Successful Transfer of Umbilical Cord Blood CD34+ Hematopoietic Stem and Progenitor-derived NK Cells in Older Acute Myeloid Leukemia Patients

Evolution of natural killer cell-targeted therapy for acute myeloid leukemia

In hematologic oncology, acute myeloid leukemia (AML) presents a significant challenge due to its complex genetic landscape and resistance to conventional therapies. Despite advances in treatment, including intensive chemotherapy and hematopoietic stem cell transplantation (HSCT), the prognosis for many patients with AML remains poor. Recently, immunotherapy has emerged as a promising approach to improve outcomes by augmenting existing treatments. Natural killer (NK) cells, a subset of innate lymphoid cells, have garnered attention for their potent cytotoxic capabilities against AML cells. In this review, we discuss the role of NK cells in AML immunosurveillance, their dysregulation in patients with AML, and various therapeutic strategies leveraging NK cells in AML treatment. We explore the challenges and prospects associated with NK cell therapy, including approaches to enhance NK cell function, overcome immune evasion mechanisms, and optimize treatment efficacy. Finally, we emphasize the importance of further research to validate and refine patient-first NK cell-based immunotherapies for AML.

Allogeneic NK cells induce the in vitro activation of monocyte-derived and conventional type-2 dendritic cells and trigger an inflammatory response under cancer-associated conditions

Natural killer (NK) cells are innate lymphocytes capable to recognize and kill virus-infected and cancer cells. In the past years, the use of allogeneic NK cells as anti-cancer therapy gained interest due to their ability to induce graft-versus-cancer responses without causing graft-versus-host disease and multiple protocols have been developed to produce high numbers of activated NK cells. While the ability of these cells to mediate tumor kill has been extensively studied, less is known about their capacity to influence the activity of other immune cells that may contribute to a concerted anti-tumor response in the tumor microenvironment (TME). In this study, we analyzed how an allogeneic off-the-shelf cord blood stem cell-derived NK-cell product influenced the activation of dendritic cells (DC). Crosstalk between NK cells and healthy donor monocyte-derived DC (MoDC) resulted in the release of IFNγ and TNF, MoDC activation, and the release of the T-cell-recruiting chemokines CXCL9 and CXCL10. Moreover, in the presence of prostaglandin-E2, NK cell/MoDC crosstalk antagonized the detrimental effect of IL-10 on MoDC maturation leading to higher expression of multiple (co-)stimulatory markers. The NK cells also induced activation of conventional DC2 (cDC2) and CD8+ T cells, and the release of TNF, GM-CSF, and CXCL9/10 in peripheral blood mononuclear cells of patients with metastatic colorectal cancer. The activated phenotype of MoDC/cDC2 and the increased release of pro-inflammatory cytokines and T-cell-recruiting chemokines resulting from NK cell/DC crosstalk should contribute to a more inflamed TME and may thus enhance the efficacy of T-cell-based therapies.

Thymic NK-Cells and Their Potential in Cancer Immunotherapy

Natural killer (NK)-cells are innate immune cells with potent anti-tumor capacity, capable of recognizing target cells without prior exposure. For this reason, NK-cells are recognized as a useful source of cell therapy. Although most NK-cells are derived from the bone marrow (BM), a separate developmental pathway in the thymus also exists, producing so-called thymic NK-cells. Unlike conventional NK-cells, thymic NK (tNK)-cells have a combined capacity for cytokine production and a natural ability to kill tumor cells in the presence of NK-cell receptor stimulatory ligands. Furthermore, tNK-cells are reported to express CD3 subunits intracellularly, without the presence of a rearranged T-cell receptor (TCR). This unique feature may enable harnessing of these cells with a TCR to combine NK- and T-cell effector properties in one cell type. The development, phenotype, and function of tNK-cells, and potential as a cell therapy is, however, poorly explored. In this review, we provide an overview of current literature on both murine and human tNK-cells in comparison to conventional BM-derived NK-cells, and discuss the potential applications of this cellular subset in the context of cancer immunotherapy.

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.

Engineering of CD34+ progenitor-derived natural killer cells with higher-affinity CD16a for enhanced antibody-dependent cellular cytotoxicity

BACKGROUND AIMS

Natural killer (NK) cell transfer is a promising cellular immunotherapy for cancer. Previously, we developed a robust method to generate large NK cell numbers from CD34+ hematopoietic stem and progenitor cells (HSPCs), which exhibit strong anti-tumor activity. However, since these cells express low levels of the Fc receptor CD16a in vitro, antibody-dependent cellular cytotoxicity (ADCC) by these cells is limited. To broaden clinical applicability of our HSPC-NK cells toward less NK-sensitive malignancies, we aimed to improve ADCC through CD16a transduction.

METHODS

Using wildtype and S197P mutant greater-affinity (both with V158) CD16a retroviral transgenes (i.e., a cleavable and noncleavable CD16a upon stimulation), we generated CD16a HSPC-transduced NK cells, with CD34+ cells isolated from umbilical cord blood (UCB) or peripheral blood after G-CSF stem cell mobilization (MPB). CD16a expressing NK cells were enriched using flow cytometry-based cell sorting. Subsequently, phenotypic analyses and functional assays were performed to investigate natural cytotoxicity and ADCC activity.

RESULTS

Mean transduction efficiency was 34% for UCB-derived HSPCs and 20% for MPB-derived HSPCs, which was enriched by flow cytometry-based cell sorting to >90% for both conditions. Expression of the transgene remained stable during the entire NK expansion cell generation process. Proliferation and differentiation of HSPCs were not hampered by the transduction process, resulting in effectively differentiated CD56+ NK cells after 5 weeks. Activation of the HSPC-derived NK cells resulted in significant shedding of wildtype CD16a transcribed from the endogenous gene, but not of the noncleavable mutant CD16a protein expressed from the transduced construct. The mean increase of CD107+IFNγ+ expressing NK cells after inducing ADCC was tenfold in enriched noncleavable CD16a HSPC-NK cells. Killing capacity of CD16a-transduced NK cells was significantly improved after addition of a tumor-targeting antibody in tumor cell lines and primary B-cell leukemia and lymphoma cells compared to unmodified HSPC-NK cells.

CONCLUSIONS

Together, these data demonstrate that the applicability of adoptive NK cell immunotherapy may be broadened to less NK-sensitive malignancies by upregulation of CD16a expression in combination with the use of tumor-targeting monoclonal antibodies.

The inhibition of ADAM17 in cord blood stem cell-derived CD16+ NK cells to enhance their cytotoxicity against acute lymphoblastic leukemia cells

Fortunately, ample efforts are being made to find the best strategy to improve the anti-leukemia capacity of NK cells for treating different types of cancer. Despite the favorable ADCC capacity of functional CD16 + NK cells for immunotherapy, when NK cells face leukemia cells, the CD16 receptor is cleaved during the process mediated by a disintegrin and metalloproteinase-17(ADAM17). Reduced CD16 expression on NK cells weakens their cytotoxicity against leukemia cells. In addition, the expression of the CD47 receptor is high in acute lymphoblastic leukemia (ALL) compared to normal cells and can be correlated with poor prognosis. In the present study, ADAM17 was inhibited in cord blood-derived CD16 + NK cells, and their activity against ALL cell lines was evaluated following blockage with anti-CD47 antibody. As the results showed, the CD16 expression was reduced in the NK cells co-cultured with ALL cell lines. However, the ADAM17 inhibition increased the CD16 expression on the NK cells. This enhanced the cytotoxicity of those cells as well as cytokine production was evaluated by measuring expression of CD107-a expression, and IFN-γ production. Moreover, the presence of the ADAM17 inhibitor increased the apoptosis effect of the generated NK cells in response to ALL cells. Therefore, the inhibition of ADAM17 is useful for the activity of CD16 + NK cells against cancer cells.

