumor microenvironment including Transforming Growth Factor β (TGF-β). Here, we address this challenge in in vitro models of MB.

METHODS

CB-derived NK cells were modified to express a dominant negative TGF-β receptor II (DNRII) using retroviral transduction. The ability of transduced CB cells to maintain function in the presence of medulloblastoma-conditioned media was then assessed.

RESULTS

We observed that the cytotoxic ability of nontransduced CB-NK cells was reduced in the presence of TGF-β-rich, medulloblastoma-conditioned media (21.21 ± 1.19% killing at E:T 5:1 in the absence vs. 14.98 ± 2.11% in the presence of medulloblastoma-conditioned media, n = 8, p = 0.02), but was unaffected in CB-derived DNRII-transduced NK cells (21.11 ± 1.84% killing at E:T 5:1 in the absence vs. 21.81 ± 3.37 in the presence of medulloblastoma-conditioned media, n = 8, p = 0.85. We also observed decreased expression of CCR2 in untransduced NK cells (mean CCR2 MFI 826 ± 117 in untransduced NK + MB supernatant from mean CCR2 MFI 1639.29 ± 215 in no MB supernatant, n = 7, p = 0.0156), but not in the transduced cells. Finally, we observed that CB-derived DNRII-transduced NK cells may protect surrounding immune cells by providing a cytokine sink for TGF-β (decreased TGF-β levels of 610 ± 265 pg/mL in CB-derived DNRII-transduced NK cells vs. 1817 ± 342 pg/mL in untransduced cells; p = 0.008).

CONCLUSIONS

CB NK cells expressing a TGF-β DNRII may have a functional advantage over unmodified NK cells in the presence of TGF-β-rich MB, warranting further investigation on its potential applications for patients with medulloblastoma.

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.

Beta-2 microglobulin knockout K562 cell-based artificial antigen presenting cells for ex vivo expansion of T lymphocytes

Aim: The human K562 leukemia cell line as a scaffold of artificial antigen presenting cells (aAPCs) for ex vivo lymphocyte expansion does not usually express major histocompatibility complex (MHC) molecules. However, when stimulated by supernatants from human T lymphocyte cultures, K562 cells upregulate β-2 microglobulin (B2M) and MHC class I expression, which would induce allo-specific T cells. Methods: We disrupted the B2M locus in K562 cells by CRISPR/Cas9 and achieved MHC class I-negative K562 cells. Results: We further generated K562-based MHC class I-negative aAPC line by zinc-finger nuclease mediated insertion of costimulatory molecules into the AAVS1 locus. This aAPC line could attenuate allogeneic immune responses but support robust antigen-independent and CD19 antigen-specific chimeric antigen receptor-T cell expansion in vitro. Conclusion: B2M-knockout K562 cells provide a new scaffold for aAPC construction and broader application in adoptive immunotherapies.

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.

Preparation of highly activated natural killer cells for advanced lung cancer therapy

Background: Natural killer (NK) cells can be used as an adoptive immunotherapy to treat cancer patients. Purpose: In this study, we evaluated the efficacy of highly activated NK (HANK) cell immunotherapy in patients with advanced lung cancer. Patients and methods: Between March 2016 and September 2017, we enrolled 13 patients who met the enrollment criteria. Donor peripheral blood monocytes were isolated from patients and the NK cells were expanded. After 12 days of culture, the cells were collected and infused intravenously on days 13 to 15. The enrolled patients received at least one course including three times of infusions. The lymphocyte subsets, cytokine production, and the expression of carcinoembryonic antigen (CEA) and thymidine kinase 1 (TK1) were measured before treatment and after the last infusion. Results: No side effects were observed. After a three-month follow-up, the percentage of patients who achieved stable disease and progressive disease was 84.6% and 15.4%. Moreover, the level of IFN-γ was significantly higher after treatment and the level of CEA decreased substantially. The overall immune function of the patients who received the NK cell therapy remained stable. Conclusion: This is the first study to describe the efficacy of NK cell therapy of patients with advanced lung cancer. These clinical observations demonstrated that NK cell is safe and efficient for advanced lung cancer therapy.

