Differential activation of cord blood and peripheral blood natural killer cells by cytokines

Revolutionizing the treatment for nasopharyngeal cancer: the impact, challenges and strategies of stem cell and genetically engineered cell therapies

Nasopharyngeal carcinoma (NPC) is a distinct malignancy of the nasopharynx and is consistently associated with the Epstein-Barr virus (EBV) infection. Its unique anatomical location and complex aetiology often result in advanced-stage disease at first diagnosis. While radiotherapy (RT) and chemotherapy have been the mainstays of treatment, they often fail to prevent tumour recurrence and metastasis, leading to high rates of treatment failure and mortality. Recent advancement in cell-based therapies, such as chimeric antigen receptor (CAR)-T cell therapy, have shown great promise in hematological malignancies and are now being investigated for NPC. However, challenges such as targeting specific tumour antigens, limited T cell persistence and proliferation, and managing treatment-related toxicities must be addressed. Extensive research is needed to enhance the effectiveness and safety of these therapies, paving the way for their integration into standard clinical practice for better management of NPC and a better quality of life for human health.

NK cells as powerful therapeutic tool in cancer immunotherapy

BACKGROUND

Natural killer (NK) cells have gained considerable attention and hold great potential for their application in tumor immunotherapy. This is mainly due to their MHC-unrestricted and pan-specific recognition capabilities, as well as their ability to rapidly respond to and eliminate target cells. To artificially generate therapeutic NK cells, various materials can be utilized, such as peripheral blood mononuclear cells (PBMCs), umbilical cord blood (UCB), induced pluripotent stem cells (iPSCs), and NK cell lines. Exploiting the therapeutic potential of NK cells to treat tumors through in vivo and in vitro therapeutic modalities has yielded positive therapeutic results.

CONCLUSION

This review provides a comprehensive description of NK cell therapeutic approaches for tumors and discusses the current problems associated with these therapeutic approaches and the prospects of NK cell therapy for tumors.

Therapeutic potential of natural killer cells in neuroimmunological diseases

Natural killer (NK) cells, a major component of the innate immune system, have prominent immunoregulatory, antitumor proliferation, and antiviral activities. NK cells act as a double-edged sword with therapeutic potential in neurological autoimmunity. Emerging evidence has identified NK cells are involved in the development and progression of neuroimmunological diseases such as multiple sclerosis, neuromyelitis optica spectrum disorders, autoimmune encephalitis, Guillain-Barré Syndrome, chronic inflammatory demyelinating polyneuropathy, myasthenia gravis, and idiopathic inflammatory myopathy. However, the regulatory mechanisms and functional roles of NK cells are highly variable in different clinical states of neuroimmunological diseases and need to be further determined. In this review, we summarize the evidence for the heterogenic involvement of NK cells in the above conditions. Further, we describe cutting-edge NK-cell-based immunotherapy for neuroimmunological diseases in preclinical and clinical development and highlight challenges that must be overcome to fully realize the therapeutic potential of NK cells.

Breaking boundaries: Current progress of anticancer NK cell-based drug development

Natural killer (NK) cell therapy is emerging as a cancer treatment. NK cells are innate cytotoxic lymphocytes that act as first-line responders to kill target cells without prior encounters. NK cells recognize cancer cells, virus-infected cells, and other types of stressed cell through a reservoir of germline-encoded receptors. NK cells are safe for allogeneic applications. Therefore, they are the ideal off-the-shelf cell, which overcome the low efficiency issue caused by the patient-by-patient nature of autologous cell therapy. Unlike T cells, NK cells cannot form a strong immune memory; therefore, they suffer from short in vivo persistence. However, different from T cells, NK cells have a reservoir of innate immune receptors targeting a variety of malignant cells. In addition, they can utilize antibody guidance in target recognition. With suitable engineering, NK cells can function as universal anticancer drugs that are not restricted to HLA and cancer types, which will benefit the large cohort of patients with rare cancer types and patients with no convenient drug targets for precision and personalized medicine. Here, we summarize and discuss the designs of current anticancer NK cell therapies.

Cord Blood-Derived Natural Killer Cell Exploitation in Immunotherapy Protocols: More Than a Promise?

Simple Summary

NK cell anti-tumor activity against hematological malignancies is well-established and many studies support their role in the control of solid tumor growth and metastasis generation. However, tumor microenvironment may affect NK cell function. Ongoing studies are aimed to design novel immunotherapeutic protocols to combine NK cell-based immunotherapy with other therapeutic strategies to improve the anti-tumor NK cell response. In this context, UCB is one of the main sources of both mature NK cells and of CD34⁺ HSPC that can generate NK cells, both in-vivo and in-vitro. UCB-derived NK cells represent a valuable tool to perform in-vitro and preclinical analyses and are already used in several clinical settings, particularly against hematological malignancies. The present review describes the characteristics of different types of UCB-derived NK cells and the in-vitro models to expand them, both for research and clinical purposes in the context of cancer immunotherapy.

