Emerging natural killer cell immunotherapies: large-scale ex vivo production of highly potent anticancer effectors

Precision Enhancement of CAR-NK Cells through Non-Viral Engineering and Highly Multiplexed Base Editing

Natural killer (NK) cells' unique ability to kill transformed cells expressing stress ligands or lacking major histocompatibility complexes (MHC) has prompted their development for immunotherapy. However, NK cells have demonstrated only moderate responses against cancer in clinical trials and likely require advanced genome engineering to reach their full potential as a cancer therapeutic. Multiplex genome editing with CRISPR/Cas9 base editors (BE) has been used to enhance T cell function and has already entered clinical trials but has not been reported in human NK cells. Here, we report the first application of BE in primary NK cells to achieve both loss-of-function and gain-of-function mutations. We observed highly efficient single and multiplex base editing, resulting in significantly enhanced NK cell function. Next, we combined multiplex BE with non-viral TcBuster transposon-based integration to generate IL-15 armored CD19 CAR-NK cells with significantly improved functionality in a highly suppressive model of Burkitt's lymphoma both in vitro and in vivo. The use of concomitant non-viral transposon engineering with multiplex base editing thus represents a highly versatile and efficient platform to generate CAR-NK products for cell-based immunotherapy and affords the flexibility to tailor multiple gene edits to maximize the effectiveness of the therapy for the cancer type being treated.

Cytokines and signaling pathways involved in differentiation potential of hematopoietic stem cells towards natural killer cells

NK cells are innate immune cells derived from common lymphoid progenitor and are developed primarily in the bone marrow. These cells respond to stress signals, inflammatory cytokines, and cancerous cells through the secretion of active immune mediators. Previous studies revealed that NK cells can be used as an essential cell in the defense against cancers. According to the literature, a set of cytokines and factors play a crucial role during differentiation of NK cells. In other words, developmental events of NK cells are regulated through multiple critical cytokines, including interleukins (ILs), kit ligand, fms-like tyrosine kinase three ligand, transforming growth factor-β, and typical γ chain family of cytokines. Among previously investigated ILs, IL-2, IL-3, IL-7, and IL-15 are the most important. In addition to ILs, transcription factors and MicroRNAs are involved in NK cell development. In this review study, after presenting a brief description of developmental stages and production of the NK cells, the factors and signaling pathways involved in differentiation of NK cells were discussed.

Landscape and Dynamics of the Transcriptional Regulatory Network During Natural Killer Cell Differentiation

Natural killer (NK) cells are essential in controlling cancer and infection. However, little is known about the dynamics of the transcriptional regulatory machinery during NK cell differentiation. In this study, we applied the assay of transposase accessible chromatin with sequencing (ATAC-seq) technique in a home-developed in vitro NK cell differentiation system. Analysis of ATAC-seq data illustrated two distinct transcription factor (TF) clusters that dynamically regulate NK cell differentiation. Moreover, two TFs from the second cluster, FOS-like 2 (FOSL2) and early growth response 2 (EGR2), were identified as novel essential TFs that control NK cell maturation and function. Knocking down either of these two TFs significantly impacted NK cell differentiation. Finally, we constructed a genome-wide transcriptional regulatory network that provides a better understanding of the regulatory dynamics during NK cell differentiation.

