Antitumor immunity induced by antibody-based natural killer cell engager therapeutics armed with not-alpha IL-2 variant

Natural killer cell-based immunotherapy for cancer

Natural killer (NK) cells are emerging as a promising tool for cancer immunotherapy due to their innate ability to selectively recognize and eliminate cancer cells. Over the past 3 decades, strategies to harness NK cells have included cytokines, small molecules, antibodies, and the adoptive transfer of autologous or allogeneic NK cells, both unmodified and genetically engineered. Despite favorable safety profiles in clinical trials, challenges such as limited in vivo persistence, exhaustion, and the suppressive tumor microenvironment continue to hinder their efficacy and durability. This review categorizes NK cell-based therapies into 3 major approaches: (i) cellular therapies, including unmodified and chimeric antigen receptor-engineered NK cells; (ii) cytokine-based strategies such as interleukin-2 and interleukin-15 derivatives; and (iii) antibody-based therapies, including immune checkpoint inhibitors and NK cell engagers. We highlight these advancements, discuss current limitations, and propose strategies to optimize NK cell-based therapies for improved cancer treatment outcomes.

Cytokines in Focus: IL-2 and IL-15 in NK Adoptive Cell Cancer Immunotherapy

NK cell adoptive cell therapy (ACT) has emerged as a promising strategy for cancer immunotherapy, offering advantages in scalability, accessibility, efficacy, and safety. Ex vivo activation and expansion protocols, incorporating feeder cells and cytokine cocktails, have enabled the production of highly functional NK cells in clinically relevant quantities. Advances in NK cell engineering, including CRISPR-mediated gene editing and chimeric Ag receptor technologies, have further enhanced cytotoxicity, persistence, and tumor targeting. Cytokine support post-adoptive transfer, particularly with IL-2 and IL-15, remains critical for promoting NK cell survival, proliferation, and anti-tumor activity despite persistent challenges such as regulatory T cell expansion and cytokine-related toxicities. This review explores the evolving roles of IL-2 and IL-15 in NK cell-based ACT, evaluating their potential and limitations, and highlights strategies to optimize these cytokines for effective cancer immunotherapy.

Natural killer cell engagers for cancer immunotherapy

This review article explores the rapidly evolving field of bi-, tri-, and multi-specific NK cell engagers (NKCEs), highlighting their potential as a cutting-edge approach in cancer immunotherapy. NKCEs offer a significant advancement over conventional monoclonal antibodies (mAbs) by enhancing Antibody-Dependent Cellular Cytotoxicity (ADCC). They achieve this by stably and selectively binding to both NK cell activating receptors and tumor-associated antigens (TAAs). Unlike traditional mAbs, which depend on the relatively transient interaction between their Fc region and CD16a, NKCEs establish more robust connections with a range of activating receptors (e.g., CD16a, NKG2D, NKp30, NKp46, NKG2C) and inhibitory receptors (e.g., Siglec-7) on NK cells, thereby increasing cancer cell killing efficacy and specificity. This review article critically examines the strategies for engineering bi-, tri-, and multi-specific NKCEs for cancer immunotherapy, providing an in-depth analysis of the latest advancements in NKCE platform technologies currently under development by pharmaceutical and biotech companies and discussing the preclinical and clinical progress of these products. While NKCEs show great promise, the review underscores the need for continued research to optimize their therapeutic efficacy and to overcome obstacles related to NK cell functionality in cancer patients. Ultimately, this article presents an overview of the current landscape and future prospects of NKCE-based cancer immunotherapy, emphasizing its potential to revolutionize cancer treatment.

Bispecific Antibodies for Lymphoid Malignancy Treatment

BACKGROUD

The introduction of highly active immunotherapies has changed the outcome of B-cell non-Hodgkin lymphomas (B-NHLs) in the last two decades. Since then, important progress has been shown using newer and more active immunotherapies, including chimeric antigen receptor T-cell therapy (CAR-T), conjugated monoclonal antibodies, and bispecific antobodies, which currently plays a significant role in the treatment of diffuse large B-cell (DLBCL), follicular (FL), and mantle cell (MCL) lymphoma.

PURPOSE

In this review, we provide an updated overview of recently completed and ongoing BsAb trials in patients with relapsed/refractory(R/R) B-NHL and Hodgkin's lymphoma, including single-agent results, emerging combinations, safety data, and novel constructs.

CONCLUSIONS

Bispecific antibodies (BsAbs) are a novel class of "off-the-shelf" T-cell-redirecting drugs capable of targeting various cell-surface antigens. New antigen targets are currently under investigation, such as CD19 × CD3 and CD30 × CD3 or CD30 × CD16, in different settings. BsAbs are among the most promising therapeutic options for lymphoma today since they have demonstrated significant single-agent activity, along with a manageable toxicity profile, in patients with heavily pretreated B-NHL.

A tetraspecific engager armed with a non-alpha IL-2 variant harnesses natural killer cells against B cell non-Hodgkin lymphoma

NK cells offer a promising alternative to T cell therapies in cancer. We evaluated IPH6501, a clinical-stage, tetraspecific NK cell engager (NKCE) armed with a non-alpha IL-2 variant (IL-2v), which targets CD20 and was developed for treating B cell non-Hodgkin lymphoma (B-NHL). CD20-NKCE-IL2v boosts NK cell proliferation and cytotoxicity, showing activity against a range of B-NHL cell lines, including those with low CD20 density. Whereas it presented reduced toxicities compared with those commonly associated with T cell therapies, CD20-NKCE-IL2v showed greater killing efficacy over a T cell engager targeting CD20 in in vitro preclinical models. CD20-NKCE-IL2v also increased the cell surface expression of NK cell-activating receptors, leading to activity against CD20-negative tumor cells. In vivo studies in nonhuman primates and tumor mouse models further validated its efficacy and revealed that CD20-NKCE-IL2v induces peripheral NK cell homing at the tumor site. CD20-NKCE-IL2v emerges as a potential alternative in the treatment landscape of B-NHL.