Abstract

In the last 20 years, Natural Killer (NK) cell-based immunotherapy has become a promising approach to target various types of cancer. Indeed, NK cells play a pivotal role in the first-line defense against tumors through major histocompatibility complex-independent immunosurveillance. Their role in the control of leukemia relapse has been clearly established and, moreover, the presence of NK cells in the tumor microenvironment (TME) generally correlates with good prognosis. However, it has also been observed that, often, NK cells poorly infiltrate the tumor tissue, and, in TME, their functions may be compromised by immunosuppressive factors that contribute to the failure of anti-cancer immune response. Currently, studies are focused on the design of effective strategies to expand NK cells and enhance their cytotoxic activity, exploiting different cell sources, such as peripheral blood (PB), umbilical cord blood (UCB) and NK cell lines. Among them, UCB represents an important source of mature NK cells and CD34⁺ Hematopoietic Stem and Progenitor Cells (HSPCs), as precursors of NK cells. In this review, we summarize the UCB-derived NK cell activity in the tumor context, review the different in-vitro models to expand NK cells from UCB, and discuss the importance of their exploitation in anti-tumor immunotherapy protocols.

Overcoming tumor resistance mechanisms in CAR-NK cell therapy

Despite the impressive results of autologous CAR-T cell therapy in refractory B lymphoproliferative diseases, CAR-NK immunotherapy emerges as a safer, faster, and cost-effective approach with no signs of severe toxicities as described for CAR-T cells. Permanently scrutinized for its efficacy, recent promising data in CAR-NK clinical trials point out the achievement of deep, high-quality responses, thus confirming its potential clinical use. Although CAR-NK cell therapy is not significantly affected by the loss or downregulation of its CAR tumor target, as in the case of CAR-T cell, a plethora of common additional tumor intrinsic or extrinsic mechanisms that could also disable NK cell function have been described. Therefore, considering lessons learned from CAR-T cell therapy, the emergence of CAR-NK cell therapy resistance can also be envisioned. In this review we highlight the processes that could be involved in its development, focusing on cytokine addiction and potential fratricide during manufacturing, poor tumor trafficking, exhaustion within the tumor microenvironment (TME), and NK cell short in vivo persistence on account of the limited expansion, replicative senescence, and rejection by patient’s immune system after lymphodepletion recovery. Finally, we outline new actively explored alternatives to overcome these resistance mechanisms, with a special emphasis on CRISPR/Cas9 mediated genetic engineering approaches, a promising platform to optimize CAR-NK cell function to eradicate refractory cancers.

Comparable transforming growth factor beta-mediated immune suppression in ex vivo-expanded natural killer cells from cord blood and peripheral blood: implications for adoptive immunotherapy

T cell-based therapies like genetically modified immune cells expressing chimeric antigen receptors have shown robust anti-cancer activity in vivo, especially in patients with blood cancers. However, extending this approach to an "off-the-shelf" setting can be challenging, as allogeneic T cells carry a significant risk of graft-versus-host disease (GVHD). By contrast, allogeneic natural killer (NK) cells recognize malignant cells without the need for prior antigen exposure and have been used safely in multiple cancer settings without the risk of GVHD. However, similar to T cells, NK cell function is negatively impacted by tumor-induced transforming growth factor beta (TGF-β) secretion, which is a ubiquitous and potent immunosuppressive mechanism employed by most malignancies. Allogeneic NK cells for adoptive immunotherapy can be sourced from peripheral blood (PB) or cord blood (CB), and the authors' group and others have previously shown that ex vivo expansion and gene engineering can overcome CB-derived NK cells' functional immaturity and poor cytolytic activity, including in the presence of exogenous TGF-β.  However, a direct comparison of the effects of TGF-β-mediated immune suppression on ex vivo-expanded CB- versus PB-derived NK cell therapy products has not previously been performed. Here the authors show that PB- and CB-derived NK cells have distinctive gene signatures that can be overcome by ex vivo expansion. Additionally, exposure to exogenous TGF-β results in an upregulation of inhibitory receptors on NK cells, a novel immunosuppressive mechanism not previously described. Finally, the authors provide functional and genetic evidence that both PB- and CB-derived NK cells are equivalently susceptible to TGF-β-mediated immune suppression. The authors believe these results provide important mechanistic insights to consider when using ex vivo-expanded, TGF-β-resistant PB- or CB-derived NK cells as novel immunotherapy agents for cancer.

Natural killer cell-targeted immunotherapy for cancer

Natural killer (NK) cells were initially described in the early 1970s as major histocompatibility complex unrestricted killers due to their ability to spontaneously kill certain tumor cells. In the past decade, the field of NK cell-based treatment has been accelerating exponentially, holding a dominant position in cancer immunotherapy innovation. Generally, research on NK cell-mediated antitumor therapies can be categorized into three areas: choosing the optimal source of allogenic NK cells to yield massively amplified "off-the-shelf" products, improving NK cell cytotoxicity and longevity, and engineering NK cells with the ability of tumor-specific recognition. In this review, we focused on NK cell manufacturing techniques, some auxiliary methods to enhance the therapeutic efficacy of NK cells, chimeric antigen receptor NK cells, and monoclonal antibodies targeting inhibitory receptors, which can significantly augment the antitumor activity of NK cells. Notably, emerging evidence suggests that NK cells are a promising constituent of multipronged therapeutic strategies, strengthening immune responses to cancer.