Current progress in cancer immunotherapy based on natural killer cells

One of the most common diseases in the present era is cancer. The common treatment methods used to control cancer include surgery, chemotherapy, and radiotherapy. Despite progress in the treatment of cancers, there still is no definite therapeutic approach. Among the currently proposed strategies, immunotherapy is a new approach that can provide better outcomes compared with existing therapies. Employing natural killer (NK) cells is one of the means of immunotherapy. As innate lymphocytes, NK cells are capable of rapidly responding to cancer cells without being sensitized or restricted to the cognate antigen in advance, as compared to T cells that are tumor antigen-specific. Latest insights into the biology of NK cells have clarified the underlying molecular mechanisms of NK cell maturation and differentiation, as well as controlling their effector functions through the investigation of the ligands and receptors engaged in recognizing cancer cells by NK cells. Elucidating the fact that NK cells recognize cancer cells could similarly show the mechanism through which cancer cells possibly avoid NK cell-dependent immune surveillance. Additionally, the expectations for novel immunotherapies by targeting NK cells have increased through the latest clinical outcomes of T-cell-targeted cancer immunotherapy. For this emerging method, researchers are still attempting to develop protocols for conferring the best proliferation and expansion medium, activation pathways, utilization dosage, transferring methods, as well as reducing possible side effects in cancer therapy. This study reviews the NK cells, their proliferation and expansion methods, and their recent applications in cancer immunotherapy.

Cytokine-induced killer cell therapy as a promising adjunctive immunotherapy for multidrug-resistant pulmonary TB: a case report

In this report, we identified a multidrug-resistant tuberculosis (MDR-TB) patient who remained acid-fast bacilli culture positive despite aggressive WHO-directed therapy. Between July 2014 and February 2015, she received eight courses of cytokine-induced killer (CIK) cell-based adoptive cellular immunotherapy in combination to the second-line anti-TB treatment. This case achieved culture conversion, and experienced no relapse during 2-year follow-up under the treatment with CIK cell-based adoptive cellular immunotherapy. Our data indicate that CIK immunotherapy is a promising adjunctive therapeutic method for improving the efficacy combined with the second-line anti-TB regimens against MDR-TB. Randomized trials are warranted to confirm the efficacy and safety of adjunctive CIK therapy in patients infected with MDR-TB.

Emerging Cellular Therapies: T Cells and Beyond

Cellular therapies, including those based on T cells, are becoming approved options for clinicians treating a range of diseases. Cytotoxic T lymphocytes (CTLs) can be modified ex vivo to express receptors such as chimeric antigen receptors (CARs) or T cell receptors, allowing them to target tumour cells when infused back into patients with particular cancers. CTLs specific for viruses can be purified ex vivo and reinfused into patients transplanted with haematopoietic stem cells to help combat viral reactivation. Regulatory T cells (Tregs) can be expanded ex vivo for infusion into patients with autoimmunity or allergy, or into those at risk of rejecting transplanted cells or tissues, or suffering graft versus host disease. Effector and regulatory T cells can also be generated by infusion of patient-derived dendritic cells (DCs) conditioned in ways to elicit anti-tumour immunity (CTLs) or Tregs. All such therapies are resource-heavy (particularly in process regulation) and so must be initially targeted to patients that have limited treatment options, but also where they have a chance of being effective.

Tuning Natural Killer Cell Anti-multiple Myeloma Reactivity by Targeting Inhibitory Signaling via KIR and NKG2A

Natural killer (NK) cells are attractive candidates for allogeneic cell-based immunotherapy due to their potent antitumor effector function and good safety profile. NK cells express killer immunoglobulin-like receptors (KIRs) and the NKG2A receptor important for NK cells education as well as providing inhibitory signals upon encountering HLA-expressing target cells. Multiple myeloma (MM) is an example of a tumor expressing relatively high levels of HLA molecules. In this review, we discuss the functional relevance of inhibitory KIRs and NKG2A for NK cells anti-MM response and strategies to lower these inhibitory signaling to enhance clinical efficacy of allogeneic NK cells in MM.

