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

Re-imagining human cell culture media: Challenges, innovations, and future directions

The development of optimized culture media is pivotal to advancements in human cell culture, underpinning progress in regenerative medicine, cell therapies, and personalized medicine. While foundational formulations like Eagle's Minimum Essential Medium (MEM) and Dulbecco's Modified Eagle Medium (DMEM) have historically enabled significant biological research, these media were primarily designed for non-human cells and do not adequately address the unique metabolic and functional requirements of human cells. This review examines the evolution of cell culture media, identifying persistent challenges in reproducibility, scalability, and ethical concerns, particularly regarding the reliance on animal-derived components such as fetal bovine serum (FBS). We highlight innovations in serum-free and chemically defined media that offer promising alternatives by enhancing consistency, aligning with Good Manufacturing Practices, and addressing ethical concerns. Emerging approaches, including omics-based profiling, high-throughput screening, and artificial intelligence (AI)-driven media design, are reshaping media optimization by enabling precise tailoring to the needs of specific human cell types and patient-derived cells. Furthermore, we discuss economic and regulatory challenges, emphasizing the need for cost-effective and scalable solutions to facilitate clinical translation. Looking forward, integrating advanced biotechnological tools such as 3D bioprinting, organ-on-a-chip systems, and personalized media formulations presents a transformative opportunity for human cell culture. These innovations, aligned with ethical and clinical standards, can drive the development of human-specific media systems that ensure reproducibility, scalability, and enhanced therapeutic potential, thereby advancing both research and clinical applications.

The Role of NK Cells in Cancer Immunotherapy: Mechanisms, Evasion Strategies, and Therapeutic Advances

Background/Objectives: Natural killer (NK) cells play a crucial role in tumor surveillance by exerting cytotoxic activity and modulating immune responses. However, tumors employ diverse evasion strategies that limit NK cell effectiveness. This review aims to explore the molecular mechanisms of NK cell activation and inhibition in cancer, the influence of the tumor microenvironment, and the latest advancements in NK cell-based immunotherapies, including adoptive NK cell transfer and Chimeric Antigen Receptor-Natural Killer (CAR-NK) cell therapies. Methods: A comprehensive literature review was conducted, prioritizing peer-reviewed studies from the last decade on NK cell biology, tumor immune evasion, and immunotherapeutic applications. The analysis includes data from preclinical models and clinical trials evaluating NK cell expansion strategies, cytokine-based stimulation, and CAR-NK cell therapy developments. Results: NK cells eliminate tumors through cytotoxic granule release, death receptor pathways, and cytokine secretion. However, tumor cells evade NK-mediated immunity by downregulating activating ligands, secreting immunosuppressive molecules, and altering the tumor microenvironment. Novel NK cell-based therapies, such as CAR-NK cells and combination approaches with immune checkpoint inhibitors, enhance NK cell persistence and therapeutic efficacy against both hematologic and solid malignancies. Clinical trials suggest improved safety profiles compared to CAR-T therapies, with reduced cytokine release syndrome and graft-versus-host disease. Conclusions: While NK cell-based immunotherapies hold great promise, challenges remain, including limited persistence and tumor-induced immunosuppression. Addressing these hurdles will be critical for optimizing NK cell therapies and advancing next-generation, off-the-shelf immunotherapeutics for broader clinical applications.

Entinostat, a histone deacetylase inhibitor, enhances CAR-NK cell anti-tumor activity by sustaining CAR expression

Allogeneic natural killer (NK) cell therapy has demonstrated significant potential in cancer immunotherapy by harnessing NK cells to target malignancies. CD138-targeting chimeric antigen receptor (CAR)-engineered NK cells offer a promising therapeutic option for multiple myeloma (MM). However, sustaining CAR expression on CAR-NK cells during ex vivo expansion poses a challenge to developing effective immunotherapies. In this study, primary NK cells were isolated, cryopreserved, and modified to express anti-CD138 CARs through retroviral transduction. Histone deacetylase inhibitors (HDACi), particularly entinostat (ENT), were applied to enhance CAR expression stability in CAR-NK cells. Our findings indicate that ENT treatment significantly improves and maintains CAR expression, thereby enhancing the cytotoxic activity of CAR-NK cells against CD138-positive multiple myeloma cells. ENT-treated CAR-NK cells exhibited prolonged persistence and more significant tumor reduction in an MM tumor-bearing mouse model, highlighting the therapeutic potential of HDACi-treated CAR-NK cells. This study provides the first evidence that HDAC inhibitors can sustain CAR expression in CAR-NK cells in a promoter-dependent manner, potentially enhancing anti-tumor efficacy in multiple myeloma and underscoring the possible need for further clinical evaluation.

