The novel tribody [(CD20)2xCD16] efficiently triggers effector cell-mediated lysis of malignant B cells

Tri-specific killer engager: unleashing multi-synergic power against cancer

Cancer continues to be a global health concern, necessitating innovative solutions for treatment. Tri-specific killer engagers (TriKEs) have emerged as a promising class of immunotherapeutic agents, offering a multifaceted approach to cancer treatment. TriKEs simultaneously engage and activate natural killer (NK) cells while specifically targeting cancer cells, representing an outstanding advancement in immunotherapy. This review explores the generation and mechanisms of TriKEs, highlighting their advantages over other immunotherapies and discussing their potential impact on clinical trials and cancer treatment. TriKEs are composed of three distinct domains, primarily antibody-derived building blocks, linked together by short amino acid sequences. They incorporate critical elements, anti-cluster of differentiation 16 (CD16) and interleukin-15 (IL-15), which activate and enhance NK cell function, together with specific antibody to target each cancer. TriKEs exhibit remarkable potential in preclinical and early clinical studies across various cancer types, making them a versatile tool in cancer immunotherapy. Comparative analyses with other immunotherapies, such as chimeric antigen receptor-T (CAR-T) cell therapy, immune checkpoint inhibitors (ICIs), cytokine therapies, and monoclonal antibodies (mAbs), reveal the unique advantages of TriKEs. They offer a safer pathway for immunotherapy by targeting cancer cells without hyperactivating T cells, reducing off-target effects and complications. The future of TriKEs involves addressing challenges related to dosing, tumor-associated antigen (TAA) expression, and NK cell suppression. Researchers are exploring innovative dosing strategies, enhancing specificity through tumor-specific antigens (TSAs), and combining TriKEs with other therapies for increased efficacy.

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.

Optimizing chemotherapy treatment outcomes using metaheuristic optimization algorithms: A case study

BACKGROUND

This study explores the dynamics of a mathematical model, utilizing ordinary differential equations (ODE), to depict the interplay between cancer cells and effector cells under chemotherapy. The stability of the equilibrium points in the model is analysed using the Jacobian matrix and eigenvalues. Additionally, bifurcation analysis is conducted to determine the optimal values for the control parameters.

OBJECTIVE

To evaluate the performance of the model and control strategies, benchmarking simulations are performed using the PlatEMO platform.

METHODS

The Pure Multi-objective Optimal Control Problem (PMOCP) and the Hybrid Multi-objective Optimal Control Problem (HMOCP) are two different forms of optimal control problems that are solved using revolutionary metaheuristic optimisation algorithms. The utilization of the Hypervolume (HV) performance indicator allows for the comparison of various metaheuristic optimization algorithms in their efficacy for solving the PMOCP and HMOCP.

RESULTS

Results indicate that the MOPSO algorithm excels in solving the HMOCP, with M-MOPSO outperforming for PMOCP in HV analysis.

CONCLUSION

Despite not directly addressing immediate clinical concerns, these findings indicates that the stability shifts at critical thresholds may impact treatment efficacy.

Novel NKG2D-directed bispecific antibodies enhance antibody-mediated killing of malignant B cells by NK cells and T cells

The activating receptor natural killer group 2, member D (NKG2D) represents an attractive target for immunotherapy as it exerts a crucial role in cancer immunosurveillance by regulating the activity of cytotoxic lymphocytes. In this study, a panel of novel NKG2D-specific single-chain fragments variable (scFv) were isolated from naïve human antibody gene libraries and fused to the fragment antigen binding (Fab) of rituximab to obtain [CD20×NKG2D] bibodies with the aim to recruit cytotoxic lymphocytes to lymphoma cells. All bispecific antibodies bound both antigens simultaneously. Two bibody constructs, [CD20×NKG2D#3] and [CD20×NKG2D#32], efficiently activated natural killer (NK) cells in co-cultures with CD20+ lymphoma cells. Both bibodies triggered NK cell-mediated lysis of lymphoma cells and especially enhanced antibody-dependent cell-mediated cytotoxicity (ADCC) by CD38 or CD19 specific monoclonal antibodies suggesting a synergistic effect between NKG2D and FcγRIIIA signaling pathways in NK cell activation. The [CD20×NKG2D] bibodies were not effective in redirecting CD8+ T cells as single agents, but enhanced cytotoxicity when combined with a bispecific [CD19×CD3] T cell engager, indicating that NKG2D signaling also supports CD3-mediated T cell activation. In conclusion, engagement of NKG2D with bispecific antibodies is attractive to directly activate cytotoxic lymphocytes or to support their activation by monoclonal antibodies or bispecific T cell engagers. As a perspective, co-targeting of two tumor antigens may allow fine-tuning of antibody cancer therapies. Our proposed combinatorial approach is potentially applicable for many existing immunotherapies but further testing in different preclinical models is necessary to explore the full potential.

Contribution of natural killer cells in innate immunity against colorectal cancer

Natural killer cells are members of the innate immune system and promote cytotoxic activity against tumor or infected cells independently from MHC recognition. NK cells are modulated by the expression of activator/inhibitory receptors. The ratio of this activator/inhibitory receptors is responsible for the cytotoxic activity of NK cells toward the target cells. Owing to the potent anti-tumor properties of NK cells, they are considered as interesting approach in tumor treatment. Colorectal cancer (CRC) is the second most common cause of death in the world and the incidence is about 2 million new cases per year. Metastatic CRC is accompanied by a poor prognosis with less than three years of overall survival. Chemotherapy and surgery are the most adopted treatments. Besides, targeted therapy and immune checkpoint blockade are novel approach to CRC treatment. In these patients, circulating NK cells are a prognostic marker. The main target of CRC immune cell therapy is to improve the tumor cell's recognition and elimination by immune cells. Adaptive NK cell therapy is the milestone to achieve the purpose. Allogeneic NK cell therapy has been widely investigated within clinical trials. In this review, we focus on the NK related approaches including CAR NK cells, cell-based vaccines, monoclonal antibodies and immunomodulatory drugs against CRC tumoral cells.