An Immunocompetent Microphysiological System to Simultaneously Investigate Effects of Anti-Tumor Natural Killer Cells on Tumor and Cardiac Microtissues

Existing first-line cancer therapies often fail to cope with the heterogeneity and complexity of cancers, so that new therapeutic approaches are urgently needed. Among novel alternative therapies, adoptive cell therapy (ACT) has emerged as a promising cancer treatment in recent years. The limited clinical applications of ACT, despite its advantages over standard-of-care therapies, can be attributed to (i) time-consuming and cost-intensive procedures to screen for potent anti-tumor immune cells and the corresponding targets, (ii) difficulties to translate in-vitro and animal-derived in-vivo efficacies to clinical efficacy in humans, and (iii) the lack of systemic methods for the safety assessment of ACT. Suitable experimental models and testing platforms have the potential to accelerate the development of ACT. Immunocompetent microphysiological systems (iMPS) are microfluidic platforms that enable complex interactions of advanced tissue models with different immune cell types, bridging the gap between in-vitro and in-vivo studies. Here, we present a proof-of-concept iMPS that supports a triple culture of three-dimensional (3D) colorectal tumor microtissues, 3D cardiac microtissues, and human-derived natural killer (NK) cells in the same microfluidic network. Different aspects of tumor-NK cell interactions were characterized using this iMPS including: (i) direct interaction and NK cell-mediated tumor killing, (ii) the development of an inflammatory milieu through enrichment of soluble pro-inflammatory chemokines and cytokines, and (iii) secondary effects on healthy cardiac microtissues. We found a specific NK cell-mediated tumor-killing activity and elevated levels of tumor- and NK cell-derived chemokines and cytokines, indicating crosstalk and development of an inflammatory milieu. While viability and morphological integrity of cardiac microtissues remained mostly unaffected, we were able to detect alterations in their beating behavior, which shows the potential of iMPS for both, efficacy and early safety testing of new candidate ACTs.

Reevaluation of NOD/SCID Mice as NK Cell-Deficient Models

Objective

Natural killer (NK) cell-deficient mice are useful models in biomedical research. NOD/SCID mice have been used as a model of this type in research. However, the actual status of NK cells in NOD/SCID mice and CB17/SCID mice in comparison with that in BALB/c mice has not been sufficiently evaluated.

Methods

Splenocytes from naïve or poly(I:C)-treated mice were isolated for phenotyping and analysis of cytotoxicity-related molecules and inhibitory receptors; for cytotoxicity assay, purified NK cells were also used.

Results

The proportion of splenic NK cells did not differ significantly between NOD/SCID and CB17/SCID mice. The perforin levels in NK cells were similar between the poly(I:C)-treated CB17/SCID and NOD/SCID mice, while the granzyme B and NKG2A/C/E levels in NK cells from NOD/SCID mice were significantly lower than those from CB17/SCID mice. Moreover, the NKG2D and Ly49A levels in NK cells from NOD/SCID mice were higher than those from CB17/SCID. The splenocytes from CB17/SCID mice showed higher cytotoxicity than those from NOD/SCID mice, while the cytotoxicity of purified NK cells basically did not differ between the two strains. After in vitro stimulation with cytokines, the splenocytes from CB17/SCID mice showed higher IFN-γ production than those from NOD/SCID mice; however, NK cells did not.

Conclusion

There was no significant difference in the proportion of splenic NK cells between CB17/SCID and NOD/SCID mice, and the function of NK cells was only partially compromised in NOD/SCID mice. Caution should be taken when considering the use of NOD/SCID mice as an NK-deficient model.

Gut Bacteria Induce Granzyme B Expression in Human Colonic ILC3s In Vitro in an IL-15-Dependent Manner

Group 3 innate lymphoid cells (ILC3s) in the gut mucosa have long been thought to be noncytotoxic lymphocytes that are critical for homeostasis of intestinal epithelial cells through secretion of IL-22. Recent work using human tonsillar cells demonstrated that ILC3s exposed to exogenous inflammatory cytokines for a long period of time acquired expression of granzyme B, suggesting that under pathological conditions ILC3s may become cytotoxic. We hypothesized that inflammation associated with bacterial exposure might trigger granzyme B expression in gut ILC3s. To test this, we exposed human colon lamina propria mononuclear cells to a panel of enteric bacteria. We found that the Gram-negative commensal and pathogenic bacteria induced granzyme B expression in a subset of ILC3s that were distinct from IL-22-producing ILC3s. A fraction of granzyme B⁺ ILC3s coexpressed the cytolytic protein perforin. Granzyme B expression was mediated, in part, by IL-15 produced upon exposure to bacteria. ILC3s coexpressing all three IL-15R subunits (IL15Rα/β/γ) increased following bacterial stimulation, potentially allowing for cis presentation of IL-15 during bacterial exposure. Additionally, a large frequency of colonic myeloid dendritic cells expressed IL-15Rα, implicating myeloid dendritic cells in trans presentation of IL-15 to ILC3s. Tonsillar ILC3s minimally expressed granzyme B when exposed to the same bacteria or to rIL-15. Overall, these data establish the novel, to our knowledge, finding that human colonic ILC3s can express granzyme B in response to a subset of enteric bacteria through a process mediated by IL-15. These observations raise new questions about the multifunctional role of human gut ILC3s.