Natural killer cell engagers: From bi-specific to tri-specific and tetra-specific engagers for enhanced cancer immunotherapy

Natural killer cell engagers (NKCEs) are a specialised subset of antibodies capable of simultaneously targeting endogenous NK cells and tumour cells, generating precise and effective cytolytic responses against cancer. This review systematically explores NK engagers as a rising star in NK-mediated immunotherapy, specifically focusing on multi-specific engagers. It examines the diverse configuration of NKCEs and how certain biologics could be employed to boost NK activity, including activating receptor engagement and cytokine incorporation. Some challenges and future perspectives of current NKCEs therapy are also discussed, including optimising pharmacokinetics, addressing the immunosuppressive tumour microenvironment and exploring potential combinatorial approaches. By offering an in-depth analysis of the current landscape and future trajectories of multi-specific NKCEs in cancer treatment, this review serves as a valuable resource for understanding this promising field of immunotherapy.

HIGHLIGHTS

Innovative NKCEs: NK cell engagers (NKCEs) represent a promising new class of immunotherapeutics targeting tumours by activating NK cells. Multi-specific formats: The transition from bi-specific to multi-specific NKCEs enhances their versatility and therapeutic efficacy.

MECHANISMS OF ACTION

NKCEs have the potential to improve NK cell activation by engaging activating receptors and incorporating cytokines.

CLINICAL POTENTIAL

Current clinical trials demonstrate the safety and efficacy of various NKCEs across different cancer types. Future research directions: Optimising NKCE designs and exploring combination therapies are essential for overcoming challenges in cancer treatment.

Natural killer cells and engagers: Powerful weapons against cancer

Natural killer (NK) cells are innate immune effectors whose functions rely on receptors binding cytokines, recognizing self-molecules, or detecting danger signals expressed by virus-infected or tumor cells. The potent cytotoxic potential makes NK cells promising candidates for cancer immunotherapy. To enhance their activity strategies include cytokine administration, blocking of immune checkpoints, and designing of antibody-based NK cell engagers (NKCEs). NKCEs represent a cutting-edge approach to cancer therapy: they strengthen the NK-to-target cell interactions and optimize tumor killing, possibly overcoming the immunosuppressive tumor microenvironment. NK cells belong to the innate lymphoid cells (ILCs) and are categorized into different subsets also including cells with a memory-like phenotype: this complexity needs to be explored in the context of cancer immunotherapy, particularly when designing NKCEs. Two strategies to enhance NK cell activity in cancer patients can be adopted: activating patients' own NK cells versus the adoptive transfer of ex vivo activated NK cells. Furthermore, the capability of NKCEs to activate γδ T cells could have a significant synergistic effect in immunotherapy.

High-Affinity Superantigen-Based Trifunctional Immune Cell Engager Synergizes NK and T Cell Activation for Tumor Suppression

The development of immune cell engagers (ICEs) can be limited by logistical and functional restrictions associated with fusion protein designs, thus limiting immune cell recruitment to solid tumors. Herein, a high affinity superantigen-based multivalent ICE is developed for simultaneous activation and recruitment of NK and T cells for tumor treatment. Yeast library-based directed evolution is adopted to identify superantigen variants possessing enhanced binding affinity to immunoreceptors expressed on human T cells and NK cells. High-affinity superantigens exhibiting improved immune-stimulatory activities are then incorporated into a superantigen-based tri-functional yeast-display-enhanced multivalent immune cell engager (STYMIE), which is functionalized with a nanobody, a Neo-2/15 cytokine, and an Fc domain for tumor targeting, immune stimulation, and prolonged circulation, respectively. Intravenous administration of STYMIE enhances NK and T cell recruitment into solid tumors, leading to enhanced inhibition in multiple tumor models. The study offers design principles for multifunctional ICEs.

Maintaining the Balance: Regulation of NK Cell Activity

Natural Killer (NK) cells, integral components of the innate immune system, play a crucial role in the protection against intracellular threats. Their cytotoxic power requires that activation is tightly controlled, and in this, they take a unique position within the immune system. Rather than depending on the engagement of a single activating receptor, their activation involves a delicate balance between inhibitory and activating signals mediated through an array of surface molecules. Only when this cumulative balance surpasses a specific threshold do NK cells initiate their activity. Remarkably, the activation threshold of NK cells remains robust even when cells express vastly different repertoires of inhibitory and activating receptors. These threshold values seem to be influenced by NK cell interactions with their environment during development and after release from the bone marrow. Understanding how NK cells integrate this intricate pattern of stimuli is an ongoing area of research, particularly relevant for cellular therapies seeking to harness the anti-cancer potential of these cells by modifying surface receptor expression. In this review, we will explore some of the current dogmas regarding NK cell activation and discuss recent literature addressing advances in our understanding of this field.