TRYBE®: an Fc-free antibody format with three monovalent targeting arms engineered for long in vivo half-life

TrYbe® is an Fc-free therapeutic antibody format, capable of engaging up to three targets simultaneously, with long in vivo half-life conferred by albumin binding. This format is shown by small-angle X-ray scattering to be conformationally flexible with favorable 'reach' properties. We demonstrate the format's broad functionality by co-targeting of soluble and cell surface antigens. The benefit of monovalent target binding is illustrated by the lack of formation of large immune complexes when co-targeting multivalent antigens. TrYbes® are manufactured using standard mammalian cell culture and protein A affinity capture processes. TrYbes® have been formulated at high concentrations and have favorable drug-like properties, including stability, solubility, and low viscosity. The unique functionality and inherent developability of the TrYbe® makes it a promising multi-specific antibody fragment format for antibody therapy.

Next Generation Immuno-Oncology Strategies: Unleashing NK Cells Activity

In recent years, immunotherapy has become a powerful therapeutic option against multiple malignancies. The unique capacity of natural killer (NK) cells to attack cancer cells without antigen specificity makes them an optimal immunotherapeutic tool for targeting tumors. Several approaches are currently being pursued to maximize the anti-tumor properties of NK cells in the clinic, including the development of NK cell expansion protocols for adoptive transfer, the establishment of a favorable microenvironment for NK cell activity, the redirection of NK cell activity against tumor cells, and the blockage of inhibitory mechanisms that constrain NK cell function. We here summarize the recent strategies in NK cell-based immunotherapies and discuss the requirement to further optimize these approaches for enhancement of the clinical outcome of NK cell-based immunotherapy targeting tumors.

Dual Fc optimization to increase the cytotoxic activity of a CD19-targeting antibody

Targeting CD19 represents a promising strategy for the therapy of B-cell malignancies. Although non-engineered CD19 antibodies are poorly effective in mediating complement-dependent cytotoxicity (CDC), antibody-dependent cell-mediated cytotoxicity (ADCC) or antibody-dependent cellular phagocytosis (ADCP), these effector functions can be enhanced by Fc-engineering. Here, we engineered a CD19 antibody with the aim to improve effector cell-mediated killing and CDC activity by exchanging selected amino acid residues in the Fc domain. Based on the clinically approved Fc-optimized antibody tafasitamab, which triggers enhanced ADCC and ADCP due to two amino acid exchanges in the Fc domain (S239D/I332E), we additionally added the E345K amino acid exchange to favor antibody hexamerization on the target cell surface resulting in improved CDC. The dual engineered CD19-DEK antibody bound CD19 and Fcγ receptors with similar characteristics as the parental CD19-DE antibody. Both antibodies were similarly efficient in mediating ADCC and ADCP but only the dual optimized antibody was able to trigger complement deposition on target cells and effective CDC. Our data provide evidence that from a technical perspective selected Fc-enhancing mutations can be combined (S239D/I332E and E345K) allowing the enhancement of ADCC, ADCP and CDC with isolated effector populations. Interestingly, under more physiological conditions when the complement system and FcR-positive effector cells are available as effector source, strong complement deposition negatively impacts FcR engagement. Both effector functions were simultaneously active only at selected antibody concentrations. Dual Fc-optimized antibodies may represent a strategy to further improve CD19-directed cancer immunotherapy. In general, our results can help in guiding optimal antibody engineering strategies to optimize antibodies’ effector functions.

Harnessing natural killer cells for cancer immunotherapy: dispatching the first responders

Natural killer (NK) cells have crucial roles in the innate immunosurveillance of cancer and viral infections. They are 'first responders' that can spontaneously recognize abnormal cells in the body, rapidly eliminate them through focused cytotoxicity mechanisms and potently produce pro-inflammatory cytokines and chemokines that recruit and activate other immune cells to initiate an adaptive response. From the initial discovery of the diverse cell surface receptors on NK cells to the characterization of regulatory events that control their function, our understanding of the basic biology of NK cells has improved dramatically in the past three decades. This advanced knowledge has revealed increased mechanistic complexity, which has opened the doors to the development of a plethora of exciting new therapeutics that can effectively manipulate and target NK cell functional responses, particularly in cancer patients. Here, we summarize the basic mechanisms that regulate NK cell biology, review a wide variety of drugs, cytokines and antibodies currently being developed and used to stimulate NK cell responses, and outline evolving NK cell adoptive transfer approaches to treat cancer.

Novel Bi-Specific Immuno-Modulatory Tribodies Potentiate T Cell Activation and Increase Anti-Tumor Efficacy

Cancer immunotherapy has already shown significant improvements by combining different antibodies specific for distinct immune checkpoints, such as Ipilimumab and Nivolumab. Here, we tested combinatorial treatments of immunomodulatory antibodies, previously generated in our laboratory, for their effects on hPBMC activation, either upon stimulation with SEB or in co-cultures with tumor cells by cytokine secretion assays. We found that some of them showed additive or synergistic effects, and on the basis of these observations, we constructed, for the first time, four novel bispecific tribodies (TR), made up of a Fab derived from one anti-IC mAb and two scFvs derived from another mAb targeting a different IC. All four TRs cotargeting either programmed cell death protein 1 (PD-1) and Lymphocyte Activating 3 (LAG-3) or programmed death-ligand 1 (PD-L1) and LAG-3 retained binding affinity for their targets and the antagonistic effects of their parental mAbs, but some of them also showed an increased ability to induce lymphocyte activation and increased in vitro cytotoxicity against tumor cells compared to parental antibodies used either alone or in combinatorial treatments. Furthermore, none of the tribodies showed significant increased cytotoxicity on human cardiomyocytes. Considering that the tribody format reduces production costs (as only one construct provides the inhibitory effects of two antibodies), has an intermediate molecular size (100 kDa) which is well suited for both tumor penetration and an acceptable half-life, we think that these novel immunomodulatory TRBs have the potential to become precious tools for therapeutic applications, particularly in monotherapy-resistant cancer patients.

The War Is on: The Immune System against Glioblastoma—How Can NK Cells Drive This Battle?