A Two-Phase Expansion Protocol Combining Interleukin (IL)-15 and IL-21 Improves Natural Killer Cell Proliferation and Cytotoxicity against Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue malignancy in children. Despite intensive research in recent decades the prognosis for patients with metastatic or relapsed diseases has hardly improved. New therapeutic concepts in anti-tumor therapy aim to modulate the patient’s immune system to increase its aggressiveness or targeted effects toward tumor cells. Besides surgery, radiotherapy and chemotherapy, immune activation by direct application of cytokines, antibodies or adoptive cell therapy are promising approaches. In the last years, adoptive transfer of natural killer (NK) cells came into the focus of translational medicine, because of their high cytotoxic potential against transformed malignant cells. A main challenge of NK cell therapy is that it requires a high amount of functional NK cells. Therefore, ex vivo NK cell expansion protocols are currently being developed. Many culturing strategies are based on the addition of feeder or accessory cells, which need to be removed prior to the clinical application of the final NK cell product. In this study, we addressed feeder cell-free expansion methods using common γ-chain cytokines, especially IL-15 and IL-21. Our results demonstrated high potential of IL-15 for NK cell expansion, while IL-21 triggered NK cell maturation and functionality. Hence, we established a two-phase expansion protocol with IL-15 to induce an early NK cell expansion, followed by short exposure to IL-21 that boosted the cytotoxic activity of NK cells against RMS cells. Further functional analyses revealed enhanced degranulation and secretion of pro-inflammatory cytokines such as interferon-γ and tumor necrosis factor-α. In a proof of concept in vivo study, we also observed a therapeutic effect of adoptively transferred IL-15 expanded and IL-21 boosted NK cells in combination with image guided high precision radiation therapy using a luciferase-transduced RMS xenograft model. In summary, this two-phased feeder cell-free ex vivo culturing protocol combined efficient expansion and high cytolytic functionality of NK cells for treatment of radiation-resistant RMS.

An overview of the potential strategies for NK cell-based immunotherapy for acute myeloid leukemia

Patients with acute myeloid leukemia (AML) have relatively low survival rates compared to patients with other pediatric cancers. Relapse is frequent with conventional treatment and is a major cause of morbidity and mortality. Natural killer (NK) cells offer an alternative approach to chemotherapy that combats relapse by substantially eradicating AML blasts. New methods for enhancing NK cell activation and expression of the activating ligand on target malignant cells will increase the likelihood of success with this approach. We review these latest discoveries in NK cell-based therapy for AML and delineate recent advances in sensitizing AML cells to NK cell-mediated immunosurveillance.

NK-92: an 'off-the-shelf therapeutic' for adoptive natural killer cell-based cancer immunotherapy

Natural killer (NK) cells are increasingly considered as immunotherapeutic agents in particular in the fight against cancers. NK cell therapies are potentially broadly applicable and, different from their T cell counterparts, do not cause graft-versus-host disease. Efficacy and clinical in vitro or in vivo expansion of primary NK cells will however always remain variable due to individual differences of donors or patients. Long-term storage of clinical NK cell lots to allow repeated clinical applications remains an additional challenge. In contrast, the established and well-characterized cell line NK-92 can be easily and reproducibly expanded from a good manufacturing practice (GMP)-compliant cryopreserved master cell bank. Moreover, no cost-intensive cell purification methods are required. To date, NK-92 has been intensively studied. The cells displayed superior cytotoxicity against a number of tumor types tested, which was confirmed in preclinical mouse studies. Subsequent clinical testing demonstrated safety of NK-92 infusions even at high doses. Despite the phase I nature of the trials conducted so far, some efficacy was noted, particularly against lung tumors. Furthermore, to overcome tumor resistance and for specific targeting, NK-92 has been engineered to express a number of different chimeric antigen receptors (CARs), including targeting, for example, CD19 or CD20 (anti-B cell malignancies), CD38 (anti-myeloma) or human epidermal growth factor receptor 2 (HER2; ErbB2; anti-epithelial cancers). The concept of an NK cell line as an allogeneic cell therapeutic produced 'off-the-shelf' on demand holds great promise for the development of effective treatments.

