Superior Expansion and Cytotoxicity of Human Primary NK and CAR-NK Cells from Various Sources via Enriched Metabolic Pathways

Exploring Glypican-3 targeted CAR-NK treatment and potential therapy resistance in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most prevalent form of primary liver cancer and the second leading cause of cancer-related mortality globally. Despite advancements in current HCC treatment, it remains a malignancy with poor prognosis. Therefore, developing novel treatment options for patients with HCC is urgently needed. Chimeric antigen receptor (CAR)-modified natural killer (NK) cells have demonstrated potent anti-tumor effects, making them as a promising immunotherapy strategy for cancer treatment. Glypican-3 (GPC3), a cell surface oncofetal glycoprotein, is highly expressed in most HCC tissues, but not in normal tissues, and functions as a key driver of carcinogenesis. Given its high expression level on the cell surface, GPC3 is considered as an attractive immunotherapy target for HCC. In this study, two GPC3-specific CAR-NK cells, NK92MI/HN3 and NK92MI/HS20, were established using NK92MI cells, a modified IL-2-independent NK cell line. These cell lines were engineered with third generation GPC3-specific CARs, and their activities were subsequently evaluated in the treatment of HCC. We found that NK92MI/HN3 cells, rather than NK92MI/HS20 cells, exhibited a significant cytotoxicity effect against GPC3+ HepG2 cells in vitro and efficiently suppressed tumor growth in a xenograft model using NSG mice. In addition, irradiated NK92MI/HN3 cells displayed similar anti-tumor efficacy to unirradiated NK92MI/HN3 cells. Furthermore, we observed that NK92MI/HN3 cells showed higher killing activity against the GPC3 isoform 2 overexpression cell line (Sk-Hep1-v2) than those with GPC3 isoform 1 overexpression cell line (Sk-Hep1-v1). This suggest that the presence of different GPC3 isoforms in HCC may impact the cytotoxicity activity of NK92MI/HN3 cells and potentially influence therapeutic outcomes. These findings highlight the effective anti-HCC effects of NK92MI/HN3 cells and reveal the role of GPC3 isoforms in influencing therapy outcomes, suggesting that isoform analysis should be considered to optimize CAR-NK therapies to improve patient outcomes.

Emerging combined CAR-NK cell therapies in cancer treatment: Finding a dancing partner

In recent decades, immunotherapy with chimeric antigen receptors (CARs) has revolutionized cancer treatment and given hope where other cancer therapies have failed. CAR-natural killer (NK) cells are NK cells that have been engineered ex vivo with a CAR on the cell membrane with high specificity for specific target antigens of tumor cells. The impressive results of several studies suggest that CAR-NK cell therapy has significant potential and successful performance in cancer treatment. Despite its effectiveness, CAR-NK cell therapy can have significant challenges when it comes to treating cancer. These challenges include tumor heterogeneity, antigen escape, an immunosuppressive tumor microenvironment, limited tissue migration from blood, exhaustion of CAR-NK cells, and inhibition by immunosuppressive checkpoint molecule signaling, etc. In CAR-T cell therapy, the use of combined approaches has shown encouraging outcomes for tumor regression and improved cancer treatment compared to single therapies. Therefore, to overcome these significant challenges in CAR-NK cells, innovative combination therapies of CAR-NK cells with other conventional therapies (e.g., chemotherapy and radiotherapy) or other immunotherapies are needed to counteract the above challenges and thereby increase the activity of CAR-NK cells. This review comprehensively discusses various cancer-treatment approaches in combination with CAR-NK cell therapy in the hope of providing valuable insights that may improve cancer treatment in the near future.

The development and application of chimeric antigen receptor natural killer (CAR-NK) cells for cancer therapy: current state, challenges and emerging therapeutic advances

Immunotherapy has transformed the landscape of cancer treatment, with chimeric antigen receptor (CAR)-engineered T (CAR-T) cell therapy emerging as a front runner in addressing some hematological malignancies. Despite its considerable efficacy, the occurrence of severe adverse effects associated with CAR-T cell therapy has limited their scope and prompted the exploration of alternative therapeutic strategies. Natural killer (NK) cells, characterized by both their innate cytotoxicity and ability to lyse target cells without the constraint of peptide specificity conferred by a major histocompatibility complex (MHC), have similarly garnered attention as a viable immunotherapy. As such, another therapeutic approach has recently emerged that seeks to combine the continued success of CAR-T cell therapy with the flexibility of NK cells. Clinical trials involving CAR-engineered NK (CAR-NK) cell therapy have exhibited promising efficacy with fewer deleterious side effects. This review aims to provide a concise overview of the cellular and molecular basis of NK cell biology, facilitating a better understanding of advancements in CAR design and manufacturing. The focus is on current approaches and strategies employed in CAR-NK cell development, exploring at both preclinical and clinical settings. We will reflect upon the achievements, advantages, and challenges intrinsic to CAR-NK cell therapy. Anticipating the maturation of CAR-NK cell therapy technology, we foresee its encouraging prospects for a broader range of cancer patients and other conditions. It is our belief that this CAR-NK progress will bring us closer to making significant strides in the treatment of refractory and recurrent cancers, as well as other immune-mediated disorders.

Metabolic programs drive function of therapeutic NK cells in hypoxic tumor environments

Limited oxygen (hypoxia) in solid tumors poses a challenge to successful immunotherapy with natural killer (NK) cells. NK cells have impaired cytotoxicity when cultured in hypoxia (1% oxygen) but not physiologic (>5%) or atmospheric oxygen (20%). We found that changes to cytotoxicity were regulated at the transcriptional level and accompanied by metabolic dysregulation. Dosing with interleukin-15 (IL-15) enhanced NK cell cytotoxicity in hypoxia, but preactivation with feeder cells bearing IL-21 and 4-1BBL was even better. Preactivation resulted in less perturbed metabolism in hypoxia; greater resistance to oxidative stress; and no hypoxia-induced loss of transcription factors (T-bet and Eomes), activating receptors, adhesion molecules (CD2), and cytotoxic proteins (TRAIL and FasL). There remained a deficit in CD122/IL-2Rβ when exposed to hypoxia, which affected IL-15 signaling. However, tri-specific killer engager molecules that deliver IL-15 in the context of anti-CD16/FcγRIII were able to bypass this deficit, enhancing cytotoxicity of both fresh and preactivated NK cells in hypoxia.

Feeder cell training shapes the phenotype and function of in vitro expanded natural killer cells

Natural killer (NK) cells are candidates for adoptive cell therapy, and the protocols for their activation and expansion profoundly influence their function and fate. The complexity of NK cell origin and feeder cell cues impacts the heterogeneity of expanded NK (eNK) cells. To explore this, we compared the phenotype and function of peripheral blood-derived NK (PB-NK) and umbilical cord blood-derived NK (UCB-NK) cells activated by common feeder cell lines, including K562, PLH, and 221.AEH. After first encounter, most PB-NK cells showed degranulation independently of cytokines production. Meanwhile, most UCB-NK cells did both. We observed that each feeder cell line uniquely influenced the activation, expansion, and ultimate fate of PB eNK and UCB eNK cells, determining whether they became cytokine producers or killer cells. In addition, they also affected the functional performance of NK cell subsets after expansion, that is, expanded conventional NK (ecNK) and expanded FcRγ- NK (eg-NK) cells. Hence, the regulation of eNK cell function largely depends on the NK cell source and the chosen expansion system. These results underscore the significance of selecting feeder cells for NK cell expansion from various sources, notably for customized adoptive cell therapies to yield cytokine-producing or cytotoxic eNK cells.

Natural Killer Cell Dysfunction In Human Bladder Cancer Is Caused By Tissue-Specific Suppression of SLAMF6 Signaling

NK cells are innate lymphocytes critical for surveillance of viruses and tumors, however the mechanisms underlying NK cell dysfunction in cancer are incompletely understood. We assessed the effector function of NK cells from bladder cancer patients and found severe dysfunction in NK cells derived from tumors versus peripheral blood. While both peripheral and tumor-infiltrating NK cells exhibited conserved patterns of inhibitory receptor over-expression, this did not explain the observed defects in NK surveillance in bladder tumors. Rather, TME-specific TGF-β and metabolic perturbations such as hypoxia directly suppressed NK cell function. Specifically, an oxygen-dependent reduction in signaling through SLAMF6 was mechanistically responsible for poor NK cell function, as tumor-infiltrating NK cells cultured ex vivo under normoxic conditions exhibited complete restoration of function, while deletion of SLAMF6 abrogated NK cell cytolytic function even under normoxic conditions. Collectively, this work highlights the role of tissue-specific factors in dictating NK cell function, and implicates SLAMF6 signaling as a rational target for immuno-modulation to improve NK cell function in bladder cancer.