Natural killer (NK) cells are innate lymphocytes that play an important role in immunosurveillance, acting alongside other immune cells in the response against various types of malignant tumors and the prevention of metastasis. Since their discovery in the 1970s, they have been thoroughly studied for their capacity to kill neoplastic cells without the need for previous sensitization, executing rapid and robust cytotoxic activity, but also helper functions. In agreement with this, NK cells are being exploited in many ways to treat cancer. The broad arsenal of NK-based therapies includes adoptive transfer of in vitro expanded and activated cells, genetically engineered cells to contain chimeric antigen receptors (CAR-NKs), in vivo stimulation of NK cells (by cytokine therapy, checkpoint blockade therapies, etc.), and tumor-specific antibody-guided NK cells, among others. In this article, we review pivotal aspects of NK cells’ biology and their contribution to immune responses against tumors, as well as providing a wide perspective on the many antineoplastic strategies using NK cells. Finally, we also discuss those approaches that have the potential to control glioblastoma—a disease that, currently, causes inevitable death, usually in a short time after diagnosis.

Molecular Aspects of Resistance to Immunotherapies-Advances in Understanding and Management of Diffuse Large B-Cell Lymphoma

Despite the unquestionable success achieved by rituximab-based regimens in the management of diffuse large B-cell lymphoma (DLBCL), the high incidence of relapsed/refractory disease still remains a challenge. The widespread clinical use of chemo-immunotherapy demonstrated that it invariably leads to the induction of resistance; however, the molecular mechanisms underlying this phenomenon remain unclear. Rituximab-mediated therapeutic effect primarily relies on complement-dependent cytotoxicity and antibody-dependent cell cytotoxicity, and their outcome is often compromised following the development of resistance. Factors involved include inherent genetic characteristics and rituximab-induced changes in effectors cells, the role of ligand/receptor interactions between target and effector cells, and the tumor microenvironment. This review focuses on summarizing the emerging advances in the understanding of the molecular basis responsible for the resistance induced by various forms of immunotherapy used in DLBCL. We outline available models of resistance and delineate solutions that may improve the efficacy of standard therapeutic protocols, which might be essential for the rational design of novel therapeutic regimens.

Targeting ADCC: A different approach to HER2 breast cancer in the immunotherapy era

The clinical outcome of patients with human epidermal growth factor receptor 2 (HER2) amplified breast carcinoma (BC) has improved with the development of anti-HER2 targeted therapies. However, patients can experience disease recurrence after curative intent and disease progression in the metastatic setting. In the current era of evolving immunotherapy agents, the understanding of the immune response against HER2 tumor cells developed by anti-HER2 antibodies (Abs) is rapidly evolving. Trastuzumab therapy promotes Natural Killer (NK) cell activation in patients with BC overexpressing HER2, indicating that the efficacy of short-term trastuzumab monotherapy, albeit direct inhibition of HER, could also be related with antibody-dependent cell-mediated cytotoxicity (ADCC). Currently, dual HER2 blockade using trastuzumab and pertuzumab is the standard of care in early and advanced disease as this combination could confer an additive effect in ADCC. In patients with disease relapse or progression, ADCC may be hampered by several factors such as FcγRIIIa polymorphism and an immunosuppressive environment, among others. Hence, new drug development strategies are being investigated aiming to boost the ADCC response triggered by anti-HER2 therapy. In this review, we summarize these strategies and the rationale, through mAbs engineering and combinatorial strategies, focusing on clinical results and ongoing trials.

Tumor cell lysis and synergistically enhanced antibody-dependent cell-mediated cytotoxicity by NKG2D engagement with a bispecific immunoligand targeting the HER2 antigen

Natural killer group 2 member D (NKG2D) plays an important role in the regulation of natural killer (NK) cell cytotoxicity in cancer immune surveillance. With the aim of redirecting NK cell cytotoxicity against tumors, the NKG2D ligand UL-16 binding protein 2 (ULBP2) was fused to a single-chain fragment variable (scFv) targeting the human epidermal growth factor receptor 2 (HER2). The resulting bispecific immunoligand ULBP2:HER2-scFv triggered NK cell-mediated killing of HER2-positive breast cancer cells in an antigen-dependent manner and required concomitant interaction with NKG2D and HER2 as revealed in antigen blocking experiments. The immunoligand induced tumor cell lysis dose-dependently and was effective at nanomolar concentrations. Of note, ULBP2:HER2-scFv sensitized tumor cells for antibody-dependent cell-mediated cytotoxicity (ADCC). In particular, the immunoligand enhanced ADCC by cetuximab, a therapeutic antibody targeting the epidermal growth factor receptor (EGFR) synergistically. No significant improvements were obtained by combining cetuximab and anti-HER2 antibody trastuzumab. In conclusion, dual-dual targeting by combining IgG1 antibodies with antibody constructs targeting another tumor associated antigen and engaging NKG2D as a second NK cell trigger molecule may be promising. Thus, the immunoligand ULBP2:HER2-scFv may represent an attractive biological molecule to promote NK cell cytotoxicity against tumors and to boost ADCC.

Harnessing CD16-Mediated NK Cell Functions to Enhance Therapeutic Efficacy of Tumor-Targeting mAbs

Simple Summary

Natural Killer (NK) cells play a major role in cancer immunotherapy based on tumor-targeting mAbs. NK cell-mediated tumor cell killing and cytokine secretion are powerfully stimulated upon interaction with IgG-opsonized tumor cells, through the aggregation of FcγRIIIA/CD16 IgG receptor. Advances in basic and translational NK cell biology have led to the development of strategies that, by improving mAb-dependent antitumor responses, may overcome the current limitations of antibody therapy attributable to tolerance, immunosuppressive microenvironment, and genotypic factors. This review provides an overview of the immunotherapeutic strategies being pursued to improve the efficacy of mAb-induced NK antitumor activity. The exploitation of antibody combinations, antibody-based molecules, used alone or combined with adoptive NK cell therapy, will be uncovered. Within the landscape of NK cell heterogeneity, we stress the role of memory NK cells as promising effectors in the next generation of immunotherapy with the aim to obtain long-lasting tumor control.

Abstract

Natural killer (NK) cells hold a pivotal role in tumor-targeting monoclonal antibody (mAb)-based activity due to the expression of CD16, the low-affinity receptor for IgG. Indeed, beyond exerting cytotoxic function, activated NK cells also produce an array of cytokines and chemokines, through which they interface with and potentiate adaptive immune responses. Thus, CD16-activated NK cells can concur to mAb-dependent “vaccinal effect”, i.e., the development of antigen-specific responses, which may be highly relevant in maintaining long-term protection of treated patients. On this basis, the review will focus on strategies aimed at potentiating NK cell-mediated antitumor functions in tumor-targeting mAb-based regimens, represented by (a) mAb manipulation strategies, aimed at augmenting recruitment and efficacy of NK cells, such as Fc-engineering, and the design of bi- or trispecific NK cell engagers and (b) the possible exploitation of memory NK cells, whose distinctive characteristics (enhanced responsiveness to CD16 engagement, longevity, and intrinsic resistance to the immunosuppressive microenvironment) may maximize therapeutic mAb antitumor efficacy.