Targeting natural killer cells: from basic biology to clinical application in hematologic malignancies

Natural killer (NK) cell belongs to innate lymphoid cell family that contributes to host immunosurveillance and defense without pre-immunization. Emerging studies have sought to understand the underlying mechanism behind NK cell dysfunction in tumor environments, and provide numerous novel therapeutic targets for tumor treatment. Strategies to enhance functional activities of NK cell have exhibited promising efficacy and favorable tolerance in clinical treatment of tumor patients, such as immune checkpoint blockade (ICB), chimeric antigen receptor NK (CAR-NK) cell, and bi/trispecific killer cell engager (BiKE/TriKE). Immunotherapy targeting NK cell provides remarkable advantages compared to T cell therapy, including a decreased rate of graft versus-host disease (GvHD) and neurotoxicity. Nevertheless, advanced details on how to support the maintenance and function of NK cell to obtain better response rate and longer duration still remain to be elucidated. This review systematically summarizes the profound role of NK cells in tumor development, highlights up-to-date advances and current challenges of therapy targeting NK cell in the clinical treatment of hematologic malignancies.

Perspectives for the Use of Umbilical Cord Blood in Transplantation and Beyond: Initiatives for an Advanced and Sustainable Public Banking Program in Greece

The umbilical cord blood (UCB) donated in public UCB banks is a source of hematopoietic stem cells (HSC) alternative to bone marrow for allogeneic HSC transplantation (HSCT). However, the high rejection rate of the donated units due to the strict acceptance criteria and the wide application of the haploidentical HSCT have resulted in significant limitation of the use of UCB and difficulties in the economic sustainability of the public UCB banks. There is an ongoing effort within the UCB community to optimize the use of UCB in the field of HSCT and a parallel interest in exploring the use of UCB for applications beyond HSCT i.e., in the fields of cell therapy, regenerative medicine and specialized transfusion medicine. In this report, we describe the mode of operation of the three public UCB banks in Greece as an example of an orchestrated effort to develop a viable UCB banking system by (a) prioritizing the enrichment of the national inventory by high-quality UCB units from populations with rare human leukocyte antigens (HLA), and (b) deploying novel sustainable applications of UCB beyond HSCT, through national and international collaborations. The Greek paradigm of the public UCB network may become an example for countries, particularly with high HLA heterogeneity, with public UCB banks facing sustainability difficulties and adds value to the international efforts aiming to sustainably expand the public UCB banking system.

Generation of human ILC3 from allogeneic and autologous CD34+ hematopoietic progenitors toward adoptive transfer

Type 3 innate lymphoid cells (ILC3) are important in tissue homeostasis. In the gut, ILC3 repair damaged epithelium and suppress inflammation. In allogeneic hematopoietic cell transplantation (HCT), ILC3 protect against graft-versus-host disease (GvHD), most likely by restoring tissue damage and preventing inflammation. We hypothesize that supplementing HCT grafts with interleukin-22 (IL-22)-producing ILC3 may prevent acute GvHD. We therefore explored ex vivo generation of human IL-22-producing ILC3 from hematopoietic stem and progenitor cells (HSPC) obtained from adult, neonatal and fetal sources. We established a stroma-free system culturing human cord blood-derived CD34+ HSPC with successive cytokine mixes for 5 weeks. We analyzed the presence of phenotypically defined ILC, their viability, proliferation and IL-22 production (after stimulation) by flow cytometry and enzyme-linked immunosorbent assay (ELISA). We found that the addition of recombinant human IL-15 and the enhancer of zeste homolog 1/2 inhibitor UNC1999 promoted ILC3 generation. Similar results were demonstrated when UNC1999 was added to CD34+ HSPC derived from healthy adult granulocyte colony-stimulating factor mobilized peripheral blood and bone marrow, but not fetal liver. UNC1999 did not negatively impact IL-22 production in any of the HSPC sources. Finally, we observed that autologous HSPC mobilized from the blood of adults with hematological malignancies also developed into ILC3, albeit with a significantly lower capacity. Together, we developed a stroma-free protocol to generate large quantities of IL-22-producing ILC3 from healthy adult human HSPC that can be applied for adoptive transfer to prevent GvHD after allogeneic HCT.

Reprogramming natural killer cells for cancer therapy

The last decade has seen rapid development in the field of cellular immunotherapy, particularly in regard to chimeric antigen receptor (CAR)-modified T cells. However, challenges, such as severe treatment-related toxicities and inconsistent quality of autologous products, have hindered the broader use of CAR-T cell therapy, highlighting the need to explore alternative immune cells for cancer targeting. In this regard, natural killer (NK) cells have been extensively studied in cellular immunotherapy and were found to exert cytotoxic effects without being restricted by human leukocyte antigen and have a lower risk of causing graft-versus-host disease; making them favorable for the development of readily available "off-the-shelf" products. Clinical trials utilizing unedited NK cells or reprogrammed NK cells have shown early signs of their effectiveness against tumors. However, limitations, including limited in vivo persistence and expansion potential, remained. To enhance the antitumor function of NK cells, advanced gene-editing technologies and combination approaches have been explored. In this review, we summarize current clinical trials of antitumor NK cell therapy, provide an overview of innovative strategies for reprogramming NK cells, which include improvements in persistence, cytotoxicity, trafficking and the ability to counteract the immunosuppressive tumor microenvironment, and also discuss some potential combination therapies.

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.

NK cells as powerful therapeutic tool in cancer immunotherapy

BACKGROUND

Natural killer (NK) cells have gained considerable attention and hold great potential for their application in tumor immunotherapy. This is mainly due to their MHC-unrestricted and pan-specific recognition capabilities, as well as their ability to rapidly respond to and eliminate target cells. To artificially generate therapeutic NK cells, various materials can be utilized, such as peripheral blood mononuclear cells (PBMCs), umbilical cord blood (UCB), induced pluripotent stem cells (iPSCs), and NK cell lines. Exploiting the therapeutic potential of NK cells to treat tumors through in vivo and in vitro therapeutic modalities has yielded positive therapeutic results.

CONCLUSION

This review provides a comprehensive description of NK cell therapeutic approaches for tumors and discusses the current problems associated with these therapeutic approaches and the prospects of NK cell therapy for tumors.

Ovarian cancer treatment and natural killer cell-based immunotherapy

Background

Ovarian cancer (OC) is one of the malignant tumors that poses a serious threat to women's health. Natural killer (NK) cells are an integral part of the immune system and have the ability to kill tumor cells directly or participate indirectly in the anti-tumor immune response. In recent years, NK cell-based immunotherapy for OC has shown remarkable potential. However, its mechanisms and effects remain unclear when compared to standard treatment.

Methods

To explore the value of NK cell-based immunotherapy in the treatment of OC, we conducted a literature review. In comparison to standard treatment, our focus was primarily on the current anti-tumor mechanisms, the clinical effect of NK cells against OC, factors affecting the structure and function of NK cells, and strategies to enhance the effectiveness of NK cells.

Results

We found that NK cells exert their therapeutic effects in OC through mechanisms such as antibody-dependent cell cytotoxicity, perforin release, and granule enzyme secretion. They also secrete IFN-γ and TNF-α or engage in Fas/FasL and TRAIL/TRAILR pathways, mediating the death of OC cells. In clinical trials, the majority of patients experienced disease stability with mild side effects after receiving NK cell-based immunotherapy, but there is still a lack of high-quality research evidence regarding its clinical effectiveness. OC and prior experience with standard treatments have an effect on NK cells, and it may be considered to maximize NK cell effects through the modulation of the tumor microenvironment or combination with other therapies.