High-dimensional single-cell analysis of human natural killer cell heterogeneity

Natural killer (NK) cells are innate lymphoid cells (ILCs) contributing to immune responses to microbes and tumors. Historically, their classification hinged on a limited array of surface protein markers. Here, we used single-cell RNA sequencing (scRNA-seq) and cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq) to dissect the heterogeneity of NK cells. We identified three prominent NK cell subsets in healthy human blood: NK1, NK2 and NK3, further differentiated into six distinct subgroups. Our findings delineate the molecular characteristics, key transcription factors, biological functions, metabolic traits and cytokine responses of each subgroup. These data also suggest two separate ontogenetic origins for NK cells, leading to divergent transcriptional trajectories. Furthermore, we analyzed the distribution of NK cell subsets in the lung, tonsils and intraepithelial lymphocytes isolated from healthy individuals and in 22 tumor types. This standardized terminology aims at fostering clarity and consistency in future research, thereby improving cross-study comparisons.

Better safe than sorry: dual targeting antibodies for cancer immunotherapy

Antibody-based therapies are revolutionizing cancer treatment and experience a steady increase from preclinical and clinical pipelines to market share. While the clinical success of monoclonal antibodies is frequently limited by low response rates, treatment resistance and various other factors, multispecific antibodies open up new prospects by addressing tumor complexity as well as immune response actuation potently improving safety and efficacy. Novel antibody approaches involve simultaneous binding of two antigens on one cell implying increased specificity and reduced tumor escape for dual tumor-associated antigen targeting and enhanced and durable cytotoxic effects for dual immune cell-related antigen targeting. This article reviews antibody and cell-based therapeutics for oncology with intrinsic dual targeting of either tumor cells or immune cells. As revealed in various preclinical studies and clinical trials, dual targeting molecules are promising candidates constituting the next generation of antibody drugs for fighting cancer.

Human NK cells and cancer

The long story of NK cells started about 50 y ago with the first demonstration of a natural cytotoxic activity within an undefined subset of circulating leukocytes, has involved an ever-growing number of researchers, fascinated by the apparently easy-to-reach aim of getting a "universal anti-tumor immune tool". In fact, in spite of the impressive progress obtained in the first decades, these cells proved far more complex than expected and, paradoxically, the accumulating findings have continuously moved forward the attainment of a complete control of their function for immunotherapy. The refined studies of these latter years have indicated that NK cells can epigenetically calibrate their functional potential, in response to specific environmental contexts, giving rise to extraordinarily variegated subpopulations, comprehensive of memory-like cells, tissue-resident cells, or cells in various differentiation stages, or distinct functional states. In addition, NK cells can adapt their activity in response to a complex body of signals, spanning from the interaction with either suppressive or stimulating cells (myeloid-derived suppressor cells or dendritic cells, respectively) to the engagement of various receptors (specific for immune checkpoints, cytokines, tumor/viral ligands, or mediating antibody-dependent cell-mediated cytotoxicity). According to this picture, the idea of an easy and generalized exploitation of NK cells is changing, and the way is opening toward new carefully designed, combined and personalized therapeutic strategies, also based on the use of genetically modified NK cells and stimuli capable of strengthening and redirecting their effector functions against cancer.

Bridging the gap with multispecific immune cell engagers in cancer and infectious diseases

By binding to multiple antigens simultaneously, multispecific antibodies are expected to substantially improve both the activity and long-term efficacy of antibody-based immunotherapy. Immune cell engagers, a subclass of antibody-based constructs, consist of engineered structures designed to bridge immune effector cells to their target, thereby redirecting the immune response toward the tumor cells or infected cells. The increasing number of recent clinical trials evaluating immune cell engagers reflects the important role of these molecules in new therapeutic approaches for cancer and infections. In this review, we discuss how different immune cell types (T and natural killer lymphocytes, as well as myeloid cells) can be bound by immune cell engagers in immunotherapy for cancer and infectious diseases. Furthermore, we explore the preclinical and clinical advancements of these constructs, and we discuss the challenges in translating the current knowledge from cancer to the virology field. Finally, we speculate on the promising future directions that immune cell engagers may take in cancer treatment and antiviral therapy.

Emerging Innate Immune Cells in Cancer Immunotherapy: Promises and Challenges

Immune checkpoint inhibitor (ICI)-based therapy has made an unprecedented impact on survival benefit for a subset of cancer patients; however, only a subset of cancer patients is benefiting from ICI therapy if all cancer types are considered. With the advanced understanding of interactions of immune effector cell types and tumors, cell-based therapies are emerging as alternatives to patients who could not benefit from ICI therapy. Pioneering work of chimeric antigen receptor T (CAR-T) therapy for hematological malignancies has brought encouragement to a broad range of development for cellular-based cancer immunotherapy, both innate immune cell-based therapies and T-cell-based therapies. Innate immune cells are important cell types due to their rapid response, versatile function, superior safety profiles being demonstrated in early clinical development, and being able to utilize multiple allogeneic cell sources. Efforts on engineering innate immune cells and exploring their therapeutic potential are rapidly emerging. Some of the therapies, such as CD19 CAR natural killer (CAR-NK) cell-based therapy, have demonstrated comparable early efficacy with CD19 CAR-T cells. These studies underscore the significance of developing innate immune cells for cancer therapy. In this review, we focus on the current development of emerging NK cells, γδ T cells, and macrophages. We also present our views on potential challenges and perspectives to overcome these challenges.