Increased lipid metabolism impairs NK cell function and mediates adaptation to the lymphoma environment

Natural killer (NK) cells play critical roles in protection against hematological malignancies but can acquire a dysfunctional state, which limits antitumor immunity. However, the underlying reasons for this impaired NK cell function remain to be uncovered. We found that NK cells in aggressive B-cell lymphoma underwent substantial transcriptional reprogramming associated with increased lipid metabolism, including elevated expression of the transcriptional regulator peroxisome activator receptor-γ (PPAR-γ). Exposure to fatty acids in the lymphoma environment potently suppressed NK cell effector response and cellular metabolism. NK cells from both diffuse large B-cell lymphoma patients and Eµ-myc B-cell lymphoma-bearing mice displayed reduced interferon-γ (IFN-γ) production. Activation of PPAR-γ partially restored mitochondrial membrane potential and IFN-γ production. Overall, our data indicate that increased lipid metabolism, while impairing their function, is a functional adaptation of NK cells to the fatty-acid rich lymphoma environment.

Natural killer cell therapy for hematologic malignancies: successes, challenges, and the future

The adoptive transfer of natural killer (NK) cells is an emerging therapy in the field of immuno-oncology. In the last 3 decades, NK cells have been utilized to harness the anti-tumor immune response in a wide range of malignancies, most notably with early evidence of efficacy in hematologic malignancies. NK cells are dysfunctional in patients with hematologic malignancies, and their number and function are further impaired by chemotherapy, radiation, and immunosuppressants used in initial therapy and hematopoietic stem cell transplantation. Restoring this innate immune deficit may lead to improved therapeutic outcomes. NK cell adoptive transfer has proven to be a safe in these settings, even in the setting of HLA mismatch, and a deeper understanding of NK cell biology and optimized expansion techniques have improved scalability and therapeutic efficacy. Here, we review the use of NK cell therapy in hematologic malignancies and discuss strategies to further improve the efficacy of NK cells against these diseases.

Recent advances in cellular therapy for malignant lymphoma

Cellular therapies for malignant lymphoma include autologous or allogeneic hematopoietic stem cell transplantation (HSCT) and adaptive cellular therapy using EBV-specific T cells, cytokine-induced killer (CIK) cells, NKT cells, NK cells, chimeric antigen receptor T (CAR-T) cells and chimeric antigen receptor NK (CAR-NK) cells. In this review we discusses recent advances of these cellular therapies and consider ways to optimize these therapies. Not only a single strategy using one of these cellular therapies, but also multi-disciplinary treatment combines with antibodies, such as an anti-tumor antibody and an immune checkpoint antibody, may be more effective for relapsed and refractory lymphoma.

Enhancing CDC and ADCC of CD19 Antibodies by Combining Fc Protein-Engineering with Fc Glyco-Engineering

Background: Native cluster of differentiation (CD) 19 targeting antibodies are poorly effective in triggering antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC), which are crucial effector functions of therapeutic antibodies in cancer immunotherapy. Both functions can be enhanced by engineering the antibody’s Fc region by altering the amino acid sequence (Fc protein-engineering) or the Fc-linked glycan (Fc glyco-engineering). We hypothesized that combining Fc glyco-engineering with Fc protein-engineering will rescue ADCC and CDC in CD19 antibodies. Results: Four versions of a CD19 antibody based on tafasitamab’s V-regions were generated: a native IgG1, an Fc protein-engineered version with amino acid exchanges S267E/H268F/S324T/G236A/I332E (EFTAE modification) to enhance CDC, and afucosylated, Fc glyco-engineered versions of both to promote ADCC. Irrespective of fucosylation, antibodies carrying the EFTAE modification had enhanced C1q binding and were superior in inducing CDC. In contrast, afucosylated versions exerted an enhanced affinity to Fcγ receptor IIIA and had increased ADCC activity. Of note, the double-engineered antibody harboring the EFTAE modification and lacking fucose triggered both CDC and ADCC more efficiently. Conclusions: Fc glyco-engineering and protein-engineering could be combined to enhance ADCC and CDC in CD19 antibodies and may allow the generation of antibodies with higher therapeutic efficacy by promoting two key functions simultaneously.

NK cells in the tumor microenvironment: Prognostic and theranostic impact. Recent advances and trends

NK cells orchestrate the tumor destruction and control metastasis in a coordinated way with other immune cells of the tumor microenvironment. However, NK cell infiltration in the tumor microenvironment is limited, and tumor cells have developed numerous mechanisms to escape NK cell attack. As a result, NK cells that have been able to infiltrate the tumors are exhausted, and metabolically and functionally impaired. Depending this impairment the prognostic and theranostic values of NK cells differ depending on the studies, the type of cancer, the stage of tumor and the nature of the tumor microenvironment. Extensive studies have been done to investigate different strategies to improve the NK cell function, and nowadays, a battery of therapeutic tools are being tested, with promising results.

Enhancing natural killer cell function with gp41-targeting bispecific antibodies to combat HIV infection

OBJECTIVE(S)

The aim of this study was to develop and evaluate the activity of bispecific antibodies (bsAbs) to enhance natural killer (NK) cell antibody-dependent cellular cytotoxicity (ADCC) against HIV-infected cells.

DESIGN

These bsAbs are based on patient-derived antibodies targeting the conserved gp41 stump of HIV Env, and also incorporate a high-affinity single chain variable fragment (scFv) targeting the activating receptor CD16 on NK cells. Overall, we expect the bsAbs to provide increased affinity and avidity over their corresponding mAbs, allowing for improved ADCC activity against Env-expressing target cells.

METHODS

bsAbs and their corresponding mAbs were expressed in 293T cells and purified. The binding of bsAbs and mAbs to their intended targets was determined using Bio-Layer Interferometry, as well as flow cytometry based binding assays on in-vitro infected cells. The ability of these bsAbs to improve NK cell activity against HIV-infected cells was tested using in-vitro co-culture assays, using flow cytometry and calcein release to analyse NK cell degranulation and target cell killing, respectively.

