NK cell-based immunotherapy for cancer

MicroRNA-130a enhances the killing ability of natural killer cells against non-small cell lung cancer cells by targeting signal transducers and activators of transcription 3

Non-small cell lung cancer (NSCLC) is a serious threat for human health and life. Natural killer (NK) cell-based immunotherapy is a promising anti-tumor strategy in various cancers including NSCLC. Emerging microRNA (miRNA) has been identified as vital regulators in NK cell-mediated immunosurveillance process. MicroRNA-130a (miR-130a) level and signal transducers and activators of transcription 3 (STAT3) mRNA level was measured by RT-qPCR assay. STAT3 protein level was determined by western blot assay. IFN-γ and TNF-α secretion was examined by corresponding ELISA kits. NK cell cytotoxicity was assessed by lactate dehydrogenase (LDH) assay. The interaction between miR-130a and STAT3 was explored by bioinformatics analysis, luciferase reporter assay and RNA immunoprecipitation (RIP) assay. We found that MiR-130a level was notably reduced and STAT3 expression was dramatically increased in primary NK cells isolated from NSCLC patients. But, miR-130a was highly expressed and STAT3 was low expressed in IL-2-activated NK-92 cells. Functional analysis revealed that miR-130a overexpression potentiated killing ability of NK cells against A549 cells. Further investigations unveiled that STAT3 was a target of miR-130a and STAT3 overexpression abrogated miR-130a-induced improvement in killing activity of NK cells against NSCLC cells. In conclusion, MiR-130a improved the killing capacity of NK cells against NSCLC cells by targeting STAT3, laying a foundation for future studies on the roles and molecular basis of miR-130a in NK cell-based immunotherapy against various cancers.

Gastroenteropancreatic neuroendocrine neoplasms and inflammation: A complex cross-talk with relevant clinical implications

Neuroendocrine neoplasms (NENs) are a group of tumors originating from the neuroendocrine system. They mainly occur in the digestive system and the respiratory tract. It is well-know a strict interaction between neuroendocrine system and inflammation, which can play an important role in NEN carcinogenesis. Inflammatory mediators, which are produced by the tumor microenvironment, can favor cancer induction and progression, and can promote immune editing. On the other hand, a balanced immune system represents a relevant step in cancer prevention through the elimination of dysplastic and cancer cells. Therefore, an inflammatory response may be both pro- and anti-tumorigenic. In this review, we provide an overview concerning the complex interplay between inflammation and gastroenteropancreatic NENs, focusing on the tumorigenesis and clinical implications in these tumors.

Lectin-like transcript 1 as a natural killer cell-mediated immunotherapeutic target for triple negative breast cancer and prostate cancer

Breast and prostate cancer are the leading causes of death in females and males, respectively. Triple negative breast cancer (TNBC) does not express the estrogen receptor, progesterone receptor, or human epidermal growth factor receptor 2, resulting in limited treatment options. Androgen deprivation therapy is the standard care for prostate cancer patients; however, metastasis and recurrence are seen in androgen-independent prostate cancer. Both prostate and breast cancer show higher resistance after recurrence and metastasis, which increases the difficulty of treatment. Natural killer (NK) cells play a critical role during innate immunity and tumor recognition and elimination. NK cell function is determined by a delicate balance of inhibitory signals and activation signals received through cell surface receptors. Lectin-like transcript 1 (LLT1, CLEC2D, OCIL) is a ligand of NK cell inhibitory receptor NKRP1A (CD161). Several studies have that reported higher expression of LLT1 is associated with the development of various tumors. Our studies revealed that TNBC and prostate cancer cells express higher levels of LLT1. In the presence of a monoclonal antibody against LLT1, NK cell-mediated killing of TNBC and prostate cancer cells were greatly enhanced. This review highlights the potential that using monoclonal antibodies to block LLT1 - NKRP1A interactions could be an effective immunotherapeutic approach to treat triple negative breast cancer and prostate cancer.

Harnessing NK Cells for Cancer Treatment

In the last years, natural killer (NK) cell-based immunotherapy has emerged as a promising therapeutic approach for solid tumors and hematological malignancies. NK cells are innate lymphocytes with an array of functional competences, including anti-cancer, anti-viral, and anti-graft-vs.-host disease potential. The intriguing idea of harnessing such potent innate immune system effectors for cancer treatment led to the development of clinical trials based on the adoptive therapy of NK cells or on the use of monoclonal antibodies targeting the main NK cell immune checkpoints. Indeed, checkpoint immunotherapy that targets inhibitory receptors of T cells, reversing their functional blocking, marked a breakthrough in anticancer therapy, opening new approaches for cancer immunotherapy and resulted in extensive research on immune checkpoints. However, the clinical efficacy of T cell-based immunotherapy presents a series of limitations, including the inability of T cells to recognize and kill HLA-I^neg tumor cells. For these reasons, new strategies for cancer immunotherapy are now focusing on NK cells. Blockade with NK cell checkpoint inhibitors that reverse their functional block may overcome the limitations of T cell-based immunotherapy, mainly against HLA-I^neg tumor targets. Here, we discuss recent anti-tumor approaches based on mAb-mediated blocking of immune checkpoints (either restricted to NK cells or shared with T cells), used either as a single agent or in combination with other compounds, that have demonstrated promising clinical responses in both solid tumors and hematological malignancies.

Biological treatment of pediatric sarcomas by combined virotherapy and NK cell therapy

BACKGROUND

In pediatric sarcomas, outcomes of established therapies still remain poor, especially due to high-grade resistances to chemotherapeutic compounds. Taking novel biological approaches into account, virotherapy was found to be efficient in many pediatric sarcoma types. Also NK cell therapy was denoted to represent a promising upcoming strategy for pediatric sarcoma patients. We here investigated a combinatorial approach employing oncolytic measles vaccine virotherapeutics (MeV) together with activated human NK cells (or PBMCs).

METHODS

The human sarcoma cell lines A673 and HT1080 were used to evaluate the efficacy of this combinatorial treatment modality. Oncolysis was determined by measuring real-time cell proliferation using the xCELLigence RTCA SP system. Furthermore, expression of receptors on NK cells and the respective ligands on A673 cells was analyzed by flow cytometry. To measure the protein release of activated NK cells a LEGENDplex™ assay was performed.