Novel biomanufacturing platform for large-scale and high-quality human T cells production

The adoptive transfer of human T cells or genetically-engineered T cells with cancer-targeting receptors has shown tremendous promise for eradicating tumors in clinical trials. The objective of this study was to develop a novel T cell biomanufacturing platform using stirred-tank bioreactor for large-scale and high-quality cellular production. First, various factors, such as bioreactor parameters, media, supplements, stimulation, seed age, and donors, were investigated. A serum-free fed-batch bioproduction process was developed to achieve 1000-fold expansion within 8 days after first stimulation and another 500-fold expansion with second stimulation. Second, this biomanufacturing process was successfully scaled up in bioreactor with dilution factor of 10, and the robustness and reproducibility of the process was confirmed by the inclusion of different donors' T cells of various qualities. Finally, T cell quality was monitored using 12 surface markers and 3 intracellular cytokines as the critical quality assessment criteria in early, middle and late stages of cell production. In this study, a new biomanufacturing platform was created to produce reliable, reproducible, high-quality, and large-quantity (i.e. > 5 billion) human T cells in stirred-tank bioreactor. This platform is compatible with the production systems of monoclonal antibodies, vaccines, and other therapeutic cells, which provides not only the proof-of-concept but also the ready-to-use new approach of T cell expansion for clinical immune therapy.

Beyond CAR T Cells: Other Cell-Based Immunotherapeutic Strategies Against Cancer

Background: Chimeric antigen receptor (CAR)-modified T cells have successfully harnessed T cell immunity against malignancies, but they are by no means the only cell therapies in development for cancer.

Main Text Summary: Systemic immunity is thought to play a key role in combatting neoplastic disease; in this vein, genetic modifications meant to explore other components of T cell immunity are being evaluated. In addition, other immune cells—from both the innate and adaptive compartments—are in various stages of clinical application. In this review, we focus on these non-CAR T cell immunotherapeutic approaches for malignancy. The first section describes engineering T cells to express non-CAR constructs, and the second section describes other gene-modified cells used to target malignancy.

Conclusions: CAR T cell therapies have demonstrated the clinical benefits of harnessing our body's own defenses to combat tumor cells. Similar research is being conducted on lesser known modifications and gene-modified immune cells, which we highlight in this review.

Development and characterization of a canine-specific anti-CD94 (KLRD-1) monoclonal antibody

Natural killer (NK) cells are non-T, non-B lymphocytes are part of the innate immune system and function without prior activation. The human NK cell surface determinant, CD94, plays a critical role in regulation of NK cell activity as a heterodimer with NKG2 subclasses. Canine NK cells are not as well defined as the human and murine equivalents, due in part to the paucity of reagents specific to cell surface markers. Canines possess NK/NKT cells that have similar morphological characteristics to those found in humans, yet little is known about their functional characteristics nor of cell surface expression of CD94. Here, we describe the development and function of a monoclonal antibody (mAb) to canine (ca) CD94. Freshly isolated canine CD94⁺ cells were CD3^+/-, CD8^+/-, CD4-, CD21-, CD5^low, NKp46⁺, and were cytotoxic against a canine target cell line. Anti-caCD94 mAb proved useful in enriching NK/NKT cells from PBMC for expansion on CTAC feeder cells in the presence of IL-2 and IL-15. The cultured cells were highly cytolytic with co-expression of NKp46 and reduced expression of CD3. Transmission electron microscopy revealed expanded CD94⁺ lymphocytes were morphologically large granular lymphocytes with large electron dense granules. Anti-caCD94 (mAb) can serve to enrich NK/NKT cells from dog peripheral blood for ex vivo expansion for HCT and is a potentially valuable reagent for studying NK/NKT regulation in the dog.