RESULTS

The bsAbs-bound gp41 with similar affinity to their corresponding mAbs had increased affinity for CD16. The bsAbs also bound to primary CD4 T cells infected in vitro with two different strains of HIV. In addition, the bsAbs induce increased NK cell degranulation and killing of autologous HIV-infected CD4 T cells.

CONCLUSION

On the basis of their in-vitro killing efficacy, bsAbs may provide a promising strategy to improve NK-mediated immune targeting of infected cells during HIV infection.

Improving Immunotherapy Against B-Cell Malignancies Using γδ T-Cell-specific Stimulation and Therapeutic Monoclonal Antibodies

Tumor antigen-targeting monoclonal antibodies (mAbs) are an important element of current cancer therapies. Some of these therapeutic mAbs enable antibody-dependent cell mediated cytotoxicity (ADCC) against tumor cells. However, cancer-related functional impairment of immune effector cells may limit the clinical efficacy of antibody treatments. We reckoned that combining mAbs with cell-based immunotherapies would provide a clinically relevant synergism and benefit for cancer patients. Here, we focus on γδ T cells, as earlier studies demonstrated that γδ T-cell-based therapies are safe and promising for several types of malignancies. Similar to natural killer cells, their antitumor effects can be enhanced using antibodies, and they could, therefore, become a versatile effector cell platform for use with a variety of licensed therapeutic mAbs against cancer. In this study, we explore the potential of a combination therapy of activated γδ T cells with rituximab and the more recently developed mAbs (obinutuzumab and daratumumab) in different B-cell malignancies in vitro. Obinutuzumab outperformed the other mAbs with regard to direct target cell lysis and ADCC by γδ T cells in several CD20 cell lines and primary lymphoma specimens. We demonstrate that comparatively few CD16 γδ T cells are sufficient to mediate a strong ADCC. Using Fc-receptor-positive B-cell lymphomas as target cells, ADCC cannot be blocked by high concentrations of immunoglobulins or anti-CD16 antibodies, but both substances can promote cell mediated target cell lysis. This study expands on earlier reports on the therapeutic potential of distinctive tumor antigen-targeting mAbs and facilitates the understanding of the mechanism and potential of ADCC by γδ T-cell subsets.

Checkpoint Inhibitors and Engineered Cells: New Weapons for Natural Killer Cell Arsenal Against Hematological Malignancies

Natural killer (NK) cells represent one of the first lines of defense against malignant cells. NK cell activation and recognition are regulated by a balance between activating and inhibitory receptors, whose specific ligands can be upregulated on tumor cells surface and tumor microenvironment (TME). Hematological malignancies set up an extensive network of suppressive factors with the purpose to induce NK cell dysfunction and impaired immune-surveillance ability. Over the years, several strategies have been developed to enhance NK cells-mediated anti-tumor killing, while other approaches have arisen to restore the NK cell recognition impaired by tumor cells and other cellular components of the TME. In this review, we summarize and discuss the strategies applied in hematological malignancies to block the immune check-points and trigger NK cells anti-tumor effects through engineered chimeric antigen receptors.

Fc-engineering significantly improves the recruitment of immune effector cells by anti-ICAM-1 antibody MSH-TP15 for myeloma therapy

Despite several therapeutic advances, patients with multiple myeloma (MM) require additional treatment options since no curative therapy exists yet. In search of a novel therapeutic antibody, we previously applied phage display with myeloma cell screening and developed TP15, a scFv targeting intercellular adhesion molecule 1 (ICAM-1/CD54). To more precisely evaluate the antibody's modes of action, fully human IgG1 antibody variants were generated bearing wild-type (MSH-TP15) or mutated Fc to either enhance (MSH-TP15 Fc-eng.) or prevent (MSH-TP15 Fc k.o.) Fc gamma receptor binding. Especially MSH-TP15 Fc-eng. induced potent antibody-dependent cell-mediated cytotoxicity (ADCC) against malignant plasma cells by efficiently recruiting NK cells and engaged macrophages for antibody-dependent cellular phagocytosis (ADCP) of tumor cells. Binding studies with truncated ICAM-1 demonstrated MSH-TP15 binding to ICAM-1 domain 1-2. Importantly, MSH-TP15 and MSH-TP15 Fc-eng. both prevented myeloma cell engraftment and significantly prolonged survival of mice in an intraperitoneal xenograft model. In the subcutaneous model MSH-TP15 Fc-eng. was superior to MSH-TP15, whereas MSH-TP15 Fc k.o. was not effective in both models - reflecting the importance of Fc-dependent mechanisms of action also in vivo. The efficient recruitment of immune cells and the potent anti-tumor activity of the Fc-engineered MSH-TP15 antibody hold significant potential for myeloma immunotherapy.

T-cell Activating Tribodies as a Novel Approach for Efficient Killing of ErbB2-positive Cancer Cells

The Tyrosine Kinase Receptor ErbB2 (HER2) when overexpressed in breast cancer (BC) is associated with poor prognosis. The monoclonal antibody Trastuzumab has become a standard treatment of ErbB2+BC. The antibody treatment has limited efficacy, often meets resistance and induces cardiotoxicity. T-cell recruiting bispecific antibody derivatives (TRBA) offer a more effective alternative to standard antibody therapy. We evaluated a panel of TRBAs targeting 3 different epitopes on the ErbB2 receptor either in a bivalent targeting tribody structure or as a monovalent scFv-fusion (BiTE format) for binding, cytotoxicity on Trastuzumab-resistant cell lines, and induction of cardiotoxicity. All three TRBAs bind with high affinity to the ErbB2 extracellular domain and a large panel of ErbB2-positive tumor cells. Tribodies had an increased in vitro cytotoxic potency as compared to BiTEs. It is interesting to note that, Tribodies targeting the epitopes on ErbB2 receptor domains I and II bind and activate lysis of mammary and gastric tumor cells more efficiently than a Tribody targeting the Trastuzumab epitope on domain IV. The first 2 are also active on Trastuzumab-resistant cancer cells lacking or masking the epitope recognized by Trastuzumab. None of the Tribodies studied showed significant toxicity on human cardiomyocytes. Altogether these results make these novel anti-ErbB2 bispecific Tribodies candidates for therapeutic development for treating ErbB2-positive Trastuzumab-resistant cancer patients.