Chimeric antigen receptor-engineered natural killer cells: a promising cancer immunotherapy

Introduction:Widespread success of CD19 chimeric antigen receptor (CAR) T cells for the treatment of hematological malignancies have shifted the focus from conventional cancer treatments toward adoptive immunotherapy. There are major efforts to improve CAR constructs and to identify new target antigens. Even though the Food and Drug Administration has approved commercialization of some CD19 CART cell therapies, there are still some limitations that restrict their widespread clinical use. The manufacture of autologous products for individual patients is logistically cumbersome and expensive and allogeneic T cell products may pose an appreciable risk of graft-versus-host disease (GVHD).Areas covered:Natural killer (NK) cells are an attractive alternative for CART-based immunotherapies. They have the innate ability to detect and eliminate malignant cells and are safer in the 'off-the-shelf' setting. This review discusses the current progress within the CAR NK cell field, including the challenges, and future prospects. Gene engineered NK cells was used as the search term in PubMed and Google Scholar through to December 2020.Expert opinion:CAR NK cell therapies hold promise as an 'off-the-shelf' cell therapy for cancer. It is hoped that an enhanced understanding of their immunobiology and molecular mechanisms of action will improve their in vivo potency.

NK Cell Adoptive Immunotherapy of Cancer: Evaluating Recognition Strategies and Overcoming Limitations

Natural killer (NK) cells, the primary effector cells of the innate immune system, utilize multiple strategies to recognize tumor cells by (1) detecting the presence of activating receptor ligands, which are often upregulated in cancer; (2) targeting cells that have a loss of major histocompatibility complex (MHC); and (3) binding to antibodies that bind to tumor-specific antigens on the tumor cell surface. All these strategies have been successfully harnessed in adoptive NK cell immunotherapies targeting cancer. In this review, we review the applications of NK cell therapies across different tumor types. Similar to other forms of immunotherapy, tumor-induced immune escape and immune suppression can limit NK cell therapies' efficacy. Therefore, we also discuss how these limitations can be overcome by conferring NK cells with the ability to redirect their tumor-targeting capabilities and survive the immune-suppressive tumor microenvironment. Finally, we also discuss how future iterations can benefit from combination therapies with other immunotherapeutic agents.

UV Light-inactivated HSV-1 Stimulates Natural Killer Cell-induced Killing of Prostate Cancer Cells

Herein we demonstrate that ultraviolet light-inactivated Herpes Simplex Virus-1 (UV-HSV-1) stimulates peripheral blood mononuclear cells (PBMCs) to lyse both androgen-sensitive and androgen-independent prostate cancer (PrCA) cell lines, but not the benign prostatic hyperplastic epithelial cell line, BPH-1, and is 1000-10,000-fold more potent at stimulating this killing than ultraviolet light-inactivated Vesicular Stomatitis Virus, adenovirus, reovirus or cytomegalovirus. Among PBMCs, natural killer (NK) cells appear to be a major cell type involved in this killing and UV-HSV-1 appears to directly and potently stimulate NK cell expression of CD69, degranulation, cytokine production, and migration to IL-8 in PC3 conditioned medium. We also found that UV-HSV-1 stimulates glycolysis in PBMCs and NK cells, and that 2-deoxyglucose and the protein kinase C inhibitor, Go6976, and the NFκB inhibitor, Bay 11-7082, all abrogate UV-HSV-1 activated killing of PC3 cells by PBMCs and NK cells. Using neutralizing anti-Toll-like receptor 2 (TLR2) we found that UV-HSV-1, like HSV-1, activates NK cells via TLR2. Taken together, these results are consistent with Toll-like receptor 2 ligands on UV-HSV-1 stimulating TLR2 on NK cells to activate protein kinase C, leading to enhanced glycolysis and NFκB activation, both of which play a critical role in this anti-PrCA innate immune response. Importantly, UV-HSV-1 synergizes with IL-15 to increase the cytolytic activity of PBMCs against PC3 cells and there was considerable donor-to-donor variation in killing ability. These results support the preclinical development of UV-HSV-1 as an adjuvant, in combination with IL-15, for cell infusions of healthy, preselected NK cells to treat PrCA.

A simple method for in vitro preparation of natural killer cells from cord blood

Background

Cord Blood (CB) has been considered a promising source of natural killer (NK) cells for cellular immunotherapy. However, it is difficult to expand the large numbers of highly pure NK cells from CB without cell sorting and feeder cells/multiple cytokines. In this study, we try to develop a simple, safe and economical method for ex vivo expansion and purification of NK cells from CB without cell sorting and feeder cells/multiple cytokines.

Results

The large numbers (mean: 1.59 × 10¹⁰) of highly pure (≥90%) NK cells from CB could be obtained through interleukin-2, group A streptococcus and zoledronate stimulation of mononuclear cells using the 21-day culture approach. When compared to resting NK cells, expanded NK cells were a higher expression of activating receptors CD16, NKG2D, NKp30, NKp44, NKp46 and activating markers CD62L and CD69, while the inhibitory receptors, CD158a and CD158b remained largely unchanged. In addition, these cells showed a higher concentration of IFN-γ, TNF-α and GM-CSF secretion and cytotoxicity to K562 cells and acute myeloid leukemia targets than resting NK cells.