Conclusions

In this review, we have summarized the current evidence of NK cell applications in the treatment of OC. Furthermore, factors and strategies that influence and enhance the role of NK cell immunotherapy are discussed.

Allogeneic NK cells induce monocyte-to-dendritic cell conversion, control tumor growth, and trigger a pro-inflammatory shift in patient-derived cultures of primary and metastatic colorectal cancer

INTRODUCTION

Natural killer (NK) cells are innate lymphocytes with a key role in the defense against tumors. Recently, allogeneic NK cell-based therapies have gained interest because of their ability to directly lyse tumor cells without inducing graft-versus-host disease. As NK cells are also able to influence the function of other immune cells (most notably dendritic cells (DC)), a better understanding of the effects of allogeneic NK cell products on the host immune system is required. In this study, we analyzed the effects of an allogeneic off-the-shelf NK cell product, on the tumor microenvironment (TME) of primary and metastatic colorectal cancer (pCRC and mCRC, respectively). Moreover, we explored if the combination of NK cells with R848, a toll-like receptors 7/8 ligand, could further enhance any pro-inflammatory effects.

METHODS

Ex vivo expanded umbilical cord blood stem cell derived NK cells were co-cultured with pCRC or mCRC single-cell suspensions in the presence or absence of R848 for 5 days, during and after which flow cytometry and cytokine release profiling were performed.

RESULTS

NK cells efficiently induced lysis of tumor cells in both pCRC and mCRC single-cell suspensions and thereby controlled growth rates during culture. They also induced differentiation of infiltrating monocytic cells to an activated DC phenotype. Importantly, this NK-mediated myeloid conversion was also apparent in cultures after tumor cell depletion and was further enhanced by combining NK cells with R848. Moreover, NK cells, and to a greater extent, the combination of NK cells and R848, triggered CD8+ and CD4+ T-cell activation as well as a reduction in activated regulatory T cell rates. Finally, the combination of NK cells and R848 induced a pro-inflammatory shift in the cytokine release profile resulting in higher levels of interferon (IFN)-γ, interleukin (IL)-2, IL-12p70, and IFN-α as well as a reduction in IL-6, in both pCRC and mCRC cultures.

CONCLUSION

Allogeneic NK cells engaged in favorable myeloid crosstalk, displayed effective antitumor activity and, when combined with R848, induced a pro-inflammatory shift of the CRC TME. These findings prompt the investigation of NK cells and R848 as a combination therapy for solid tumors.

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.

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.

A pilot study of cord blood-derived natural killer cells as maintenance therapy after autologous hematopoietic stem cell transplantation

Natural killer (NK) cell based immunotherapy is an emerging strategy in hematologic malignancies because allogeneic NK cells can provide potent antitumor immunity without inducing graft-versus-host disease. Thus, we expanded cord blood-derived NK (CB-NK) cells ex vivo from random (MHC mismatched and KIR mismatched) donors, and investigate the feasibility and efficacy of repeated infusions CB-NK cells as maintenance therapy after autologous hematopoietic stem cell transplantation (ASCT). Thirty-one patients with acute myeloid leukemia and high-risk lymphoma received ASCT and the adoptive CB-NK cell multiple infusions for maintenance therapy. Patients received a median dose of 5.98 × 107/kg (range, 1.87-17.69 × 107/kg) CB-NK cells and 23 patients completed four infusions, 8 patients received three infusions. Only mild infusion reactions occurred in 15.5% of 116 infusions. Compared to a contemporaneous cohort of 90 patients who did not receive NK cell therapy, the adoptive transfer of CB-NK cells as maintenance treatment showed a tendency of difference in decreasing the relapse rate between CB-NK group and control group (9.7% vs 24.4%). The patients who receiving NK cell infusions had a better PFS and OS than controls (4 year PFS, 84.4 ± 8.3% vs 73.5 ± 5.4%; and 4 year OS, 100% vs 78.1 ± 5.4%) . These findings demonstrate safety and validity of maintenance therapy using CB-NK cells multiple infusions after ASCT, and it is worthy of further clinical trial verification.

Enhancing cord blood stem cell-derived NK cell growth and differentiation through hyperosmosis

BACKGROUND

Natural killer (NK) cells hold great promise in treating diverse hematopoietic and solid tumors. Despite their availability from peripheral blood and cord blood, stem cell-derived NK cells offer an 'off-the-shelf' solution. Hematopoietic stem and progenitor cells (HSPCs) derived from cord blood pose no risk to the newborn or mother and are virtually ideal sources for NK cell differentiation.

METHODS

We developed a modified protocol to differentiate HSPCs to NK cells under serum-free conditions using defined factors. The HSPC-derived NK (HSC-NK) cells could be expanded in a K562 feeder cell-dependent manner. Furthermore, using lentivirus transduction, chimeric antigen receptor (CAR)-modified HSPCs could be differentiated into NK cells, leading to the establishment of CAR-NK cells.

RESULTS

The efficiency of NK cell differentiation from HSPCs was increased through the simple modulation of osmotic pressure by the addition of sodium chloride or glucose. Furthermore, the hyperosmosis-primed HSC-NK cells exhibited enhanced proliferation capacity and maintained normal functional characteristics, including transcriptome and antitumor efficacy. The optimized protocol yielded approximately 1.8 million NK cells from a single CD34-positive cell within a 28-day cycle, which signifies more than a ten-fold increase in efficiency relative to the conventional methods. This optimized protocol was also suitable for generating CAR-NK cells with high yields compared to standard conditions.

CONCLUSIONS

The results of this study establish high osmotic pressure as a simple yet powerful adjustment that significantly enhances the efficiency and functionality of HSC-NK cells, including CAR-NK cells. This optimized protocol could lead to cost-effective, high-yield NK cell therapies, potentially revolutionizing cancer immunotherapy strategies.

Good manufacturing practice production of CD34+ progenitor-derived NK cells for adoptive immunotherapy in acute myeloid leukemia

Allogeneic natural killer (NK) cell-based immunotherapy is a promising, well-tolerated adjuvant therapeutic approach for acute myeloid leukemia (AML). For reproducible NK cell immunotherapy, a homogenous, pure and scalable NK cell product is preferred. Therefore, we developed a good manufacturing practice (GMP)-compliant, cytokine-based ex vivo manufacturing process for generating NK cells from CD34+ hematopoietic stem and progenitor cells (HSPC). This manufacturing process combines amongst others IL15 and IL12 and the aryl hydrocarbon receptor antagonist StemRegenin-1 (SR1) to generate a consistent and active NK cell product that fits the requirements for NK cell immunotherapy well. The cell culture protocol was first optimized to generate NK cells with required expansion and differentiation capacity in GMP-compliant closed system cell culture bags. In addition, phenotype, antitumor potency, proliferative and metabolic capacity were evaluated to characterize the HSPC-NK product. Subsequently, seven batches were manufactured for qualification of the process. All seven runs demonstrated consistent results for proliferation, differentiation and antitumor potency, and preliminary specifications for the investigational medicinal product for early clinical phase trials were set. This GMP-compliant manufacturing process for HSPC-NK cells (named RNK001 cells) is used to produce NK cell batches applied in the clinical trial 'Infusion of ex vivo-generated allogeneic natural killer cells in combination with subcutaneous IL2 in patients with acute myeloid leukemia' approved by the Dutch Ethics Committee (EudraCT 2019-001929-27).