Synthetic short mRNA prevents metastasis via innate-adaptive immunity

Although most cancer deaths are caused by metastasis, there are no effective therapeutic approaches. This study describes the efficacy of a short synthetic mRNA (s-mRNA) designed by the sequence of non-vesicular extracellular IL1β-mRNA found in the pre-metastatic lung of tumor-bearing mice. The administration of s-mRNA inhibits murine lung metastasis by inducing the innate and adaptive immune systems. s-mRNA binds to ZC3H12D, an RNA-binding protein on natural killer cells and cytotoxic T lymphocytes. The ZC3H12D-s-mRNA complex translocated to the nucleus without being involved in translation. This process induces cytolytic activity and cell death in cancer cells without inducing a cytokine storm, and immune cells retain their antitumor activity. Although the antitumor activity of cytotoxic lymphocytes declines as the disease progresses in cancer patients, s-mRNA induces sustained high killing capacities of natural killer cells and cytotoxic T lymphocytes from colon cancer patients. Therefore, s-mRNA could be a breakthrough solution to prevent metastasis.

Allogeneic chimeric antigen receptor cell therapies for cancer: progress made and remaining roadblocks

Chimeric antigen receptor (CAR) T cells are revolutionizing cancer therapy, particularly for haematological malignancies, conferring durable and sometimes curative responses in patients with advanced-stage disease. The CAR T cell products currently approved for clinical use are all autologous and are often effective; however, in patients who are lymphopenic and/or heavily pretreated with chemotherapy, autologous T cells can be difficult to harvest in sufficient numbers or have functional impairments that might ultimately render them less efficacious. Moreover, autologous products take several weeks to produce, and each product can be used in only one patient. By contrast, allogeneic CAR T cells can be produced for many patients using T cells from a single healthy donor, can be optimized for safety and efficacy, can be instantly available for 'off-the-shelf' use and, therefore, might also be more cost-effective. Despite these potential advantages, the development of allogeneic CAR T cells has lagged behind that of autologous products, owing to the additional challenges such as avoiding graft-versus-host disease and host-mediated graft rejection. Over the past few years, the development of advanced genome-editing techniques has facilitated the generation of novel allogeneic CAR T cell products. Furthermore, CAR cell products derived from other cell types such as induced pluripotent stem cells and natural killer cells are being investigated for clinical use. In this Review, we discuss the potential of allogeneic CAR cell products to expand life-saving immunotherapy to a much broader population of patients in the coming years, the progress made to date and strategies to overcome remaining hurdles.

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.

Manufacturing Cell and Gene Therapies: Challenges in Clinical Translation

The safety and efficacy of both cell and gene therapies have been demonstrated in numerous preclinical and clinical trials. Chimeric antigen receptor T (CAR-T) cell therapy, which leverages the technologies of both cell and gene therapies, has also shown great promise for treating various cancers. Advancements in pertinent fields have also highlighted challenges faced while manufacturing cell and gene therapy products. Potential problems and obstacles must be addressed to ease the clinical translation of individual therapies. Literature reviews of representative cell-based, gene-based, and cell-based gene therapies with regard to their general manufacturing processes, the challenges faced during manufacturing, and QC specifications are limited. We review the general manufacturing processes of cell and gene therapies, including those involving mesenchymal stem cells, viral vectors, and CAR-T cells. The complexities associated with the manufacturing processes and subsequent QC/validation processes may present challenges that could impede the clinical progression of the products. This article addresses these potential challenges. Further, we discuss the use of the manufacturing model and its impact on cell and gene therapy.

Progress on Electro-Enhancement of Cell Manufacturing

With the long persistence of complex, chronic diseases in society, there is increasing motivation to develop cells as living medicine to treat diseases ranging from cancer to wounds. While cell therapies can significantly impact healthcare, the shortage of starter cells meant that considerable raw materials must be channeled solely for cell expansion, leading to expensive products with long manufacturing time which can prevent accessibility by patients who either cannot afford the treatment or have highly aggressive diseases and cannot wait that long. Over the last three decades, there has been increasing knowledge on the effects of electrical modulation on proliferation, but to the best of the knowledge, none of these studies went beyond how electro-control of cell proliferation may be extended to enhance industrial scale cell manufacturing. Here, this review is started by discussing the importance of maximizing cell yield during manufacturing before comparing strategies spanning biomolecular/chemical/physical to modulate cell proliferation. Next, the authors describe how factors governing invasive and non-invasive electrical stimulation (ES) including capacitive coupling electric field may be modified to boost cell manufacturing. This review concludes by describing what needs to be urgently performed to bridge the gap between academic investigation of ES to industrial applications.