New immune cell engagers for cancer immunotherapy

There have been major advances in the immunotherapy of cancer in recent years, including the development of T cell engagers - antibodies engineered to redirect T cells to recognize and kill cancer cells - for the treatment of haematological malignancies. However, the field still faces several challenges to develop agents that are consistently effective in a majority of patients and cancer types, such as optimizing drug dose, overcoming treatment resistance and improving efficacy in solid tumours. A new generation of T cell-targeted molecules was developed to tackle these issues that are potentially more effective and safer. In addition, agents designed to engage the antitumour activities of other immune cells, including natural killer cells and myeloid cells, are showing promise and have the potential to treat a broader range of cancers.

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.

The present and future of bispecific antibodies for cancer therapy

Bispecific antibodies (bsAbs) enable novel mechanisms of action and/or therapeutic applications that cannot be achieved using conventional IgG-based antibodies. Consequently, development of these molecules has garnered substantial interest in the past decade and, as of the end of 2023, 14 bsAbs have been approved: 11 for the treatment of cancer and 3 for non-oncology indications. bsAbs are available in different formats, address different targets and mediate anticancer function via different molecular mechanisms. Here, we provide an overview of recent developments in the field of bsAbs for cancer therapy. We focus on bsAbs that are approved or in clinical development, including bsAb-mediated dual modulators of signalling pathways, tumour-targeted receptor agonists, bsAb-drug conjugates, bispecific T cell, natural killer cell and innate immune cell engagers, and bispecific checkpoint inhibitors and co-stimulators. Finally, we provide an outlook into next-generation bsAbs in earlier stages of development, including trispecifics, bsAb prodrugs, bsAbs that induce degradation of tumour targets and bsAbs acting as cytokine mimetics.

Therapeutic approaches to enhance natural killer cell cytotoxicity

Enhancing the cytotoxicity of natural killer (NK) cells has emerged as a promising strategy in cancer immunotherapy, due to their pivotal role in immune surveillance and tumor clearance. This literature review provides a comprehensive overview of therapeutic approaches designed to augment NK cell cytotoxicity. We analyze a wide range of strategies, including cytokine-based treatment, monoclonal antibodies, and NK cell engagers, and discuss criteria that must be considered when selecting an NK cell product to combine with these strategies. Furthermore, we discuss the challenges and limitations associated with each therapeutic strategy, as well as the potential for combination therapies to maximize NK cell cytotoxicity while minimizing adverse effects. By exploring the wealth of research on this topic, this literature review aims to provide a comprehensive resource for researchers and clinicians seeking to develop and implement novel therapeutic strategies that harness the full potential of NK cells in the fight against cancer. Enhancing NK cell cytotoxicity holds great promise in the evolving landscape of immunotherapy, and this review serves as a roadmap for understanding the current state of the field and the future directions in NK cell-based therapies.

Potent Apoptosis Induction by a Novel Trispecific B7-H3xCD16xTIGIT 2+1 Common Light Chain Natural Killer Cell Engager

Valued for their ability to rapidly kill multiple tumor cells in succession as well as their favorable safety profile, NK cells are of increasing interest in the field of immunotherapy. As their cytotoxic activity is controlled by a complex network of activating and inhibiting receptors, they offer a wide range of possible antigens to modulate their function by antibodies. In this work, we utilized our established common light chain (cLC)-based yeast surface display (YSD) screening procedure to isolate novel B7-H3 and TIGIT binding monoclonal antibodies. The chicken-derived antibodies showed single- to low-double-digit nanomolar affinities and were combined with a previously published CD16-binding Fab in a 2+1 format to generate a potent NK engaging molecule. In a straightforward, easily adjustable apoptosis assay, the construct B7-H3xCD16xTIGIT showed potent apoptosis induction in cancer cells. These results showcase the potential of the TIGIT NK checkpoint in combination with activating receptors to achieve increased cytotoxic activity.

Trial watch: bispecific antibodies for the treatment of relapsed or refractory large B-cell lymphoma

Immunotherapy has shaped the treatment approach to diffuse large B-cell lymphoma (DLBCL), with rituximab leading to remarkable improvements in outcomes for both relapsed and treatment-naïve patients. Recently, groundbreaking immunotherapies like chimeric antigen receptor T-cells have entered the treatment arena for relapsed/refractory (R/R) DLBCL and gained regulatory approval in several countries. The concept of harnessing a patient's own T-cells to combat cancer has been further explored through the development of bispecific antibodies (BsAbs), a class of engineered antibody products designed to simultaneously target two different antigens. These novel drugs have demonstrated impressive single-agent activity and manageable toxicity in patients with heavily pretreated B-cell non-Hodgkin lymphoma. In this review, we provide an up-to-date overview of recently completed or ongoing BsAbs trials in patients with R/R DLBCL, including single-agent results, emerging combination data, and novel constructs.

CAR-mediated targeting of NK cells overcomes tumor immune escape caused by ICAM-1 downregulation

BACKGROUND

The antitumor activity of natural killer (NK) cells can be enhanced by specific targeting with therapeutic antibodies that trigger antibody-dependent cell-mediated cytotoxicity (ADCC) or by genetic engineering to express chimeric antigen receptors (CARs). Despite antibody or CAR targeting, some tumors remain resistant towards NK cell attack. While the importance of ICAM-1/LFA-1 interaction for natural cytotoxicity of NK cells is known, its impact on ADCC induced by the ErbB2 (HER2)-specific antibody trastuzumab and ErbB2-CAR-mediated NK cell cytotoxicity against breast cancer cells has not been investigated.