Conclusion

We develop a simple, safe and economical method to obtain high yield, purity, and functionality NK cells from CB without cell sorting and feeder cells/multiple cytokines.

Natural killer cells and cancer therapy, what we know and where we are going

Natural killer (NK) cells are among the significant components of innate immune system and they have come to the first line of defense against tumor cells developing inside the body. CD56lo/CD16+ NK cells are highly cytotoxic and CD56hi NK cells can produce cytokines and perform a regulatory function. Specific features of NK cells have made them a unique choice for cancer immunotherapy. Simple interventions like cytokine-injection to boost the internal NK cells were the first trials to target these cells. Nowadays, many other types of intervention are under investigation, such as adoptive NK cell immunotherapy. In this paper, we will discuss the biology and function of NK cells in cancer immunosurveillance and therapeutic approaches against cancer via using NK cells.

Ex Vivo-expanded Natural Killer Cells Derived From Long-term Cryopreserved Cord Blood are Cytotoxic Against Primary Breast Cancer Cells

With over 600,000 units of umbilical cord blood (CB) stored on a global scale, it is important to elucidate the therapeutic abilities of this cryopreserved reservoir. In the advancing field of natural killer (NK) cell cancer immunotherapy, CB has proven to be a promising and noninvasive source of therapeutic NK cells. Although studies have proven the clinical efficacy of using long-term cryopreserved CB in the context of hematopoietic stem cell transplantations, little is known about its use for the ex vivo expansion of effector immune cells. Therefore, our group sought to derive ex vivo-expanded NK cells from long-term cryopreserved CB, using an artificial antigen presenting cell-mediated expansion technique. We compared the expansion potential and antitumor effector function of CB-derived NK (CB-NK) cells expanded from fresh (n=4), short-term cryopreserved (<1-year old, n=5), and long-term cryopreserved (1-10-year old, n=5) CB. Here, we demonstrated it is possible to obtain an exponential amount of expanded CB-NK cells from long-term cryopreserved CB. Ex vivo-expanded CB-NK cells had an increased surface expression of activating markers and showed potent antitumor function by producing robust levels of proinflammatory cytokines, interferon-γ, and tumor necrosis factor-α. Moreover, expanded CB-NK cells (n=3-5) demonstrated cytotoxicity towards primary breast cancer cells (n=2) derived from a triple-negative breast cancer and an estrogen receptor-positive/progesterone receptor-positive breast cancer patient. Long-term cryopreservation had no effect on the expansion potential or effector function of expanded CB-NK cells. Therefore, we propose that long-term cryopreserved CB remains clinically useful for the ex vivo expansion of therapeutic NK cells.

Natural Killer Cells as Allogeneic Effectors in Adoptive Cancer Immunotherapy

Natural killer (NK) cells are attractive within adoptive transfer settings in cancer immunotherapy due to their potential for allogeneic use; their alloreactivity is enhanced under conditions of killer immunoglobulin-like receptor (KIR) mismatch with human leukocyte antigen (HLA) ligands on cancer cells. In addition to this, NK cells are platforms for genetic modification, and proliferate in vivo for a shorter time relative to T cells, limiting off-target activation. Current clinical studies have demonstrated the safety and efficacy of allogeneic NK cell adoptive transfer therapies as a means for treatment of hematologic malignancies and, to a lesser extent, solid tumors. However, challenges associated with sourcing allogeneic NK cells have given rise to controversy over the contribution of NK cells to graft-versus-host disease (GvHD). Specifically, blood-derived NK cell infusions contain contaminating T cells, whose activation with NK-stimulating cytokines has been known to lead to heightened release of proinflammatory cytokines and trigger the onset of GvHD in vivo. NK cells sourced from cell lines and stem cells lack contaminating T cells, but can also lack many phenotypic characteristics of mature NK cells. Here, we discuss the available published evidence for the varying roles of NK cells in GvHD and, more broadly, their use in allogeneic adoptive transfer settings to treat various cancers.

Maturation of the immune system in the fetus and the implications for congenital CMV

Congenital cytomegalovirus (CMV) infection is the most prevalent and consequential congenital infection, among others, that affects approximately 0.6% of all live births worldwide. Timing of maternal infection and maternal immune status largely determine the likelihood of a symptomatic infection. However, recent studies suggest that the fetal immune system, long perceived as naïve and immature, may also play a role in deciding the outcome of congenital CMV infection. Here, we review the development of four immune cells most pertinent to CMV control in the human fetus. αβT cells, B cells, natural killer (NK) cells, and γδT cells are all present, mature and partially functional in utero, and are capable of mounting some form of response to congenital CMV infection. Whether this response is negligible, effective, or harmful remains an open question. Expanding our knowledge of normal and abnormal immune development could provide clinicians with more accurate tools for the detection, monitoring, and treatment of congenital CMV infection in fetuses.