Interfering with KIR and NKG2A immune checkpoint axes to unleash NK cell immunotherapy

Due to their intrinsic ability to eliminate malignant cells, natural killer (NK) cells emerge as a promising immunotherapy for cancer. While clinical studies have affirmed the safety of NK cell infusions and combination therapies have demonstrated encouraging outcomes in hematological malignancies, the efficacy of NK cell immunotherapeutic interventions remains heterogeneous across patient cohorts. Moreover, the implementation of NK cell immunotherapy in solid tumors presents notable challenges. Interfering with key NK cell inhibitory signaling pathways by targeting inhibitory killer cell immunoglobulin-like receptors (KIRs) and CD94/NK group 2 member A (NKG2A), holds promise for unleashing the full potential of NK cell-based immunotherapy. In this review, we provide an overview of the current approaches for interfering with inhibitory KIR and NKG2A signaling, exploring a selection of the multitude of combination strategies available. We discuss the significance of maintaining the delicate balance between achieving optimal suppression of NK cell inhibition and ensuring effective activation of anti-tumor effector function, while preserving the favorable safety profiles. The consideration of strategies to modulate inhibitory signaling pathways associated with KIR and NKG2A presents promising avenues for enhancing the efficacy of NK cell immunotherapy.

Scalable process development of NK and CAR-NK expansion in a closed bioreactor

Production of large amounts of functional NK and CAR-NK cells represents one of the bottlenecks for NK-based immunotherapy. In this study, we developed a large-scale, reliable, and practicable NK and CAR-NK production using G-Rex 100M bioreactors, which depend on a gas-permeable membrane technology. This system holds large volumes of medium with enhanced oxygen delivery, creating conditions conducive to large-scale PBNK and CAR-NK expansions for cancer therapy. Both peripheral blood NK cells (PBNKs) and CAR-NKs expanded in these bioreactors retained similar immunophenotypes and exhibited comparable cytotoxicity towards hepatocellular carcinoma (HCC) cells akin to that of NK and CAR-NK cells expanded in G-Rex 6 well bioreactors. Importantly, cryopreservation minimally affected the cytotoxicity of NK cells expanded using the G-Rex 100M bioreactors, establishing a robust platform for scaled-up NK and CAR-NK cell production. This method is promising for the development of "off-the-shelf" NK cells, supporting the future clinical implementation of NK cell immunotherapy.

A Critical Role of Culture Medium Selection in Maximizing the Purity and Expansion of Natural Killer Cells

Natural killer (NK) cells hold promise in cancer treatment due to their ability to spontaneously lyse cancer cells. For clinical use, high quantities of pure, functional NK cells are necessary. Combining adherence-based isolation with specialized media showed the unreliability of the isolation method, but demonstrated the superiority of the NK MACS® medium, particularly in suboptimal conditions. Neither human pooled serum, fetal calf serum (FCS), human platelet lysate, nor chemically defined serum replacement could substitute human AB serum. Interleukin (IL-)2, IL-15, IL-21, and combined CD2/NKp46 stimulation were assessed. IL-21 and CD2/NKp46 stimulation increased cytotoxicity, but reduced NK cell proliferation. IL-15 stimulation alone achieved the highest proliferation, but the more affordable IL-2 performed similarly. The RosetteSep™ human NK cell enrichment kit was effective for isolation, but the presence of peripheral blood mononuclear cells (PBMCs) in the culture enhanced NK cell proliferation, despite similar expression levels of CD16, NKp46, NKG2D, and ICAM-1. In line with this, purified NK cells cultured in NK MACS® medium with human AB serum and IL-2 demonstrated high cytotoxicity against primary glioblastoma stem cells.

S309-CAR-NK cells bind the Omicron variants in vitro and reduce SARS-CoV-2 viral loads in humanized ACE2-NSG mice

Recent progress on chimeric antigen receptor (CAR)-NK cells has shown promising results in treating CD19-positive lymphoid tumors with minimal toxicities [including graft versus host disease (GvHD) and cytokine release syndrome (CRS) in clinical trials. Nevertheless, the use of CAR-NK cells in combating viral infections has not yet been fully explored. Previous studies have shown that CAR-NK cells expressing S309 single-chain fragment variable (scFv), hereinafter S309-CAR-NK cells, can bind to SARS-CoV-2 wildtype pseudotyped virus (PV) and effectively kill cells expressing wild-type spike protein in vitro. In this study, we further demonstrate that the S309-CAR-NK cells can bind to different SARS-CoV-2 variants, including the B.1.617.2 (Delta), B.1.621 (Mu), and B.1.1.529 (Omicron) variants in vitro. We also show that S309-CAR-NK cells reduce virus loads in the NOD/SCID gamma (NSG) mice expressing the human angiotensin-converting enzyme 2 (hACE2) receptor challenged with SARS-CoV-2 wild-type (strain USA/WA1/2020). Our study demonstrates the potential use of S309-CAR-NK cells for inhibiting infection by SARS-CoV-2 and for the potential treatment of COVID-19 patients unresponsive to otherwise currently available therapeutics.

IMPORTANCE

Chimeric antigen receptor (CAR)-NK cells can be "off-the-shelf" products that treat various diseases, including cancer, infections, and autoimmune diseases. In this study, we engineered natural killer (NK) cells to express S309 single-chain fragment variable (scFv), to target the Spike protein of SARS-CoV-2, hereinafter S309-CAR-NK cells. Our study shows that S309-CAR-NK cells are effective against different SARS-CoV-2 variants, including the B.1.617.2 (Delta), B.1.621 (Mu), and B.1.1.529 (Omicron) variants. The S309-CAR-NK cells can (i) directly bind to SARS-CoV-2 pseudotyped virus (PV), (ii) competitively bind to SARS-CoV-2 PV with 293T cells expressing the human angiotensin-converting enzyme 2 (hACE2) receptor (293T-hACE2 cells), (iii) specifically target and lyse A549 cells expressing the spike protein, and (iv) significantly reduce the viral loads of SARS-CoV-2 wild-type (strain USA/WA1/2020) in the lungs of NOD/SCID gamma (NSG) mice expressing hACE2 (hACE2-NSG mice). Altogether, the current study demonstrates the potential use of S309-CAR-NK immunotherapy as an alternative treatment for COVID-19 patients.

Mesenchymal Stromal Cells Increase the Natural Killer Resistance of Circulating Tumor Cells via Intercellular Signaling of cGAS-STING-IFNβ-HLA

Circulating tumor cells (CTCs) shed from primary tumors must overcome the cytotoxicity of immune cells, particularly natural killer (NK) cells, to cause metastasis. The tumor microenvironment (TME) protects tumor cells from the cytotoxicity of immune cells, which is partially executed by cancer-associated mesenchymal stromal cells (MSCs). However, the mechanisms by which MSCs influence the NK resistance of CTCs remain poorly understood. This study demonstrates that MSCs enhance the NK resistance of cancer cells in a gap junction-dependent manner, thereby promoting the survival and metastatic seeding of CTCs in immunocompromised mice. Tumor cells crosstalk with MSCs through an intercellular cGAS-cGAMP-STING signaling loop, leading to increased production of interferon-β (IFNβ) by MSCs. IFNβ reversely enhances the type I IFN (IFN-I) signaling in tumor cells and hence the expression of human leukocyte antigen class I (HLA-I) on the cell surface, protecting the tumor cells from NK cytotoxicity. Disruption of this loop reverses NK sensitivity in tumor cells and decreases tumor metastasis. Moreover, there are positive correlations between IFN-I signaling, HLA-I expression, and NK tolerance in human tumor samples. Thus, the NK-resistant signaling loop between tumor cells and MSCs may serve as a novel therapeutic target.

IGSF8 is an innate immune checkpoint and cancer immunotherapy target

Antigen presentation defects in tumors are prevalent mechanisms of adaptive immune evasion and resistance to cancer immunotherapy, whereas how tumors evade innate immunity is less clear. Using CRISPR screens, we discovered that IGSF8 expressed on tumors suppresses NK cell function by interacting with human KIR3DL2 and mouse Klra9 receptors on NK cells. IGSF8 is normally expressed in neuronal tissues and is not required for cell survival in vitro or in vivo. It is overexpressed and associated with low antigen presentation, low immune infiltration, and worse clinical outcomes in many tumors. An antibody that blocks IGSF8-NK receptor interaction enhances NK cell killing of malignant cells in vitro and upregulates antigen presentation, NK cell-mediated cytotoxicity, and T cell signaling in vivo. In syngeneic tumor models, anti-IGSF8 alone, or in combination with anti-PD1, inhibits tumor growth. Our results indicate that IGSF8 is an innate immune checkpoint that could be exploited as a therapeutic target.

