Genetic Engineering and Enrichment of Human NK Cells for CAR-Enhanced Immunotherapy of Hematological Malignancies

Unlocking the Potential of CAR-NK Cell Therapy: Overcoming Barriers and Challenges in the Treatment of Myeloid Malignancies

Myeloid malignancies include various types of cancers that arise from the abnormal development or proliferation of myeloid cells within the bone marrow. Chimeric antigen receptor (CAR) T cell treatments, which show great potential for B cell and plasma cell cancers, face major challenges when used for myeloid malignancies. CAR natural killer (NK) cell-based immunotherapy encounters several challenges in treating myeloid cancers, including (i) poor gene transfer efficiency and expansion platforms in vitro, (ii) limited proliferation and persistence in vivo, (iii) antigenic heterogeneity, and (iv) an immunosuppressive tumor microenvironment. Despite these hurdles, "off-the-shelf" CAR-NK treatments showed encouraging results, marked by enhanced proliferation, prolonged persistence, enhanced tumor infiltration, and improved adaptability. This review offers a summary of the biological traits and cellular sources of NK cells along with a discussion of contemporary CAR designs. Furthermore, it addresses the challenges observed in preclinical research and clinical trials related to CAR-NK cell therapy for myeloid cancers, suggesting enhancement strategies.

Efficacy of chimeric antigen receptor engineered natural killer cells in the treatment of hematologic malignancies: a systematic review and meta-analysis of preclinical studies

BACKGROUND

Chimeric antigen receptor (CAR) engineered NK cells (CAR-NK) are a novel approach to the immunotherapy of hematologic malignancies which seeks to overcome some of the challenges faced by CAR-T cells (CAR-T). With few published clinical studies, preclinical studies can identify strategies to accelerate clinical translation. We conducted a systematic review on the preclinical in vivo use of CAR-NK for the treatment of hematologic malignancies to assess these therapies in a holistic and unbiased manner.

METHODS

Our protocol was registered with PROSPERO (ID: CRD42023438375). We performed a search of OVID MEDLINE, OVID Embase, and Embase for animal studies employing human CAR-NK cells in the treatment of hematologic malignancies. Screening of studies for eligibility criteria was performed in duplicate. Our primary outcomes were survival and reduction in tumor volume. Data extraction from individual experiments was performed by one reviewer using DigitizeitTM software and verified by a second reviewer. Meta-analysis and subgroup analyses were performed using Comprehensive Meta-AnalysisTM software. Information for descriptive outcomes was extracted in duplicate by two independent reviewers. Risk of bias was assessed using the SYRCLE Risk of Bias Tool for Animal Studies.

RESULTS

A total of 34 papers met eligibility criteria. Overall, CD19 was the most common antigen targeted however there was substantial diversity in antigenic targets, source material for generating CAR-NK cells, and NK cell modifications. Mice treated with CAR-NK therapy survived significantly longer than untreated mice (median survival ratio of 1.18, 95% CI: 1.10-1.27, P < 0.001), and mice treated with nonengineered NK cells (median survival ratio 1.13, 95% CI: 1.03-1.23, P < 0.001). Similarly, treatment with CAR-NK significantly reduced the tumor burden when compared to untreated mice (ratio of mean tumor volume 0.23, 95% CI: 0.17-0.32, P < 0.001) or mice treated with nonengineered NK cells (ratio of mean tumor volume 0.37, 95% CI: 0.28-0.51, P < 0.001). Subgroup analysis showed that cotreatment with IL-15 reduced tumor volume but did not increase survival. In general, CAR-NK cell persistence was short but was increased by IL-15.

CONCLUSIONS

CAR-NK shows promise for the treatment of hematologic malignancies in preclinical models.

Chimeric antigen receptor natural killer cell therapy: A systematic review of preclinical studies for hematologic and solid malignancies

Advancements in the field of CAR-T therapy have brought about a revolution in the treatment of numerous types of cancer in the past ten years. However, despite the remarkable success achieved thus far, certain barriers impede the widespread implementation of this therapy such as intricate manufacturing processes and treatment-associated toxicities. As an alternative, chimeric antigen receptor-engineered natural killer cell (CAR-NK) therapy presents a viable opportunity for a simpler and more cost-effective "off-the-shelf" treatment option, which is likely to result in fewer adverse reactions. A total of 71 studies were included in this review. Eligible studies were searched and reviewed from the databases of PubMed, Web of Science and Scopus. Based on data extracted from articles, we concluded that CAR-NK cell efficiency can vary considerably depending on factors such as tumor model, dosage, CAR generation and expansion method. Furthermore, investigating consequences of utilizing various constructs and generations of CAR-NK cells on their anti-tumor activity examined in this review.