Cytokines can counteract the inhibitory effect of MEK-i on NK-cell function

Oncogene-targeted therapies based on mutated BRAF- and/or MEK-specific inhibitors have been developed for melanoma treatment. Although these drugs induce tumor regression in a high percentage of patients, clinical responses are frequently limited in time and tumors often recur. Recent studies suggested that the combination of BRAF/MEK inhibition with immunotherapy could represent a promising strategy for the cure of melanoma. NK cells are suitable effectors for tumor immunotherapy. Here we show that PLX4032 (a mutant BRAF^V600 inhibitor) had no effect on the functional properties of NK cells cultured in the presence of IL-2 or IL-15. In contrast, PD0325901 (a MEK inhibitor) induced the down-regulation of the main activating NK receptors and inhibited NK cell function. Importantly, PD0325901 did not affect the anti-tumor activity of NK cells that had been exposed to a combination of IL-15 and IL-18. In addition, both PLX4032 and PD0325901 did not exert any inhibitory effect on in vitro IL-2 or IL-15 pre-activated NK cells.

Our data may provide a rationale for future clinical protocols that combine IL-15/IL-18 cytokine administration with MEK inhibitors. In addition, they suggest that oncogene-targeting drugs are compatible with NK-based adoptive therapy.

Redirected Primary Human Chimeric Antigen Receptor Natural Killer Cells As an "Off-the-Shelf Immunotherapy" for Improvement in Cancer Treatment

Primary human natural killer (NK) cells recognize and subsequently eliminate virus infected cells, tumor cells, or other aberrant cells. However, cancer cells are able to develop tumor immune escape mechanisms to undermine this immune control. To overcome this obstacle, NK cells can be genetically modified to express chimeric antigen receptors (CARs) in order to improve specific recognition of cancer surface markers (e.g., CD19, CD20, and ErbB2). After target recognition, intracellular CAR domain signaling (CD3ζ, CD28, 4-1BB, and 2B4) leads to activation of PI3K or DNAX proteins (DAP10, DAP12) and finally to enhanced cytotoxicity, proliferation, and/or interferon γ release. This mini-review summarizes both the first preclinical trials with CAR-engineered primary human NK cells and the translational implications for “off-the-shelf immunotherapy” in cancer treatment. Signal transduction in NK cells as well as optimization of CAR signaling will be described, becoming more and more a focal point of interest in addition to redirected T cells. Finally, strategies to overcome off-target effects will be discussed in order to improve future clinical trials and to avoid attacking healthy tissues.

Graft-versus-Leukemia Effect Following Hematopoietic Stem Cell Transplantation for Leukemia

The success of hematopoietic stem cell transplantation (HSCT) lies with the ability of the engrafting immune system to remove residual leukemia cells via a graft-versus-leukemia effect (GvL), caused either spontaneously post-HSCT or via donor lymphocyte infusion. GvL effects can also be initiated by allogenic mismatched natural killer cells, antigen-specific T cells, and activated dendritic cells of leukemic origin. The history and further application of this GvL effect and the main mechanisms will be discussed and reviewed in this chapter.

Natural killer cells differentiated in vitro from cord blood CD34+ cells are more advantageous for use as an immunotherapy than peripheral blood and cord blood natural killer cells

BACKGROUND AIMS

Natural killer (NK) cells have the potential to become a successful immunotherapy as they can target malignant cells without being direct effectors of graft-versus-host disease. Our group has previously shown that large numbers of functional NK cells can be differentiated in vitro from umbilical cord blood (CB) CD34⁺ cells. To produce a clinically relevant and effective immunotherapy, we hypothesized that it is essential that the NK cells are able to proliferate and persist in vivo while maintaining an optimal activation status and killing capacity.

METHODS

We evaluated the proliferation capacity, telomere length and terminal differentiation markers expressed by NK cells differentiated in vitro. We also determined how their cytotoxicity compared with peripheral blood (PB) NK cells and CBNK cells when targeting patient acute myeloid leukemia (AML) blasts and solid tumor cell lines.

RESULTS

We found that the differentiated NK cells could respond to interleukin-2 and proliferate in vitro. Telomere length was significantly increased, whereas CD57 expression was significantly reduced compared with PBNK cells. The cytotoxicity of the differentiated NK cells was equivalent to that of the PBNK and CBNK cell controls, and priming consistently led to higher levels of killing of patient leukemic blasts and solid tumor cell lines in vitro. Interestingly, this activation step was not required to observe killing of patient AML blasts in vivo.

CONCLUSION

We are able to generate NK cells from CBCD34⁺ cells in high numbers, allowing for multiple infusions of highly cytotoxic NK cells that have potential to further proliferate in vivo, making them a desirable product for application as an immunotherapy in the clinic.

Umbilical Cord Blood Natural Killer Cells, Their Characteristics, and Potential Clinical Applications

Natural killer (NK) cells are lymphocytes of the innate immune system able to kill different targets such as cancer cells and virally infected cells without prior activation making then attractive candidates for cancer immunotherapy. Umbilical cord blood (UCB) has become a source of hematopoietic stem cells for transplantation but as we gain a better understanding of the characteristics of each immune cell that UCB contains, we will also be able to develop new cell therapies for cancer. In this review, we present what is currently known of the phenotype and functions of UCB NK cells and how these cells could be used in the future for cancer immunotherapy.