RESULTS

Monotherapy with MeV led to a time- and dose-dependent oncolytic reduction of A673 and HT1080 sarcoma tumor cell masses. Concurrently, such MeV infections did not change the expression of NK cell ligands MICA/B, ULBP1, 2, and 3, CD112, and CD155. As shown by real-time proliferation assays, infections of A673 and HT1080 sarcoma cells with MeV followed by co-culture with activated NK cells or PBMCs led to enhanced sarcoma cell destruction when compared to the respective monotherapies. In parallel, this dual therapy resulted in an increased release of granzymes, perforin, and granulysin from NK cells. In contrast, expression of activation and ontogenesis receptors on NK cells was not found to be altered after co-culture with MeV-infected A673 sarcoma cells.

CONCLUSIONS

Taken together, the combined treatment strategy comprising oncolytic MeV and activated NK cells resulted in enhanced oncolysis of A673 and HT1080 cells when compared to the respective monotherapies. In parallel, we observed an increased release of NK cell activation markers upon co-culture with MeV-infected A673 human sarcoma cells. These results support the onset of clinical trials combining oncolytic virotherapy with NK cell based immunotherapies.

Natural Killer Cells: Diverse Functions in Tumor Immunity and Defects in Pre-neoplastic and Neoplastic Stages of Tumorigenesis

Natural killer (NK) cells are the key immune effectors with the ability to mediate selection and differentiation of a number of different cancer stem cells/undifferentiated tumors via lysis, and secreted or membrane-bound interferon (IFN)-γ and tumor necrosis factor (TNF)-α, respectively, leading to curtailment of tumor growth and metastasis. In this review, we present an overview of our recent findings on the biology and significance of NK cells in selection and differentiation of stem-like tumors using in vitro and in vivo studies conducted in humanized-BLT mice and in cancer patients. In addition, we present current advances in NK cell expansion and therapeutic delivery, and discuss the utility of allogeneic supercharged NK cells in the treatment of cancer patients. Moreover, we discuss the potential loss of NK cell numbers and function at the neoplastic and pre-neoplastic stages of tumorigenesis in induction and progression of pancreatic cancer. Therefore, because of their indispensable role in targeting cancer stem-like/undifferentiated tumors, NK cells should be placed high in the armamentarium of tumor immunotherapy. A combination of allogeneic supercharged NK cells with other immunotherapeutic strategies such as oncolytic viruses, antibody-dependent cellular cytotoxicity (ADCC)-inducing antibodies, checkpoint inhibitors, chimeric antigen receptor (CAR) T cells, CAR NK cells, and chemotherapeutic and radiotherapeutic strategies can be used for the ultimate goal of tumor eradication.

Immune cells within the tumor microenvironment: Biological functions and roles in cancer immunotherapy

The immune cells within the tumor microenvironment (TME) play important roles in tumorigenesis. It has been known that these tumor associated immune cells may possess tumor-antagonizing or tumor-promoting functions. Although the tumor-antagonizing immune cells within TME tend to target and kill the cancer cells in the early stage of tumorigenesis, the cancer cells seems to eventually escape from immune surveillance and even inhibit the cytotoxic function of tumor-antagonizing immune cells through a variety of mechanisms. The immune evasion capability, as a new hallmark of cancer, accidently provides opportunities for new strategies of cancer therapy, namely harnessing the immune cells to battle the cancer cells. Recently, the administrations of immune checkpoint modulators (represented by anti-CTLA4 and anti-PD antibodies) and adoptive immune cells (represented by CAR-T) have exhibited unexpected antitumor effect in multiple types of cancer, bringing a new era for cancer therapy. Here, we review the biological functions of immune cells within TME and their roles in cancer immunotherapy, and discuss the perspectives of the basic studies for improving the effectiveness of the clinical use.

Antitumor effects of immunity-enhancing traditional Chinese medicine

Traditional Chinese Medicine (TCM) has been traditionally used to treat patients with cancers in China. It not only alleviates the symptoms of tumor patients and improves their quality of life, but also controls the size of tumors and prolongs the survival of tumor patients. While some herbs of TCM may exert therapeutic effects by directly targeting cancer cells or reducing side effects caused by antitumor drugs, others can control tumor growth and metastasis via enhancing antitumor immunity. In particular, TCM can exert antitumor effects by upregulating immune responses even in immunosuppressive tumor microenvironment. For instance, it reduces the number of M2-type macrophages and Treg cells in the tumor tissue. Although extensive reviews on directly killing cancer cells by TCM have been conducted, a review of anticancer activity of TCM solely based on its immunity-enhancing capacity is unusual. This review will summarize research progress of antitumor TCM that regulates the immune system, including both innate immunity, such as macrophages, dendritic cells, natural killer cells and MDSCs, and adaptive immunity, including CD4⁺/CD8⁺ T lymphocytes, regulatory T cells (Tregs) and B cells. As cancer immunotherapy has recently achieved certain success, it is expected that the clinical applications of immunity-enhancing TCM or traditional medicine for treating various cancer patients will be expanded. Further studies on the mechanisms by which TCM regulates immunity will provide new insights into how TCM controls tumor growth and metastasis, and may help improve its therapeutic effects on various cancers in clinic.

Postablation Immune Microenvironment: Synergy between Interventional Oncology and Immuno-oncology

Current tumor thermal ablation techniques rely on extreme temperatures to induce irreversible cellular injury and coagulative tissue necrosis. Ablation-induced cellular injury or death releases cancer neoantigens and activates the cancer-immunity cycle, potentially generating tumor-specific immune effectors. However, multiple negative regulatory modulators exist at each step of the cycle, mitigating meaningful and therapeutic anticancer effect provided by the immune system. Recent studies have focused on the introduction and testing of adjuvant immunotherapy combined with ablation to synergistically shift the equilibrium out of inhibitory immune modulation. This article reviews the immune microenvironment in relation to image-guided ablation techniques and discusses current and upcoming novel strategies to take advantage of antitumor immunity.

Characterization and Potential Applications of Dog Natural Killer Cells in Cancer Immunotherapy

Natural killer (NK) cells of the innate immune system are a key focus of research within the field of immuno-oncology based on their ability to recognize and eliminate malignant cells without prior sensitization or priming. However, barriers have arisen in the effective translation of NK cells to the clinic, in part because of critical species differences between mice and humans. Companion animals, especially dogs, are valuable species for overcoming many of these barriers, as dogs develop spontaneous tumors in the setting of an intact immune system, and the genetic and epigenetic factors that underlie oncogenesis appear to be similar between dogs and humans. Here, we summarize the current state of knowledge for dog NK cells, including cell surface marker phenotype, key NK genes and genetic regulation, similarities and differences of dog NK cells to other mammals, especially human and mouse, expression of canonical inhibitory and activating receptors, ex vivo expansion techniques, and current and future clinical applications. While dog NK cells are not as well described as those in humans and mice, the knowledge of the field is increasing and clinical applications in dogs can potentially advance the field of human NK biology and therapy. Better characterization is needed to truly understand the similarities and differences of dog NK cells with mouse and human. This will allow for the canine model to speed clinical translation of NK immunotherapy studies and overcome key barriers in the optimization of NK cancer immunotherapy, including trafficking, longevity, and maximal in vivo support.