Chimeric antigen receptor-natural killer cell therapy: current advancements and strategies to overcome challenges

Chimeric antigen receptor-natural killer (CAR-NK) cell therapy is a novel immunotherapy targeting cancer cells via the generation of chimeric antigen receptors on NK cells which recognize specific cancer antigens. CAR-NK cell therapy is gaining attention nowadays owing to the ability of CAR-NK cells to release potent cytotoxicity against cancer cells without side effects such as cytokine release syndrome (CRS), neurotoxicity and graft-versus-host disease (GvHD). CAR-NK cells do not require antigen priming, thus enabling them to be used as "off-the-shelf" therapy. Nonetheless, CAR-NK cell therapy still possesses several challenges in eliminating cancer cells which reside in hypoxic and immunosuppressive tumor microenvironment. Therefore, this review is envisioned to explore the current advancements and limitations of CAR-NK cell therapy as well as discuss strategies to overcome the challenges faced by CAR-NK cell therapy. This review also aims to dissect the current status of clinical trials on CAR-NK cells and future recommendations for improving the effectiveness and safety of CAR-NK cell therapy.

Building a Better Defense: Expanding and Improving Natural Killer Cells for Adoptive Cell Therapy

Natural killer (NK) cells have gained attention as a promising adoptive cell therapy platform for their potential to improve cancer treatments. NK cells offer distinct advantages over T-cells, including major histocompatibility complex class I (MHC-I)-independent tumor recognition and low risk of toxicity, even in an allogeneic setting. Despite this tremendous potential, challenges persist, such as limited in vivo persistence, reduced tumor infiltration, and low absolute NK cell numbers. This review outlines several strategies aiming to overcome these challenges. The developed strategies include optimizing NK cell expansion methods and improving NK cell antitumor responses by cytokine stimulation and genetic manipulations. Using K562 cells expressing membrane IL-15 or IL-21 with or without additional activating ligands like 4-1BBL allows "massive" NK cell expansion and makes multiple cell dosing and "off-the-shelf" efforts feasible. Further improvements in NK cell function can be reached by inducing memory-like NK cells, developing chimeric antigen receptor (CAR)-NK cells, or isolating NK-cell-based tumor-infiltrating lymphocytes (TILs). Memory-like NK cells demonstrate higher in vivo persistence and cytotoxicity, with early clinical trials demonstrating safety and promising efficacy. Recent trials using CAR-NK cells have also demonstrated a lack of any major toxicity, including cytokine release syndrome, and, yet, promising clinical activity. Recent data support that the presence of TIL-NK cells is associated with improved overall patient survival in different types of solid tumors such as head and neck, colorectal, breast, and gastric carcinomas, among the most significant. In conclusion, this review presents insights into the diverse strategies available for NK cell expansion, including the roles played by various cytokines, feeder cells, and culture material in influencing the activation phenotype, telomere length, and cytotoxic potential of expanded NK cells. Notably, genetically modified K562 cells have demonstrated significant efficacy in promoting NK cell expansion. Furthermore, culturing NK cells with IL-2 and IL-15 has been shown to improve expansion rates, while the presence of IL-12 and IL-21 has been linked to enhanced cytotoxic function. Overall, this review provides an overview of NK cell expansion methodologies, highlighting the current landscape of clinical trials and the key advancements to enhance NK-cell-based adoptive cell therapy.

Interleukin-21 as an adjuvant in cancer immunotherapy: Current advances and future directions

Immunotherapy has revolutionized cancer treatment. However, it's well-recognized that a considerable proportion of patients fail to benefit from immunotherapy, and to improve immunotherapy response is clinically urgent. Insufficient immune infiltration and immunosuppressive tumor microenvironments (TME) are main contributors to immunotherapy resistance. Thus sustaining functional self-renewal capacity for immune cells and subverting immune-suppressive signals are potential strategies for boosting the efficacy of immunotherapy. Interleukin-21 (IL-21), a crucial cytokine, which could enhance cytotoxic function of immune cells and reduces immunosuppressive cells enrichment in TME, shows promising orientations as an immunoadjuvant in tumor immunotherapy. This review focuses on IL-21 in cancer treatment, including function and mechanisms of IL-21, preclinical and clinical studies, and future directions for IL-21-assisted therapies.

T cell senescence: a new perspective on immunotherapy in lung cancer

T cell senescence is an indication of T cell dysfunction. The ability of senescent T cells to respond to cognate antigens is reduced and they are in the late stage of differentiation and proliferation; therefore, they cannot recognize and eliminate tumor cells in a timely and effective manner, leading to the formation of the suppressive tumor microenvironment. Establishing methods to reverse T cell senescence is particularly important for immunotherapy. Aging exacerbates profound changes in the immune system, leading to increased susceptibility to chronic, infectious, and autoimmune diseases. Patients with malignant lung tumors have impaired immune function with a high risk of recurrence, metastasis, and mortality. Immunotherapy based on PD-1, PD-L1, CTLA-4, and other immune checkpoints is promising for treating lung malignancies. However, T cell senescence can lead to low efficacy or unsuccessful treatment results in some immunotherapies. Efficiently blocking and reversing T cell senescence is a key goal of the enhancement of tumor immunotherapy. This study discusses the characteristics, mechanism, and expression of T cell senescence in malignant lung tumors and the treatment strategies.

Chimeric antigen receptor-based natural killer cell immunotherapy in cancer: from bench to bedside

Immunotherapy has rapidly evolved in the past decades in the battle against cancer. Chimeric antigen receptor (CAR)-engineered T cells have demonstrated significant success in certain hematologic malignancies, although they still face certain limitations, including high costs and toxic effects. Natural killer cells (NK cells), as a vital component of the immune system, serve as the "first responders" in the context of cancer development. In this literature review, we provide an updated understanding of NK cell development, functions, and their applications in disease therapy. Furthermore, we explore the rationale for utilizing engineered NK cell therapies, such as CAR-NK cells, and discuss the differences between CAR-T and CAR-NK cells. We also provide insights into the key elements and strategies involved in CAR design for engineered NK cells. In addition, we highlight the challenges currently encountered and discuss the future directions in NK cell research and utilization, including pre-clinical investigations and ongoing clinical trials. Based on the outstanding antitumor potential of NK cells, it is highly likely that they will lead to groundbreaking advancements in cancer treatment in the future.

Methodological Approaches for Increasing the Retroviral Transduction Efficiency of Primary NK Cells

BACKGROUND

The growing attention to NK cells for cancer cell therapy is associated with the need to establish highly efficient protocols for their genetic modification, particularly by retroviral transduction.

OBJECTIVE

In this work, we have optimized several stages of the retroviral-based modification process, and determined the distribution of the amino acid transporter ASCT2 between NK cell subsets.

METHODS

Retroviral particles were produced using the Phoenix Ampho cell line transfected with the calcium phosphate method . We used RD114-based retroviral transduction for lymphocyte cell lines and primary NK cells.

RESULTS

We have determined the optimal time to collect the RD114-pseudotyped viral supernatants resulting in the titer of viral particles required for efficient NK cell modification to be between 48 and 72 hours. Retroviral modification by retronectin-based method did not alter NK cell functional activity and cell survival. We identified differences in the Multiplicity of Infection (MOI) among cell lines that were partially associated with the ASCT2 surface expression. Cells with higher ASCT2 levels were more susceptible to transduction with RD114-pseudotyped viral particles. Higher ASCT2 expression levels were revealed in activated CD57+ and KIR2DL2DL3+ NK cells compared to their negative counterparts.

CONCLUSION

Our findings provide a more nuanced understanding of NK cell transduction, offering valuable insights for improving therapeutic applications involving NK cell modification.

Sufficiently activated mature natural killer cells derived from peripheral blood mononuclear cells substantially enhance antitumor activity

BACKGROUND

Peripheral blood-derived natural killer (NK) cells spontaneously lyse tumor cells without prior sensitization. However, NK cells in peripheral blood (PBNK cells) are in a resting state and exhibit inhibitory phenotypes and impaired cytotoxicity. Thus, strengthening the cytotoxic effector function of PBNK cells and improving NK cell expansion in vitro for a convenient allogeneic therapy are essential.