Old game, new players: Linking classical theories to new trends in transplant immunology

The evolutionary emergence of an efficient immune system has a fundamental role in our survival against pathogenic attacks. Nevertheless, this same protective mechanism may also establish a negative consequence in the setting of disorders such as autoimmunity and transplant rejection. In light of the latter, although research has long uncovered main concepts of allogeneic recognition, immune rejection is still the main obstacle to long-term graft survival. Therefore, in order to define effective therapies that prolong graft viability, it is essential that we understand the underlying mediators and mechanisms that participate in transplant rejection. This multifaceted process is characterized by diverse cellular and humoral participants with innate and adaptive functions that can determine the type of rejection or promote graft acceptance. Although a number of mediators of graft recognition have been described in traditional immunology, recent studies indicate that defining rigid roles for certain immune cells and factors may be more complicated than originally conceived. Current research has also targeted specific cells and drugs that regulate immune activation and induce tolerance. This review will give a broad view of the most recent understanding of the allogeneic inflammatory/tolerogenic response and current insights into cellular and drug therapies that modulate immune activation that may prove to be useful in the induction of tolerance in the clinical setting.

Immunotherapy after hematopoietic stem cell transplantation using umbilical cord blood-derived products

Umbilical cord blood (UCB) is being increasingly used as a source of hematopoietic stem cells (HSC) for transplantation. UCB transplantation (UCBT) has some advantages such as less stringent HLA-matching requirements, fast availability of the graft and reduced incidence and severity of graft-versus-host disease. However, UCBT is also associated with a higher incidence of infection, graft failure, slow engraftment and slow immune reconstitution. UCB is mainly used as a source of HSC; however, it is also rich in immune cells that could be used to treat some of the main complications post-UCBT as well as other diseases, thus implicating the use of UCB for immunotherapy. Here, we aim to describe some of the therapies currently developed that use UCB as a cell source, focusing in particular on regulatory T cells and natural killer cells.

The newborn human NK cell repertoire is phenotypically formed but functionally reduced

BACKGROUND

Infection is a leading cause of death worldwide in babies under 1 month of age. Better vaccines and therapeutics are desperately needed for this vulnerable population.

METHODS

Because newborns rely heavily on the innate immune system, we evaluated cell phenotype and function of some of the earliest cellular responders during infection, natural killer (NK) cells. We used mass cytometry to provide a comprehensive comparison of NK cells from umbilical cord blood and adult peripheral blood.

RESULTS

In unsupervised analyses, including viSNE and principal component analysis, the structure of the cord blood and adult NK cell repertoires are highly similar, distinguishable mainly by maturity-related markers expressed on rare subpopulations of cells. However, in functional analyses, cord blood NK cells show reduced degranulation and cytokine production following target recognition, as well as antibody-dependent cell-mediated cytotoxicity and apoptosis induction in targets.

CONCLUSIONS

These findings show that the structure of the NK cell repertoire is intact at birth, suggesting great potential for vaccine and therapeutic strategies targeting this cell population. © 2016 International Clinical Cytometry Society.

UV-inactivated HSV-1 potently activates NK cell killing of leukemic cells

Herein we demonstrate that oncolytic herpes simplex virus-1 (HSV-1) potently activates human peripheral blood mononuclear cells (PBMCs) to lyse leukemic cell lines and primary acute myeloid leukemia samples, but not healthy allogeneic lymphocytes. Intriguingly, we found that UV light-inactivated HSV-1 (UV-HSV-1) is equally effective in promoting PBMC cytolysis of leukemic cells and is 1000- to 10 000-fold more potent at stimulating innate antileukemic responses than UV-inactivated cytomegalovirus, vesicular stomatitis virus, reovirus, or adenovirus. Mechanistically, UV-HSV-1 stimulates PBMC cytolysis of leukemic cells, partly via Toll-like receptor-2/protein kinase C/nuclear factor-κB signaling, and potently stimulates expression of CD69, degranulation, migration, and cytokine production in natural killer (NK) cells, suggesting that surface components of UV-HSV-1 directly activate NK cells. Importantly, UV-HSV-1 synergizes with interleukin-15 (IL-15) and IL-2 in inducing activation and cytolytic activity of NK cells. Additionally, UV-HSV-1 stimulates glycolysis and fatty acid oxidation-dependent oxygen consumption in NK cells, but only glycolysis is required for their enhanced antileukemic activity. Last, we demonstrate that T cell-depleted human PBMCs exposed to UV-HSV-1 provide a survival benefit in a murine xenograft model of human acute myeloid leukemia (AML). Taken together, our results support the preclinical development of UV-HSV-1 as an adjuvant, alone or in combination with IL-15, for allogeneic donor mononuclear cell infusions to treat AML.

Improving natural killer cell cancer immunotherapy

PURPOSE OF REVIEW

Natural killer (NK) cells are innate lymphoid cells specialized to eliminate malignant cells via direct cytotoxicity and immunoregulatory cytokine production. As such, NK cells are ideal as cellular therapy for cancer patients, and several studies have provided proof of principle that adoptively transferred NK cells can induce remissions in patients with leukemia. A clear understanding of the mechanisms underlying NK cell antitumor responses, including target cell recognition, activation status, and negative regulatory signals will improve NK cellular therapy for cancer patients.