Natural Killer Cells for Therapy of Leukemia

Clinical application of natural killer (NK) cells against leukemia is an area of intense investigation. In human leukocyte antigen-mismatched allogeneic hematopoietic stem cell transplantations (HSCT), alloreactive NK cells exert powerful anti-leukemic activity in preventing relapse in the absence of graft-versus-host disease, particularly in acute myeloid leukemia patients. Adoptive transfer of donor NK cells post-HSCT or in non-transplant scenarios may be superior to the currently widely used unmanipulated donor lymphocyte infusion. This concept could be further improved through transfusion of activated NK cells. Significant progress has been made in good manufacturing practice (GMP)-compliant large-scale production of stimulated effectors. However, inherent limitations remain. These include differing yields and compositions of the end-product due to donor variability and inefficient means for cryopreservation. Moreover, the impact of the various novel activation strategies on NK cell biology and in vivo behavior are barely understood. In contrast, reproduction of the third-party NK-92 drug from a cryostored GMP-compliant master cell bank is straightforward and efficient. Safety for the application of this highly cytotoxic cell line was demonstrated in first clinical trials. This novel 'off-the-shelf' product could become a treatment option for a broad patient population. For specific tumor targeting chimeric-antigen-receptor-engineered NK-92 cells have been designed.

The antileukemic potential of natural killer cells

The antileukemic potential of natural killer (NK) cells has over the years raised considerable interest and new immune-based treatment protocols characterized by the infusion of freshly isolated or ex vivo activated and expanded effectors have been designed. Several aspects still need to be addressed, including the optimal timing of NK infusion during the course of the disease, the best preparative regimen, the origin of NK cells and the possible need of ex vivo NK cell manipulation before the infusion. The aims of this review are to discuss the experimental and clinical data available on the role played by NK cells for leukemia patients and to revise the different good manufacturing practice protocols for ex vivo manipulation of these effector cells.

Selection and expansion of natural killer cells for NK cell-based immunotherapy

Natural killer (NK) cells have been used in several clinical trials as adaptive immunotherapy. The low numbers of these cells in peripheral blood mononuclear cells (PBMC) have resulted in various approaches to preferentially expand primary NK cells from PBMC. While some clinical trials have used the addition of interleukin 2 (IL-2) to co-stimulate the expansion of purified NK cells from allogeneic donors, recent studies have shown promising results in achieving in vitro expansion of NK cells to large numbers for adoptive immunotherapy. NK cell expansion requires multiple cell signals for survival, proliferation and activation. Thus, expansion strategies have been focused either to substitute these factors using autologous feeder cells or to use genetically modified allogeneic feeder cells. Recent developments in the clinical use of genetically modified NK cell lines with chimeric antigen receptors, the development of expansion protocols for the clinical use of NK cell from human embryonic stem cells and induced pluripotent stem cells are challenging improvements for NK cell-based immunotherapy. Transfer of several of these protocols to clinical-grade production of NK cells necessitates adaptation of good manufacturing practice conditions, and the development of freezing conditions to establish NK cell stocks will require some effort and, however, should enhance the therapeutic options of NK cells in clinical medicine.

"Adherent" versus Other Isolation Strategies for Expanding Purified, Potent, and Activated Human NK Cells for Cancer Immunotherapy

Natural killer (NK) cells have long been hypothesized to play a central role in the development of new immunotherapies to combat a variety of cancers due to their intrinsic ability to lyse tumor cells. For the past several decades, various isolation and expansion methods have been developed to harness the full antitumor potential of NK cells. These protocols have varied greatly between laboratories and several have been optimized for large-scale clinical use despite associated complexity and high cost. Here, we present a simple method of "adherent" enrichment and expansion of NK cells, developed using both healthy donors' and cancer patients' peripheral blood mononuclear cells (PBMCs), and compare its effectiveness with various published protocols to highlight the pros and cons of their use in adoptive cell therapy. By building upon the concepts and data presented, future research can be adapted to provide simple, cost-effective, reproducible, and translatable procedures for personalized treatment with NK cells.