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.

The Pluripotent Path to Immunotherapy

Adoptive cell therapy (ACT) enhances the patient's own immune cells' ability to identify and eliminate cancer cells. Several immune cell types are currently being applied in autologous ACT, including T cells, natural killer (NK) cells, and macrophages. The cells' inherent antitumor capacity can be used, or they can be targeted toward tumor-associated antigen through expression of a chimeric antigen receptor (CAR). Although CAR-based ACT has achieved great results in hematologic malignancies, the accessibility of ACT is limited by the autologous nature of the therapy. Induced pluripotent stem cells (iPSCs) hold the potential to address this challenge, because they can provide an unlimited source for the in vitro generation of immune cells. Various immune subsets have been generated from iPSC for application in ACT, including several T-cell subsets (αβT cells, mucosal-associated invariant T cells, invariant NKT [iNKT] cells, and γδT cells), as well as NK cells, macrophages, and neutrophils. iPSC-derived αβT, NK, and iNKT cells are currently being tested in phase I clinical trials. The ability to perform (multiplexed) gene editing at the iPSC level and subsequent differentiation into effector populations not only expands the arsenal of ACT but allows for development of ACT utilizing cell types which cannot be efficiently obtained from peripheral blood or engineered and expanded in vitro.

A structural, genetic and clinical comparison of CAR-T cells and CAR-NK cells: companions or competitors?

In recent years, following the groundbreaking achievements of chimeric antigen receptor (CAR) T cell therapy in hematological cancers, and advancements in cell engineering technologies, the exploration of other immune cells has garnered significant attention. CAR-Therapy extended beyond T cells to include CAR natural killer (NK) cells and CAR-macrophages, which are firmly established in the clinical trial landscape. Less conventional immune cells are also making their way into the scene, such as CAR mucosal-associated invariant T (MAIT) cells. This progress is advancing precision medicine and facilitating the development of ready-to-use biological treatments. However, in view of the unique features of natural killer cells, adoptive NK cell immunotherapy has emerged as a universal, allogenic, "off-the shelf" therapeutic strategy. CAR-NK cytotoxic cells present targeted tumor specificity but seem to be devoid of the side effects associated with CAR-T cells. CAR-NK cells appear to be potentially promising candidates for cancer immunotherapy. However, their application is hindered by significant challenges, particularly the limited persistence of CAR-NK cells in the body, which poses a hurdle to their sustained effectiveness in treating cancer. Based upon the foregoing, this review discusses the current status and applications of both CAR-T cells and CAR-NK cells in hematological cancers, and provides a comparative analysis of the structure, genetics, and clinical outcomes between these two types of genetically modified immune cells.

Advanced multiparametric image spectroscopy and super-resolution microscopy reveal a minimal model of CD95 signal initiation

Unraveling the concentration-dependent spatiotemporal organization of receptors in the plasma membrane is crucial to understand cell signal initiation. A paradigm of this process is the oligomerization of CD95 during apoptosis signaling, with different oligomerization models being discussed. Here, we establish the molecular-sensitive approach cell lifetime Förster resonance energy transfer image spectroscopy to determine CD95 configurations in live cells. These data are corroborated by stimulated emission depletion microscopy, confocal photobleaching step analysis, and fluorescence correlation spectroscopy. We probed CD95 interactions for concentrations of ~10 to 1000 molecules per square micrometer, over nanoseconds to hours, and molecular to cellular scales. Quantitative benchmarking was achieved establishing high-fidelity monomer and dimer controls. While CD95 alone is primarily monomeric (~96%) and dimeric (4%), the addition of ligand induces oligomerization to dimers/trimers (~15%) leading to cell death. This study highlights molecular concentration effects and oligomerization dynamics. It reveals a minimal model, where small CD95 oligomers suffice to efficiently initiate signaling.