MATERIALS AND METHODS

Pure cytokine activation and expansion of NK cells (super NK [SNK]) from peripheral blood mononuclear cells were studied. Markers of activated and inhibited NK cells and cytokine secretion by NK cells were examined using flow cytometry. NK cell antitumor activity in vitro was assessed using lactate dehydrogenase (LDH) cytotoxicity assay and an Incucyte real-time imaging system. Additionally, the function of SNK cells against ascites caused by ovarian cancer in NOD-Prkdc(em26Cd52)il2rg(em26Cd22)/Nju (NCG) mice was determined. In a further investigation of the differences between PBNK and SNK, the mRNA of both cells was sequenced and analyzed.

RESULTS

Human peripheral blood mononuclear cells showed selective NK cell expansion upon cytokine activation and culture. Both SNK and PBNK cells expressed activation markers, but at different levels, and SNK cells secreted more cytokines related to cytotoxicity than PBNK cells did. Accordingly, SNK cells exhibited strong antitumor activity ex vivo and improved NCG mice survival after intraperitoneal ovarian cancer transplantation. Mechanistically, SNK cells expressed more genes associated with nucleotide metabolism, fatty acid, and ATP metabolism than PBNK cells.

CONCLUSION

SNK cells derived from peripheral blood mononuclear cells have sufficiently activated mature characteristics and high antitumor activity, rendering them a highly promising and essential therapeutic approach for cancer treatment.

Chimeric antigen receptor natural killer cells: a promising antitumor immunotherapy

Chimeric antigen receptor (CAR) T cells have been successfully used in adoptive cell therapy for malignancies. However, some obstacles, including side effects such as graft-versus-host disease and cytokine release syndrome, therapy resistance, limited sources, as well as high cost, limited the application of CAR T cells. Recently, CAR natural killer (NK) cells have been pursued as the effector cells for adoptive immunotherapy for their attractive merits of strong intrinsic antitumor activity and relatively mild side effects. Additionally, CAR NK cells can be available from various sources and do not require strict human leukocyte antigen matching, which suggests them as promising "off-the-shelf" products for clinical application. Although the use of CAR NK cells is restrained by the limited proliferation and impaired efficiency within the immunosuppressive tumor microenvironment, further investigation in optimizing CAR structure and combination therapies will overcome these challenges. This review will summarize the advancement of CAR NK cells, CAR NK cell manufacture, the clinical outcomes of CAR NK therapy, the challenges in the field, and prospective solutions. Besides, we will discuss the emerging application of other immune cells for CAR engineering. Collectively, this comprehensive review will provide a valuable and informative summary of current progress and evaluate challenges and future opportunities of CAR NK cells in tumor treatment.

Harnessing Natural Killer Cells for Lung Cancer Therapy

Lung cancer is the leading cause of cancer-related death worldwide. Although natural killer (NK) cells are garnering interest as a potential anticancer therapy because they selectively recognize and eliminate cancer cells, their use in treating solid tumors, including lung cancer, has been limited due to impediments to their efficacy, such as their limited ability to reach tumor tissues, the reduced antitumor activity of tumor-infiltrating NK cells, and the suppressive tumor microenvironment (TME). This comprehensive review provides an in-depth analysis of the cross-talk between the lung cancer TME and NK cells. We highlight the various mechanisms used by the TME to modulate NK-cell phenotypes and limit infiltration, explore the role of the TME in limiting the antitumor activity of NK cells, and discuss the current challenges and obstacles that hinder the success of NK-cell-based immunotherapy for lung cancer. Potential opportunities and promising strategies to address these challenges have been implemented or are being developed to optimize NK-cell-based immunotherapy for lung cancer. Through critical evaluation of existing literature and emerging trends, this review provides a comprehensive outlook on the future of NK-cell-based immunotherapy for treating lung cancer.

Phenotypic and functional characterisation of locally produced natural killer cells ex vivo expanded with the K562-41BBL-mbIL21 cell line

We characterised the expansion, phenotype and functional activity of natural killer (NK) cells obtained for a clinical trial. Nineteen expansion procedures were performed to obtain NK cell products for 16 patients. NK cells were expanded ex vivo from haploidentical donor peripheral blood mononuclear cells in the presence of the locally generated feeder cell line K-562 with ectopic expression of 4-1BBL and mbIL-21. The median duration of expansion was 18 days (interquartile range 15-19). The median number of live cells yielded was 2.26 × 109 (range 1.6-3.4 × 109) with an NK content of 96.6% (range 95.1-97.9%). The median NK cell fold expansion was 171 (range 124-275). NK cell fold expansion depended on the number of seeded NK cells, the initial level of C-myc expression and the initial number of mature and immature NK cells. The majority of expanded NK cells had the phenotype of immature activated cells (NKG2A + , double bright CD56 +  + CD16 +  + , CD57-) expressing NKp30, NKp44, NKp46, NKG2D, CD69, HLA-DR and CD96. Despite the expression of exhaustion markers, expanded NK cells exhibited high cytolytic activity against leukaemia cell lines, high degranulation activity and cytokine production. There was a noted decrease in the functional activity of NK cells in tests against the patient's blasts.In conclusion, NK cells obtained by ex vivo expansion with locally generated K562-41BBL-mbIL21 cells had a relatively undifferentiated phenotype and enhanced cytolytic activity against cancer cell lines. Expansion of NK cells with feeder cells yielded a sufficient quantity of the NK cell product to reach high cell doses or increase the frequency of cell infusions for adoptive immunotherapy. Registered at clinicaltrials.gov as NCT04327037.

Expanded clinical-grade NK cells exhibit stronger effects than primary NK cells against HCMV infection

Cytomegalovirus (CMV) reactivation remains a common complication and leads to high mortality in patients who undergo allogeneic hematopoietic stem cell transplantation (allo-HSCT). Early natural killer (NK) cell reconstitution may protect against the development of human CMV (HCMV) infection post-HSCT. Our previous data showed that ex vivo mbIL21/4-1BBL-expanded NK cells exhibited high cytotoxicity against leukemia cells. Nevertheless, whether expanded NK cells have stronger anti-HCMV function is unknown. Herein, we compared the anti-HCMV functions of ex vivo expanded NK cells and primary NK cells. Expanded NK cells showed higher expression of activating receptors, chemokine receptors and adhesion molecules; stronger cytotoxicity against HCMV-infected fibroblasts; and better inhibition of HCMV propagation in vitro than primary NK cells. In HCMV-infected humanized mice, expanded NK cell infusion resulted in higher NK cell persistence and more effective tissue HCMV elimination than primary NK cell infusion. A clinical cohort of 20 post-HSCT patients who underwent adoptive NK cell infusion had a significantly lower cumulative incidence of HCMV infection (HR = 0.54, 95% CI = 0.32-0.93, p = 0.042) and refractory HCMV infection (HR = 0.34, 95% CI = 0.18-0.65, p = 0.009) than controls and better NK cell reconstitution on day 30 post NK cell infusion. In conclusion, expanded NK cells exhibit stronger effects than primary NK cells against HCMV infection both in vivo and in vitro.

Advancements in CAR-NK therapy: lessons to be learned from CAR-T therapy

Advancements in chimeric antigen receptor engineered T-cell (CAR-T) therapy have revolutionized treatment for several cancer types over the past decade. Despite this success, obstacles including the high price tag, manufacturing complexity, and treatment-associated toxicities have limited the broad application of this therapy. Chimeric antigen receptor engineered natural killer cell (CAR-NK) therapy offers a potential opportunity for a simpler and more affordable "off-the-shelf" treatment, likely with fewer toxicities. Unlike CAR-T, CAR-NK therapies are still in early development, with few clinical trials yet reported. Given the challenges experienced through the development of CAR-T therapies, this review explores what lessons we can apply to build better CAR-NK therapies. In particular, we explore the importance of optimizing the immunochemical properties of the CAR construct, understanding factors leading to cell product persistence, enhancing trafficking of transferred cells to the tumor, ensuring the metabolic fitness of the transferred product, and strategies to avoid tumor escape through antigen loss. We also review trogocytosis, an important emerging challenge that likely equally applies to CAR-T and CAR-NK cells. Finally, we discuss how these limitations are already being addressed in CAR-NK therapies, and what future directions may be possible.