Enabling Large-Scale Ex Vivo Production of Megakaryocytes from CD34+ Cells Using Gas-Permeable Surfaces

Patients suffering from acute or sustained thrombocytopenia require platelet transfusions, which are entirely donor-based and limited by challenges related to storage and fluctuating supply. Developing cell-culture technologies will enable ex vivo and donor-independent platelet production. However, critical advancements are needed to improve scalability and increase megakaryocyte (Mk) culture productivity. To address these needs, we evaluated Mk production from mobilized peripheral blood CD34⁺ cells cultured on a commercially available gas-permeable silicone rubber membrane, which provides efficient gas exchange, and investigated the use of fed-batch media dilution schemes. Starting with a cell-surface density of 40 × 10³ CD34⁺ cells per cm² (G40D), culturing cells on the membrane for the first 5 days and employing media dilutions yielded 39 ± 19 CD41⁺ CD42b⁺ Mks per input CD34⁺ cell by day 11-a 2.2-fold increase compared with using standard culture surfaces and full media exchanges. By day 7, G40D conditions generated 1.5-fold more CD34⁺ cells and nearly doubled the numbers of Mk progenitors. The increased number of Mk progenitors coupled with media dilutions, potentially due to the retention of interleukin (IL)-3, increased Mk production in G40D. Compared with controls, G40D had higher viability, yielded threefold more Mks per milliliter of media used and exhibited lower mean ploidy, but had higher numbers of high-ploidy Mks. Finally, G40D-Mks produced proplatelets and platelet-like-particles that activate and aggregate upon stimulation. These results highlight distinct improvements in Mk cell-culture and demonstrate how new technologies and techniques are needed to enable clinically relevant production of Mks for platelet generation and cell-based therapies.

Scaling up the Manufacturing Process of Adoptive T Cell Immunotherapy

Adoptive T cell immunotherapy, involving the reprogramming of immune cells to target specific cancer or virus-infected cells, has been recognized as a promising novel approach for the treatment of complex diseases. The impressive global momentum of this therapeutic approach has highlighted the urgent need for establishing it as an effective and standardized onco-therapeutic approach in a large manufacturing scale. However, given its heterogeneity and uncertainty in nature, adoptive T cell immunotherapy is associated with a high failure rate that restricts its manufacturing to a limited number of institutions worldwide. It is undoubted that quite a few major challenges must be met before engineered T cells can be considered as a reliable, safe, and effective remedy for a broad range of diseases with global-wise patient benefits. Here, the fundamental challenges that as yet remain unsolved in the manufacturing process before adoptive T cell therapy can be considered as a key element in the next generation of precision medicine is reviewed. It is proposed that it is necessary to adopt a closed system, automation, cost-effective manufacturing model, and quality-by-design (QbD) strategy to enable scaled up manufacturing of adoptive T cell immunotherapy; and it is challenging to choose appropriate bioreactors, parameters, and infrastructure in this process.

NK Cells Expressing a Chimeric Activating Receptor Eliminate MDSCs and Rescue Impaired CAR-T Cell Activity against Solid Tumors

Solid tumors are refractory to cellular immunotherapies in part because they contain suppressive immune effectors such as myeloid-derived suppressor cells (MDSCs) that inhibit cytotoxic lymphocytes. Strategies to reverse the suppressive tumor microenvironment (TME) should also attract and activate immune effectors with antitumor activity. To address this need, we developed gene-modified natural killer (NK) cells bearing a chimeric receptor in which the activating receptor NKG2D is fused to the cytotoxic ζ-chain of the T-cell receptor (NKG2D.ζ). NKG2D.ζ-NK cells target MDSCs, which overexpress NKG2D ligands within the TME. We examined the ability of NKG2D.ζ-NK cells to eliminate MDSCs in a xenograft TME model and improve the antitumor function of tumor-directed chimeric antigen receptor (CAR)-modified T cells. We show that NKG2D.ζ-NK cells are cytotoxic against MDSCs, but spare NKG2D ligand-expressing normal tissues. NKG2D.ζ-NK cells, but not unmodified NK cells, secrete proinflammatory cytokines and chemokines in response to MDSCs at the tumor site and improve infiltration and antitumor activity of subsequently infused CAR-T cells, even in tumors for which an immunosuppressive TME is an impediment to treatment. Unlike endogenous NKG2D, NKG2D.ζ is not susceptible to TME-mediated downmodulation and thus maintains its function even within suppressive microenvironments. As clinical confirmation, NKG2D.ζ-NK cells generated from patients with neuroblastoma killed autologous intratumoral MDSCs capable of suppressing CAR-T function. A combination therapy for solid tumors that includes both NKG2D.ζ-NK cells and CAR-T cells may improve responses over therapies based on CAR-T cells alone.