METHODS

Here we used NK-92 cells expressing high-affinity Fc receptor FcγRIIIa in combination with trastuzumab or ErbB2-CAR engineered NK-92 cells (NK-92/5.28.z) as well as primary human NK cells combined with trastuzumab or modified with the ErbB2-CAR and tested cytotoxicity against cancer cells varying in ICAM-1 expression or alternatively blocked LFA-1 on NK cells. Furthermore, we specifically stimulated Fc receptor, CAR and/or LFA-1 to study their crosstalk at the immunological synapse and their contribution to degranulation and intracellular signaling in antibody-targeted or CAR-targeted NK cells.

RESULTS

Blockade of LFA-1 or absence of ICAM-1 significantly reduced cell killing and cytokine release during trastuzumab-mediated ADCC against ErbB2-positive breast cancer cells, but not so in CAR-targeted NK cells. Pretreatment with 5-aza-2'-deoxycytidine induced ICAM-1 upregulation and reversed NK cell resistance in ADCC. Trastuzumab alone did not sufficiently activate NK cells and required additional LFA-1 co-stimulation, while activation of the ErbB2-CAR in CAR-NK cells induced efficient degranulation independent of LFA-1. Total internal reflection fluorescence single molecule imaging revealed that CAR-NK cells formed an irregular immunological synapse with tumor cells that excluded ICAM-1, while trastuzumab formed typical peripheral supramolecular activation cluster (pSMAC) structures. Mechanistically, the absence of ICAM-1 did not affect cell-cell adhesion during ADCC, but rather resulted in decreased signaling via Pyk2 and ERK1/2, which was intrinsically provided by CAR-mediated targeting. Furthermore, while stimulation of the inhibitory NK cell checkpoint molecule NKG2A markedly reduced FcγRIIIa/LFA-1-mediated degranulation, retargeting by CAR was only marginally affected.

CONCLUSIONS

Downregulation of ICAM-1 on breast cancer cells is a critical escape mechanism from trastuzumab-triggered ADCC. In contrast, CAR-NK cells are able to overcome cancer cell resistance caused by ICAM-1 reduction, highlighting the potential of CAR-NK cells in cancer immunotherapy.

Research Progress of Nanomaterials Acting on NK Cells in Tumor Immunotherapy and Imaging

The prognosis for cancer patients has declined dramatically in recent years due to the challenges in treating malignant tumors. Tumor immunotherapy, which includes immune target inhibition and chimeric antigen receptor cell treatment, is currently evolving quickly. Among them, natural killer (NK) cells are gradually becoming another preferred cell immunotherapy after T cell immunotherapy due to their unique killing effects in innate and adaptive immunity. NK cell therapy has shown encouraging outcomes in clinical studies; however, there are still some problems, including limited efficacy in solid tumors, inadequate NK cell penetration, and expensive treatment expenses. Noteworthy benefits of nanomaterials include their chemical specificity, biocompatibility, and ease of manufacturing; these make them promising instruments for enhancing NK cell anti-tumor immune responses. Nanomaterials can promote NK cell homing and infiltration, participate in NK cell modification and non-invasive cell tracking and imaging modes, and greatly increase the effectiveness of NK cell immunotherapy. The introduction of NK cell-based immunotherapy research and a more detailed discussion of nanomaterial research in NK cell-based immunotherapy and molecular imaging will be the main topics of this review.

Natural killer cell therapies

Natural killer (NK) cells are lymphocytes of the innate immune system. A key feature of NK cells is their ability to recognize a wide range of cells in distress, particularly tumour cells and cells infected with viruses. They combine both direct effector functions against their cellular targets and participate in the generation, shaping and maintenance of a multicellular immune response. As our understanding has deepened, several therapeutic strategies focused on NK cells have been conceived and are currently in various stages of development, from preclinical investigations to clinical trials. Here we explore in detail the complexity of NK cell biology in humans and highlight the role of these cells in cancer immunity. We also analyse the harnessing of NK cell immunity through immune checkpoint inhibitors, NK cell engagers, and infusions of preactivated or genetically modified, autologous or allogeneic NK cell products.

Combined use of NK cells and radiotherapy in the treatment of solid tumors

Natural killer (NK) cells are innate lymphocytes possessing potent tumor surveillance and elimination activity. Increasing attention is being focused on the role of NK cells in integral antitumor strategies (especially immunotherapy). Of note, therapeutic efficacy is considerable dependent on two parameters: the infiltration and cytotoxicity of NK cells in tumor microenvironment (TME), both of which are impaired by several obstacles (e.g., chemokines, hypoxia). Strategies to overcome such barriers are needed. Radiotherapy is a conventional modality employed to cure solid tumors. Recent studies suggest that radiotherapy not only damages tumor cells directly, but also enhances tumor recognition by immune cells through altering molecular expression of tumor or immune cells via the in situ or abscopal effect. Thus, radiotherapy may rebuild a NK cells-favored TME, and thus provide a cost-effective approach to improve the infiltration of NK cells into solid tumors, as well as elevate immune-activity. Moreover, the radioresistance of tumor always hampers the response to radiotherapy. Noteworthy, the puissant cytotoxic activity of NK cells not only kills tumor cells directly, but also increases the response of tumors to radiation via activating several radiosensitization pathways. Herein, we review the mechanisms by which NK cells and radiotherapy mutually promote their killing function against solid malignancies. We also discuss potential strategies harnessing such features in combined anticancer care.