CAR-cell therapy in the era of solid tumor treatment: current challenges and emerging therapeutic advances

In the last decade, Chimeric Antigen Receptor (CAR)-T cell therapy has emerged as a promising immunotherapeutic approach to fight cancers. This approach consists of genetically engineered immune cells expressing a surface receptor, called CAR, that specifically targets antigens expressed on the surface of tumor cells. In hematological malignancies like leukemias, myeloma, and non-Hodgkin B-cell lymphomas, adoptive CAR-T cell therapy has shown efficacy in treating chemotherapy refractory patients. However, the value of this therapy remains inconclusive in the context of solid tumors and is restrained by several obstacles including limited tumor trafficking and infiltration, the presence of an immunosuppressive tumor microenvironment, as well as adverse events associated with such therapy. Recently, CAR-Natural Killer (CAR-NK) and CAR-macrophages (CAR-M) were introduced as a complement/alternative to CAR-T cell therapy for solid tumors. CAR-NK cells could be a favorable substitute for CAR-T cells since they do not require HLA compatibility and have limited toxicity. Additionally, CAR-NK cells might be generated in large scale from several sources which would suggest them as promising off-the-shelf product. CAR-M immunotherapy with its capabilities of phagocytosis, tumor-antigen presentation, and broad tumor infiltration, is currently being investigated. Here, we discuss the emerging role of CAR-T, CAR-NK, and CAR-M cells in solid tumors. We also highlight the advantages and drawbacks of CAR-NK and CAR-M cells compared to CAR-T cells. Finally, we suggest prospective solutions such as potential combination therapies to enhance the efficacy of CAR-cells immunotherapy.

Metabolic regulation of NK cell function: implications for immunotherapy

Natural killer (NK) cells are innate immune lymphocytes capable of rapidly responding to tumors and infection without prior sensitization. There is increasing interest and success in harnessing NK cell function for the treatment of disease, in particular cancers. NK cell activation is dependent on integration of signals through cytokine and germline-encoded activating and inhibitory receptors. The availability of metabolic fuels and pathways is required for NK effector functions including proliferation, killing, and production of interferon gamma (IFN-γ). An understanding of NK cell immunometabolism is thus essential for developing immunotherapy approaches that will allow for optimal effector functions in patients. Studies in mice and humans have demonstrated stimulation-dependent metabolic changes that are required for NK cell function. Here we review the most recent findings in NK cell immunometabolism relevant to disease models and translation to therapy of patients.

Autologous ex vivo expanded NK cells combined with PD-1 inhibitor improved ascitic fluid immune microenvironment of peritoneal metastatic pancreatic cancer: a case study

The presence of peritoneal metastasis in patients with pancreatic cancer is associated with poor prognosis. Chemotherapy and radiotherapy may result in poor prognosis in patients with pancreatic cancer. However, immunotherapy improves prognosis even at an advanced stage of the disease. The present study reported a case of a combined therapy of autologous ex vivo expanded natural killer (NK) cells and programmed cell death 1 (PD-1) inhibitor in a patient with pancreatic cancer and peritoneal metastasis. The NK cells were expanded ex vivo and intravenously injected. This was followed by intravenous administration of two dosages of PD-1 inhibitor. Computed tomography and magnetic resonance imaging were performed to assess the size of tumor before and after the combined therapy. In addition, the blood sample and ascites were collected and analyzed before and after the combined therapy. Flow cytometry was carried out to measure the subsets of T cells and macrophages in the collected ascites. Meanwhile, the levels of cytokines in the ascites were quantified through enzyme-linked immunosorbent assay, and Luminex assays were conducted on the supernatant. It was revealed that after the combined therapy, cancer cells disappeared in the ascites, and the T cells were activated, which could be confirmed by the decreased levels of PD-1 and T cell immunoglobulin and mucin domain-containing protein 3. Also, the functioning of macrophages was improved, as shown by the increased level of CD86 and the reduced levels of CD206 and HLA-DR. Notably, the levels of cytokines (transforming growth factor-β, vascular endothelial growth factor, and interleukin-10) in ascites were significantly upregulated after the combined therapy. In conclusion, it was evident that NK cells combined with PD-1 inhibitor improved the immune microenvironment of carcinomatosis in the peritoneal cavity. Therefore, the combined therapy may be beneficial for suppressing pancreatic cancer and the presence of metastases in the peritoneal cavity. However, there is a need for additional randomized studies to confirm the efficacy of combined therapy.

Expansion of KRAS hotspot mutations reactive T cells from human pancreatic tumors using autologous T cells as the antigen-presenting cells

Adoptive cell therapy (ACT) with expanded tumor-infiltrating lymphocytes (TIL) or TCR gene-modified T cells (TCR-T) that recognize mutant KRAS neo-antigens can mediate tumor regression in patients with advanced pancreatic ductal adenocarcinoma (PDAC) (Tran et al in N Engl J Med, 375:2255-2262, 2016; Leidner et al in N Engl J Med, 386:2112-2119, 2022). The mutant KRAS-targeted ACT holds great potential to achieve durable clinical responses for PDAC, which has had no meaningful improvement over 40 years. However, the wide application of mutant KRAS-centric ACT is currently limited by the rarity of TIL that recognize the mutant KRAS. In addition, PDAC is generally recognized as a poorly immunogenic tumor, and TILs in PDAC are less abundant than in immunogenic tumors such as melanoma. To increase the success rate of TIL production, we adopted a well-utilized K562-based artificial APC (aAPC) that expresses 4-1BBL as the costimulatory molecules to enhance the TIL production from PDCA. However, stimulation with K562-based aAPC led to a rapid loss of specificity to mutant KRAS. To selectively expand neo-antigen-specific T cells, particularly mKRAS, from the TILs, we used tandem mini gene-modified autologous T cells (TMG-T) as the novel aAPC. Using this modified IVS protocol, we successfully generated TIL cultures specifically reactive to mKRAS (G12V). We believe that autologous TMG-T cells provide a reliable source of autologous APC to expand a rare population of neoantigen-specific T cells in TILs.

Cutting-Edge CAR Engineering: Beyond T Cells

Chimeric antigen receptor (CAR)-T adoptive cell therapy is one of the most promising advanced therapies for the treatment of cancer, with unprecedented outcomes in haematological malignancies. However, it still lacks efficacy in solid tumours, possibly because engineered T cells become inactive within the immunosuppressive tumour microenvironment (TME). In the TME, cells of the myeloid lineage (M) are among the immunosuppressive cell types with the highest tumour infiltration rate. These cells interact with other immune cells, mediating immunosuppression and promoting angiogenesis. Recently, the development of CAR-M cell therapies has been put forward as a new candidate immunotherapy with good efficacy potential. This alternative CAR strategy may increase the efficacy, survival, persistence, and safety of CAR treatments in solid tumours. This remains a critical frontier in cancer research and opens up a new possibility for next-generation personalised medicine to overcome TME resistance. However, the exact mechanisms of action of CAR-M and their effect on the TME remain poorly understood. Here, we summarise the basic, translational, and clinical results of CAR-innate immune cells and CAR-M cell immunotherapies, from their engineering and mechanistic studies to preclinical and clinical development.

Chimeric antigen receptor-engineered NK cells: new weapons of cancer immunotherapy with great potential

Chimeric antigen receptor (CAR)-engineered T (CAR-T) cells have obtained prominent achievement in the clinical immunotherapy of hematological malignant tumors, leading to a rapid development of cellular immunotherapy in cancer treatment. Scientists are also aware of the prospective advantages of CAR engineering in cellular immunotherapy. Due to various limitations such as the serious side effects of CAR-T therapy, researchers began to investigate other immune cells for CAR modification. Natural killer (NK) cells are critical innate immune cells with the characteristic of non-specifically recognizing target cells and with the potential to become "off-the-shelf" products. In recent years, many preclinical studies on CAR-engineered NK (CAR-NK) cells have shown their remarkable efficacy in cancer therapy and their superiority over autologous CAR-T cells. In this review, we summarize the generation, mechanisms of anti-tumor activity and unique advantages of CAR-NK cells, and then analyze some challenges and recent clinical trials about CAR-NK cells therapy. We believe that CAR-NK therapy is a promising prospect for cancer immunotherapy in the future.

Natural Killer Cell Expansion and Cytotoxicity Differ Depending on the Culture Medium Used

Background

Adoptive cell therapy using umbilical cord blood (UCB)-derived allogeneic natural killer (NK) cells has shown encouraging results. However, because of the insufficient availability of NK cells and limited UCB volume, more effective culture methods are required. NK cell expansion and functionality are largely affected by the culture medium. While human serum is a major affecting component in culture media, the way it regulates NK cell functionality remains elusive. We elucidated the effects of different culture media and human serum supplementation on UCB NK cell expansion and functionality.

Methods

UCB NK cells were cultured under stimulation with K562-OX40L-mbIL-18/21 feeder cells and IL-2 and IL-15 in serum-containing and serum-free culture media. The effects of the culture media and human serum supplementation on NK cell expansion and cytotoxicity were evaluated by analyzing the expansion rate, activating and inhibitory receptor levels, and the cytotoxicity of the UCB NK cells.