Molecular characteristics and immune microenvironment of gastrointestinal stromal tumours: targets for therapeutic strategies

Gastrointestinal stromal tumours (GISTs) are the most common mesenchymal tumours, arising mainly from the interstitial cells of Cajal (ICCs) of the gastrointestinal tract. As radiotherapy and chemotherapy are generally ineffective for GISTs, the current primary treatment is surgical resection. However, surgical resection is not choice for most patients. Therefore, new therapeutic strategies are urgently needed. Targeted therapy, represented by tyrosine kinase inhibitors (TKIs), and immunotherapy, represented by immune checkpoint inhibitor therapies and chimeric antigen receptor T-cell immunotherapy (CAR-T), offer new therapeutic options in GISTs and have shown promising treatment responses. In this review, we summarize the molecular classification and immune microenvironment of GISTs and discuss the corresponding targeted therapy and immunotherapy options. This updated knowledge may provide more options for future therapeutic strategies and applications in GISTs.

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.

Chimeric antigen receptor (CAR) modified T Cells in acute myeloid leukemia: limitations and expectations

Acute myeloid leukemia (AML) is an aggressive hematologic malignancy with a poor prognosis despite the advent of novel therapies. Consequently, a major need exists for new therapeutic options, particularly for patients with relapsed/refractory (R/R) AML. In recent years, it has been possible to individualize the treatment of a subgroup of patients, particularly with the emergence of multiple targeted therapies. Nonetheless, a considerable number of patients remain without therapeutic options, and overall prognosis remains poor because of a high rate of disease relapse. In this sense, cellular therapies, especially chimeric antigen receptor (CAR)-T cell therapy, have dramatically shifted the therapeutic options for other hematologic malignancies, such as diffuse large B cell lymphoma and acute lymphoblastic leukemia. In contrast, effectively treating AML with CAR-based immunotherapy poses major biological and clinical challenges, most of them derived from the unmet need to identify target antigens with expression restricted to the AML blast without compromising the viability of the normal hematopoietic stem cell counterpart. Although those limitations have hampered CAR-T cell therapy translation to the clinic, there are several clinical trials where target antigens, such as CD123, CLL-1 or CD33 are being used to treat AML patients showing promising results. Moreover, there are continuing efforts to enhance the specificity and efficacy of CAR-T cell therapy in AML. These endeavors encompass the exploration of novel avenues, including the development of dual CAR-T cells and next-generation CAR-T cells, as well as the utilization of gene editing tools to mitigate off-tumor toxicities. In this review, we will summarize the ongoing clinical studies and the early clinical results reported with CAR-T cells in AML, as well as highlight CAR-T cell limitations and the most recent approaches to overcome these barriers. We will also discuss how and when CAR-T cells should be used in the context of AML.

Adoptive cell therapy for solid tumors beyond CAR-T: Current challenges and emerging therapeutic advances

Adoptive cellular immunotherapy using immune cells expressing chimeric antigen receptors (CARs) is a highly specific anti-tumor immunotherapy that has shown promise in the treatment of hematological malignancies. However, there has been a slow progress toward the treatment of solid tumors owing to the complex tumor microenvironment that affects the localization and killing ability of the CAR cells. Solid tumors with a strong immunosuppressive microenvironment and complex vascular system are unaffected by CAR cell infiltration and attack. To improve their efficacy toward solid tumors, CAR cells have been modified and upgraded by "decorating" and "pruning". This review focuses on the structure and function of CARs, the immune cells that can be engineered by CARs and the transformation strategies to overcome solid tumors, with a view to broadening ideas for the better application of CAR cell therapy for the treatment of solid tumors.

Uncovering the cellular and omics characteristics of natural killer cells in the bone marrow microenvironment of patients with acute myeloid leukemia

BACKGROUND

Acute myeloid leukemia (AML) is a highly heterogeneous hematologic malignancy and the most frequently acute leukemia of stem cell precursors and the myeloid derivatives in adult. Longitudinal studies have indicated the therapeutic landscape and drug resistance for patients with AML are still intractable, which largely attribute to the deficiency of detailed information upon the pathogenesis.