Chemokine (C-X-C motif) ligand 1 maintains the immune surveillance function of natural killer cells via the PDK2/mTOR signaling pathway

Chemokine (C-X-C motif) ligand 1 (CXCL1) is mainly expressed on neutrophils and macrophages and has neutrophil chemoattractant activity. However, natural killer (NK) cells also express CXCL1. We were curious about the role played by CXCL1 in NK cells. Knocking out CXCL1 in hematopoietic cells does not affect the occurrence of NK cells; however, it does hinder NK cell maturity. CXCL1 deletion enhances the expression of immature markers and decreases the expression of functional markers in NK cells, which may explain why it hinders the maturation of NK cells. Specific knockout of CXCL1 in NK cells (CXCL1flox/flox Ncr1-cre) leads to impaired IFN-γ production and degranulation of NK cells. The lack of CXCL1 may prevent IFN-γ production and degranulation of NK cells by inhibiting the phosphorylation of AKTS473 and S6. Therefore, we have discovered a new role for CXCL1 in regulating NK cell development and immune surveillance, providing a novel theoretical basis for immunotherapy based on NK cells and potential therapeutic targets for the clinical use of NK cells. 1. Knockout of CXCL1 in hematopoietic cells inhibits the maturation of NK cells. 2. Knockout of CXCL1 in NK cells inhibits the clearance of lymphoma by NK cells and reduces IFN-γ production and CD107 expression in NK cells. 3. CXCL1 activates the PKD2/mTOR signaling pathway, and promotes the production of IFN-γ and the expression of CD107a in NK cells.

Immune dysregulation and potential targeted therapy in myelodysplastic syndrome

Myelodysplastic syndrome (MDS) is a heterogeneous group of clonal hematological diseases and a high risk for transformation to acute myeloid leukemia (AML). The identification of key genetic alterations in MDS has enhanced our understanding of the pathogenesis and evolution. In recent years, it has been found that both innate and adaptive immune signaling are activated in the hematopoietic niche of MDS with aberrant cytokine secretion in the bone marrow microenvironment. It is also clear that immune dysregulation plays an important role in the occurrence and progression of MDS, especially the destruction of the bone marrow microenvironment, including hematopoiesis and stromal components. The purpose of this review is to explore the role of immune cells, the immune microenvironment, and cytokines in the pathogenesis of MDS. Insights into the mechanisms of these variants may facilitate the development of novel effective treatments to prevent disease progression.

NKG2A gene variant predicts outcome of immunotherapy in AML and modulates the repertoire and function of NK cells

BACKGROUND

The natural killer (NK) complex (NKC) harbors multiple genes such as KLRC1 (encoding NKG2A) and KLRK1 (encoding NKG2D) that are central to regulation of NK cell function. We aimed at determining to what extent NKC haplotypes impact on NK cell repertoire and function, and whether such gene variants impact on outcome of IL-2-based immunotherapy in acute myeloid leukemia (AML).

METHODS

Genotype status of NKG2D rs1049174 and NKG2A rs1983526 was determined using the TaqMan-Allelic discrimination approach. To dissect the impact of single nucloetide polymorphim (SNP) on NK cell function, we engineered the K562 cell line with CRISPR to be killed in a highly NKG2D-dependent fashion. NK cells were assayed for degranulation, intracellular cytokine production and cytotoxicity using flow cytometry.

RESULTS

In AML patients receiving immunotherapy, the NKG2A gene variant, rs1983526, was associated with superior leukemia-free survival and overall survival. We observed that superior NK degranulation from individuals with the high-cytotoxicity NKG2D variant was explained by presence of a larger, highly responsive NKG2A+ subset. Notably, NK cells from donors homozygous for a favorable allele encoding NKG2A mounted stronger cytokine responses when challenged with leukemic cells, and NK cells from AML patients with this genotype displayed higher accumulation of granzyme B during histamine dihydrochloride/IL-2 immunotherapy. Additionally, among AML patients, the NKG2A SNP defined a subset of patients with HLA-B-21 TT with a strikingly favorable outcome.

CONCLUSIONS

The study results imply that a dimorphism in the NKG2A gene is associated with enhanced NK cell effector function and improved outcome of IL-2-based immunotherapy in AML.

Cell Reprogramming Techniques: Contributions to Cancer Therapy

The reprogramming of terminally differentiated cells over the past few years has become important for induced pluripotent stem cells (iPSCs) in the field of regenerative medicine and disease drug modeling. At the same time, iPSCs have also played an important role in human cancer research. iPSCs derived from cancer patients can be used to simulate the early progression of cancer, for drug testing, and to study the molecular mechanism of cancer occurrence. In recent years, with the application of cellular immunotherapy in cancer therapy, patient-derived iPSC-induced immune cells (T, natural killer, and macrophage cells) solve the problem of immune rejection and have higher immunogenicity, which greatly improves the therapeutic efficiency of immune cell therapy. With the continuous progress of cancer differentiation therapy, iPSC technology can reprogram cancer cells to a more primitive pluripotent undifferentiated state, and successfully reverse cancer cells to a benign phenotype by changing the epigenetic inheritance of cancer cells. This article reviews the recent progress of cell reprogramming technology in human cancer research, focuses on the application of reprogramming technology in cancer immunotherapy and the problems solved, and summarizes the malignant phenotype changes of cancer cells in the process of reprogramming and subsequent differentiation.

Early TRAIL-engagement elicits potent multimodal targeting of melanoma by CD34+ progenitor cell-derived NK cells

Umbilical cord blood (UCB) CD34⁺ progenitor cell-derived natural killer (NK) cells exert efficient cytotoxicity against various melanoma cell lines. Of interest, the relative cytotoxic performance of individual UCB donors was consistent throughout the melanoma panel and correlated with IFNγ, TNF, perforin and granzyme B levels. Importantly, intrinsic perforin and Granzyme B load predicts NK cell cytotoxic capacity. Exploring the mode of action revealed involvement of the activating receptors NKG2D, DNAM-1, NKp30, NKp44, NKp46 and most importantly of TRAIL. Strikingly, combinatorial receptor blocking led to more pronounced inhibition of cytotoxicity (up to 95%) than individual receptor blocking, especially in combination with TRAIL-blocking, suggesting synergistic cytotoxic NK cell activity via engagement of multiple receptors which was also confirmed in a spheroid model. Importantly, lack of NK cell-related gene signature in metastatic melanomas correlates with poor survival highlighting the clinical significance of NK cell therapies as a promising treatment for high-risk melanoma patients.

Immunotherapy for myelodysplastic syndrome and acute myeloid leukemia: where do we stand?

INTRODUCTION

Myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) are generally characterized by a poor prognosis with currently available therapies. Immunotherapies have already seen success in treating a variety of malignant disorders, and their role in managing myeloid cancers is evolving rapidly.

AREAS COVERED

This is a review of the immunotherapies tested in MDS and AML, including immune checkpoint inhibitors, bispecific antibodies, and cell therapies such as chimeric antigen receptor (CAR) T cell therapy, T cell receptor (TCR) engineered T cells, and natural killer (NK) cells, with a focus on clinical trials conducted to date and future directions.

EXPERT OPINION

Initial clinical trials exploring checkpoint inhibitors in MDS and AML have demonstrated high toxicity and disappointing efficacy. However, ongoing trials adding novel checkpoint inhibitors to standard therapy are more promising. Technological advances are improving the outlook for bispecific antibodies, and cellular therapies like adoptive NK cell infusion have favorable efficacy and tolerability in early trials. As our understanding of the immune microenvironment in MDS and AML improves, the role for immunotherapy in the treatment of these diseases will become clearer.

Leveraging CD16 fusion receptors to remodel the immune response for enhancing anti-tumor immunotherapy in iPSC-derived NK cells

BACKGROUND

The cytotoxicity of NK cells is largely dependent on IgG Fc receptor CD16a, which mediates antibody-dependent cell-mediated cytotoxicity (ADCC). The high-affinity and non-cleavable CD16 (hnCD16) is developed and demonstrated a multi-tumor killing potential. However, the hnCD16 receptor activates a single CD16 signal and provides limited tumor suppression. How to exploit the properties of hnCD16 and incorporate NK cell-specific activation domains is a promising development direction to further improve the anti-tumor activity of NK cells.