Single peptides and combination modalities for triple negative breast cancer

Unlike other types of breast cancers (BCs), no specific therapeutic targets have been established for triple negative breast cancer (TNBC). Therefore, chemotherapy and radiotherapy are the only available adjuvant therapeutic choices for TNBC. New emerging reports show that TNBC is associated with higher numbers of intratumoral tumor infiltrating lymphocytes. This is indicative of host anti-TNBC immune surveillance and suggesting that immunotherapy can be considered as a therapeutic approach for TNBC management. Recent progress in molecular mechanisms of tumor-immune system interaction and cancer vaccine development studies, fast discoveries and FDA approvals of immune checkpoint inhibitors, chimeric antigen receptor T-cells, and oncolytic virotherapy have significantly attracted attention and research directions toward the immunotherapeutic approach to TNBC. Here in this review different aspects of TNBC immunotherapies including the host immune system-tumor interactions, the tumor microenvironment, the relevant molecular targets for immunotherapy, and clinical trials in the field are discussed.

The Good and the Bad of Natural Killer Cells in Virus Control: Perspective for Anti-HBV Therapy

Immune modulatory therapies are widely believed to represent potential therapeutic strategies for chronic hepatitis B infection (CHB). Among the cellular targets for immune interventions, Natural Killer (NK) cells represent possible candidates because they have a key role in anti-viral control by producing cytokines and by exerting cytotoxic functions against virus-infected cells. However, in patients with chronic hepatitis B, NK cells have been described to be more pathogenic than protective with preserved cytolytic activity but with a poor capacity to produce anti-viral cytokines. In addition, NK cells can exert a regulatory activity and possibly suppress adaptive immune responses in the setting of persistent viral infections. Consequently, a potential drawback of NK-cell targeted modulatory interventions is that they can potentiate the suppressive NK cell effect on virus-specific T cells, which further causes impairment of exhausted anti-viral T cell functions. Thus, clinically useful NK-cell modulatory strategies should be not only suited to improve positive anti-viral NK cell functions but also to abrogate T cell suppression by NK cell-mediated T cell killing. This review outlines the main NK cell features with a particular focus on CHB infection. It describes different mechanisms involved in NK-T cell interplay as well as how NK cells can have positive anti-viral effector functions and negative suppressive effects on T cells activity. This review discusses how modulation of their balance can have potential therapeutic implications.

Natural Killer Cell Therapy: A New Treatment Paradigm for Solid Tumors

In treatments of solid tumors, adoptive transfer of ex vivo expanded natural killer (NK) cells has dawned as a new paradigm. Compared with cytotoxic T lymphocytes, NK cells take a unique position targeting tumor cells that evade the host immune surveillance by down-regulating self-antigen presentation. Recent findings highlighted that NK cells can even target cancer stem cells. The efficacy of allogeneic NK cells has been widely investigated in the treatment of hematologic malignancies. In solid tumors, both autologous and allogeneic NK cells have demonstrated potential efficacy. In allogeneic NK cell therapy, the mismatch between the killer cell immunoglobulin-like receptor (KIR) and human leukocyte antigen (HLA) can be harnessed to increase the antitumor activity. However, the allogeneic NK cells cause more adverse events and can be rejected by the host immune system after repeated injections. In this regard, the autologous NK cell therapy is safer. This article reviews the published results of clinical trials and discusses strategies to enhance the efficacy of the NK cell therapy. The difference in immunophenotype of the ex vivo expanded NK cells resulted from different culture methods may affect the final efficacy. Furthermore, currently available standard anticancer therapy, molecularly targeted agents, and checkpoint inhibitors may directly or indirectly enhance the efficacy of NK cell therapy. A recent study discovered that NK cell specific genetic defects are closely associated with the tumor immune microenvironment that determines clinical outcomes. This finding warrants future investigations to find the implication of NK cell specific genetic defects in cancer development and treatment, and NK cell deficiency syndrome should be revisited to enhance our understanding. Overall, it is clear that NK cell therapy is safe and promises a new paradigm for the treatment of solid tumors.

Immunotherapy Based on Dendritic Cell-Targeted/-Derived Extracellular Vesicles-A Novel Strategy for Enhancement of the Anti-tumor Immune Response

Dendritic cell (DC)-based anti-tumor vaccines have great potential for the treatment of cancer. To date, a large number of clinical trials involving DC-based vaccines have been conducted with a view to treating tumors of different histological origins. However, DC-based vaccines had several drawbacks, including problems with targeted delivery of tumor antigens to DCs and prolong storage of cellular vaccines. Therefore, the development of other immunotherapeutic approaches capable of enhancing the immunogenicity of existing DC-based vaccines or directly triggering anti-tumor immune responses is of great interest. Extracellular vesicles (EVs) are released by almost all types of eukaryotic cells for paracrine signaling. EVs can interact with target cells and change their functional activity by delivering different signaling molecules including mRNA, non-coding RNA, proteins, and lipids. EVs have potential benefits as natural vectors for the delivery of RNA and other therapeutic molecules targeted to DCs, T-lymphocytes, and tumor cells; therefore, EVs are a promising entity for the development of novel cell-free anti-tumor vaccines that may be a favourable alternative to DC-based vaccines. In the present review, we discuss the anti-tumor potential of EVs derived from DCs, tumors, and other cells. Methods of EV isolation are systematized, and key molecules carried by EVs that are necessary for the activation of a DC-mediated anti-tumor immune response are analyzed with a focus on the RNA component of EVs. Characteristics of anti-tumor immune responses induced by EVs in vitro and in vivo are reviewed. Finally, perspectives and challenges with the use of EVs for the development of anti-tumor cell-free vaccines are considered.