METHODS

In this study, we compared the cellular phenotype of resident NK cells (rAML-NKs, rHD-NKs) and expanded NK cells (eAML-NKs, eHD-NKs) from bone marrow of AML patients (AML) and healthy donors (HD). Then, we took advantage of the co-culture strategy for the evaluation of the in vitro cytotoxicity of NK cells upon diverse tumor cell lines (e.g., K562, Nalm6, U937). With the aid of RNA-sequencing (RNA-SEQ) and bioinformatics analyses (e.g., GOBP analysis, KEGG analysis, GSEA, volcano plot), we verified the similarities and differences of the omics features between eAML-NKs and eHD-NKs.

RESULTS

Herein, we verified the sharp decline in the content of total resident NK cells (CD3-CD56+) in rAML-NKs compared to rHD-NKs. Differ from the expanded eHD-NKs, eAML-NKs revealed decline in diverse NK cell subsets (NKG2D+, CD25+, NKp44+, NKp46+) and alterations in cellular vitality but conservations in cytotoxicity. According to transcriptomic analysis, AML-NKs and HD-NKs showed multifaceted distinctions in gene expression profiling and genetic variations.

CONCLUSIONS

Collectively, our data revealed the variations in the cytobiological and transcriptomic features between AML-NKs and HD-NKs in bone marrow environment. Our findings would benefit the further development of novel biomarkers for AML diagnosis and NK cell-based cytotherapy in future.

A promising natural killer cell-based model and a nomogram for the prognostic prediction of clear-cell renal cell carcinoma

BACKGROUND

Clear-cell renal cell carcinoma (ccRCC) is one of prevalent kidney malignancies with an unfavorable prognosis. There is a need for a robust model to predict ccRCC patient survival and guide treatment decisions.

METHODS

RNA-seq data and clinical information of ccRCC were obtained from the TCGA and ICGC databases. Expression profiles of genes related to natural killer (NK) cells were collected from the Immunology Database and Analysis Portal database. Key NK cell-related genes were identified using consensus clustering algorithms to classify patients into distinct clusters. A NK cell-related risk model was then developed using Least Absolute Shrinkage and Selection Operator (LASSO) Cox regression to predict ccRCC patient prognosis. The relationship between the NK cell-related risk score and overall survival, clinical features, tumor immune characteristics, as well as response to commonly used immunotherapies and chemotherapy, was explored. Finally, the NK cell-related risk score was validated using decision tree and nomogram analyses.

RESULTS

ccRCC patients were stratified into 3 molecular clusters based on expression of NK cell-related genes. Significant differences were observed among the clusters in terms of prognosis, clinical characteristics, immune infiltration, and therapeutic response. Furthermore, six NK cell-related genes (DPYSL3, SLPI, SLC44A4, ZNF521, LIMCH1, and AHR) were identified to construct a prognostic model for ccRCC prediction. The high-risk group exhibited poor survival outcomes, lower immune cell infiltration, and decreased sensitivity to conventional chemotherapies and immunotherapies. Importantly, the quantitative real-time polymerase chain reaction (qRT-PCR) confirmed significantly high DPYSL3 expression and low SLC44A4 expression in ACHN cells. Finally, the decision tree and nomogram consistently show the dramatic prediction performance of the risk score on the survival outcome of the ccRCC patients.

CONCLUSIONS

The six-gene model based on NK cell-related gene expression was validated and found to accurately mirror immune microenvironment and predict clinical outcomes, contributing to enhanced risk stratification and therapy response for ccRCC patients.

Research Hotspots and Trends of NK Cell Immunotherapy for Acute Myeloid Leukemia: A Bibliometric Analysis From 2000 to 2023

BACKGROUND

Natural killer (NK) cell immunotherapy has shown promising therapeutic potential for acute myeloid leukemia (AML), especially with advancements in chimeric antigen receptor-engineered NK cells (CAR-NK) and artificial intelligence (AI). Despite these developments, the field lacks comprehensive bibliometric analyses to identify research hotspots and trends, which could guide future precision treatments.

METHODS

A bibliometric analysis of NK cell immunotherapy for AML was conducted using literature from 2000 to 2023 retrieved from the Web of Science Core Collection database. Data visualization tools like CiteSpace, VOSviewer, and RStudio were employed to analyze publication trends, country contributions, institutional collaborations, influential authors, and research themes.