Natural killer cels in immunotherapy for cancer

Cancer is the second leading cause of death worldwide behind cardiovascular diseases. Late stage of cancer at diagnosis and low efficacy of traditional cancer treatments result in low survival rate in cancer patients. Modern techniques to kill tumor cells are therefore needed. Over the last decade novel anticancer treatments have emerged from advances in our understanding of tumor cell biology, and a number of molecular and biologic targets have been identified. Chimeric antigen receptor T cell (CAR-T cell) therapy is a novel adoptive immunotherapy, which is used predominantly in the treatment of hematological malignancies. Moreover, it has been evidenced that cells of the innate immune system are key players at initiating and regulating adaptive immune responses. Studies focusing on innate immune cells for cancer immunotherapy show promising results. In this review, we describe functions of natural killer cells and analyze the rationale for using natural killer cells in cancer therapy.

Closed loop bioreactor system for the ex vivo expansion of human T cells

BACKGROUND AIM

Translation of therapeutic cell therapies to clinical-scale products is critical to realizing widespread success. Currently, however, there are limited tools that are accessible at the research level and readily scalable to clinical-scale needs.

METHODS

We herein developed and assessed a closed loop bioreactor system in which (i) a highly gas-permeable silicone material was used to fabricate cell culture bags and (ii) dynamic flow was introduced to allow for dissociation of activated T-cell aggregates.

RESULTS

Using this system, we find superior T-cell proliferation compared with conventional bag materials and flasks, especially at later time points. Furthermore, intermittent dynamic flow could easily break apart T-cell clusters.

CONCLUSIONS

Our novel closed loop bioreactor system is amenable to enhanced T-cell proliferation and has broader implications for being easily scaled for use in larger need settings.

Optimization of Large-Scale Expansion and Cryopreservation of Human Natural Killer Cells for Anti-Tumor Therapy

Allogeneic natural killer (NK) cell therapy is a potential therapeutic approach for a variety of solid tumors. We established an expansion method for large-scale production of highly purified and functionally active NK cells, as well as a freezing medium for the expanded NK cells. In the present study, we assessed the effect of cryopreservation on the expanded NK cells in regards to viability, phenotype, and anti-tumor activity. NK cells were enormously expanded (about 15,000-fold expansion) with high viability and purity by stimulating CD3⁺ T cell-depleted peripheral blood mononuclear cells (PBMCs) with irradiated autologous PBMCs in the presence of IL-2 and OKT3 for 3 weeks. Cell viability was slightly reduced after freezing and thawing, but cytotoxicity and cytokine secretion were not significantly different. In a xenograft mouse model of hepatocellular carcinoma cells, cryopreserved NK cells had slightly lower anti-tumor efficacy than freshly expanded NK cells, but this was overcome by a 2-fold increased dose of cryopreserved NK cells. In vivo antibody-dependent cell cytotoxicity (ADCC) activity of cryopreserved NK cells was also demonstrated in a SCID mouse model injected with Raji cells with rituximab co-administration. Therefore, we demonstrated that expanded/frozen NK cells maintain viability, phenotype, and anti-tumor activity immediately after thawing, indicating that expanded/frozen NK cells can provide ‘ready-to-use’ cell therapy for cancer patients.