Genetic reprogramming for NK cell cancer immunotherapy with CRISPR/Cas9

Natural killer cells are potent cytotoxic lymphocytes specialized in recognizing and eliminating transformed cells, and in orchestrating adaptive anti-tumour immunity. However, NK cells are usually functionally exhausted in the tumour microenvironment. Strategies such as checkpoint blockades are under investigation to overcome NK cell exhaustion in order to boost anti-tumour immunity. The discovery and development of the CRISPR/Cas9 technology offer a flexible and efficient gene-editing capability in modulating various pathways that mediate NK cell exhaustion, and in arming NK cells with novel chimeric antigen receptors to specifically target tumour cells. Despite the high efficiency in its gene-editing capability, difficulty in the delivery of the CRISPR/Cas9 system remains a major bottleneck for its therapeutic applications, particularly for NK cells. The current review discusses feasible approaches to deliver the CRISPR/Cas9 systems, as well as potential strategies in gene-editing for NK cell immunotherapy for cancers.

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.

NK Cell Metabolism and Tumor Microenvironment

Natural Killer (NK) cells are characterized by their potential to kill tumor cells by different means without previous sensitization and have, therefore, become a valuable tool in cancer immunotherapy. However, their efficacy against solid tumors is still poor and further studies are required to improve it. One of the major restrictions for NK cell activity is the immunosuppressive tumor microenvironment (TME). There, tumor and other immune cells create the appropriate conditions for tumor proliferation while, among others, preventing NK cell activation. Furthermore, NK cell metabolism is impaired in the TME, presumably due to nutrient and oxygen deprivation, and the higher concentration of tumor-derived metabolic end products, such as lactate. This metabolic restriction of NK cells limits their effector functions, and it could represent a potential target to focus on to improve the efficacy of NK cell-based therapies against solid tumors. In this review, we discuss the potential effect of TME into NK cell metabolism and its influence in NK cell effector functions.

The emerging role of epigenetic therapeutics in immuno-oncology

The past decade has seen the emergence of immunotherapy as a prime approach to cancer treatment, revolutionizing the management of many types of cancer. Despite the promise of immunotherapy, most patients do not have a response or become resistant to treatment. Thus, identifying combinations that potentiate current immunotherapeutic approaches will be crucial. The combination of immune-checkpoint inhibition with epigenetic therapy is one such strategy that is being tested in clinical trials, encompassing a variety of cancer types. Studies have revealed key roles of epigenetic processes in regulating immune cell function and mediating antitumour immunity. These interactions make combined epigenetic therapy and immunotherapy an attractive approach to circumvent the limitations of immunotherapy alone. In this Review, we highlight the basic dynamic mechanisms underlying the synergy between immunotherapy and epigenetic therapies and detail current efforts to translate this knowledge into clinical benefit for patients.

Genetically engineered T cells for cancer immunotherapy

T cells in the immune system protect the human body from infection by pathogens and clear mutant cells through specific recognition by T cell receptors (TCRs). Cancer immunotherapy, by relying on this basic recognition method, boosts the antitumor efficacy of T cells by unleashing the inhibition of immune checkpoints and expands adaptive immunity by facilitating the adoptive transfer of genetically engineered T cells. T cells genetically equipped with chimeric antigen receptors (CARs) or TCRs have shown remarkable effectiveness in treating some hematological malignancies, although the efficacy of engineered T cells in treating solid tumors is far from satisfactory. In this review, we summarize the development of genetically engineered T cells, outline the most recent studies investigating genetically engineered T cells for cancer immunotherapy, and discuss strategies for improving the performance of these T cells in fighting cancers.

Natural Killer Cell-Mediated Cellular Therapy of Hematological Malignancies

Our understanding on the mechanisms of graft versus tumor/leukemia (GvT/GvL) and graft versus host (GvH) effects has tremendously evolved within the past decades. During the search for a mechanism that augments GvT/GvL without increasing GvH effects, natural killer (NK) cells have clearly attracted attention. Current approaches of NK cell immunotherapy for hematological malignancies involve using methods for in vivo potentiation of NK cell proliferation and activity; adoptive transfer of NK cells from autologous and allogeneic sources [cord blood mononuclear cells, peripheral blood mononuclear cells, CD34⁺ stem cells] and NK cell lines; and genetic modification of NK cells. Several cytokines, including interleukin-2 and interleukin-15 take part in the development of NK cells and have been shown to boost NK cell effects both in vivo and ex vivo. Monoclonal antibodies directed towards certain targets, including stimulating CD16, blockade of NK cell receptors, and redirection of cytotoxicity to tumor cells via bi- or tri-specific engagers may promote NK cell function. Despite the relative disappointment with autologous NK cell infusions, the future holds promise in adoptive transfer of allogeneic NK cells and the development of novel cellular therapeutic strategies, such as chimeric antigen receptor-modified NK cell immunotherapy. In this review, we summarize the current status of NK cell-related mechanisms in the therapy of hematologic malignancies, and discuss the future perspectives on adoptive NK cell transfer and other novel cellular immunotherapeutic strategies.

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.

A Natural Impact: NK Cells at the Intersection of Cancer and HIV Disease

Despite efficient suppression of plasma viremia in people living with HIV (PLWH) on cART, evidence of HIV-induced immunosuppression remains, and normally benign and opportunistic pathogens become major sources of co-morbidities, including virus-induced cancers. In fact, cancer remains a primary cause of death even in virally suppressed PLWH. Natural killer (NK) cells provide rapid early responses to HIV infection, contribute substantially to disease modulation and vaccine protection, and are also major therapeutic targets for cancer immunotherapy. However, much like other lymphocyte populations, recent burgeoning evidence suggests that in chronic conditions like HIV, NK cells can become functionally exhausted with impaired cytotoxic function, altered cytokine production and impaired antibody-dependent cell-mediated cytotoxicity. Recent work suggests functional anergy is likely due to low-level ongoing virus replication, increased inflammatory cytokines, or increased presence of MHC^low target cells. Indeed, HIV-induced loss of NK cell-mediated control of lytic EBV infection has been specifically shown to cause lymphoma and also increases replication of CMV. In this review, we will discuss current understanding of NK cell modulation of HIV disease, reciprocal exhaustion of NK cells, and how this may impact increased cancer incidences and prospects for NK cell-targeted immunotherapies. Finally, we will review the most recent evidence supporting adaptive functions of NK cells and highlight the potential of adaptive NK cells for cancer immunotherapy.