Bispecific antibodies enhance tumor-infiltrating T cell cytotoxicity against autologous HER-2-expressing high-grade ovarian tumors

Epithelial ovarian cancer displays the highest mortality of all gynecological tumors. A relapse of the disease even after successful surgical treatment is a significant problem. Resistance against the current platinum‐based chemotherapeutic standard regime requires a detailed ex vivo immune profiling of tumor‐infiltrating cells and the development of new therapeutic strategies.

In this study, we phenotypically and functionally characterize tumor cells and autologous tumor‐derived αβ and γδ T lymphocyte subsets. Tumor‐infiltrating (TIL) and tumor‐ascites lymphocytes (TAL) were ex vivo isolated out of tumor tissue and ascites, respectively, from high‐grade ovarian carcinoma patients (FIGO‐stage IIIa‐IV). We observed an increased γδ T cell percentage in ascites compared to tumor‐tissue and blood of these patients, whereas CD8⁺ αβ T cells were increased within TAL and TIL. The number of Vδ1 and non‐Vδ1/Vδ2‐expressing γδ T cells was increased in the ascites and in the tumor tissue compared to the blood of the same donors. Commonly in PBL, the Vγ9 chain of the γδ T cell receptor is usually associated exclusively with the Vδ2 chain. Interestingly, we detected Vδ1 and non‐Vδ1/Vδ2 T cells co‐expressing Vγ9, which is so far not described for TAL and TIL.

Importantly, our data demonstrated an expression of human epidermal growth factor receptor (HER)‐2 on high‐grade ovarian tumors, which can serve as an efficient tumor antigen to target CD3 TIL or selectively Vγ9‐expressing γδ T cells by bispecific antibodies (bsAbs) to ovarian cancer cells. Our bsAbs efficiently enhance cytotoxicity of TIL and TAL against autologous HER‐2‐expressing ovarian cells.

NK cells to cure cancer

Natural Killer (NK) cells are innate lymphocytes able to mediate immune-surveillance and clearance of viral infected and tumor-transformed cells. Growing experimental and clinical evidence highlighted a dual role of NK cells either in the control of cancer development/progression or in promoting the onset of immune-suppressant tumor microenvironments. Indeed, several mechanisms of NK cell-mediated tumor escape have been described and these includes cancer-induced aberrant expression of activating and inhibitory receptors (i.e. NK cell immune checkpoints), impairments of NK cell migration to tumor sites and altered NK cell effector-functions. These phenomena highly contribute to tumor progression and metastasis formation. In this review, we discuss the latest insights on those NK cell receptors and related molecules that are currently being implemented in clinics either as possible prognostic factors or therapeutic targets to unleash NK cell anti-tumor effector-functions in vivo. Moreover, we address here the major recent advances in regard to the genetic modification and ex vivo expansion of anti-tumor specific NK cells used in innovative adoptive cellular transfer approaches.

Natural Killer Cells as Key Players of Tumor Progression and Angiogenesis: Old and Novel Tools to Divert Their Pro-Tumor Activities into Potent Anti-Tumor Effects

Immune cells, as a consequence of their plasticity, can acquire altered phenotype/functions within the tumor microenvironment (TME). Some of these aberrant functions include attenuation of targeting and killing of tumor cells, tolerogenic/immunosuppressive behavior and acquisition of pro-angiogenic activities. Natural killer (NK) cells are effector lymphocytes involved in tumor immunosurveillance. In solid malignancies, tumor-associated NK cells (TANK cells) in peripheral blood and tumor-infiltrating NK (TINK) cells show altered phenotypes and are characterized by either anergy or reduced cytotoxicity. Here, we aim at discussing how NK cells can support tumor progression and how induction of angiogenesis, due to TME stimuli, can be a relevant part on the NK cell-associated tumor supporting activities. We will review and discuss the contribution of the TME in shaping NK cell response favoring cancer progression. We will focus on TME-derived set of factors such as TGF-β, soluble HLA-G, prostaglandin E₂, adenosine, extracellular vesicles, and miRNAs, which can exhibit a dual function. On one hand, these factors can suppress NK cell-mediated activities but, on the other hand, they can induce a pro-angiogenic polarization in NK cells. Also, we will analyze the impact on cancer progression of the interaction of NK cells with several TME-associated cells, including macrophages, neutrophils, mast cells, cancer-associated fibroblasts, and endothelial cells. Then, we will discuss the most relevant therapeutic approaches aimed at potentiating/restoring NK cell activities against tumors. Finally, supported by the literature revision and our new findings on NK cell pro-angiogenic activities, we uphold NK cells to a key host cellular paradigm in controlling tumor progression and angiogenesis; thus, we should bear in mind NK cells like a TME-associated target for anti-tumor therapeutic approaches.

Natural Killer Cells in Cancer Immunotherapy

Natural killer (NK) cells have evolved to complement T and B cells in host defense against pathogens and cancer. They recognize infected cells and tumors using a sophisticated array of activating, costimulatory, and inhibitory receptors that are expressed on NK cell subsets to create extensive functional diversity. NK cells can be targeted to kill with exquisite antigen specificity by antibody-dependent cellular cytotoxicity. NK and T cells share many of the costimulatory and inhibitory receptors that are currently under evaluation in the clinic for cancer immunotherapy. As with T cells, genetic engineering is being employed to modify NK cells to specifically target them to tumors and to enhance their effector functions. As the selective pressures exerted by immunotherapies to augment CD8+T cell responses may result in loss of MHC class I, NK cells may provide an important fail-safe to eliminate these tumors by their capacity to eliminate tumors that are “missing self.”