Challenges of NK cell-based immunotherapy in the new era

Natural killer cells (NKs) have a great potential for cancer immunotherapy because they can rapidly and directly kill transformed cells in the absence of antigen presensitization. Various cellular sources, including peripheral blood mononuclear cells (PBMCs), stem cells, and NK cell lines, have been used for producing NK cells. In particular, NK cells that expanded from allogeneic PBMCs exhibit better efficacy than those that did not. However, considering the safety, activities, and reliability of the cell products, researchers must develop an optimal protocol for producing NK cells from PBMCs in the manufacture setting and clinical therapeutic regimen. In this review, the challenges on NK cell-based therapeutic approaches and clinical outcomes are discussed.

Haploidentical natural killer cells induce remissions in non-Hodgkin lymphoma patients with low levels of immune-suppressor cells

We report a novel phase 2 clinical trial in patients with poor prognosis refractory non-Hodgkin lymphoma (NHL) testing the efficacy of haploidentical donor natural killer (NK) cell therapy (NK dose 0.5-3.27 × 107 NK cells/kg) with rituximab and IL-2 (clinicaltrials.gov NCT01181258). Therapy was tolerated without graft-versus-host disease, cytokine release syndrome, or neurotoxicity. Of 14 evaluable patients, 4 had objective responses (29%; 95% CI 12-55%) at 2 months: 2 had complete response lasting 3 and 9 months. Circulating donor NK cells persisted for at least 7 days after infusion at the level 0.6-16 donor NK cells/µl or 0.35-90% of total CD56 cells. Responding patients had lower levels of circulating host-derived Tregs (17 ± 4 vs. 307 ± 152 cells/µL; p = 0.008) and myeloid-derived suppressor cells at baseline (6.6 ± 1.4% vs. 13.0 ± 2.7%; p = 0.06) than non-responding patients. Lower circulating Tregs correlated with low serum levels of IL-10 (R 2 = 0.64; p < 0.003; n = 11), suggestive of less immunosuppressive milieu. Low expression of PD-1 on recipient T cells before therapy was associated with response. Endogenous IL-15 levels were higher in responders than non-responding patients at the day of NK cell infusion (mean ± SEM: 30 ± 4; n = 4 vs. 19.0 ± 4.0 pg/ml; n = 8; p = 0.02) and correlated with day 14 NK cytotoxicity as measured by expression of CD107a (R 2 = 0.74; p = 0.0009; n = 12). In summary, our observations support development of donor NK cellular therapies for advanced NHL as a strategy to overcome chemoresistance. Therapeutic efficacy may be further improved through disruption of the immunosuppressive environment and infusion of exogenous IL-15.

Hurdles Associated with the Translational Use of Genetically Modified Cells

Purpose of Review

Recent advancements in the use of genetically modified hematopoietic stem cells (HSCs) and the emergent use of chimeric antigen receptor (CAR) T-cell immunotherapy has highlighted issues associated with the use of genetically engineered cellular products. This review explores some of the challenges linked with translating the use of genetically modified cells.

Recent Findings

The use of genetically modified HSCs for ADA-SCID now has European approval and the U.S. Food and Drug Administration recently approved the use of CAR-T cells for relapsed/refractory B-cell acute lymphoblastic leukemia. Current good manufacturing processes have now been developed for the collection, expansion, storage, modification, and administration of genetically modified cells.

Summary

Genetically engineered cells can be used for several therapeutic purposes. However, significant challenges remain in making these cellular therapeutics readily available. A better understanding of this technology along with improvements in the manufacturing process is allowing the translation process to become more standardized.

Chimeric Antigen Receptor Expressing Natural Killer Cells for the Immunotherapy of Cancer

Adoptive cell therapy has emerged as a powerful treatment for advanced cancers resistant to conventional agents. Most notable are the remarkable responses seen in patients receiving autologous CD19-redirected chimeric antigen receptor (CAR) T cells for the treatment of B lymphoid malignancies; however, the generation of autologous products for each patient is logistically cumbersome and has restricted widespread clinical use. A banked allogeneic product has the potential to overcome these limitations, yet allogeneic T-cells (even if human leukocyte antigen-matched) carry a major risk of graft-versus-host disease (GVHD). Natural killer (NK) cells are bone marrow-derived innate lymphocytes that can eliminate tumors directly, with their activity governed by the integration of signals from activating and inhibitory receptors and from cytokines including IL-15, IL-12, and IL-18. NK cells do not cause GVHD or other alloimmune or autoimmune toxicities and thus, can provide a potential source of allogeneic “off-the-shelf” cellular therapy, mediating major anti-tumor effects without inducing potentially lethal alloreactivity such as GVHD. Given the multiple unique advantages of NK cells, researchers are now exploring the use of CAR-engineered NK cells for the treatment of various hematological and non-hematological malignancies. Herein, we review preclinical data on the development of CAR-NK cells, advantages, disadvantages, and current obstacles to their clinical use.