Astragaloside III Enhances Anti-Tumor Response of NK Cells by Elevating NKG2D and IFN-γ

Natural killer (NK) cells play an irreplaceable role in the development of colon cancer, in which antitumor function of NK cells was impaired. Astragaloside III is a natural compound from Astragalus that has been shown to have immunomodulatory effects in various systems. However, few studies have evaluated the antitumor effects of Astragaloside III through stimulating systemic immunity and regulating NK cells. In this study, flow cytometry, immunohistochemical analysis, and immunofunctional assays were performed to elucidate the functions of Astragaloside III in restoring antitumor function of NK cells. We demonstrated that Astragaloside III significantly elevated the expression of natural killer group 2D (NKG2D), Fas, and interferon-γ (IFN-γ) production in NK cells, leading to increased tumor-killing ability. Experiments in cell co-culture assays and CT26-bearing mice model further confirmed that Astragaloside III could effectively impede tumor growth by increasing infiltration of NK cells into tumor and upregulating the antitumor response of NK cells. We further revealed that Astragaloside III increased IFN-γ secretion of NK cells by enhancing the expression of transcription factor T-bet. In conclusion, the effective anti-tumor function of Astragaloside III was achieved through up-regulation of the immune response of NK cells and elevation of NKG2D, Fas, and IFN-γ production.

An Historical Overview: The Discovery of How NK Cells Can Kill Enemies, Recruit Defense Troops, and More

Natural killer (NK) cells were originally defined as effector lymphocytes of innate immunity characterized by the unique ability of killing tumor and virally infected cells without any prior priming and expansion of specific clones. The "missing-self" theory, proposed by Klas Karre, the seminal discovery of the first prototypic HLA class I-specific inhibitory receptors, and, later, of the Natural Cytotoxicity Receptors (NCRs) by Alessandro Moretta, provided the bases to understand the puzzling behavior of NK cells. Actually, those discoveries proved crucial also for many of the achievements that, along the years, have contributed to the modern view of these cells. Indeed, NK cells, besides killing susceptible targets, are now known to functionally interact with different immune cells, sense pathogens using TLR, adapt their responses to the local environment, and, even, mount a sort of immunological memory. In this review, we will specifically focus on the main activating NK receptors and on their crucial role in the ever-increasing number of functions assigned to NK cells and other innate lymphoid cells (ILCs).

Cancer Immunotherapy Based on Natural Killer Cells: Current Progress and New Opportunities

Cancer immunotherapy has been firmly established as a new milestone for cancer therapy, with the development of multiple immune cells as therapeutic tools. Natural killer (NK) cells are innate immune cells endowed with potent cytolytic activity against tumors, and meanwhile act as regulatory cells for the immune system. The efficacy of NK cell-mediated immunotherapy can be enhanced by immune stimulants such as cytokines and antibodies, and adoptive transfer of activated NK cells expanded ex vivo. In addition, NK cells can arm themselves with chimeric antigen receptors (CARs), which may greatly enhance their anti-tumor activity. Most recently, extracellular vesicles (EVs) derived from NK cells show promising anti-tumor effects in preclinical studies. Herein, we carefully review the current progress in these NK cell-based immunotherapeutic strategies (NK cells combined with stimulants, adoptive transfer of NK cells, CAR-NK cells, and NK EVs) for the treatment of cancers, and discussed the challenges and opportunities for opening a new horizon for cancer immunotherapy.

Aptamer-Engineered Natural Killer Cells for Cell-Specific Adaptive Immunotherapy

Natural killer (NK) cells are a key component of the innate immune system as they can attack cancer cells without prior sensitization. However, due to lack of cell-specific receptors, NK cells are not innately able to perform targeted cancer immunotherapy. Aptamers are short single-stranded oligonucleotides that specifically recognize their targets with high affinity in a similar manner to antibodies. To render NK cells with target-specificity, synthetic CD30-specific aptamers are anchored on cell surfaces to produce aptamer-engineered NK cells (ApEn-NK) without genetic alteration or cell damage. Under surface-anchored aptamer guidance, ApEn-NK specifically bind to CD30-expressing lymphoma cells but do not react to off-target cells. The resulting specific cell binding of ApEn-NK triggers higher apoptosis/death rates of lymphoma cells compared to parental NK cells. Additionally, experiments with primary human NK cells demonstrate the potential of ApEn-NK to specifically target and kill lymphoma cells, thus presenting a potential new approach for targeted immunotherapy by NK cells.

Human CAR NK Cells: A New Non-viral Method Allowing High Efficient Transfection and Strong Tumor Cell Killing

CAR-NK cells may represent a valuable tool, complementary to CAR-T cells, in adoptive immunotherapy of leukemia and solid tumors. However, gene transfer to human NK cells is a challenging task, particularly with non-virus-based techniques. Here, we describe a new procedure allowing efficient electroporation-based transfection of plasmid DNA, including CAR and CCR7 genes, in resting or cytokine-expanded human NK cell populations and NK-92 cell line. This procedure may offer a suitable platform for a safe and effective use of CAR-NK cells in adoptive immunotherapy of cancer.

CD28 Homolog Is a Strong Activator of Natural Killer Cells for Lysis of B7H7+ Tumor Cells

The CD28-B7 family of receptor-ligand pairs regulates lymphocyte responses through costimulation and coinhibition. It includes checkpoint inhibitors, such as PD-1, which limit antitumor and antivirus T-cell responses. CD28 homolog (CD28H) and B7H7 have been identified as a receptor-ligand pair in this family, which has costimulatory activity in T cells. Here, we show that CD28H is expressed in primary natural killer (NK) cells and that it is a strong activator of NK cells through selective synergy with receptors NKp46 and 2B4 to induce degranulation, lysis of target cells, and production of proinflammatory cytokines. Expression of B7H7 on target cells enhanced both natural and antibody-dependent cellular cytotoxicity of NK cells. Mutation of tyrosine 192 on the CD28H cytoplasmic tail abolished NK-cell activation through CD28H. As B7H7 is broadly expressed in tumor tissues, we engineered a CD28H chimeric antigen receptor (CD28H-CAR) consisting of full-length CD28H fused to the cytoplasmic domain of T-cell receptor ζ chain. Remarkably, expression of CD28H-CAR in NK cells triggered lysis of B7H7⁺ HLA-E⁺ tumor cells by overriding inhibition by the HLA-E receptor NKG2A. The cytoplasmic domains of CD28H and of the ζ chain were both required for this activity. Thus, CD28H is a powerful activation receptor of NK cells that broadens their antitumor activity and holds promise as a component of NK-based CARs for cancer immunotherapy.