METHODS

To expand the applications of hnCD16-mediated ADCC for NK cell-based immunotherapy in cancer, we designed the hnCD16 Fusion Receptor (FR) constructs with the ectodomain of hnCD16 fused with NK cell-specific activating domains in the cytoplasm. FR constructs were transduced into CD16-negative NK cell line and human iPSC-derived NK (iNK) cells and effective FR constructs were screened. The up-regulation of immune activation- and cytokine-releasing-related pathways in FR-transduced NK cells was screened and validated by RNA sequencing and multiplex cytokines release assay, respectively. The tumor-killing efficiency was tested in vitro and in vivo via co-culture with tumor cell lines and xenograft mice-bearing human B-cell lymphoma, respectively.

RESULTS

We screened the most effective combination to kill B cell lymphoma, which was fused with the ectodomain of hnCD16a, NK-specific co-stimulators (2B4 and DAP10) and CD3ζ in cytoplasmic domains. The screened construct showed excellent cytotoxicity effects and sharp multiple cytokines releasing both in the NK cell line and iNK cells. The transcriptomic analysis and validation assays of hnCD16- and hnCD16FR-transduced NK cells showed that hnCD16FR transduction remodeled immune-related transcriptome in NK cells, where significant upregulation of genes related to cytotoxicity, high cytokines releasing, induced tumor cell apoptosis, and ADCC in comparison with hnCD16 transduction were highlighted. In vivo xenograft studies demonstrated that a single low-dose regimen of engineered hnCD16FR iPSC-derived NK cells co-administered with anti-CD20 mAb treatment mediated potent activity and significantly improved survival.

CONCLUSION

We developed a novel hnCD16FR construct that exhibits more potent cytotoxicity than reported hnCD16, which is a promising approach to treat malignancies with improved ADCC properties. We also offer a rationale for NK activation domains that remodel immune response to enhance CD16 signaling in NK cells.

Cell therapy in end-stage liver disease: replace and remodel

Liver disease is prevalent worldwide. When it reaches the end stage, mortality rises to 50% or more. Although liver transplantation has emerged as the most efficient treatment for end-stage liver disease, its application has been limited by the scarcity of donor livers. The lack of acceptable donor organs implies that patients are at high risk while waiting for suitable livers. In this scenario, cell therapy has emerged as a promising treatment approach. Most of the time, transplanted cells can replace host hepatocytes and remodel the hepatic microenvironment. For instance, hepatocytes derived from donor livers or stem cells colonize and proliferate in the liver, can replace host hepatocytes, and restore liver function. Other cellular therapy candidates, such as macrophages and mesenchymal stem cells, can remodel the hepatic microenvironment, thereby repairing the damaged liver. In recent years, cell therapy has transitioned from animal research to early human studies. In this review, we will discuss cell therapy in end-stage liver disease treatment, especially focusing on various cell types utilized for cell transplantation, and elucidate the processes involved. Furthermore, we will also summarize the practical obstacles of cell therapy and offer potential solutions.

Umbilical cord blood derived cellular therapy: advances in clinical development

While cord blood (CB) is primarily utilized in allogeneic hematopoietic cell transplantation (HCT), the development of novel cell therapy products from CB is a growing and developing field. Compared to adult blood, CB is characterized by a higher percentage of hematopoietic stem cells (HSCs) and progenitor cells, less mature immune cells that retain a high capacity of proliferation, and stronger immune tolerance that requires less stringent HLA-matching when used in the allogenic setting. Given that CB is an FDA regulated product and along with its unique cellular composition, CB lends itself as a readily available and safe starting material for the development of off-the-shelf cell therapies. Moreover, non-hematologic cells such as mesenchymal stem cell (MSCs) residing in CB or CB tissue also have potential in regenerative medicine and inflammatory and autoimmune conditions. In this review, we will focus on recent clinical development on CB-derived cellular therapies in the field of oncology, including T-cell therapies such as chimeric antigen receptor (CAR) T-cells, regulatory T-cells, and virus-specific T-cells; NK-cell therapies, such as NK cell engagers and CAR NK-cells; CB-HCT and various modifications; as well as applications of MSCs in HCT.

NK cell defects: implication in acute myeloid leukemia

Acute Myeloid Leukemia (AML) is a complex disease with rapid progression and poor/unsatisfactory outcomes. In the past few years, the focus has been on developing newer therapies for AML; however, relapse remains a significant problem. Natural Killer cells have strong anti-tumor potential against AML. This NK-mediated cytotoxicity is often restricted by cellular defects caused by disease-associated mechanisms, which can lead to disease progression. A stark feature of AML is the low/no expression of the cognate HLA ligands for the activating KIR receptors, due to which these tumor cells evade NK-mediated lysis. Recently, different Natural Killer cell therapies have been implicated in treating AML, such as the adoptive NK cell transfer, Chimeric antigen receptor-modified NK (CAR-NK) cell therapy, antibodies, cytokine, and drug treatment. However, the data available is scarce, and the outcomes vary between different transplant settings and different types of leukemia. Moreover, remission achieved by some of these therapies is only for a short time. In this mini-review, we will discuss the role of NK cell defects in AML progression, particularly the expression of different cell surface markers, the available NK cell therapies, and the results from various preclinical and clinical trials.

Harnessing novel strategies and cell types to overcome immune tolerance during adoptive cell therapy in cancer

Cell therapy encompasses an expanding spectrum of cell-based regimes for the treatment of human ailments, such as the use of immune cells, in particular T cells, for combating tumors and the modulation of inflammatory immune responses. In this review, we focus on cell therapy in the immuno-oncology space, which is largely driven by interests and demands from the clinics for better solutions to target various hard-to-treat cancers. We discuss recent advances in various types of cell therapies, including T cell receptor-T cells, chimeric antigen receptor (CAR)-T cells, tumor-infiltrating lymphocytes and natural killer cells. Particularly, the present review focuses on the strategies to improve therapeutic responses by either enhancing tumor recognition or the resilience of infused immune cells within tumor microenvironment. Finally, we discuss the potential of other innate or innate-like immune cell types currently being explored as promising CAR-cell alternatives that seek to address the limitations of conventional adoptive cell therapies.

Addressing Natural Killer Cell Dysfunction and Plasticity in Cell-Based Cancer Therapeutics

Natural killer (NK) cells are cytotoxic group 1 innate lymphoid cells (ILC), known for their role as killers of stressed, cancerous, and virally infected cells. Beyond this cytotoxic function, NK cell subsets can influence broader immune responses through cytokine production and have been linked to central roles in non-immune processes, such as the regulation of vascular remodeling in pregnancy and cancer. Attempts to exploit the anti-tumor functions of NK cells have driven the development of various NK cell-based therapies, which have shown promise in both pre-clinical disease models and early clinical trials. However, certain elements of the tumor microenvironment, such as elevated transforming growth factor (TGF)-β, hypoxia, and indoalemine-2,3-dioxygenase (IDO), are known to suppress NK cell function, potentially limiting the longevity and activity of these approaches. Recent studies have also identified these factors as contributors to NK cell plasticity, defined by the conversion of classical cytotoxic NK cells into poorly cytotoxic, tissue-resident, or ILC1-like phenotypes. This review summarizes the current approaches for NK cell-based cancer therapies and examines the challenges presented by tumor-linked NK cell suppression and plasticity. Ongoing efforts to overcome these challenges are discussed, along with the potential utility of NK cell therapies to applications outside cancer.