Large-scale expansion of Vγ9Vδ2 T cells with engineered K562 feeder cells in G-Rex vessels and their use as chimeric antigen receptor-modified effector cells

Vγ9Vδ2 T cells are a minor subset of lymphocytes in the peripheral blood that has been extensively investigated for their tolerability, safety and anticancer efficacy. A hindrance to the broad application of these cells for adoptive cellular immunotherapy has been attaining clinically appropriate numbers of Vγ9Vδ2 T cells. Furthermore, Vγ9Vδ2 T cells exist at low frequencies among cancer patients. We, therefore, sought to conceive an economical method that allows for a quick and robust large-scale expansion of Vγ9Vδ2 T cells. A two-step protocol was developed, in which peripheral blood mononuclear cells (PBMCs) from healthy donors or cancer patients were activated with Zometa and interleukin (IL)-2, followed by co-culturing with gamma-irradiated, CD64-, CD86- and CD137L-expressing K562 artificial antigen-presenting cells (aAPCs) in the presence of the anti-CD3 antibody OKT3. We optimized the co-culture ratio of K562 aAPCs to immune cells, and migrated this method to a G-Rex cell growth platform to derive clinically relevant cell numbers in a Good Manufacturing Practice (GMP)-compliant manner. We further include a depletion step to selectively remove αβ T lymphocytes. The method exhibited high expansion folds and a specific enrichment of Vγ9Vδ2 T cells. Expanded Vγ9Vδ2 T cells displayed an effector memory phenotype with a concomitant down-regulated expression of inhibitory immune checkpoint receptors. Finally, we ascertained the cytotoxic activity of these expanded cells by using nonmodified and chimeric antigen receptor (CAR)-engrafted Vγ9Vδ2 T cells against a panel of solid tumor cells. Overall, we report an efficient approach to generate highly functional Vγ9Vδ2 T cells in massive numbers suitable for clinical application in an allogeneic setting.

HLA-DR+ NK cells are mostly characterized by less mature phenotype and high functional activity

NK cells change their phenotype and functional characteristics during activation. In this work, we searched for a relationship of HLA-DR expression with differentiation stages and functional activity of NK cells ex vivo and stimulated in vitro with IL-2 challenged with gene modified feeder K562 cells expressing membrane-bound IL-21 (K562-mbIL21). This stimulation technique has been described for NK cell expansion in clinical use. We have observed that HLA-DR expression in freshly isolated circulating NK cells was mostly associated with less differentiated CD56bright CD57- cells, although in some individuals it could also be found in terminally differentiated CD57+ cells. Ex vivo HLA-DR+ NK cells possessed better capacity to produce IFN-γ in response to cytokine stimulation compared to their HLA-DR- counterparts. In vitro activation with IL-2 and K562-mbIL21 induces an increase in HLA-DR-positive NK cell proportion, again mostly among CD56bright CD57- NK cells. This happened in particular due to appearance of HLA-DR+ expression de novo in HLA-DR-negative cells. Acquired in vitro HLA-DR expression was associated with NK cell proliferation activity, more intense cytokine-induced IFN-γ production, increased degranulation toward feeder cells, and higher expression of CD86 and NKG2D. Thus, stimulation with IL-2/K562-mbIL21 causes a significant phenotype and functional shift during NK cell activation and expansion.