Carnosic acid enhances the anti-lung cancer effect of cisplatin by inhibiting myeloid-derived suppressor cells

Cisplatin and other platinum-based drugs are used frequently for treatment of lung cancer. However, their clinical performance are usually limited by drug resistance or toxic effects. Carnosic acid, a polyphenolic diterpene isolated from Rosemary (Rosemarinus officinalis), has been reported to have several pharmacological and biological activities. In the present study, the combination effect of cisplatin plus carnosic acid on mouse LLC (Lewis lung cancer) xenografts and possible underlying mechanism of action were examined. LLC-bearing mice were treated with intraperitoneal injection with cisplatin, oral gavage with carnosic acid, or combination with cisplatin and carnosic acid, respectively. Combination of carnosic acid and cisplatin yielded significantly better anti-growth and pro-apoptotic effects on LLC xenografts than drugs alone. Mechanistic study showed that carnosic acid treatment boosted the function of CD8⁺ T cells as evidenced by higher IFN-γ secretion and higher expression of FasL, perforin as well as granzyme B. In the meantime, the proportion of MDSC (myeloid-derived suppressor cells) in tumor tissues were reduced by carnosic acid treatment and the mRNA levels of iNOS2, Arg-1, and MMP9, which are the functional markers for MDSC, were reduced. In conclusion, our study proved that the functional suppression of MDSC by carnosic acid promoted the lethality of CD8⁺ T cells, which contributed to the enhancement of anti-lung cancer effect of cisplatin.

Engineering advanced cancer therapies with synthetic biology

Engineered immune-cell-based cancer therapies have demonstrated robust efficacy in B cell malignancies, but challenges such as the lack of ideal targetable tumour antigens, tumour-mediated immunosuppression and severe toxicity still hinder their therapeutic efficacy and broad applicability. Synthetic biology can be used to overcome these challenges and create more robust, effective adaptive therapies that enable the specific targeting of cancer cells while sparing healthy cells. In this Progress article, we review recently developed gene circuit therapies for cancer using immune cells, nucleic acids and bacteria as chassis. We conclude by discussing outstanding challenges and future directions for realizing these gene circuit therapies in the clinic.

Soluble Fc-Disabled Herpes Virus Entry Mediator Augments Activation and Cytotoxicity of NK Cells by Promoting Cross-Talk between NK Cells and Monocytes

CD160 is highly expressed by NK cells and is associated with cytolytic effector activity. Herpes virus entry mediator (HVEM) activates NK cells for cytokine production and cytolytic function via CD160. Fc-fusions are a well-established class of therapeutics, where the Fc domain provides additional biological and pharmacological properties to the fusion protein including enhanced serum t 1/2 and interaction with Fc receptor-expressing immune cells. We evaluated the specific function of HVEM in regulating CD160-mediated NK cell effector function by generating a fusion of the HVEM extracellular domain with human IgG1 Fc bearing CD16-binding mutations (Fc*) resulting in HVEM-(Fc*). HVEM-(Fc*) displayed reduced binding to the Fc receptor CD16 (i.e., Fc-disabled HVEM), which limited Fc receptor-induced responses. HVEM-(Fc*) functional activity was compared with HVEM-Fc containing the wild type human IgG1 Fc. HVEM-(Fc*) treatment of NK cells and PBMCs caused greater IFN-γ production, enhanced cytotoxicity, reduced NK fratricide, and no change in CD16 expression on human NK cells compared with HVEM-Fc. HVEM-(Fc*) treatment of monocytes or PBMCs enhanced the expression level of CD80, CD83, and CD40 expression on monocytes. HVEM-(Fc*)-enhanced NK cell activation and cytotoxicity were promoted via cross-talk between NK cells and monocytes that was driven by cell-cell contact. In this study, we have shown that soluble Fc-disabled HVEM-(Fc*) augments NK cell activation, IFN-γ production, and cytotoxicity of NK cells without inducing NK cell fratricide by promoting cross-talk between NK cells and monocytes without Fc receptor-induced effects. Soluble Fc-disabled HVEM-(Fc*) may be considered as a research and potentially therapeutic reagent for modulating immune responses via sole activation of HVEM receptors.

Innate lymphoid cells: A potential link between microbiota and immune responses against cancer

The adaptive immune system plays a crucial role in anti-tumor surveillance. Enhancement of T cell responses through checkpoint blockade has become a major therapeutic avenue of intervention for several tumors. Because it shapes immune responses and regulates their amplitude and duration, the microbiota has a substantial impact on anti-tumor immunity. Innate lymphoid cells (ILCs) comprise a heterogeneous population of lymphocytes devoid of antigen-specific receptors that mirror T helper cells in their ability to secrete cytokines that activate immune responses. Ongoing studies suggest that ILCs contribute to anti-tumor responses. Moreover, since ILCs are present at barrier surfaces, they are stimulated by the microbiota and, reciprocally, influence the composition of the microbiota by regulating the surface barrier microenvironment. Thus, ILC-microbiota cross-talk may in part underpin the effects of the microbiota on anti-tumor responses. In this article, we review current evidence linking ILCs to cancer and discuss the potential impact of ILC-microbiota cross-talk in anti-tumor immune responses.

Designing Magnetically Responsive Biohybrids Composed of Cord Blood-Derived Natural Killer Cells and Iron Oxide Nanoparticles

We report the generation of magnetically responsive, cord blood-derived natural killer (NK) cells using iron oxide nanoparticles (IONPs). NK cells are a promising immune cell population for cancer cell therapy as they can target and lyse target tumor cells without prior education. However, NK cells cannot home to disease sites based on antigen recognition, instead relying primarily on external stimuli and chemotactic gradients for transport. Hence, we hypothesized that conjugating IONPs onto the surface of NK cells provides an added feature of magnetic homing to the NK cells, improving their therapeutic function. We describe a robust design for conjugating the IONPs onto the surface of NK cells, which maintains their intrinsic phenotype and function. The conferred magnetic-responsiveness is utilized to improve the cytolytic function of the NK cells for target cells in 2D and 3D models. These findings demonstrate the feasibility of improving NK cell homing and therapeutic efficacy with our NK:IONP "biohybrid".