Immunophenotypic and functional characterization of ex vivo expanded natural killer cells for clinical use in acute lymphoblastic leukemia patients

The management of acute lymphoblastic leukemia (ALL) patients has witnessed profound changes in recent years. Nonetheless, most patients tend to relapse, underlining the need for new therapeutic approaches. The anti-leukemic potential of natural killer (NK) cells has over the years raised considerable interest. In this study, we developed an efficient method for the expansion and activation of NK cells isolated from healthy donors and ALL patients for clinical use. NK cell products were derived from peripheral blood mononuclear cells of 35 healthy donors and 4 B-lineage ALL by immunomagnetic CD3 T cell depletion followed by CD56 cell enrichment. Isolated NK cells were expanded and stimulated in serum-free medium supplemented with irradiated autologous feeder cells and autologous plasma in the presence of clinical grade interleukin (IL)-2 and IL-15 for 14 days. Healthy donor NK cells expanded on average 34.9 ± 10.4 fold and were represented, after expansion, by a highly pure population of CD3(-)CD56(+) cells showing a significant upregulation of natural cytotoxicity receptors, activating receptors and maturation markers. These expanded effectors showed cytolytic activity against K562 cells and, most importantly, against primary adult B-lineage ALL blasts. NK cells could be efficiently isolated and expanded-on average 39.5 ± 20.3 fold-also from primary B-lineage ALL samples of patients in complete remission. The expanded NK cells from these patients showed a significantly increased expression of the NKG2D- and DNAM1-activating receptors and were cytotoxic against K562 cells. These data provide the basis for developing new immunotherapeutic strategies for the management of ALL patients.

A good manufacturing practice method to ex vivo expand natural killer cells for clinical use

BACKGROUND

Great interest has been raised recently by the design of new adoptive immunotherapeutic strategies based on the in vivo infusion of ex vivo-expanded and activated natural killer (NK) cells. The development of good manufacturing practice (GMP) methods for the efficient production of fully functional NK cells is mandatory for clinical application.

MATERIALS AND METHODS

Peripheral blood mononuclear cells were obtained by leukapheresis and processed in the GMP facility. For NK-cell enrichment, a two-step immunomagnetic procedure consisting of CD3(+) T-cell depletion followed by CD56(+) cell positive selection was used. Isolated NK cells were suspended in serum-free medium containing autologous plasma, interleukin (IL)-2 and IL-15 in the presence of irradiated autologous feeder cells and cultured for 14 days at 37 °C. IL-2 and IL-15 were also added during the last 24 hours of culture. Expanded cells underwent full quality control testing for cytogenetic characteristics, viability, sterility, phenotype and endotoxin status; functional tests, such as degranulation assays and cytotoxicity, were performed on expanded NK cells before cryopreservation and after thawing.

RESULTS

NK-cell populations expanded on average 15.7±4.7 fold by day 14, with a viability of 96% ±0.5. At the end of the incubation period, 97% ±1.1 of the expanded population was CD56(+) NK cells; these effector cells showed significant up-regulation of the activating receptors NKG2D and DNAM-1. Functional tests demonstrated that expanded NK cells are fully functional with no difference whether tested before cryopreservation or after thawing.

DISCUSSION

These data provide the basis for developing new NK-cell-based immunotherapeutic strategies for the treatment of patients with cancer.

Ex vivo generation of highly purified and activated natural killer cells from human peripheral blood

Adoptive immunotherapy using natural killer (NK) cells has been a promising treatment for intractable malignancies; however, there remain a number of difficulties with respect to the shortage and limited anticancer potency of the effector cells. We here established a simple feeder-free method to generate purified (>90%) and highly activated NK cells from human peripheral blood-derived mononuclear cells (PBMCs). Among the several parameters, we found that CD3 depletion, high-dose interleukin (IL)-2, and use of a specific culture medium were sufficient to obtain highly purified, expanded (∼200-fold) and activated CD3(-)/CD56(+) NK cells from PBMCs, which we designated zenithal-NK (Z-NK) cells. Almost all Z-NK cells expressed the lymphocyte-activated marker CD69 and showed dramatically high expression of activation receptors (i.e., NKG2D), interferon-γ, perforin, and granzyme B. Importantly, only 2 hours of reaction at an effector/target ratio of 1:1 was sufficient to kill almost all K562 cells, and the antitumor activity was also replicated in tumor-bearing mice in vivo. Cytolysis was specific for various tumor cells, but not for normal cells, irrespective of MHC class I expression. These findings strongly indicate that Z-NK cells are purified, expanded, and near-fully activated human NK cells and warrant further investigation in a clinical setting.