Umbilical Cord Blood Transplantation: Connecting Its Origin to Its Future

Transplantation of umbilical cord blood (UCB) is an attractive alternative source of hematopoietic stem cells (HSCs). The unique properties of cord blood and its distinct immune tolerance and engraftment kinetics compared to bone marrow (BM) and peripheral blood progenitor cells, permit a wider disparity in human leukocyte antigen levels between a cord blood donor and recipient after an unrelated umbilical cord blood transplant (UCBT). In addition, it is readily available and has a lowered risk of graft-versus-host disease (GvHD), with similar long-term clinical outcomes, compared to BM transplants. However, the relatively low number of cells administered by UCB units, as well as the associated delayed engraftment and immune reconstitution, pose limitations to the wide application of UCBT. Research into several aspects of UCBT has been evaluated, including the ex vivo expansion of cord blood HSCs and the process of fucosylation to enhance engraftment. Additionally, UCB has also been used in the treatment of several neurodegenerative and cardiovascular disorders with varying degrees of success. In this article, we will discuss the biology, clinical indications, and benefits of UCBT in pediatric and adult populations. We will also discuss future directions for the use of cord blood.

The natural killer cell immunotherapy platform: an overview of the landscape of clinical trials in liquid and solid tumors

The translation of natural killer (NK) cells to the treatment of malignant disease has made significant progress in the last few decades. With a variety of available sources and improvements in both in vitro and in vivo NK cell expansion, the NK cell immunotherapy platform has come into its own. The enormous effort continues to further optimize this platform, including ways to enhance NK cell persistence, trafficking to the tumor microenvironment, and cytotoxicity. As this effort bears fruit, it is translated into a plethora of clinical trials in patients with advanced malignancies. The adoptive transfer of NK cells, either as a standalone therapy or in combination with other immunotherapies, has been applied for the treatment of both liquid and solid tumors, with numerous early-phase trials showing promising results. This review aims to summarize the key advantages of NK cell immunotherapy, highlight several of the current approaches being taken for its optimization, and give an overview of the landscape of clinical trials translating this platform into clinic.

Allogeneic natural killer cell therapy

Interest in adoptive cell therapy for treating cancer is exploding owing to early clinical successes of autologous chimeric antigen receptor (CAR) T lymphocyte therapy. However, limitations using T cells and autologous cell products are apparent as they (1) take weeks to generate, (2) utilize a 1:1 donor-to-patient model, (3) are expensive, and (4) are prone to heterogeneity and manufacturing failures. CAR T cells are also associated with significant toxicities, including cytokine release syndrome, immune effector cell-associated neurotoxicity syndrome, and prolonged cytopenias. To overcome these issues, natural killer (NK) cells are being explored as an alternative cell source for allogeneic cell therapies. NK cells have an inherent ability to recognize cancers, mediate immune functions of killing and communication, and do not induce graft-versus-host disease, cytokine release syndrome, or immune effector cell-associated neurotoxicity syndrome. NK cells can be obtained from blood or cord blood or be derived from hematopoietic stem and progenitor cells or induced pluripotent stem cells, and can be expanded and cryopreserved for off-the-shelf availability. The first wave of point-of-care NK cell therapies led to the current allogeneic NK cell products being investigated in clinical trials with promising preliminary results. Basic advances in NK cell biology and cellular engineering have led to new translational strategies to block inhibition, enhance and broaden target cell recognition, optimize functional persistence, and provide stealth from patients' immunity. This review details NK cell biology, as well as NK cell product manufacturing, engineering, and combination therapies explored in the clinic leading to the next generation of potent, off-the-shelf cellular therapies for blood cancers.

An in vitro model to monitor natural killer cell effector functions against breast cancer cells derived from human tumor tissue

Adoptive natural killer (NK) cell-based immunotherapy poses a promising treatment approach in cancer. Despite minimal toxicities associated with NK cell infusion, the potential of NK cell therapy is inhibited by the immunosuppressive tumor microenvironment (TME). Multiple approaches to improve anti-cancer NK cell effector functions are being investigated. While much of this preclinical research is currently performed with commercially available tumor cell lines, this approach lacks the influence of the TME and heterogeneity of the primary tumor in patients. Here, we describe a comprehensive protocol for NK cell cytotoxicity- and degranulation assays against tumor cells derived from primary breast cancer tissue. Treatments to boost NK cell anti-tumor effector functions can be implemented in this model. Moreover, by using culture supernatants in follow up assays or by including additional cell types in the co-culture system, other NK cell effector mechanisms that further orchestrate innate and adaptive immunity could be studied.

Peripheral blood persistence and expansion of transferred non-genetically modified Natural Killer cells might not be necessary for clinical activity

Natural killer (NK) cells are innate lymphocytes that react without previous exposition to virus infected or malignant cells and stimulate adaptive immune response to build a long-lasting immunity against it. To that end, tissue resident NK cells are predominantly regulatory as opposed to cytotoxic. In the hematopoietic stem cell transplant (HSCT) setting, which curative potential relies on the graft versus leukemia effect, NK cells are known to play a significant role. This knowledge has paved the way to the active investigation on its anti-tumor effect outside the stem cell transplant scenario. Based on the relevant literature on the adoptive transfer of non-genetically modified NK cells for the treatment of relapsed/refractory acute leukemia and on our own experience, we discuss the role of donor cell peripheral blood persistence and expansion and its lack of correlation with anti-leukemia activity.

Manipulating NK cellular therapy from cancer to invasive fungal infection: promises and challenges

The ideal strategy to fight an infection involves both (i) weakening the invading pathogen through conventional antimicrobial therapy, and (ii) strengthening defense through the augmentation of host immunity. This is even more pertinent in the context of invasive fungal infections whereby the majority of patients have altered immunity and are unable to mount an appropriate host response against the pathogen. Natural killer (NK) cells fit the requirement of an efficient, innate executioner of both tumour cells and pathogens – their unique, targeted cell killing mechanism, combined with other arms of the immune system, make them potent effectors. These characteristics, together with their ready availability (given the various sources of extrinsic NK cells available for harvesting), make NK cells an attractive choice as adoptive cellular therapy against fungi in invasive infections. Improved techniques in ex vivo NK cell activation with expansion, and more importantly, recent advances in genetic engineering including state-of-the-art chimeric antigen receptor platform development, have presented an opportune moment to harness this novel therapeutic as a key component of a multipronged strategy against invasive fungal infections.

How I treat high-risk acute myeloid leukemia using preemptive adoptive cellular immunotherapy

Allogeneic hematopoietic stem cell transplantation (alloHSCT) is a potentially curative treatment for patients with high-risk acute leukemias, but unfortunately disease recurrence remains the major cause of death in these patients. Infusion of donor lymphocytes (DLI) has the potential to restore graft-versus-leukemia immunologic surveillance; however, efficacy varies across different hematologic entities. Although relapsed chronic myeloid leukemia, transplanted in chronic phase, has proven remarkably susceptible to DLI, response rates are more modest for relapsed acute myeloid leukemia and acute lymphoblastic leukemia. To prevent impending relapse, a number of groups have explored administering DLI preemptively on detection of measurable residual disease (MRD) or mixed chimerism. Evidence for the effectiveness of this strategy, although encouraging, comes from only a few, mostly single-center retrospective, nonrandomized studies. This article seeks to (1) discuss the available evidence supporting this approach while highlighting some of the inherent challenges of MRD-triggered treatment decisions post-transplant, (2) portray other forms of postremission cellular therapies, including the role of next-generation target-specific immunotherapies, and (3) provide a practical framework to support clinicians in their decision-making process when considering preemptive cellular therapy for this difficult-to-treat patient population.

Natural killer cells in sepsis: Friends or foes?