Overcoming Resistance to Natural Killer Cell Based Immunotherapies for Solid Tumors

Despite advances in the diagnostic and therapeutic modalities, the prognosis of several solid tumor malignancies remains poor. Different factors associated with solid tumors including a varied genetic signature, complex molecular signaling pathways, defective cross talk between the tumor cells and immune cells, hypoxic and immunosuppressive effects of tumor microenvironment result in a treatment resistant and metastatic phenotype. Over the past several years, immunotherapy has emerged as an attractive therapeutic option against multiple malignancies. The unique ability of natural killer (NK) cells to target cancer cells without antigen specificity makes them an ideal candidate for use against solid tumors. However, the outcomes of adoptive NK cell infusions into patients with solid tumors have been disappointing. Extensive studies have been done to investigate different strategies to improve the NK cell function, trafficking and tumor targeting. Use of cytokines and cytokine analogs has been well described and utilized to enhance the proliferation, stimulation and persistence of NK cells. Other techniques like blocking the human leukocyte antigen-killer cell receptors (KIR) interactions with anti-KIR monoclonal antibodies, preventing CD16 receptor shedding, increasing the expression of activating NK cell receptors like NKG2D, and use of immunocytokines and immune checkpoint inhibitors can enhance NK cell mediated cytotoxicity. Using genetically modified NK cells with chimeric antigen receptors and bispecific and trispecific NK cell engagers, NK cells can be effectively redirected to the tumor cells improving their cytotoxic potential. In this review, we have described these strategies and highlighted the need to further optimize these strategies to improve the clinical outcome of NK cell based immunotherapy against solid tumors.

Natural Killer Cells and Current Applications of Chimeric Antigen Receptor-Modified NK-92 Cells in Tumor Immunotherapy

Natural killer (NK) cells are innate immune cells that can be activated rapidly to target abnormal and virus-infected cells without prior sensitization. With significant advancements in cell biology technologies, many NK cell lines have been established. Among these cell lines, NK-92 cells are not only the most widely used but have also been approved for clinical applications. Additionally, chimeric antigen receptor-modified NK-92 cells (CAR-NK-92 cells) have shown strong antitumor effects. In this review, we summarize established human NK cell lines and their biological characteristics, and highlight the applications of NK-92 cells and CAR-NK-92 cells in tumor immunotherapy.

Strategies and Techniques for NK Cell Phenotyping

Therapies based on activating the immune system, that is, immunotherapy, are now widely implemented in clinical praxis in patients with advanced cancer. Although cancer immunotherapy can result in long-lasting clinical responses, the majority of patients do not respond or develop resistance. Furthermore, cancer immunotherapy is being increasingly combined with other forms of immunotherapy or conventional cancer therapies. It is therefore much needed to identify biomarkers that can precisely classify what patients will benefit from the treatment without any major adverse events and to further develop the efficacy of cancer immunotherapy. While much attention has been focused on monitoring T cell responses in cancer immunotherapy, recent reports have shown that NK cells also play a major role in the response to cancer immunotherapy. The gold standard for immunoprofiling of NK cells is flow cytometry, but other technologies have emerged and include mass cytometry, multiplex immunohistochemistry, and single-cell RNA-sequencing. In this chapter we provide a detailed protocol to profile NK cells using flow cytometry, and a brief introduction to other techniques.

Recent advances in research on aspartate β-hydroxylase (ASPH) in pancreatic cancer: A brief update

Pancreatic cancer (PC) is a highly aggressive tumor, often difficult to diagnose and treat. Aspartate β-hydroxylase (ASPH) is a type II transmembrane protein and the member of α-ketoglutarate-dependent dioxygenase family, found to be overexpressed in different cancer types, including PC. ASPH appears to be involved in the regulation of proliferation, invasion and metastasis of PC cells through multiple signaling pathways, suggesting its role as a tumor biomarker and therapeutic target. In this review, we briefly summarize the possible mechanisms of action of ASPH in PC and recent progress in the therapeutic approaches targeting ASPH.

Molecular Mechanisms Directing Migration and Retention of Natural Killer Cells in Human Tissues

A large body of data shows that Natural Killer (NK) cells are immune effectors exerting a potent cytolytic activity against tumors and virus infected cells. The discovery and characterization of several inhibitory and activating receptors unveiled most of the mechanisms allowing NK cells to spare healthy cells while selectively attacking abnormal tissues. Nevertheless, the mechanisms ruling NK cell subset recirculation among the different compartments of human body have only lately started to be investigated. This is particularly true for pathological settings such as tumors or infected tissues but also for para-physiological condition like pregnant human uterine mucosa. It is becoming evident that the microenvironment associated to a particular clinical condition can deeply influence the migratory capabilities of NK cells. In this review we describe the main mechanisms and stimuli known to regulate the expression of chemokine receptors and other molecules involved in NK cell homing to either normal or pathological/inflamed tissues, including tumors or organs such as lung and liver. We will also discuss the role played by the chemokine/chemokine receptor axes in the orchestration of physiological events such as NK cell differentiation, lymphoid organ retention/egress and recruitment to decidua during pregnancy.

Tissue-Resident Lymphocytes Across Innate and Adaptive Lineages

Lymphocytes are an integral component of the immune system. Classically, all lymphocytes were thought to perpetually recirculate between secondary lymphoid organs and only traffic to non-lymphoid tissues upon activation. In recent years, a diverse family of non-circulating lymphocytes have been identified. These include innate lymphocytes, innate-like T cells and a subset of conventional T cells. Spanning the innate-adaptive spectrum, these tissue-resident lymphocytes carry out specialized functions and cross-talk with other immune cell types to maintain tissue integrity and homeostasis both at the steady state and during pathological conditions. In this review, we provide an overview of the heterogeneous tissue-resident lymphocyte populations, discuss their development, and highlight their functions both in the context of microbial infection and cancer.

NK Cell Education in Tumor Immune Surveillance: DNAM-1/KIR Receptor Ratios as Predictive Biomarkers for Solid Tumor Outcome

Natural killer cell (NKc)-based therapies offer promising outcomes in patients with tumors, but they could improve with appropriate selection of donors and optimization of methods to expand NKcs in vitro Education through licensing interactions of inhibitory killer cell immunoglobulin-like receptors (iKIR) and NKG2A with their cognate HLA class-I ligands optimizes NKc functional competence. This work has evaluated the role of licensing interactions in NKc differentiation and the survival of cancer patients. We have analyzed KIR and KIR-ligand genes, and the expression of activating (CD16 and DNAM-1/CD226) and inhibitory (NKG2A and iKIRs) receptors on peripheral blood NKcs in 621 healthy controls and 249 solid cancer patients (80 melanoma, 80 bladder, and 89 ovarian). Licensing interactions upregulated the expression of activating CD226, reduced that of iKIR receptors, and shifted the CD226/iKIR receptor ratio on NKc membranes to activating receptors. A high tumor burden decreased CD226 expression, reduced the ratio of CD226/iKIR, and negatively affected patient survival. The progression-free survival (38.1 vs. 67.0 months, P < 0.002) and overall survival (56.3 vs. 99.6 months, P < 0.00001) were significantly shorter in patients with lower expression of CD226 on NKcs. Hence, transformed cells can downmodulate these licensing-driven receptor rearrangements as a specific mechanism to escape NKc immune surveillance. Our results suggest the importance of the CD226/iKIR receptor ratio of NKcs induced by licensing interactions as critical determinants for solid cancer immune surveillance, and may provide predictive biomarkers for patient survival that may also improve the selection of donors for NKc immunotherapy.