RESULTS

The analysis identified 1513 studies, with the United States and China leading global contributions. Notable institutions include the University of Minnesota and MD Anderson Cancer Center. Hot topics include allogeneic NK therapy, CAR-NK cell therapy, and memory-like NK cells. Emerging trends highlight the integration of intelligent NK cells and combinatory therapies, offering promising avenues for AML treatment. Despite progress, challenges such as NK cell expansion, activation, and resistance mechanisms remain critical areas for research.

CONCLUSION

This study provides a comprehensive overview of the research landscape, highlighting the transformative potential of NK cell immunotherapy in AML. It underscores the need for international collaboration and continued innovation to overcome existing challenges and advance precision therapies.

Plasmacytoid dendritic cell expansion in myeloid neoplasms: A novel distinct subset of myeloid neoplasm?

Plasmacytoid dendritic cells (pDCs) are a specific dendritic cell type stemming from the myeloid lineage. Clinically and pathologically, neoplasms associated with pDCs are classified as blastic plasmacytoid dendritic cell neoplasm (BPDCN), mature plasmacytoid dendritic myeloid neoplasm (MPDMN) and pDC expansion in myeloid neoplasms (MNs). BPDCN was considered a rare and aggressive neoplasm in the 2016 World Health Organization (WHO) classification. MPDMN, known as mature pDC-derived neoplasm, is closely related to MNs and was first recognized in the latest 2022 WHO classification, proposing a new concept that acute myeloid leukemia cases could show clonally expanded pDCs (pDC-AML). With the advances in detection techniques, an increasing number of pDC expansion in MNs have been reported, but whether the pathogenesis is similar to that of MPDMN remains unclear. This review focuses on patient characteristics, diagnosis and treatment of pDC expansion in MNs to gain further insight into this novel and unique provisional subtype.

Exploiting innate immunity for cancer immunotherapy

Immunotherapies have revolutionized the treatment paradigms of various types of cancers. However, most of these immunomodulatory strategies focus on harnessing adaptive immunity, mainly by inhibiting immunosuppressive signaling with immune checkpoint blockade, or enhancing immunostimulatory signaling with bispecific T cell engager and chimeric antigen receptor (CAR)-T cell. Although these agents have already achieved great success, only a tiny percentage of patients could benefit from immunotherapies. Actually, immunotherapy efficacy is determined by multiple components in the tumor microenvironment beyond adaptive immunity. Cells from the innate arm of the immune system, such as macrophages, dendritic cells, myeloid-derived suppressor cells, neutrophils, natural killer cells, and unconventional T cells, also participate in cancer immune evasion and surveillance. Considering that the innate arm is the cornerstone of the antitumor immune response, utilizing innate immunity provides potential therapeutic options for cancer control. Up to now, strategies exploiting innate immunity, such as agonists of stimulator of interferon genes, CAR-macrophage or -natural killer cell therapies, metabolic regulators, and novel immune checkpoint blockade, have exhibited potent antitumor activities in preclinical and clinical studies. Here, we summarize the latest insights into the potential roles of innate cells in antitumor immunity and discuss the advances in innate arm-targeted therapeutic strategies.

Expanding the role of combined immunochemotherapy and immunoradiotherapy in the management of head and neck cancer (Review)

Immunotherapy has become one of the most promising approaches in tumor therapy, and there are numerous associated clinical trials in China. As an immunosuppressive tumor, head and neck squamous cell carcinoma (HNSCC) carries a high mutation burden, making immune checkpoint inhibitors promising candidates in this field due to their unique mechanism of action. The present review outlines a comprehensive multidisciplinary cancer treatment approach and elaborates on how combining immunochemotherapy and immunoradiotherapy guidelines could enhance clinical efficacy in patients with HNSCC. Furthermore, the present review explores the immunology of HNSCC, current immunotherapeutic strategies to enhance antitumor activity, ongoing clinical trials and the future direction of the current immune landscape in HNSCC. Advanced-stage HNSCC presents with a poor prognosis, low survival rates and minimal improvement in patient survival trends over time. Understanding the potential of immunotherapy and ways to combine it with surgery, chemotherapy and radiotherapy confers good prospects for the management of human papillomavirus (HPV)-positive HNSCC, as well as other HPV-positive malignancies. Understanding the immune system and its effect on HNSCC progression and metastasis will help to uncover novel biomarkers for the selection of patients and to enhance the efficacy of treatments. Further research on why current immune checkpoint inhibitors and targeted drugs are only effective for some patients in the clinic is needed; therefore, further research is required to improve the overall survival of affected patients.