Sepsis is one of the major causes of death in the hospital worldwide. The pathology of sepsis is tightly associated with dysregulation of innate immune responses. The contribution of macrophages, neutrophils, and dendritic cells to sepsis is well documented, whereas the role of natural killer (NK) cells, which are critical innate lymphoid lineage cells, remains unclear. In some studies, the activation of NK cells has been reported as a risk factor leading to severe organ damage or death. In sharp contrast, some other studies revealed that triggering NK cell activity contributes to alleviating sepsis. In all, although there are several reports on NK cells in sepsis, whether they exert detrimental or protective effects remains unclear. Here, we will review the available experimental and clinical studies about the opposing roles of NK cells in sepsis, and we will discuss the prospects for NK cell-based immunotherapeutic strategies for sepsis.

Leveraging Natural Killer Cell Innate Immunity against Hematologic Malignancies: From Stem Cell Transplant to Adoptive Transfer and Beyond

Numerous recent advancements in T-cell based immunotherapies have revolutionized the treatment of hematologic malignancies. In the race towards the first approved allogeneic cellular therapy product, there is growing interest in utilizing natural killer (NK) cells as a platform for off-the-shelf cellular therapies due to their scalable manufacturing potential, potent anti-tumor efficacy, and superior safety profile. Allogeneic NK cell therapies are now being actively explored in the setting of hematopoietic stem cell transplantation and adoptive transfer. Increasingly sophisticated gene editing techniques have permitted the engineering of chimeric antigen receptors, ectopic cytokine expression, and tumor recognition signals to improve the overall cytotoxicity of NK cell therapies. Furthermore, the enhancement of antibody-dependent cellular cytotoxicity has been achieved through the use of NK cell engagers and combination regimens with monoclonal antibodies that act synergistically with CD16-expressing NK cells. Finally, a greater understanding of NK cell biology and the mechanisms of resistance have allowed the preclinical development of NK checkpoint blockade and methods to modulate the tumor microenvironment, which have been evaluated in early phase trials. This review will discuss the recent clinical advancements in NK cell therapies in hematologic malignancies as well as promising avenues of future research.

Natural killer cells in clinical development as non-engineered, engineered, and combination therapies

Natural killer (NK) cells are unique immune effectors able to kill cancer cells by direct recognition of surface ligands, without prior sensitization. Allogeneic NK transfer is a highly valuable treatment option for cancer and has recently emerged with hundreds of clinical trials paving the way to finally achieve market authorization. Advantages of NK cell therapies include the use of allogenic cell sources, off-the-shelf availability, and no risk of graft-versus-host disease (GvHD). Allogeneic NK cell therapies have reached the clinical stage as ex vivo expanded and differentiated non-engineered cells, as chimeric antigen receptor (CAR)-engineered or CD16-engineered products, or as combination therapies with antibodies, priming agents, and other drugs. This review summarizes the recent clinical status of allogeneic NK cell-based therapies for the treatment of hematological and solid tumors, discussing the main characteristics of the different cell sources used for NK product development, their use in cell manufacturing processes, the engineering methods and strategies adopted for genetically modified products, and the chosen approaches for combination therapies. A comparative analysis between NK-based non-engineered, engineered, and combination therapies is presented, examining the choices made by product developers regarding the NK cell source and the targeted tumor indications, for both solid and hematological cancers. Clinical trial outcomes are discussed and, when available, assessed in comparison with preclinical data. Regulatory challenges for product approval are reviewed, highlighting the lack of specificity of requirements and standardization between products. Additionally, the competitive landscape and business field is presented. This review offers a comprehensive overview of the effort driven by biotech and pharmaceutical companies and by academic centers to bring NK cell therapies to pivotal clinical trial stages and to market authorization.

Tumor MHC class I expression alters cancer-associated myelopoiesis driven by host NK cells

Downregulation of MHC class I (MHCI) molecules on tumor cells is recognized as a resistance mechanism of cancer immunotherapy. Given that MHCI molecules are potent regulators of immune responses, we postulated that the expression of MHCI by tumor cells influences systemic immune responses. Accordingly, mice-bearing MHCI-deficient tumor cells showed reduced tumor-associated extramedullary myelopoiesis in the spleen. Depletion of natural killer (NK) cells abrogated these differences, suggesting an integral role of immune-regulatory NK cells during tumor progression. Cytokine-profiling revealed an upregulation of TNF-α by NK cells in tumors and spleen in mice-bearing MHCI expressing tumors, and inhibition of TNF-α enhanced host myelopoiesis in mice receiving adoptive transfer of tumor-experienced NK cells. Our study highlights a critical role of NK cells beyond its identity as a killer lymphocyte and more importantly, the potential host responses to a localized tumor as determined by its MHCI expression.

Autologous cultured adipose derived mesenchymal stem cells combined with hyaluronic acid hydrogel in the treatment of discogenic low back pain: a study protocol for a phase II randomised controlled trial

INTRODUCTION

Discogenic low back pain (DLBP) is a common disease, and its occurrence is closely related to intervertebral disc (IVD) degeneration. At present, none of the traditional treatment methods can repair the degenerated IVD. The emergence of stem cell therapy makes it possible to repair and regenerate IVD tissue, among which adipose derived mesenchymal stem cells (ADMSCs) transplantation therapy has become a hot spot of current research. Therefore, this trial aimed to investigate the safety and efficacy of using autologous cultured ADMSCs combined with hyaluronic acid (HA) hydrogel in the treatment of DLBP.

METHODS AND ANALYSIS

This study is a randomised, dose-escalation, placebo-controlled, double-blind, single-centre, phase II clinical trial to evaluate the efficacy and safety of autologous cultured ADMSCs combined with HA hydrogel in the treatment of patients with DLBP. The 100 eligible patients will be randomly divided into three experimental groups with different doses and one placebo control group in a ratio of 1:1:1:1. All patients will undergo liposuction to obtain ADMSCs, followed by autologous cultured ADMSC mixtures or placebo transplantation after 3 weeks. The patients will be followed up to 24 months after the transplant. The primary end point of this trial is the Visual Analogue Scale. Secondary end points include the Oswestry Disability Index, Japanese Orthopaedic Association Scores, the Mos 36-item short form, the Modic classification, Pfirrmann grade, height and segment range of motion of the IVD, vital signs (temperature, pulse, respiration, blood pressure), blood routine, liver and kidney function, immunological examination, urinalysis and treatment emergent adverse events.

ETHICS AND DISSEMINATION

The study protocol has been approved by the Ethics Committee of the First Affiliated Hospital of Dalian Medical University and registered in the Chinese Clinical Trial Registry. Dissemination of the results will be presented at a conference and in peer-reviewed publications.

TRIAL REGISTRATION NUMBER

ChiCTR2200058291.

Natural killer cells in antitumour adoptive cell immunotherapy

Natural killer (NK) cells comprise a unique population of innate lymphoid cells endowed with intrinsic abilities to identify and eliminate virally infected cells and tumour cells. Possessing multiple cytotoxicity mechanisms and the ability to modulate the immune response through cytokine production, NK cells play a pivotal role in anticancer immunity. This role was elucidated nearly two decades ago, when NK cells, used as immunotherapeutic agents, showed safety and efficacy in the treatment of patients with advanced-stage leukaemia. In recent years, following the paradigm-shifting successes of chimeric antigen receptor (CAR)-engineered adoptive T cell therapy and the advancement in technologies that can turn cells into powerful antitumour weapons, the interest in NK cells as a candidate for immunotherapy has grown exponentially. Strategies for the development of NK cell-based therapies focus on enhancing NK cell potency and persistence through co-stimulatory signalling, checkpoint inhibition and cytokine armouring, and aim to redirect NK cell specificity to the tumour through expression of CAR or the use of engager molecules. In the clinic, the first generation of NK cell therapies have delivered promising results, showing encouraging efficacy and remarkable safety, thus driving great enthusiasm for continued innovation. In this Review, we describe the various approaches to augment NK cell cytotoxicity and longevity, evaluate challenges and opportunities, and reflect on how lessons learned from the clinic will guide the design of next-generation NK cell products that will address the unique complexities of each cancer.