Nanomaterials for modulating innate immune cells in cancer immunotherapy

Cancer immunotherapy has been intensively investigated in both preclinical and clinical studies. Whereas chemotherapies use cytotoxic drugs to kill tumor cells, cancer immunotherapy is based on the ability of the immune system to fight cancer. Tumors are intimately associated with the immune system: they can suppress the immune response and/or control immune cells to support tumor growth. Immunotherapy has yielded promising results in clinical practice, but some patients show limited responses. This may reflect the complexities of the relationship between a tumor and the immune system. In an effort to improve the current immunotherapies, researchers have exploited nanomaterials in creating new strategies to cure tumors via modulation of the immune system in tumor tissues. Although extensive studies have examined the use of immune checkpoint-based immunotherapy, rather less work has focused on manipulating the innate immune cells. This review examines the recent approaches and challenges in the use of nanomaterials to modulate innate immune cells.

Natural Killer Cells: Development, Maturation, and Clinical Utilization

Natural killer (NK) cells are the predominant innate lymphocyte subsets that mediate anti-tumor and anti-viral responses, and therefore possess promising clinical utilization. NK cells do not express polymorphic clonotypic receptors and utilize inhibitory receptors (killer immunoglobulin-like receptor and Ly49) to develop, mature, and recognize “self” from “non-self.” The essential roles of common gamma cytokines such as interleukin (IL)-2, IL-7, and IL-15 in the commitment and development of NK cells are well established. However, the critical functions of pro-inflammatory cytokines IL-12, IL-18, IL-27, and IL-35 in the transcriptional-priming of NK cells are only starting to emerge. Recent studies have highlighted multiple shared characteristics between NK cells the adaptive immune lymphocytes. NK cells utilize unique signaling pathways that offer exclusive ways to genetically manipulate to improve their effector functions. Here, we summarize the recent advances made in the understanding of how NK cells develop, mature, and their potential translational use in the clinic.

Cord blood-derived cytokine-induced killer cells combined with blinatumomab as a therapeutic strategy for CD19+ tumors

BACKGROUND

Cytokine-induced killer cells (CIKs) are an advanced therapeutic medicinal product (ATMP) that has shown therapeutic activity in clinical trials but needs optimization. We developed a novel strategy using CIKs from banked cryopreserved cord blood units (CBUs) combined with bispecific antibody (BsAb) blinatumomab to treat CD19⁺ malignancies.

METHODS

CB-CIKs were expanded in vitro and fully characterized in comparison with peripheral blood (PB)-derived CIKs.

RESULTS

CB-CIKs, like PB-CIKs, were mostly CD3⁺ T cells with mean 45% CD3⁺CD56⁺ and expressing mostly TCR(T cell receptor)αβ with a TH1 phenotype. CB-CIK cultures had, however, a larger proportion of CD4⁺ cells, mostly CD56^-, as well as a greater proportion of naïve CCR7⁺CD45RA⁺ and a lower percentage of effector memory cells, compared with PB-CIKs. CB-CIKs were very similar to PB-CIKs in their expression of a large panel of co-stimulatory and inhibitory/exhaustion markers, except for higher CD28 expression among CD8⁺ cells. Like PB-CIKs, CB-CIKs were highly cytotoxic in vitro against natural killer (NK) cell targets and efficiently lysed CD19⁺ tumor cells in the presence of blinatumomab, with 30-60% lysis of target cells at very low effector:target ratios. Finally, both CB-CIKs and PB-CIKs, combined with blinatumomab, showed significant therapeutic activity in an aggressive PDX Ph⁺ CD19⁺ acute lymphoblastic leukemia model in NOD-SCID mice, without sign of toxicity or graft-versus-host disease. The improved expansion protocol was finally validated in good manufacturing practice conditions, showing reproducible expansion of CIKs from cryopreserved cord blood units with a median of 28.8 × 10⁶ CIK/kg.

DISCUSSION

We conclude that CB-CIKs, combined with bispecific T-cell-engaging antibodies, offer a novel, effective treatment strategy for leukemia.

NK cells shape pancreatic and oral tumor microenvironments; role in inhibition of tumor growth and metastasis

We have recently shown that natural killer (NK) cells select and differentiate cancer stem cells (CSCs)/undifferentiated tumors via secreted and membrane bound IFN-gamma (IFN-γ) and TNF-alpha (TNF-α), preventing tumor growth and inducing remodeling of the tumor microenvironment. Since many conventional therapeutic strategies, including chemotherapy and radiotherapy remain fairly unsuccessful in treating CSCs/poorly differentiated tumors, there has been an increasing interest in NK cell-targeted immunotherapy for the treatment of aggressive tumors. In our recent studies, we used humanized-BLT (hu-BLT) mouse model with transplanted human bone marrow, liver and thymus to demonstrate the efficacy of adoptive transfer of ex vivo expanded, super-charged NK cells in selection and differentiation of stem-like tumors within the context of a fully reconstituted human immune system. Furthermore, we have demonstrated that CSCs differentiated with split-anergized NK cells prior to implantation in hu-BLT mice were not able to grow or metastasize. However, when NK cell-mediated tumor differentiation was blocked by the addition of antibodies to IFN-γ and TNF-α, tumors grew and metastasized. In this review, we present current advances in NK cell expansion and therapeutic delivery, and discuss the utility of allogeneic super-charged NK cells in treatment of cancer patients. In addition, NK suppression occurs not only at the stage of overt cancer, but also at the pre-neoplastic stage. Therefore, due to the indispensable role of NK cells in targeting CSCs/undifferentiated tumors and their role in differentiation of the tumors, NK cells should be placed high in the armamentarium of tumor immunotherapy.

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.