RECENT FINDINGS

Clinical studies have demonstrated the safety and preliminary efficacy of NK cell adoptive transfer, especially in hematologic malignancies. Various NK cell sources, isolation techniques, activation approaches, and ex-vivo expansion strategies are under investigation. New approaches have been developed and are being tested to optimize NK cell therapy, including ways to better target NK cells to malignant cells, increase their functional competence, facilitate expansion in patients, and limit inhibitory signals or cells.

SUMMARY

NK cells represent a promising cellular immunotherapy for the treatment of cancer. In addition to adoptive cellular therapy, adjunct treatments that optimize NK cell targeting and function will enhance their potency and broaden their potential use to many cancer types.

The Application of Natural Killer Cell Immunotherapy for the Treatment of Cancer

Natural killer (NK) cells are essential components of the innate immune system and play a critical role in host immunity against cancer. Recent progress in our understanding of NK cell immunobiology has paved the way for novel NK cell-based therapeutic strategies for the treatment of cancer. In this review, we will focus on recent advances in the field of NK cell immunotherapy, including augmentation of antibody-dependent cellular cytotoxicity, manipulation of receptor-mediated activation, and adoptive immunotherapy with ex vivo-expanded, chimeric antigen receptor (CAR)-engineered, or engager-modified NK cells. In contrast to T lymphocytes, donor NK cells do not attack non-hematopoietic tissues, suggesting that an NK-mediated antitumor effect can be achieved in the absence of graft-vs.-host disease. Despite reports of clinical efficacy, a number of factors limit the application of NK cell immunotherapy for the treatment of cancer, such as the failure of infused NK cells to expand and persist in vivo. Therefore, efforts to enhance the therapeutic benefit of NK cell-based immunotherapy by developing strategies to manipulate the NK cell product, host factors, and tumor targets are the subject of intense research. In the preclinical setting, genetic engineering of NK cells to express CARs to redirect their antitumor specificity has shown significant promise. Given the short lifespan and potent cytolytic function of mature NK cells, they are attractive candidate effector cells to express CARs for adoptive immunotherapies. Another innovative approach to redirect NK cytotoxicity towards tumor cells is to create either bispecific or trispecific antibodies, thus augmenting cytotoxicity against tumor-associated antigens. These are exciting times for the study of NK cells; with recent advances in the field of NK cell biology and translational research, it is likely that NK cell immunotherapy will move to the forefront of cancer immunotherapy over the next few years.

Natural Killer Cells Improve Hematopoietic Stem Cell Engraftment by Increasing Stem Cell Clonogenicity In Vitro and in a Humanized Mouse Model

Cord blood (CB) is increasingly used as a source of hematopoietic stem cells (HSC) for transplantation. Low incidence and severity of graft-versus-host disease (GvHD) and a robust graft-versus-leukemia (GvL) effect are observed following CB transplantation (CBT). However, its main disadvantages are a limited number of HSC per unit, delayed immune reconstitution and a higher incidence of infection. Unmanipulated grafts contain accessory cells that may facilitate HSC engraftment. Therefore, the effects of accessory cells, particularly natural killer (NK) cells, on human CB HSC (CBSC) functions were assessed in vitro and in vivo. CBSC cultured with autologous CB NK cells showed higher levels of CXCR4 expression, a higher migration index and a higher number of colony forming units (CFU) after short-term and long-term cultures. We found that CBSC secreted CXCL9 following interaction with CB NK cells. In addition, recombinant CXCL9 increased CBSC clonogenicity, recapitulating the effect observed of CB NK cells on CBSC. Moreover, the co-infusion of CBSC with CB NK cells led to a higher level of CBSC engraftment in NSG mouse model. The results presented in this work offer the basis for an alternative approach to enhance HSC engraftment that could improve the outcome of CBT.

Revving up Natural Killer Cells and Cytokine-Induced Killer Cells Against Hematological Malignancies

Natural killer (NK) cells belong to innate immunity and exhibit cytolytic activity against infectious pathogens and tumor cells. NK-cell function is finely tuned by receptors that transduce inhibitory or activating signals, such as killer immunoglobulin-like receptors, NK Group 2 member D (NKG2D), NKG2A/CD94, NKp46, and others, and recognize both foreign and self-antigens expressed by NK-susceptible targets. Recent insights into NK-cell developmental intermediates have translated into a more accurate definition of culture conditions for the in vitro generation and propagation of human NK cells. In this respect, interleukin (IL)-15 and IL-21 are instrumental in driving NK-cell differentiation and maturation, and hold great promise for the design of optimal NK-cell culture protocols. Cytokine-induced killer (CIK) cells possess phenotypic and functional hallmarks of both T cells and NK cells. Similar to T cells, they express CD3 and are expandable in culture, while not requiring functional priming for in vivo activity, like NK cells. CIK cells may offer some advantages over other cell therapy products, including ease of in vitro propagation and no need for exogenous administration of IL-2 for in vivo priming. NK cells and CIK cells can be expanded using a variety of clinical-grade approaches, before their infusion into patients with cancer. Herein, we discuss GMP-compliant strategies to isolate and expand human NK and CIK cells for immunotherapy purposes, focusing on clinical trials of adoptive transfer to patients with hematological malignancies.