Tribody [(HER2)2xCD16] Is More Effective Than Trastuzumab in Enhancing γδ T Cell and Natural Killer Cell Cytotoxicity Against HER2-Expressing Cancer Cells

An enhanced expression of human epidermal growth factor receptor 2 (HER2, ErbB2) often occurs in an advanced stage of breast, ovarian, gastric or esophageal cancer, and pancreatic ductal adenocarcinoma (PDAC). Commonly, HER2 expression is associated with poor clinical outcome or chemoresistance in ovarian and breast cancer patients. Treatment with humanized anti-HER2 monoclonal antibodies, such as trastuzumab or pertuzumab, has improved the outcome of patients with HER2-positive metastatic gastric or breast cancer, but not all patients benefit. In this study, the bispecific antibody [(HER2)₂xCD16] in the tribody format was employed to re-direct CD16-expressing γδ T lymphocytes as well as natural killer (NK) cells to the tumor-associated cell surface antigen HER2 to enhance their cytotoxic anti-tumor activity. Tribody [(HER2)₂xCD16] comprises two HER2-specific single chain fragment variable fused to a fragment antigen binding directed to the CD16 (FcγRIII) antigen expressed on γδ T cells and NK cells. Our results revealed the superiority of tribody [(HER2)₂xCD16] compared to trastuzumab in triggering γδ T cell and NK cell-mediated lysis of HER2-expressing tumor cells, such as PDAC, breast cancer, and autologous primary ovarian tumors. The increased efficacy of [(HER2)₂xCD16] can be explained by an enhanced degranulation of immune cells. Although CD16 expression was decreased on γδ T cells in several PDAC patients and the number of tumor-infiltrating NK cells and γδ T cells was impaired in ovarian cancer patients, [(HER2)₂xCD16] selectively enhanced cytotoxicity of cells from these patients. Here, unique anti-tumor properties of tribody [(HER2)₂xCD16] are identified which beyond addressing HER2 overexpressing solid tumors may allow to treat with similar immunoconstructs combined with the adoptive transfer of γδ T cells and NK cells refractory hematological malignancies. A major advantage of γδ T cells and NK cells in the transplant situation of refractory hematological malignancies is given by their HLA-independent killing and a reduced graft-versus-host disease.

Hepatocellular carcinoma: Prospects for natural killer cell immunotherapy

Liver disease is a growing cause of death in the United Kingdom and the incidence of hepatocellular carcinoma (HCC) is rising (http://www.cancerresearchuk.org/). The combination of an immunosuppressive environment within the liver and suboptimal host anti-tumour immune responses may account for the poor survival outcome of HCC. Understanding how tumours evade immune recognition coupled with new insights into the unique immunological environment within the liver will be critical to developing liver-specific immunotherapies.

Therapeutic Antibodies: What Have We Learnt from Targeting CD20 and Where Are We Going?

Therapeutic monoclonal antibodies (mAbs) have become one of the fastest growing classes of drugs in recent years and are approved for the treatment of a wide range of indications, from cancer to autoimmune disease. Perhaps the best studied target is the pan B-cell marker CD20. Indeed, the first mAb to receive approval by the Food and Drug Administration for use in cancer treatment was the CD20-targeting mAb rituximab (Rituxan®). Since its approval for relapsed/refractory non-Hodgkin's lymphoma in 1997, rituximab has been licensed for use in the treatment of numerous other B-cell malignancies, as well as autoimmune conditions, including rheumatoid arthritis. Despite having a significant impact on the treatment of these patients, the exact mechanisms of action of rituximab remain incompletely understood. Nevertheless, numerous second- and third-generation anti-CD20 mAbs have since been developed using various strategies to enhance specific effector functions thought to be key for efficacy. A plethora of knowledge has been gained during the development and testing of these mAbs, and this knowledge can now be applied to the design of novel mAbs directed to targets beyond CD20. As we enter the "post-rituximab" era, this review will focus on the lessons learned thus far through investigation of anti-CD20 mAb. Also discussed are current and future developments relating to enhanced effector function, such as the ability to form multimers on the target cell surface. These strategies have potential applications not only in oncology but also in the improved treatment of autoimmune disorders and infectious diseases. Finally, potential approaches to overcoming mechanisms of resistance to anti-CD20 therapy are discussed, chiefly involving the combination of anti-CD20 mAbs with various other agents to resensitize patients to treatment.

A novel Fc-engineered human ICAM-1/CD54 antibody with potent anti-myeloma activity developed by cellular panning of phage display libraries

To identify antibodies suitable for multiple myeloma (MM) immunotherapy, a cellular screening approach was developed using plasma cell lines JK-6L and INA-6 and human synthetic single-chain fragment variable (scFv) phage libraries. Isolated phage antibodies were screened for myeloma cell surface reactivity. Due to its binding characteristics, phage PIII-15 was selected to generate the scFv-Fc fusion protein TP15-Fc with an Fc domain optimized for FcγRIIIa binding. Various MM cell lines and patient-derived CD138-positive malignant plasma cells, but not granulocytes, B or T lymphocytes from healthy donors were recognized by TP15-Fc. Human intercellular adhesion molecule-1 (ICAM-1/CD54) was identified as target antigen by using transfected Chinese hamster ovary (CHO) cells. Of note, no cross-reactivity of TP15-Fc with mouse ICAM-1 transfected cells was detected. TP15-Fc was capable to induce antibody-dependent cell-mediated cytotoxicity (ADCC) against different human plasma cell lines and patients' myeloma cells with peripheral blood mononuclear cells (PBMC) and purified NK cells. Importantly, TP15-Fc showed potent in vivo efficacy and completely prevented growth of human INA-6.Tu1 plasma cells in a xenograft SCID/beige mouse model. Thus, the novel ADCC-optimized TP15-Fc exerts potent anti-myeloma activity and has promising characteristics to be further evaluated for MM immunotherapy.

An Fc Double-Engineered CD20 Antibody with Enhanced Ability to Trigger Complement-Dependent Cytotoxicity and Antibody-Dependent Cell-Mediated Cytotoxicity

BACKGROUND

Engineering of the antibody's fragment crystallizable (Fc) by modifying the amino acid sequence (Fc protein engineering) or the glycosylation pattern (Fc glyco-engineering) allows enhancing effector functions of tumor targeting antibodies. Here, we investigated whether complement-dependent cytotoxicity (CDC) and antibody-dependent cell-mediated cytotoxicity (ADCC) of CD20 antibodies could be improved simultaneously by combining Fc protein engineering and glyco-engineering technologies.