The bispecific immunoligand ULBP2-aCEA redirects natural killer cells to tumor cells and reveals potent anti-tumor activity against colon carcinoma

NKG2D, an activating receptor expressed on NK cells and T cells, is critically involved in tumor immunosurveillance. In this study, we explored the potential therapeutic utility of the NKG2D ligand ULBP2 for the treatment of colon carcinoma. To this end we designed a fusion protein consisting of human ULBP2 and an antibody-derived single chain targeting the tumor carcinoembryonic antigen (CEA). The bispecific recombinant fusion protein re-directed NK cells towards malignant cells by binding to both, tumor cells and NK cells, and triggered NK cell-mediated target cell killing in vitro. Moreover, tumor growth was significantly delayed in a syngeneic colon carcinoma mouse model in response to immunoligand treatment. The anti-tumor activity could be attributed to the stimulation of immune cells with an elevated expression of the activation marker CD69 on NK, T and NKT cells and the infiltration of CD45+ immune cells into the solid tumor. In summary, it was demonstrated that immunoligands provide specific tumor targeting by NK cells and exert anti-tumor activity in vitro and in vivo. This technology represents a novel immunotherapeutic strategy for solid tumors with the potential to be further developed for clinical applications.

Human natural killer cells acting as phagocytes against Candida albicans and mounting an inflammatory response that modulates neutrophil antifungal activity

BACKGROUND

Natural killer (NK) cells are innate lymphocytes with potent cytotoxic activity. Whereas activity of NK cells has been demonstrated against the fungal pathogens Aspergillus fumigatus and Cryptococcus neoformans, little was known about their interaction with Candida albicans.

METHODS

Primary human NK cells were isolated from buffy coats, primed with a cytokine cocktail and used for confrontation assays with C. albicans. Interaction was monitored and quantified using live cell imaging, confocal microscopy, flow cytometry, and enzyme-linked immunosorbent assay.

RESULTS

Human NK cells actively recognized C. albicans, resulting in degranulation and secretion of granulocyte-macrophage colony-stimulating factor, interferon γ, and tumor necrosis factor α . Uniquely, activation of NK cells was triggered by actin-dependent phagocytosis. Antifungal activity of NK cells against C. albicans could be detected and mainly attributed to secreted perforin. However, NK cells were unable to inhibit filamentation of C. albicans. Human polymorphonuclear neutrophils (PMNs) counteracted the proinflammatory reaction of NK cells by preventing direct contact between NK cells and the fungal pathogen. Activation of PMNs was enhanced in the presence of NK cells, resulting in increased fungicidal activity.

CONCLUSIONS

Our results show a unique pattern of NK cell interaction with C. albicans, which involves direct proinflammatory activation and modulation of PMN activity. For the first time, phagocytosis of a pathogen is shown to contribute to NK cell activation.

Interferon-Beta combined with interleukin-2 restores human natural cytotoxicity impaired in vitro by ionizing radiations