Chimeric antigen receptor (CAR)-transduced natural killer cells in tumor immunotherapy

Natural killer (NK) cells are potential effector cells in cell-based cancer immunotherapy, particularly in the control of hematological malignancies. The chimeric antigen receptor (CAR) is an artificially modified fusion protein that consists of an extracellular antigen recognition domain fused to an intracellular signaling domain. T cells genetically modified with a CAR have demonstrated remarkable success in the treatment of hematological cancers. Compared to T cells, CAR-transduced NK cells (CAR-NK) exhibit several advantages, such as safety in clinical use, the mechanisms by which they recognize cancer cells, and their abundance in clinical samples. Human primary NK cells and the NK-92 cell line have been successfully transduced to express CARs against both hematological cancers and solid tumors in pre-clinical and clinical trials. However, many challenges and obstacles remain, such as the ex vivo expansion of CAR-modified primary NK cells and the low transduction efficiency of NK cells. Many strategies and technologies have been developed to improve the safety and therapeutic efficacy in CAR-based immunotherapy. Moreover, NK cells express a variety of activating receptors (NKRs), such as CD16, NKG2D, CD226 and NKp30, which might specifically recognize the ligands expressed on tumor cells. Based on the principle of NKR recognition, a strategy that targets NKRs is rapidly emerging. Given the promising clinical progress described in this review, CAR- and NKR-NK cell-based immunotherapy are likely promising new strategies for cancer therapy.

Inhibiting TGF-beta signaling preserves the function of highly activated, in vitro expanded natural killer cells in AML and colon cancer models

Natural killer cells harnessed from healthy individuals can be expanded ex vivo using various platforms to produce large doses for adoptive transfer into cancer patients. During such expansion, NK cells are increasingly activated and more efficient at killing cancer cells. Adoptive transfer however introduces these activated cells into a highly immunosuppressive tumor microenvironment mediated in part by excessive transforming growth factor beta (TGF-beta) from both cancer cells and their surrounding stroma. This microenvironment ultimately limits the clinical efficacy of NK cell therapy. In this study, we examined the use of a TGF-beta receptor kinase inhibitor, LY2157299, in preserving the cytotoxic function of ex vivo expanded, highly activated NK cells following sustained exposure to pathologic levels of TGF-beta in vitro and in a liver metastases model of colon cancer. Using myeloid leukemia and colon cancer cell lines, we show that the TGF-beta driven impairment of NK cell cytotoxicity is mitigated by LY2157299. We demonstrate this effect using quantitative cytotoxicity assays as well as by showing a preserved activated phenotype with high NKG2D/CD16 expression and enhanced cytokine production. In a mouse liver metastases model of colon cancer, we observed significantly improved eradication of liver metastases in mice treated with adoptive NK cells combined with LY2157299 compared with mice receiving NK cells or TGF beta inhibition alone. We propose that the therapeutic efficacy of adoptive NK cell therapy clinically will be markedly enhanced by complementary approaches targeting TGF-beta signaling in vivo.

Clinical grade manufacturing of genetically modified, CAR-expressing NK-92 cells for the treatment of ErbB2-positive malignancies

BACKGROUND

The NK-92/5.28.z cell line (also referred to as HER2.taNK) represents a stable, lentiviral-transduced clone of ErbB2 (HER2)-specific, second-generation CAR-expressing derivative of clinically applicable NK-92 cells. This study addresses manufacturing-related issues and aimed to develop a GMP-compliant protocol for the generation of NK-92/5.28.z therapeutic doses starting from a well-characterized GMP-compliant master cell bank.

MATERIALS AND METHODS

Commercially available GMP-grade culture media and supplements (fresh frozen plasma, platelet lysate) were evaluated for their ability to support expansion of NK-92/5.28.z. Irradiation sensitivity and cytokine release were also investigated.