Chimeric antigen receptor engineered natural killer cells for cancer therapy

Natural killer (NK) cells, a unique component of the innate immune system, are inherent killers of stressed and transformed cells. Based on their potent capacity to kill cancer cells and good tolerance of healthy cells, NK cells have been successfully employed in adoptive cell therapy to treat cancer patients. In recent years, the clinical success of chimeric antigen receptor (CAR)-T cells has proven the vast potential of gene-manipulated immune cells as the main force to fight cancer. Following the lessons learned from mature gene-transfer technologies and advanced strategies in CAR-T therapy, NK cells have been rapidly explored as a promising candidate for CAR-based therapy. An exponentially growing number of studies have employed multiple sources of CAR-NK cells to target a wide range of cancer-related antigens, showing remarkable outcomes and encouraging safety profiles. Clinical trials of CAR-NK cells have also shown their impressive therapeutic efficacy in the treatment of hematological tumors, but CAR-NK cell therapy for solid tumors is still in the initial stages. In this review, we present the favorable profile of NK cells as a potential platform for CAR-based engineering and then summarize the outcomes and strategies of CAR-NK therapies in up-to-date preclinical and clinical investigations. Finally, we evaluate the challenges remaining in CAR-NK therapy and describe existing strategies that can assist us in devising future prospective solutions.

Natural killer cells strengthen antitumor activity of cisplatin by immunomodulation and ameliorate cisplatin-induced side effects

PURPOSE

Cisplatin-based chemotherapy is now an important treatment for improving bladder cancer prognosis. However, challenges in clinical treatment remain due to the numerous side effects of chemotherapy. Natural killer (NK) cells regulate certain immune responses and play a significant role in tumor surveillance and control. The efficacy of NK cells combined with cisplatin for chemoimmunotherapy in bladder cancer remains poorly understood.

METHODS

In this study, we established an MB49 tumor-bearing mouse model, tumor growth was measured in a control group and in groups treated with cisplatin, NK cells or both. Organ indices, biochemical indicators of blood serum, and expression of apoptotic proteins were used to assess the extent of organ damage. ELISA and immunohistochemistry were used to analyze the levels of immune cells and cytokine expression in serum, spleen, and tumor tissue.

RESULTS

NK cells combined with cisplatin exhibited better antitumor activity. NK cells also alleviated the organ damage caused by cisplatin and improved the survival rate. Treatment with NK cells increased the expression of IL-2 and IFN-γ as well as the number of CD4 + T cells. Additionally, cisplatin increased the expression of natural killer group 2, member D (NKG2D) ligands thus activating NK cells to kill tumor cells.

CONCLUSION

NK cells could alleviate the side effects of cisplatin treatment and enhance antitumor activity. The combination of NK cells and cisplatin thus provides a promising option for chemoimmunotherapy for bladder cancer.

Clinical application and prospect of immune checkpoint inhibitors for CAR-NK cell in tumor immunotherapy

Chimeric antigen receptor (CAR) engineering of natural killer (NK) cells is an attractive research field in tumor immunotherapy. While CAR is genetically engineered to express certain molecules, it retains the intrinsic ability to recognize tumor cells through its own receptors. Additionally, NK cells do not depend on T cell receptors for cytotoxic killing. CAR-NK cells exhibit some differences to CAR-T cells in terms of more precise killing, numerous cell sources, and increased effectiveness in solid tumors. However, some problems still exist with CAR-NK cell therapy, such as cytotoxicity, low transfection efficiency, and storage issues. Immune checkpoints inhibit immune cells from performing their normal killing function, and the clinical application of immune checkpoint inhibitors for cancer treatment has become a key therapeutic strategy. The application of CAR-T cells and immune checkpoint inhibitors is being evaluated in numerous ongoing basic research and clinical studies. Immune checkpoints may affect the function of CAR-NK cell therapy. In this review, we describe the combination of existing CAR-NK cell technology with immune checkpoint therapy and discuss the research of CAR-NK cell technology and future clinical treatments. We also summarize the progress of clinical trials of CAR-NK cells and immune checkpoint therapy.

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.