It is well known that ionizing radiations induce a marked downregulation of antigen-dependent and natural immunity for a prolonged period of time. This is due, at least in part, to radiation-induced apoptosis of different lymphocyte subpopulations, including natural killer (NK) cells. Aim of this study was to investigate the capability of Beta Interferon (β-IFN) and Interleukin-2 (IL2), alone or in combination, to restore the functional activity of the natural immune system. Mononuclear cells (MNCs) obtained from intact or in vitro irradiated human peripheral blood were treated in vitro with β-IFN immediately before or at the end of the 4-day treatment with IL2. Time-course analysis was performed on the NK activity, the total number and the apoptotic fraction of CD16+ and CD56+ cells, the 2 main NK effector cell subpopulations. The results indicate that radiation-induced impairment of natural cytotoxicity of MNC could be successfully antagonized by the β-IFN+IL2 combination, mainly when exposure to β-IFN preceded IL2 treatment. This radioprotective effect is paralleled by lower levels of radiation-induced apoptosis and increased expression of the antiapoptotic Bcl-2 protein. Since natural immunity can play a significant role in antitumor host's resistance, these results could provide the rational basis for a cytokine-based pharmacological strategy able to restore immune responsiveness and to afford possible therapeutic benefits in cancer patients undergoing radiotherapy.

Inhibition of intracellular antiviral defense mechanisms augments lentiviral transduction of human natural killer cells: implications for gene therapy

Adoptive immunotherapy with genetically modified natural killer (NK) cells is a promising approach for cancer treatment. Yet, optimization of highly efficient and clinically applicable gene transfer protocols for NK cells still presents a challenge. In this study, we aimed at identifying conditions under which optimum lentiviral gene transfer to NK cells can be achieved. Our results demonstrate that stimulation of NK cells with interleukin (IL)-2 and IL-21 supports efficient transduction using a VSV-G pseudotyped lentiviral vector. Moreover, we have identified that inhibition of innate immune receptor signaling greatly enhances transduction efficiency. We were able to boost the efficiency of lentiviral genetic modification on average 3.8-fold using BX795, an inhibitor of the TBK1/IKKɛ complex acting downstream of RIG-I, MDA-5, and TLR3. We have also observed that the use of BX795 enhances lentiviral transduction efficiency in a number of human and mouse cell lines, indicating a broadly applicable, practical, and safe approach that has the potential of being applicable to various gene therapy protocols.

Generation of natural killer cells from hematopoietic stem cells in vitro for immunotherapy

Natural killer (NK) cells are part of the innate immune system and are an alluring option for immunotherapy due to their ability to kill infected cells or cancer cells without prior sensitization. Throughout the past 20 years, different groups have been able to reproduce NK cell development in vitro, and NK cell ontogeny studies have provided the basis for the establishment of protocols to produce NK cells in vitro for immunotherapy. Here, we briefly discuss NK cell development and NK cell immunotherapy approaches. We review the factors needed for NK cell differentiation in vitro, which stem cell sources have been used, published protocols, challenges and future directions for Good Manufacturing Practice protocols.

Phase 1 Clinical Trial of Trametes versicolor in Women with Breast Cancer

Introduction. Orally administered preparations from the Trametes versicolor (Tv) mushroom have been hypothesized to improve immune response in women with breast cancer after standard chemotherapy and radiotherapy. Methods. A phase I, two-center, dose escalation study was done to determine the maximum tolerated dose of a Tv preparation when taken daily in divided doses for 6 weeks after recent completion of radiotherapy. Eleven participants were recruited and nine women completed the study. Each cohort was comprised of three participants given one of three doses of Tv (3, 6, or 9 grams). Immune data was collected pre- and postradiation, at 3 on-treatment time points and after a 3-week washout. Results. Nine adverse events were reported (7 mild, 1 moderate, and 1 severe), suggesting that Tv was well tolerated. Immunological results indicated trends in (1) increased lymphocyte counts at 6 and 9 grams/day; (2) increased natural killer cell functional activity at 6 grams/day; (3) dose-related increases in CD8(+) T cells and CD19(+) B cells , but not CD4(+) T cells or CD16(+)56(+) NK cells. Conclusion. These findings show that up to 9 grams/day of a Tv preparation is safe and tolerable in women with breast cancer in the postprimary treatment setting. This Tv preparation may improve immune status in immunocompromised breast cancer patients following standard primary oncologic treatment.

Cell therapy: promise fulfilled?