Evaluating a combination treatment of NK cells and reovirus against bladder cancer cells using an in vitro assay to simulate intravesical therapy

Intravesical treatment using either reovirus or natural killer (NK) cells serves as an efficient strategy for the treatment of bladder cancer cells (BCCs); however, corresponding monotherapies have often shown modest cytotoxicity. The potential of a locoregional combination using high-dose reovirus and NK cell therapy in an intravesical approach has not yet been studied. In this study, we evaluated the effectiveness of reoviruses and expanded NK cells (eNK) as potential strategies for the treatment of bladder cancer. The anti-tumor effects of mono-treatment with reovirus type 3 Dearing strain (RC402 and RP116) and in combination with interleukin (IL)-18/-21-pretreated eNK cells were investigated on BCC lines (5637, HT-1376, and 253J-BV) using intravesical therapy to simulate in vitro model. RP116 and IL-18/-21-pretreated eNK cells exhibited effective cytotoxicity against grade 1 carcinoma (5637 cells) when used alone, but not against HT-1376 (grade 2 carcinoma) and 253J-BV cells (derived from a metastatic site). Notably, combining RP116 with IL-18/-21-pretreated eNK cells displayed effective cytotoxicity against both HT-1376 and 253J-BV cells. Our findings underscore the potential of a combination therapy using reoviruses and NK cells as a promising strategy for treating bladder cancer.

Efficacy of natural killer cell therapy combined with chemoradiotherapy in murine models of head and neck squamous cell carcinoma

BACKGROUND AIMS

Natural killer (NK) cell-based cancer immunotherapy is effective when combined with other treatment modalities such as irradiation and chemotherapy. NK cell's antitumor function to treat solid tumor, including head and neck squamous cell carcinoma (HNSCC), has been targeted recently. This study assessed NK cell recruitment in response to chemoradiation therapy (CRT) in HNSCC.

METHODS

Ex vivo expansion of NK cell, flow cytometry, cell viability assay, cytotoxicity assay, immunohistochemistry, and animal model were performed.

RESULTS

Mouse NK cells were recruited to the tumor site by CRT in a nude mouse model. Furthermore, expanded and activated human NK cells (eNKs) were recruited to the tumor site in response to CRT, and CRT enhanced the anti-tumor activity of eNK in an NOD/SCID IL-2Rγnull mouse model. Various HNSCC cancer cell lines exhibited different NK cell ligand activation patterns in response to CRT that correlated with NK cell-mediated cytotoxicity.

CONCLUSIONS

Identifying the activation patterns of NK cell ligands during CRT might improve patient selection for adjuvant NK cell immunotherapy combined with CRT. This is the first study to investigate the NK cell's antitumor function and recruitment with CRT in HNSCC mouse model.

Comparison of the different anti-CD16 antibody clones in the activation and expansion of peripheral blood NK cells

Natural killer (NK) cells are promising tool for cancer treatment. Methods have been developed for large-scale NK cell expansion, including feeder cell-based methods or methods involving stimulation with NK cell activating signals, such as anti-CD16 antibodies. Different clones of anti-CD16 antibodies are available; however, a comprehensive comparison of their differential effects on inducing NK cell activation and expansion has not been conducted among these various clones under the same experimental conditions. Herein, we found that the NK cell expansion rate differed depending on the various anti-CD16 antibodies (CB16, 3G8, B73.1, and MEM-154) coated on microbeads when stimulated with genetically engineered feeder cells, K562‑membrane-bound IL‑18, and mbIL‑21 (K562‑mbIL‑18/-21). Only the CB16 clone combination caused enhanced NK cell expansion over K562‑mbIL‑18/-21 stimulation alone with similar NK cell functionality. Treatment with the CB16 clone once on the initial day of NK cell expansion was sufficient to maximize the combination effect. Overall, we developed a more enhanced NK expansion system by merging a feeder to effectively stimulate CD16 with the CB16 clone.

Multifaceted characterization of the biological and transcriptomic signatures of natural killer cells derived from cord blood and placental blood

Background

Perinatal blood including umbilical cord blood and placental blood are splendid sources for allogeneic NK cell generation with high cytotoxicity of combating pathogenic microorganism and malignant tumor. Despite the generation of NK cells from the aforementioned perinatal blood, yet the systematical and detailed information of the biological and transcriptomic signatures of UC-NKs and P-NKs before large-scale clinical applications in disease remodeling is still largely obscure.

Methods

Herein, we took advantage of the “3IL”-based strategy for high-efficient generation of NK cells from umbilical cord blood and placental blood (UC-NKs and P-NKs), respectively. On the one hand, we conducted flow cytometry (FCM) assay and coculture to evaluate the subpopulations, cellular vitality and cytotoxic activity of the aforementioned NK cells. On the other hand, with the aid of RNA-SEQ and multiple bioinformatics analyses, we further dissected the potential diversities of UC-NKs and P-NKs from the perspectives of transcriptomes.

Results

On the basis of the “3IL” strategy, high-efficient NKs were generated from mononuclear cells (MNCs) in perinatal blood. P-NKs revealed comparable ex vivo expansion but preferable activation and cytotoxicity upon K562 cells over UC-NKs. Both of the two NKs showed diversity in cellular vitality and transcriptome including apoptotic cells, cell cycle, gene expression profiling and the accompanied multifaceted biological processes.

Conclusions

Our data revealed the multifaceted similarities and differences of UC-NKs and P-NKs both at the cellular and molecular levels. Our findings supply new references for allogeneic NK cell-based immunotherapy in regenerative medicine and will benefit the further exploration for illuminating the underlying mechanism as well.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-022-02697-6.

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.