Impact of antibody architecture and paratope valency on effector functions of bispecific NKp30 x EGFR natural killer cell engagers

Natural killer (NK) cells emerged as a promising effector population that can be harnessed for anti-tumor therapy. In this work, we constructed NK cell engagers (NKCEs) based on NKp30-targeting single domain antibodies (sdAbs) that redirect the cytotoxic potential of NK cells toward epidermal growth factor receptor (EGFR)-expressing tumor cells. We investigated the impact of crucial parameters such as sdAb location, binding valencies, the targeted epitope on NKp30, and the overall antibody architecture on the redirection capacity. Our study exploited two NKp30-specific sdAbs, one of which binds a similar epitope on NKp30 as its natural ligand B7-H6, while the other sdAb addresses a non-competing epitope. For EGFR-positive tumor targeting, humanized antigen-binding domains of therapeutic antibody cetuximab were used. We demonstrate that NKCEs bivalently targeting EGFR and bivalently engaging NKp30 are superior to monovalent NKCEs in promoting NK cell-mediated tumor cell lysis and that the architecture of the NKCE can substantially influence killing capacities depending on the NKp30-targeting sdAb utilized. While having a pronounced impact on NK cell killing efficacy, the capabilities of triggering antibody-dependent cellular phagocytosis or complement-dependent cytotoxicity were not significantly affected comparing the bivalent IgG-like NKCEs with cetuximab. However, the fusion of sdAbs can have a slight impact on the NK cell release of immunomodulatory cytokines, as well as on the pharmacokinetic profile of the NKCE due to unfavorable spatial orientation within the molecule architecture. Ultimately, our findings reveal novel insights for the engineering of potent NKCEs triggering the NKp30 axis.

Killer instincts: natural killer cells as multifactorial cancer immunotherapy

Natural killer (NK) cells integrate heterogeneous signals for activation and inhibition using germline-encoded receptors. These receptors are stochastically co-expressed, and their concurrent engagement and signaling can adjust the sensitivity of individual cells to putative targets. Against cancers, which mutate and evolve under therapeutic and immunologic pressure, the diversity for recognition provided by NK cells may be key to comprehensive cancer control. NK cells are already being trialled as adoptive cell therapy and targets for immunotherapeutic agents. However, strategies to leverage their naturally occurring diversity and agility have not yet been developed. In this review, we discuss the receptors and signaling pathways through which signals for activation or inhibition are generated in NK cells, focusing on their roles in cancer and potential as targets for immunotherapies. Finally, we consider the impacts of receptor co-expression and the potential to engage multiple pathways of NK cell reactivity to maximize the scope and strength of antitumor activities.

Viral escape from NK-cell-mediated immunosurveillance: A lesson for cancer immunotherapy?

Natural killer (NK) cells are innate lymphocytes that participate in immune responses against virus-infected cells and tumors. As a countermeasure, viruses and tumors employ strategies to evade NK-cell-mediated immunosurveillance. In this review, we examine immune evasion strategies employed by viruses, focusing on examples from human CMV and severe acute respiratory syndrome coronavirus 2. We explore selected viral evasion mechanisms categorized into three classes: (1) providing ligands for the inhibitory receptor NKG2A, (2) downregulating ligands for the activating receptor NKG2D, and (3) inducing the immunosuppressive cytokine transforming growth factor (TGF)-β. For each class, we draw parallels between immune evasion by viruses and tumors, reviewing potential opportunities for overcoming evasion in cancer therapy. We suggest that in-depth investigations of host-pathogen interactions between viruses and NK cells will not only deepen our understanding of viral immune evasion but also shed light on how NK cells counter such evasion attempts. Thus, due to the parallels of immune evasion by viruses and tumors, we propose that insights gained from antiviral NK-cell responses may serve as valuable lessons that can be leveraged for designing future cancer immunotherapies.

Cattle-derived knob paratopes grafted onto peripheral loops of the IgG1 Fc region enable the generation of a novel symmetric bispecific antibody format

In this work we present a novel symmetric bispecific antibody format based on engraftments of cattle-derived knob paratopes onto peripheral loops of the IgG1 Fc region. For this, knob architectures obtained from bovine ultralong CDR-H3 antibodies were inserted into the AB loop or EF loop of the CH3 domain, enabling the introduction of an artificial binding specificity into an IgG molecule. We demonstrate that inserted knob domains largely retain their binding affinities, resulting into bispecific antibody derivatives versatile for effector cell redirection. Essentially, generated bispecifics demonstrated adequate biophysical properties and were not compromised in their Fc mediated functionalities such as FcRn or FcγRIIIa binding.