Cord Blood-Derived Natural Killer Cell Exploitation in Immunotherapy Protocols: More Than a Promise?

Simple Summary

NK cell anti-tumor activity against hematological malignancies is well-established and many studies support their role in the control of solid tumor growth and metastasis generation. However, tumor microenvironment may affect NK cell function. Ongoing studies are aimed to design novel immunotherapeutic protocols to combine NK cell-based immunotherapy with other therapeutic strategies to improve the anti-tumor NK cell response. In this context, UCB is one of the main sources of both mature NK cells and of CD34⁺ HSPC that can generate NK cells, both in-vivo and in-vitro. UCB-derived NK cells represent a valuable tool to perform in-vitro and preclinical analyses and are already used in several clinical settings, particularly against hematological malignancies. The present review describes the characteristics of different types of UCB-derived NK cells and the in-vitro models to expand them, both for research and clinical purposes in the context of cancer immunotherapy.

Abstract

In the last 20 years, Natural Killer (NK) cell-based immunotherapy has become a promising approach to target various types of cancer. Indeed, NK cells play a pivotal role in the first-line defense against tumors through major histocompatibility complex-independent immunosurveillance. Their role in the control of leukemia relapse has been clearly established and, moreover, the presence of NK cells in the tumor microenvironment (TME) generally correlates with good prognosis. However, it has also been observed that, often, NK cells poorly infiltrate the tumor tissue, and, in TME, their functions may be compromised by immunosuppressive factors that contribute to the failure of anti-cancer immune response. Currently, studies are focused on the design of effective strategies to expand NK cells and enhance their cytotoxic activity, exploiting different cell sources, such as peripheral blood (PB), umbilical cord blood (UCB) and NK cell lines. Among them, UCB represents an important source of mature NK cells and CD34⁺ Hematopoietic Stem and Progenitor Cells (HSPCs), as precursors of NK cells. In this review, we summarize the UCB-derived NK cell activity in the tumor context, review the different in-vitro models to expand NK cells from UCB, and discuss the importance of their exploitation in anti-tumor immunotherapy protocols.

Chemical priming of natural killer cells with branched polyethylenimine for cancer immunotherapy

Background

Due to their powerful immune surveillance activity and ability to kill and clear cancer cells, natural killer (NK) cells are an emerging anticancer immunotherapeutic agent. Therefore, there is much interest in developing efficient technologies that further enhance the therapeutic antitumor efficacy of NK cells.

Methods

To produce chemically primed NK cells, we screened polymers with various electric charges and examined their ability to enhance the cytotoxicity of NK cells. The effect of primary amine and electric charges of 25 kDa branched polyethylenimine (25KbPEI) was investigated by fluorination of the chemical. The role of 25KbPEI in determining the major priming mechanism was investigated in terms of calcium influx into NK cells. In vivo therapeutic efficacy of chemically primed NK cells was evaluated against solid tumor mouse model of triple negative breast and ovarian cancers.

Results

Chem_NK that was produced by the priming activity of 25KbPEI showed potent antitumor activity to various cancer cells. Chem_NK showed an activated phenotype, which manifests as increased expression of activating/adhesion/chemokine receptors and perforin accumulation, leading to enhanced migration ability and antitumor activity. Chem_NK display potent therapeutic efficacy against in vivo mouse model of triple negative breast and ovarian cancers. Fluorination of the primary amine group reduces the activity of 25KbPEI to prime NK cells, indicating that the cationic charge on the chemical plays a critical role in NK cell activation. A major priming mechanism was 25KbPEI-mediated calcium influx into NK cells, which occurred mainly via the Ca2⁺-permeable non-selective cation channel transient receptor potential melastatin 2.

Conclusions

NK cells can be chemically primed with 25KbPEI to express potent antitumor activity as well as enhanced migration ability. Because PEI is a biocompatible and Food and Drug Administration-approved chemical for biomedical use, these results suggest a cost-effective and simple method of producing therapeutic NK cells.

Natural killer cells: the next wave in cancer immunotherapy

Immunotherapies focusing on rejuvenating T cell activities, like PD-1/PD-L1 and CTLA-4 blockade, have unprecedentedly revolutionized the landscape of cancer treatment. Yet a previously underexplored component of the immune system - natural killer (NK) cell, is coming to the forefront of immunotherapeutic attempts. In this review, we discuss the contributions of NK cells in the success of current immunotherapies, provide an overview of the current preclinical and clinical strategies at harnessing NK cells for cancer treatment, and highlight that NK cell-mediated therapies emerge as a major target in the next wave of cancer immunotherapy.

Generation of universal natural killer cells from a cryopreserved cord blood mononuclear cell-derived induced pluripotent stem cell library

Natural killer (NK) cells play a key role in innate immunity and are regarded as a promising candidate for cellular immunotherapy. Natural killer cells may be generated from different sources, including induced pluripotent stem cells (iPSCs); these stem cells produce an abundant amount of NK cells to meet the needs of a wide range of clinical applications. Autologous iPSCs are expensive and labor-intensive to prepare, while allogeneic iPSCs require human leukocyte antigen (HLA) matched cells to avoid the risk of immune rejection. In the current study, we prepared HLA-matched iPSCs using HLA common haplotype homozygous (HLAh) donors from cryopreserved human cord blood (CB) sourced from the Tianjin Cord Blood Public Bank. This approach was designed to generate a CB-derived iPSC library from HLAh donors and use it to produce off-the-shelf NK cells. Starting with readily available cryopreserved CB mononuclear cells (cryoCBMCs), we produced cryoCBMC-derived iPSCs (cryoCB-iPSCs). These cryoCB-iPSCs were induced to generate embryoid bodies (EBs) using an improved 3D suspension culture method, and induced NK (iNK) cells were differentiated from EBs. iNK cells expressed specific surface markers of NK cells, exhibited cytotoxicity comparable with NK cells generated from CB (CB-NK) and peripheral blood (PB-NK), and expressed lower levels of KIRs and HLA-DR compared to CB-NK and PB-NK. Taken together, we have shown that an iPSC library can be established from HLAh cryoCBMCs, and cryoCB-iPSCs can be used to generate a large number of 'universal' NK cells for future clinical applications.

Natural killer cell homing and trafficking in tissues and tumors: from biology to application

Natural killer (NK) cells, a subgroup of innate lymphoid cells, act as the first line of defense against cancer. Although some evidence shows that NK cells can develop in secondary lymphoid tissues, NK cells develop mainly in the bone marrow (BM) and egress into the blood circulation when they mature. They then migrate to and settle down in peripheral tissues, though some special subsets home back into the BM or secondary lymphoid organs. Owing to its success in allogeneic adoptive transfer for cancer treatment and its "off-the-shelf" potential, NK cell-based immunotherapy is attracting increasing attention in the treatment of various cancers. However, insufficient infiltration of adoptively transferred NK cells limits clinical utility, especially for solid tumors. Expansion of NK cells or engineered chimeric antigen receptor (CAR) NK cells ex vivo prior to adoptive transfer by using various cytokines alters the profiles of chemokine receptors, which affects the infiltration of transferred NK cells into tumor tissue. Several factors control NK cell trafficking and homing, including cell-intrinsic factors (e.g., transcriptional factors), cell-extrinsic factors (e.g., integrins, selectins, chemokines and their corresponding receptors, signals induced by cytokines, sphingosine-1-phosphate (S1P), etc.), and the cellular microenvironment. Here, we summarize the profiles and mechanisms of NK cell homing and trafficking at steady state and during tumor development, aiming to improve NK cell-based cancer immunotherapy.