Cellular immunotherapy has been widely accepted as a new powerful modality of cancer treatment. The last 2 decades have seen impressive results in its application against haemato-oncologic malignancies, melanomas and prostate carcinoma. Cellular immunotherapy has since found applicability beyond cancer into autoimmunity and continues to expand in its clinical applicability. The discovery that stem cells have the ability to differentiate into more mature cell types, like neurones and myocardium, has focused research on using exogenous cells to repair damaged tissues. This led to numerous clinical trials using stem cells in myocardial infarction, cardiomyopathy and spinal cord damage. Results have ranged from modest to significant clinical outcomes with continuing debate on the exact process of regeneration achieved. The intertwining between cell therapy and transfusion medicine now includes research on progenitor cells for the production of mature red cells. It is also clear that cell therapy has enabled an improved understanding of the pathogenesis and clinical course of many diseases, while perhaps its role in regenerative medicine is most enticing. However, the critical role of manufacturing in terms of cost, complexity, reproducibility, and regulatory matters remains a central issue in the consideration of whether cell therapy has met all of its promise.

Interleukin-15 supports generation of highly potent clinical-grade natural killer cells in long-term cultures for targeting hematological malignancies

OBJECTIVE

Interleukin (IL)-15 is a promising novel cytokine for natural killer (NK) cell activation and survival. We studied the effects of IL-15 compared to IL-2 on NK cells in long-term cultures for clinical translation.

MATERIALS AND METHODS

CD56(+)CD3(-) NK cells were expanded with IL-2 or IL-15 for 2 to 4 weeks within lymphokine-activated killer (LAK) cell cultures (LAK-NK) in serum-enriched AIM V or CellGro Stem Cell Growth Medium (SCGM). Cell growth, viability, and NK cell content were monitored and cytotoxicity assessed in a flow cytometric cytotoxicity assay.

RESULTS

IL-15 (100-1000 U/mL) could replace IL-2 (1000 U/mL) in AIM V cultures to achieve efficient LAK cell expansion. However, IL-15-stimulated LAK cells exceeded cytotoxicity of IL-2-stimulated LAK cells against K562, notably at later culture points. In the powerful CellGro SCGM, LAK cells expanded over 28 days an average of 905-fold ± 320-fold standard error of the mean (SEM) for IL-2 (500 U/mL) and 484-fold ± 98-fold SEM for IL-15 (500 U/mL), and NK cells within such LAK cultures expanded an average of 2320-fold ± 975-fold SEM for IL-2 and 1084-fold ± 309-fold SEM for IL-15. Importantly, such IL-15-activated LAK-NK cells retained enhanced cytotoxicity at later culture points against K562 as well. IL-15-stimulated effectors were also highly cytotoxic against hematological targets MOLT-4 and KU812 and nontoxic against autologous nonmalignant cells. Interestingly, IL-15-LAK-NK cells showed overall significant upregulation of the main activating and inhibitory NK cell receptors after long-term cytokine stimulation.

CONCLUSIONS

Our results demonstrate the potential for IL-15 to support large-scale expansion of clinical-grade LAK-NK effectors, which could retain enhanced longer-term potency and preserve activation receptors in therapy of hematological malignancies. Protocols are readily clinically translatable.

Natural killer cell-based therapies

Allotransplantation of natural killer (NK) cells has been shown to be a key factor in the control and cure of at least some hematologic diseases, such as acute myeloid leukemia or pediatric acute lymphocytic leukemia. These results support the idea that stimulation of NK cells could be an important therapeutic tool in many diseases, and several such approaches are now in clinical trials, sometimes with conflicting results. In parallel, recent advances in the understanding of the molecular mechanisms governing NK-cell maturation and activity show that NK-cell effector functions are controlled by complex mechanisms that must be taken into account for optimal design of therapeutic protocols. We review here innovative protocols based on allotransplantation, use of NK-cell therapies, and use of newly available drug candidates targeting NK-cell receptors, in the light of fundamental new data on NK-cell biology.