Preclinical assessment of CAR-NK cell-mediated killing efficacy and pharmacokinetics in a rapid zebrafish xenograft model of metastatic breast cancer

Natural killer (NK) cells are attractive effectors for adoptive immunotherapy of cancer. Results from first-in-human studies using chimeric antigen receptor (CAR)-engineered primary NK cells and NK-92 cells are encouraging in terms of efficacy and safety. In order to further improve treatment strategies and to test the efficacy of CAR-NK cells in a personalized manner, preclinical screening assays using patient-derived tumor samples are needed. Zebrafish (Danio rerio) embryos and larvae represent an attractive xenograft model to study growth and dissemination of patient-derived tumor cells because of their superb live cell imaging properties. Injection into the organism's circulation allows investigation of metastasis, cancer cell-to-immune cell-interactions and studies of the tumor cell response to anti-cancer drugs. Here, we established a zebrafish larval xenograft model to test the efficacy of CAR-NK cells against metastatic breast cancer in vivo by injecting metastatic breast cancer cells followed by CAR-NK cell injection into the Duct of Cuvier (DoC). We validated the functionality of the system with two different CAR-NK cell lines specific for PD-L1 and ErbB2 (PD-L1.CAR NK-92 and ErbB2.CAR NK-92 cells) against the PD-L1-expressing MDA-MB-231 and ErbB2-expressing MDA-MB-453 breast cancer cell lines. Injected cancer cells were viable and populated peripheral regions of the larvae, including the caudal hematopoietic tissue (CHT), simulating homing of cancer cells to blood forming sites. CAR-NK cells injected 2.5 hours later migrated to the CHT and rapidly eliminated individual cancer cells throughout the organism. Unmodified NK-92 also demonstrated minor in vivo cytotoxicity. Confocal live-cell imaging demonstrated intravascular migration and real-time interaction of CAR-NK cells with MDA-MB-231 cells, explaining the rapid and effective in vivo cytotoxicity. Thus, our data suggest that zebrafish larvae can be used for rapid and cost-effective in vivo assessment of CAR-NK cell potency and to predict patient response to therapy.

Principles and current clinical landscape of NK cell engaging bispecific antibody against cancer

Monoclonal antibody-based targeted therapies have greatly improved treatment options for patients by binding to the innate immune system. However, the long-term efficacy of such antibodies is limited by mechanisms of drug resistance. Over the last 50 years, with advances in protein engineering technology, more and more bispecific antibody (bsAb) platforms have been engineered to meet diverse clinical needs. Bispecific NK cell engagers (BiKEs) or tri-specific NK cell engagers (TriKEs) allow for direct targeting of immune cells to tumors, and therefore resistance and serious adverse effects are greatly reduced. Many preclinical and clinical trials are currently underway, depicting the promise of antibody-based natural killer cell engager therapeutics. In this review, we compile worldwide efforts to explore the involvement of NK cells in bispecific antibodies. With a particular emphasis on lessons learned, we focus on preclinical and clinical studies in malignancies and discuss the reasons for the limited success of NK-cell engagers against solid tumors, offering plausible new ideas for curing some advanced cancers shortly.

Bi- and trispecific immune cell engagers for immunotherapy of hematological malignancies

Immune cell engagers are engineered antibodies with at least one arm binding a tumor-associated antigen and at least another one directed against an activating receptor in immune effector cells: CD3 for recruitment of T cells and CD16a for NK cells. The first T cell engager (the anti-CD19 blinatumomab) was approved by the FDA in 2014, but no other one hit the market until 2022. Now the field is gaining momentum, with three approvals in 2022 and 2023 (as of May): the anti-CD20 × anti-CD3 mosunetuzumab and epcoritamab and the anti-B cell maturation antigen (BCMA) × anti-CD3 teclistamab, and another three molecules in regulatory review. T cell engagers will likely revolutionize the treatment of hematological malignancies in the short term, as they are considerably more potent than conventional monoclonal antibodies recognizing the same tumor antigens. The field is thriving, with a plethora of different formats and targets, and around 100 bispecific T cell engagers more are already in clinical trials. Bispecific NK cell engagers are also in early-stage clinical studies and may offer similar efficacy with milder side effects. Trispecific antibodies (engaging either T cell or NK cell receptors) raise the game even further with a third binding moiety, which allows either the targeting of an additional tumor-associated antigen to increase specificity and avoid immune escape or the targeting of additional costimulatory receptors on the immune cell to improve its effector functions. Altogether, these engineered molecules may change the paradigm of treatment for relapsed or refractory hematological malignancies.

B7-H3 in Pediatric Tumors: Far beyond Neuroblastoma

B7-H3 is a 4Ig transmembrane protein that emerged as a tumor-associated antigen in neuroblastoma. It belongs to the B7 family, shows an immunoregulatory role toward NK and T cells, and, therefore, has been included in the growing family of immune checkpoints. Besides neuroblastoma, B7-H3 is expressed by many pediatric cancers including tumors of the central nervous system, sarcomas, and acute myeloid leukemia. In children, particularly those affected by solid tumors, the therapeutic protocols are aggressive and cause important life-threatening side effects. Moreover, despite the improved survival observed in the last decade, a relevant number of patients show therapy resistance and fatal relapses. Immunotherapy represents a new frontier in the cure of cancer patients and the targeting of tumor antigens or immune checkpoints blockade showed exciting results in adults. In this encouraging scenario, researchers and clinicians are exploring the possibility to use immunotherapeutics targeting B7-H3; these include mAbs and chimeric antigen receptor T-cells (CAR-T). These tools are rapidly evolving to improve the efficacy and decrease the unwanted side effects; drug-conjugated mAbs, bi-tri-specific mAbs or CAR-T, and, very recently, NK cell engagers (NKCE), tetra-specific molecules engaging a tumor-associated antigen and NK cells, have been generated. Preclinical data are promising, and clinical trials are ongoing. Hopefully, the B7-H3 targeting will provide important benefits to cancer patients.