Results

The optimal medium for NK cell expansion was Dulbecco’s modified Eagle’s medium/Ham’s F12 with supplements and that for cytotoxicity was AIM V supplemented with Immune Cell Serum Replacement. Shifting media is an advantageous strategy for obtaining several highly functional UCB NK cells. Live cell imaging and killing time measurement revealed that human serum enhanced NK cell proliferation but delayed target recognition, resulting in reduced cytotoxicity.

Conclusions

Culture medium supplementation with human serum strongly affects UCB NK cell expansion and functionality. Thus, culture media should be carefully selected to ensure both NK cell quantity and quality for adoptive cell therapy.

Characterization of age-related immune features after autologous NK cell infusion: Protocol for an open-label and randomized controlled trial

Background

Aging is usually accompanied by functional declines of the immune system, especially in T-cell responses. However, little is known about ways to alleviate this.

Methods

Here, 37 middle-aged healthy participants were recruited, among which 32 were intravenously administrated with expanded NK cells and 5 with normal saline. Then, we monitored changes of peripheral senescent and exhausted T cells within 4 weeks after infusion by flow cytometry, as well as serum levels of senescence-associated secretory phenotype (SASP)-related factors. In vitro co-culture assays were performed to study NK-mediated cytotoxic activity against senescent or exhausted T cells. Functional and phenotypic alteration of NK cells before and after expansion was finally characterized.

Results

After NK cell infusion, senescent CD28-, CD57+, CD28-CD57+, and CD28-KLRG1+ CD4+ and CD8+ T-cell populations decreased significantly, so did PD-1+ and TIM-3+ T cells. These changes were continuously observed for 4 weeks. Nevertheless, no significant changes were observed in the normal saline group. Moreover, SASP-related factors including IL-6, IL-8, IL-1α, IL-17, MIP-1α, MIP-1β, and MMP1 were significantly decreased after NK cell infusion. Further co-culture assays showed that expanded NK cells specifically and dramatically eliminated senescent CD4+ T cells other than CD28+CD4+ T cells. They also showed improved cytotoxic activity, with different expression patterns of activating and inhibitory receptors including NKG2C, NKG2A, KLRG1, LAG3, CD57, and TIM3.

Conclusion

Our findings imply that T-cell senescence and exhaustion is a reversible process in healthy individuals, and autologous NK cell administration can be introduced to alleviate the aging.

Clinical Trial Registration

ClinicalTrials.gov, ChiCTR-OOh-17011878.

Recent findings on chimeric antigen receptor (CAR)-engineered immune cell therapy in solid tumors and hematological malignancies

Advancements in adoptive cell therapy over the last four decades have revealed various new therapeutic strategies, such as chimeric antigen receptors (CARs), which are dedicated immune cells that are engineered and administered to eliminate cancer cells. In this context, CAR T-cells have shown significant promise in the treatment of hematological malignancies. However, many obstacles limit the efficacy of CAR T-cell therapy in both solid tumors and hematological malignancies. Consequently, CAR-NK and CAR-M cell therapies have recently emerged as novel therapeutic options for addressing the challenges associated with CAR T-cell therapies. Currently, many CAR immune cell trials are underway in various human malignancies around the world to improve antitumor activity and reduce the toxicity of CAR immune cell therapy. This review will describe the comprehensive literature of recent findings on CAR immune cell therapy in a wide range of human malignancies, as well as the challenges that have emerged in recent years.

Selective Expansion of NKG2C+ Adaptive NK Cells Using K562 Cells Expressing HLA-E

Adaptive natural killer (NK) cells expressing self-specific inhibitory killer-cell immunoglobulin-like receptors (KIRs) can be expanded in vivo in response to human cytomegalovirus (HCMV) infection. Developing a method to preferentially expand this subset is essential for effective targeting of allogeneic cancer cells. A previous study developed an in vitro method to generate single KIR+ NK cells for enhanced targeting of the primary acute lymphoblastic leukemia cells; however, the expansion rate was quite low. Here, we present an effective expansion method using genetically modified K562-HLA-E feeder cells for long-term proliferation of adaptive NK cells displaying highly differentiated phenotype and comparable cytotoxicity, CD107a, and interferon-γ (IFN-γ) production. More importantly, our expansion method achieved more than a 10,000-fold expansion of adaptive NK cells after 6 weeks of culture, providing a high yield of alloreactive NK cells for cell therapy against cancer.

Overcoming tumor resistance mechanisms in CAR-NK cell therapy

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

CAR NK cell therapy in hematologic malignancies and solid tumors; obstacles and strategies to overcome the challenges

Adoptive cell treatment (ACT) utilizing chimeric antigen receptors (CAR) diverts the specificity of safe cells against a target-specific antigen and portrays exceptional potential for cancer treatment. While CAR T cell treatment has risen as a breakthrough with unprecedented results within the therapeutic procedures of human malignancies, different deficiencies including challenging and costly generation processes, strict patient qualification criteria, and undesirable toxicity have ruined its application. Unlike T cells, the application of natural killer (NK) cells has attracted consideration as a reasonable alternative owing to the major histocompatibility complex (MHC)-independency, shorter life expectancy, the potential to create an off-the-shelf immune product, and potent antitumor properties. In this article, we provide an updated review of the differences between CAR T and CAR NK cells, current enhancements in CAR NK design, the available sources for collecting NK cells, and strategies for the transduction step of the CARs to NK cells. Furthermore, we focus on the published and ongoing preclinical and clinical studies of CAR NK treatment strategies both in hematologic malignancies and solid tumors. We also discuss limitations and plausible solutions to improve the perseverance, function, safety, and efficacy of CAR NK cells with a special focus on solid tumors.

[Comparison of the characteristics of NK cells after two different methods of expansion and observation of the clinical efficacy in patients who relapsed post allogeneic hematopoietic stem cell transplantation]

Objective: To explore the differences in the biological effects of different expansion systems on natural killer (NK) cells, as well as the safety and preliminary clinical efficacy in the treatment of patients with recurrence after allogeneic hematopoietic stem cell transplantation (allo-HSCT) . Methods: Peripheral blood cells from healthy donors were stimulated with either CD3 combined with CD52 or K562 feeder cells loaded with IL-21/4-1BB to induce NK cell expansion. Changes in the NK cell phenotype, cytokine secretion, and cytotoxicity before and after expansion were detected. We also evaluated the safety and clinical efficacy of two different expansion strategies for patients received NK infusion. Results: Compared with the CD3/CD52 monoclonal antibody amplification system, the feeder cell expansion group had a higher purity of NK cells and higher expression ratios of NK cell surface activation receptors such as DNAM-1 and NKp30, while inhibitory receptor CTLA-4 expression was low and NKG2D/CD25/CD69/ Trail/PD-1/TIM-3/TIGIT had no statistically significant differences between the groups. Further functional results showed that the expression level of KI67 in NK cells after expansion in the two groups increased significantly, especially in the feeder cell expansion group. Simultaneously, the perforin and granzyme B levels of NK cells in the feeder cell expansion group were significantly higher than in the CD3/CD52 expansion group. A retrospective analysis of eight patients who received monoclonal antibody-expanded NK cell reinfusion and nine patients with trophoblast cell-expanded NK cell reinfusion was done. The disease characteristics of the two groups were comparable, NK cell reinfusion was safe, and there were no obvious adverse reactions. Clinical prognostic results showed that in the CD3/CD52 monoclonal antibody amplification group, the MRD conversion rate was 50% (2/4) , and the feeder cell expansion group was 50% (3/6) . After 5 years of follow-up from allo-HSCT, three patients in the monoclonal antibody expansion group had long-term survival without leukemia, and the remaining five patients had died; two patients died in the feeder cell expansion group, and the other six patients had long-term survival. Six cases had GVHD before NK cell reinfusion, and GVHD did not aggravate or even relieved after NK cell reinfusion. Conclusions: Preliminary results show that the biological characteristics of NK cells with diverse expansion strategies are significantly different, which may affect the clinical prognosis of patients with recurrence or persistent minimal residual disease after HSCT. The two groups of patients treated with NK cells from different expansion strategies had no obvious adverse reactions after NK cell infusion, but efficacy still needs to be further confirmed.