RESULTS

NK-92/5.28.z cells can be grown to clinically applicable cell doses of 5 × 108 cells/L in a 5-day batch culture without loss of viability and potency. X-Vivo 10 containing recombinant transferrin supplemented with 5% FFP and 500 IU/mL IL-2 in VueLife 750-C1 bags showed the best results. Platelet lysate was less suited to support NK-92/5.28.z proliferation. Irradiation with 10 Gy completely abrogated NK-92/5.28.z proliferation and preserved viability and potency for at least 24 h. NK-92/5.28.z showed higher baseline cytokine release compared to NK-92, which was significantly increased upon encountering ErbB2(+) targets [GZMB (twofold), IFN-γ (fourfold), IL-8 (24-fold) and IL-10 (fivefold)]. IL-6 was not released by NK cells, but was observed in some stimulated targets. Irradiation resulted in upregulation of IL-8 and downregulation of sFasL, while other cytokines were not impacted.

CONCLUSION

Our concept suggests NK-92/5.28.z maintenance culture from which therapeutic doses up to 5 × 109 cells can be expanded in 10 L within 5 days. This established process is feasible to analyze NK-92/5.28.z in phase I/II trials.

Anticancer cellular immunotherapies derived from umbilical cord blood

INTRODUCTION

The lack of highly effective drugs in many malignancies has prompted scientific interest in the development of alternative treatment strategies. Cellular immunotherapy involving the adoptive transfer of immune cells that potently recognize and eliminate malignantly transformed cells has become a promising new tool in the anticancer armory. Studies suggest that the unique biological properties of umbilical cord blood (UCB) cells could precipitate enhanced anticancer activity; hence, UCB could be an optimal source for immunotherapy with the potential to provide products with 'off-the-shelf' availability.

AREAS COVERED

In this review, the authors summarize data on the transfer of naturally occurring or genetically modified UCB cells to treat cancer. The focus within is on the phenotypic and functional differences compared to other sources, the alloreactive and anticancer properties, and manufacturing of these products. Therapies utilizing cytokine-induced killer (CIK) cells, natural killer (NK) cells and chimeric antigen receptor (CAR) T-cells, are discussed.

EXPERT OPINION

The cellular immunotherapy field has become a growing, exciting area that has generated much enthusiasm. There is evidence that anticancer immunotherapy with UCB-derived products is feasible and safe; however, considering the limited number of clinical trials using UCB-derived products, further studies are warranted to facilitate translation into clinical practice.

Natural killer-92 cells maintain cytotoxic activity after long-term cryopreservation in novel DMSO-free media

Natural killer (NK) cells are a critical part of the innate immune system, and have emerged as attractive targets for immunotherapies for various malignancies. Alongside the need for expansion of NK cells to reach clinically useful numbers, a critical component in the availability of NK cells for allogeneic therapy is cryopreservation. While a continuously-growing cell line such as NK-92 can avoid issues associated with isolating, activating, expanding, and manufacturing large numbers of peripheral blood-derived NKs, cryopreservation of these cells has not made much progress. NK cells are highly sensitive to freezing and thawing, while the use of DMSO during cryopreservation raises serious safety concerns. In this work, we evaluated a number of cryoprotectants that do not contain DMSO for their capacity to cryopreserve NK-92 cells over long-term while retaining their cytotoxic activity and viability, with the aim of identifying potential replacements to DMSO for safe clinical use of these cells.

Developmental and Functional Control of Natural Killer Cells by Cytokines

Natural killer (NK) cells are effective in combating infections and tumors and as such are tempting for adoptive transfer therapy. However, they are not homogeneous but can be divided into three main subsets, including cytotoxic, tolerant, and regulatory NK cells, with disparate phenotypes and functions in diverse tissues. The development and functions of such NK cells are controlled by various cytokines, such as fms-like tyrosine kinase 3 ligand (FL), kit ligand (KL), interleukin (IL)-3, IL-10, IL-12, IL-18, transforming growth factor-β, and common-γ chain family cytokines, which operate at different stages by regulating distinct signaling pathways. Nevertheless, the specific roles of each cytokine that regulates NK cell development or that shapes different NK cell functions remain unclear. In this review, we attempt to describe the characteristics of each cytokine and the existing protocols to expand NK cells using different combinations of cytokines and feeder cells. A comprehensive understanding of the role of cytokines in NK cell development and function will aid the generation of better efficacy for adoptive NK cell treatment.