Murine models to study human NK cells in human solid tumors

Since the first studies, the mouse models have provided crucial support for the most important discoveries on NK cells, on their development, function, and circulation within normal and tumor tissues. Murine tumor models were initially set to study murine NK cells, then, ever more sophisticated human-in-mice models have been developed to investigate the behavior of human NK cells and minimize the interferences from the murine environment. This review presents an overview of the models that have been used along time to study NK cells, focusing on the most popular NOG and NSG models, which work as recipients for the preparation of human-in-mice tumor models, the study of transferred human NK cells, and the evaluation of various enhancers of human NK cell function, including cytokines and chimeric molecules. Finally, an overview of the next generation humanized mice is also provided along with a discussion on how traditional and innovative in-vivo and in-vitro approaches could be integrated to optimize effective pre-clinical studies.

Defining and using immune archetypes to classify and treat cancer

Tumours are surrounded by a host immune system that can suppress or promote tumour growth. The tumour microenvironment (TME) has often been framed as a singular entity, suggesting a single type of immune state that is defective and in need of therapeutic intervention. By contrast, the past few years have highlighted a plurality of immune states that can surround tumours. In this Perspective, we suggest that different TMEs have 'archetypal' qualities across all cancers - characteristic and repeating collections of cells and gene-expression profiles at the level of the bulk tumour. We discuss many studies that together support a view that tumours typically draw from a finite number (around 12) of 'dominant' immune archetypes. In considering the likely evolutionary origin and roles of these archetypes, their associated TMEs can be predicted to have specific vulnerabilities that can be leveraged as targets for cancer treatment with expected and addressable adverse effects for patients.

Innate lymphoid cells and innate-like T cells in cancer - at the crossroads of innate and adaptive immunity

Immunotherapies targeting conventional T cells have revolutionized systemic treatment for many cancers, yet only a subset of patients benefit from these approaches. A better understanding of the complex immune microenvironment of tumours is needed to design the next generation of immunotherapeutics. Innate lymphoid cells (ILCs) and innate-like T cells (ILTCs) are abundant, tissue-resident lymphocytes that have recently been shown to have critical roles in many types of cancers. ILCs and ILTCs rapidly respond to changes in their surrounding environment and act as the first responders to bridge innate and adaptive immunity. This places ILCs and ILTCs as pivotal orchestrators of the final antitumour immune response. In this Review, we outline hallmarks of ILCs and ILTCs and discuss their emerging role in antitumour immunity, as well as the pathophysiological adaptations leading to their pro-tumorigenic function. We explore the pleiotropic, in parts redundant and sometimes opposing, mechanisms that underlie the delicate interplay between the different subsets of ILCs and ILTCs. Finally, we highlight their role in amplifying and complementing conventional T cell functions and summarize immunotherapeutic strategies for targeting ILCs and ILTCs in cancer.

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.

NKp46-specific single domain antibodies enable facile engineering of various potent NK cell engager formats

Herein, we describe the generation of potent NK cell engagers (NKCEs) based on single domain antibodies (sdAbs) specific for NKp46 harboring the humanized Fab version of Cetuximab for tumor targeting. After immunization of camelids, a plethora of different VHH domains were retrieved by yeast surface display. Upon reformatting into Fc effector-silenced NKCEs targeting NKp46 and EGFR in a strictly monovalent fashion, the resulting bispecific antibodies elicited potent NK cell-mediated killing of EGFR-overexpressing tumor cells with potencies (EC50 killing) in the picomolar range. This was further augmented via co-engagement of Fcγ receptor IIIa (FcγRIIIa). Importantly, NKp46-specific sdAbs enabled the construction of various NKCE formats with different geometries and valencies which displayed favorable biophysical and biochemical properties without further optimization. By this means, killing capacities were further improved significantly. Hence, NKp46-specific sdAbs are versatile building blocks for the construction of different NKCE formats.

Trispecific antibodies for cancer immunotherapy

Despite the clinical success of monoclonal and bispecific antibodies, there are still limitations in the therapeutic effect of malignant tumours, such as low response rate, treatment resistance, and so on, inspiring the exploration of trispecific antibodies (TsAbs). TsAbs further improve the safety and efficacy and has great clinical potential through three targets combination and formats optimization. This article reviews the development history and the target combination features of TsAbs. Although there are still great challenges in the clinical application of TsAbs, it is undeniable that TsAbs may be a breakthrough in the development of antibody drugs.

Generation and engineering of potent single domain antibody-based bispecific IL-18 mimetics resistant to IL-18BP decoy receptor inhibition

Here, we generated bispecific antibody (bsAb) derivatives that mimic the function of interleukin (IL)-18 based on single domain antibodies (sdAbs) specific to IL-18 Rα and IL-18 Rβ. For this, camelids were immunized, followed by yeast surface display (YSD)-enabled discovery of VHHs targeting the individual receptor subunits. Upon reformatting into a strictly monovalent (1 + 1) bispecific sdAb architecture, several bsAbs triggered dose-dependent IL-18 R downstream signaling on IL-18 reporter cells, as well as IFN-γ release by peripheral blood mononuclear cells in the presence of low-dose IL-12. However, compared with IL-18, potencies and efficacies were considerably attenuated. By engineering paratope valencies and the spatial orientation of individual paratopes within the overall design architecture, we were able to generate IL-18 mimetics displaying significantly augmented functionalities, resulting in bispecific cytokine mimetics that were more potent than IL-18 in triggering proinflammatory cytokine release. Furthermore, generated IL-18 mimetics were unaffected from inhibition by IL-18 binding protein decoy receptor. Essentially, we demonstrate that this strategy enables the generation of IL-18 mimetics with tailor-made cytokine functionalities.