Innovative Strategies to Improve the Clinical Application of NK Cell-Based Immunotherapy

Natural killer cells constitute a part of the innate immune system that mediates an effective immune response towards virus-infected and malignant cells. In recent years, research has focused on exploring and advancing NK cells as an active immunotherapy platform. Despite major advances, there are several key challenges that need to be addressed for the effective translation of NK cell research to clinical applications. This review highlights some of these challenges and the innovative strategies being developed to overcome them, including in vitro expansion, in vivo persistence, infiltration to the tumor site, and prevention of exhaustion.

Feeder Cells at the Interface of Natural Killer Cell Activation, Expansion and Gene Editing

Genome engineered natural killer (NK) cell therapies are emerging as a promising cancer immunotherapy platform with potential advantages and remaining uncertainties. Feeder cells induce activation and proliferation of NK cells via cell surface receptor-ligand interactions, supported by cytokines. Feeder cell expanded NK cell products have supported several NK cell adoptive transfer clinical trials over the past decade. Genome engineered NK cell therapies, including CAR-NK cells, seek to combine innate and alloreactive NK cell anti-tumor activity with antigen specific targeting or additional modifications aimed at improving NK cell persistence, homing or effector function. The profound activating and expansion stimulus provided by feeder cells is integral to current applications of clinical-scale genome engineering approaches in donor-derived, primary NK cells. Herein we explore the complex interactions that exist between feeder cells and both viral and emerging non-viral genome editing technologies in NK cell engineering. We focus on two established clinical-grade feeder systems; Epstein-Barr virus transformed lymphoblastoid cell lines and genetically engineered K562.mbIL21.4-1BBL feeder cells.

Natural Killer (NK) and CAR-NK Cell Expansion Method using Membrane Bound-IL-21-Modified B Cell Line

Chimeric antigen receptor (CAR)-modified immune cell therapy has become an emerging treatment for cancers and infectious diseases. NK-based immunotherapy, particularly CAR-NK cell, is one of the most promising 'off-the-shelf' development without severe life-threatening toxicity. However, the bottleneck for developing a successful CAR-NK therapy is achieving sufficient numbers of non-exhaustive, long-lived, 'off-the-shelf' CAR-NK cells from a third party. Here, we developed a new CAR-NK expansion method using an Epstein-Barr virus- (EBV) transformed B cell line expressing a genetically modified membrane form of interleukin-21 (IL-21). In this protocol, step-by-step procedures are provided to expand NK and CAR-NK cells from cord blood and peripheral blood, as well as solid organ tissues. This work will significantly enhance the clinical development of CAR-NK immunotherapy.

Natural killer cell-targeted immunotherapy for cancer

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

Importance of T, NK, CAR T and CAR NK Cell Metabolic Fitness for Effective Anti-Cancer Therapy: A Continuous Learning Process Allowing the Optimization of T, NK and CAR-Based Anti-Cancer Therapies

Simple Summary

Cancer treatments are evolving at a very rapid pace. Some of the most novel anti-cancer medicines under development rely on the modification of immune cells in order to transform them into potent tumor-killing cells. However, the tumor microenvironment (TME) is competing for nutrients with these harnessed immune cells and therefore paralyzes their metabolic effective and active anti-cancer activities. Here we describe strategies to overcome these hurdles imposed on immune cell activity, which lead to therapeutic approaches to enhance metabolic fitness of the patient’s immune system with the objective to improve their anti-cancer capacity.

Abstract

Chimeric antigen receptor (CAR) T and CAR NK cell therapies opened new avenues for cancer treatment. Although original successes of CAR T and CAR NK cells for the treatment of hematological malignancies were extraordinary, several obstacles have since been revealed, in particular their use for the treatment of solid cancers. The tumor microenvironment (TME) is competing for nutrients with T and NK cells and their CAR-expressing counterparts, paralyzing their metabolic effective and active states. Consequently, this can lead to alterations in their anti-tumoral capacity and persistence in vivo. High glucose uptake and the depletion of key amino acids by the TME can deprive T and NK cells of energy and building blocks, which turns them into a state of anergy, where they are unable to exert cytotoxic activity against cancer cells. This is especially true in the context of an immune-suppressive TME. In order to re-invigorate the T, NK, CAR T and CAR NK cell-mediated antitumor response, the field is now attempting to understand how metabolic pathways might change T and NK responses and functions, as well as those from their CAR-expressing partners. This revealed ways to metabolically rewire these cells by using metabolic enhancers or optimizing pre-infusion in vitro cultures of these cells. Importantly, next-generation CAR T and CAR NK products might include in the future the necessary metabolic requirements by improving their design, manufacturing process and other parameters. This will allow the overcoming of current limitations due to their interaction with the suppressive TME. In a clinical setting, this might improve their anti-cancer effector activity in synergy with immunotherapies. In this review, we discuss how the tumor cells and TME interfere with T and NK cell metabolic requirements. This may potentially lead to therapeutic approaches that enhance the metabolic fitness of CAR T and CAR NK cells, with the objective to improve their anti-cancer capacity.

CAR-NK cells from engineered pluripotent stem cells: Off-the-shelf therapeutics for all patients

Clinical success of adoptive cell therapy with chimeric antigen receptor (CAR) T cells for treating hematological malignancies has revolutionized the field of cellular immunotherapy. However, due to the nature of utilizing autologous T cells, affordability and availability are major hurdles, in addition to scientific challenges relating to CAR-T therapy optimization. Natural killer (NK) cell is a specialized immune effector cell type that recognizes and kills targets without human leukocyte antigen (HLA) restriction and prior sensitization. CAR-NK cells do not cause graft vs host disease and can be obtained from unrelated donors as well as pluripotent stem cells (PSC), representing an ideal off-the-shelf therapeutics readily available for patients. Furthermore, unlike cytotoxic T cells, NK cells specifically target and eliminate cancer stem cells, which are the cells causing relapse and metastasis. PSCs can be genetically manipulated and engineered with CARs at the pluripotent stage, which allows the establishment of permanent, stable, and clonal PSC-CAR lines for the manufacture of unlimited homogenous CAR-NK cells. Multiple master PSC-CAR cell banks targeting a variety of antigens for cancer, viral infection, and autoimmune diseases provide inexhaustible cell sources for all patients. Development of a next-generation 3D bioreactor platform for PSC expansion and NK cell production overcomes major barriers related to cost and scalability for CAR-NK product.

Preclinical studies of chimeric antigen receptor-modified natural killer cells in cancer immunotherapy: a review

INTRODUCTION

As one of the most efficacious methods of cancer immunotherapy, chimeric antigen receptor-modified immune cells have recently drawn enormous attention. After the great success achieved with CAR-T-cells in cancer treatment both in preclinical setting and in the clinic, other types of immune cells, including natural killer (NK)-cells and macrophages, have been evaluated for their anti-cancer effects along with their potential superiority against CAR-T-cells, especially in terms of safety. First introduced by Tran et al. almost 26 years ago, CAR-NK-cells are now being considered as efficient immunotherapeutic modalities in various types of cancers, not only in preclinical setting but also in numerous phase I and II clinical studies.

AREAS COVERED

In this review, we aim to provide a comprehensive survey of the preclinical studies on CAR-NK-cells' development, with an evolutional approach on CAR structures and their associated signaling moieties. Current NK-cell sources and modes of gene transfer are also reviewed.

EXPERT OPINION

CAR-NK-cells have appeared as safe and effective immunotherapeutic tools in preclinical settings; however, designing CAR structures with an eye on their specific biology, along with choosing the optimal cell source and gene transfer method require further investigation to support clinical studies.

Chimeric Antigen Receptor-Engineered Natural Killer (CAR NK) Cells in Cancer Treatment; Recent Advances and Future Prospects

Natural Killer (NK) cells are critical members of the innate immunity lymphocytes and have a critical role in host defense against malignant cells. Adoptive cell therapy (ACT) using chimeric antigen receptor (CAR) redirects the specificity of the immune cell against a target-specific antigen. ACT has recently created an outstanding opportunity for cancer treatment. Unlike CAR-armored T cells which hadnsome shortcomings as the CAR-receiving construct, Major histocompatibility complex (MHC)-independency, shorter lifespan, the potential to produce an off-the-shelf immune product, and potent anti-tumor properties of the NK cells has introduced NK cells as a potent alternative target for expression of CAR. Here, we aim to provide an updated overview on the current improvements in CAR NK design and immunobiology and describe the potential of CAR-modified NK cells as an alternative “off-the-shelf” carrier of CAR. We also provide lists for the sources of NK cells in the process of CAR NK cell production, different methods for transduction of the CAR genetic sequence to NK cells, the differences between CAR T and CAR NK, and CAR NK-targeted tumor antigens in current studies. Additionally, we provide data on recently published preclinical and clinical studies of CAR NK therapy and a list of finished and ongoing clinical trials. For achieving CAR NK products with higher efficacy and safety, we discuss current challenges in transduction and expansion of CAR NK cells, CAR NK therapy side effects, and challenges that limit the optimal efficacy of CAR NK cells and recommend possible solutions to enhance the persistence, function, safety, and efficacy of CAR NK cells with a special focus on solid tumors.

CAR-NK Cells Effectively Target SARS-CoV-2-Spike-Expressing Cell Lines In Vitro

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is highly contagious and presents a significant public health issue. Current therapies used to treat coronavirus disease 2019 (COVID-19) include monoclonal antibody cocktail, convalescent plasma, antivirals, immunomodulators, and anticoagulants. The vaccines from Pfizer and Moderna have recently been authorized for emergency use, which are invaluable for the prevention of SARS-CoV-2 infection. However, their long-term side effects are not yet documented, and populations with immunocompromised conditions (e.g., organ-transplantation and immunodeficient patients) may not be able to mount an effective immune response. In addition, there are concerns that wide-scale immunity to SARS-CoV-2 may introduce immune pressure that could select for escape mutants to the existing vaccines and monoclonal antibody therapies. Emerging evidence has shown that chimeric antigen receptor (CAR)- natural killer (NK) immunotherapy has potent antitumor response in hematologic cancers with minimal adverse effects in recent studies, however, the potentials of CAR-NK cells in treating COVID-19 has not yet been fully exploited. Here, we improve upon a novel approach for the generation of CAR-NK cells for targeting SARS-CoV-2 and its various mutants. CAR-NK cells were generated using the scFv domain of S309 (henceforward, S309-CAR-NK), a SARS-CoV and SARS-CoV-2 neutralizing antibody (NAbs) that targets the highly conserved region of SARS-CoV-2 spike (S) glycoprotein and is therefore more likely to recognize different variants of SARS-CoV-2 isolates. S309-CAR-NK cells can specifically bind to pseudotyped SARS-CoV-2 virus and its D614G, N501Y, and E484K mutants. Furthermore, S309-CAR-NK cells can specifically kill target cells expressing SARS-CoV-2 S protein in vitro and show superior killing activity and cytokine production, compared to that of the recently reported CR3022-CAR-NK cells. Thus, these results pave the way for generating 'off-the-shelf' S309-CAR-NK cells for treatment in high-risk individuals as well as provide an alternative strategy for patients unresponsive to current vaccines.

CAR-NK Cells in the Treatment of Solid Tumors

CAR-T (chimeric antigen receptor T) cells have emerged as a milestone in the treatment of patients with refractory B-cell neoplasms. However, despite having unprecedented efficacy against hematological malignancies, the treatment is far from flawless. Its greatest drawbacks arise from a challenging and expensive production process, strict patient eligibility criteria and serious toxicity profile. One possible solution, supported by robust research, is the replacement of T lymphocytes with NK cells for CAR expression. NK cells seem to be an attractive vehicle for CAR expression as they can be derived from multiple sources and safely infused regardless of donor-patient matching, which greatly reduces the cost of the treatment. CAR-NK cells are known to be effective against hematological malignancies, and a growing number of preclinical findings indicate that they have activity against non-hematological neoplasms. Here, we present a thorough overview of the current state of knowledge regarding the use of CAR-NK cells in treating various solid tumors.

T-Cell Dysfunction as a Limitation of Adoptive Immunotherapy: Current Concepts and Mitigation Strategies

Simple Summary

T cells are immune cells that can be used to target infections or cancers. Adoptive T-cell immunotherapy leverages these properties and/or confers new features to T cells through ex vivo manipulations prior to their use in patients. However, as a “living drug,” the function of these cells can be hampered by several built-in physiological constraints and external factors that limit their efficacy. Manipulating T cells ex vivo can impart dysfunctional features to T cells through repeated stimulations and expansion, but it also offers many opportunities to improve the therapeutic potential of these cells, including emerging interventions to prevent or reverse T-cell dysfunction developing ex vivo or after transfer in patients. This review outlines the various forms of T-cell dysfunction, emphasizes how it affects various types of T-cell immunotherapy approaches, and describes current and anticipated strategies to limit T-cell dysfunction.

Abstract

Over the last decades, cellular immunotherapy has revealed its curative potential. However, inherent physiological characteristics of immune cells can limit the potency of this approach. Best defined in T cells, dysfunction associated with terminal differentiation, exhaustion, senescence, and activation-induced cell death, undermine adoptive cell therapies. In this review, we concentrate on how the multiple mechanisms that articulate the various forms of immune dysfunction impact cellular therapies primarily involving conventional T cells, but also other lymphoid subtypes. The repercussions of immune cell dysfunction across the full life cycle of cell therapy, from the source material, during manufacturing, and after adoptive transfer, are discussed, with an emphasis on strategies used during ex vivo manipulations to limit T-cell dysfunction. Applicable to cellular products prepared from native and unmodified immune cells, as well as genetically engineered therapeutics, the understanding and potential modulation of dysfunctional features are key to the development of improved cellular immunotherapies.

CAR-NK Cells Effectively Target the D614 and G614 SARS-CoV-2-infected Cells

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is highly contagious presenting a significant public health issue. Current therapies used to treat coronavirus disease 2019 (COVID-19) include monoclonal antibody cocktail, convalescent plasma, antivirals, immunomodulators, and anticoagulants, though the current therapeutic options remain limited and expensive. The vaccines from Pfizer and Moderna have recently been authorized for emergency use, which are invaluable for the prevention of SARS-CoV-2 infection. However, their long-term side effects are not yet to be documented, and populations with immunocompromised conditions (e.g., organ-transplantation and immunodeficient patients) may not be able to mount an effective immune response. In addition, there are concerns that wide-scale immunity to SARS-CoV-2 may introduce immune pressure that could select for escape mutants to the existing vaccines and monoclonal antibody therapies. Emerging evidence has shown that chimeric antigen receptor (CAR)- natural killer (NK) immunotherapy has potent antitumor response in hematologic cancers with minimal adverse effects in recent studies, however, the potentials of CAR-NK cells in preventing and treating severe cases of COVID-19 has not yet been fully exploited. Here, we improve upon a novel approach for the generation of CAR-NK cells for targeting SARS-CoV-2 and its D614G mutant. CAR-NK cells were generated using the scFv domain of S309 (henceforward, S309-CAR-NK), a SARS-CoV and SARS-CoV-2 neutralizing antibody that targets the highly conserved region of SARS-CoV-2 spike (S) glycoprotein, therefore would be more likely to recognize different variants of SARS-CoV-2 isolates. S309-CAR-NK cells can specifically bind to pseudotyped SARS-CoV-2 virus and its D614G mutant. Furthermore, S309-CAR-NK cells can specifically kill target cells expressing SARS-CoV-2 S protein in vitro and show superior killing activity and cytokine production, compared to that of the recently published CR3022-CAR-NK cells. Thus, these results pave the way for generating 'off-the-shelf' S309-CAR-NK cells for treatment in high-risk individuals as well as provide an alternative strategy for patients unresponsive to current vaccines.

Natural Killer Cells in Immunotherapy: Are We Nearly There?

Natural killer (NK) cells are potent anti-tumor and anti-microbial cells of our innate immune system. They are equipped with a vast array of receptors that recognize tumor cells and other pathogens. The innate immune activity of NK cells develops faster than the adaptive one performed by T cells, and studies suggest an important immunoregulatory role for each population against the other. The association, observed in acute myeloid leukemia patients receiving haploidentical killer-immunoglobulin-like-receptor-mismatched NK cells, with induction of complete remission was the determinant to begin an increasing number of clinical studies administering NK cells for the treatment of cancer patients. Unfortunately, even though transfused NK cells demonstrated safety, their observed efficacy was poor. In recent years, novel studies have emerged, combining NK cells with other immunotherapeutic agents, such as monoclonal antibodies, which might improve clinical efficacy. Moreover, genetically-modified NK cells aimed at arming NK cells with better efficacy and persistence have appeared as another option. Here, we review novel pre-clinical and clinical studies published in the last five years administering NK cells as a monotherapy and combined with other agents, and we also review chimeric antigen receptor-modified NK cells for the treatment of cancer patients. We then describe studies regarding the role of NK cells as anti-microbial effectors, as lessons that we could learn and apply in immunotherapy applications of NK cells; these studies highlight an important immunoregulatory role performed between T cells and NK cells that should be considered when designing immunotherapeutic strategies. Lastly, we highlight novel strategies that could be combined with NK cell immunotherapy to improve their targeting, activity, and persistence.