METHODS AND RESULTS

Four variants of the CD20 antibody rituximab were generated: a native IgG1, a variant carrying the EFTAE modification (S267E/H268F/S324T/G236A/I332E) for enhanced CDC as well as glyco-engineered, non-fucosylated derivatives of both to boost ADCC. The antibodies bound CD20 specifically with similar affinity. Antibodies with EFTAE modification were more efficacious in mediating CDC, irrespective of fucosylation, than antibodies with wild-type sequences due to enhanced C1q binding. In contrast, non-fucosylated variants had an enhanced affinity to FcγRIIIA and improved ADCC activity. Importantly, the double-engineered antibody lacking fucose and carrying the EFTAE modification mediated both CDC and ADCC with higher efficacy than the native CD20 IgG1 antibody.

CONCLUSION

Combining glyco-engineering and protein engineering technologies offers the opportunity to simultaneously enhance ADCC and CDC activities of therapeutic antibodies. This approach may represent an attractive strategy to further improve antibody therapy of cancer and deserves further evaluation.

Natural killer cells unleashed: Checkpoint receptor blockade and BiKE/TriKE utilization in NK-mediated anti-tumor immunotherapy

Natural killer (NK) cells have long been known to mediate anti-tumor responses without prior sensitization or recognition of specific tumor antigens. However, the tumor microenvironment can suppress NK cell function resulting in tumor escape and disease progression. Despite recent advances in cytokine therapy and NK cell adoptive transfer, tumor expression of ligands to NK - expressed checkpoint receptors can still suppress NK mediated tumor lysis. This review will explore many of the checkpoint receptors tumors utilize to manipulate the NK cell response as well as some of the current and upcoming pharmacological solutions to limit tumor suppression of NK cell function. Furthermore, we will discuss the potential to use these drugs in combinational therapies with novel antibody reagents such as bi- and tri-specific killer engagers (BiKEs and TriKEs) against tumor-specific antigens to enhance NK cell-mediated tumor rejection.

Antibody-dependent cell cytotoxicity: immunotherapy strategies enhancing effector NK cells

Antibody-dependent cellular cytotoxicity (ADCC) is a set of mechanisms that target cells coated with IgG antibodies of the proper subclasses (IgG1 in the human) to be the prey of cell-to-cell cytolysis executed by immune cells expressing FcRIIIA (CD16A). These effectors include not only natural killer (NK) cells but also other CD16⁺ subsets such as monocyte/macrophages, NKT cells or γδ T cells. In cancer therapy, ADCC is exploited by antibodies that selectively recognize proteins on the surface of malignant cells. An approach to enhance antitumor activity is to act on effector cells so they are increased in their numbers or enhanced in their individual (on a cell per cell basis) ADCC performance. This enhancement can be therapeutically attained by cytokines (that is, interleukin (IL)-15, IL-21, IL-18, IL-2); immunostimulatory monoclonal antibodies (that is, anti-CD137, anti-CD96, anti-TIGIT, anti-KIR, anti-PD-1); TLR agonists or by adoptive infusions of ex vivo expanded NK cells which can be genetically engineered to become more efficient effectors. In conjunction with approaches optimizing IgG1 Fc affinity to CD16, acting on effector cells offers hope to achieve synergistic immunotherapy strategies.

HER2-specific immunoligands engaging NKp30 or NKp80 trigger NK-cell-mediated lysis of tumor cells and enhance antibody-dependent cell-mediated cytotoxicity

NK cells detect tumors through activating surface receptors, which bind self-antigens that are frequently expressed upon malignant transformation. To increase the recognition of tumor cells, the extracellular domains of ligands of the activating NK cell receptors NKp30, NKp80 and DNAM-1 (i.e. B7-H6, AICL and PVR, respectively) were fused to a single-chain fragment variable (scFv) targeting the human epidermal growth factor receptor 2 (HER2), which is displayed by various solid tumors. The resulting immunoligands, designated B7-H6:HER2-scFv, AICL:HER2-scFv, and PVR:HER2-scFv, respectively, bound HER2 and the addressed NK cell receptor. However, whereas B7-H6:HER2-scFv and AICL:HER2-scFv triggered NK cells to kill HER2-positive breast cancer cells at nanomolar concentrations, PVR:HER2-scFv was not efficacious. Moreover, NK cell cytotoxicity was enhanced synergistically when B7-H6:HER2-scFv or AICL:HER2-scFv were applied in combination with another HER2-specific immunoligand engaging the stimulatory receptor NKG2D. In contrast, no improvements were achieved by combining B7-H6:HER2-scFv with AICL:HER2-scFv. Additionally, B7-H6:HER2-scFv and AICL:HER2-scFv enhanced antibody-dependent cell-mediated cytotoxicity (ADCC) by the therapeutic antibodies trastuzumab and cetuximab synergistically, with B7-H6:HER2-scFv exhibiting a higher efficacy. In summary, antibody-derived proteins engaging NKp30 or NKp80 may represent attractive biologics to further enhance anti-tumor NK cell responses and may provide an innovative approach to sensitize tumor cells for antibody-based immunotherapy.

Monitoring and functional characterization of the lymphocytic compartment in pancreatic ductal adenocarcinoma patients

BACKGROUND/OBJECTIVES

Pancreatic ductal adenocarcinoma (PDAC) still has a poor prognosis and current treatments including immunotherapy often fail. This might be due to the pronounced immunosuppressive milieu impairing infiltration and function of immune effector cells. This study aimed at a comprehensive analysis of immune cells in PDAC patients by determining absolute and relative peripheral blood cell numbers of immune cell subsets along with their functional capacity.

METHODS

Whole blood cells or isolated peripheral blood mononuclear cells were characterized by flow cytometry. PDAC tissues were analyzed by immunohistochemistry. Anti-tumor activity of immune effector cells was determined by RTCA system.

RESULTS

Our data demonstrate that relative CD4⁺ memory- and regulatory T cell numbers were enhanced, whereas determination of absolute cell numbers revealed generally lower immune cell numbers in PDAC patients compared to healthy controls. γδ T cells accumulated at higher numbers compared to αβ T cells in the malignant ductal epithelium of PDAC tissues indicating that γδ T cells infiltrate into the tumor. Cytotoxicity against tumor cells of even small numbers of T- and NK cells could be induced by a bispecific antibody targeting CD3⁺ T cells to human epidermal growth factor receptor (HER)2 expressing PDAC cells or Trastuzumab. Importantly, a critical number of γδ T cells was required for significant tumor cell killing by a bispecific antibody engaging the γδ T cell receptor on γδ T cells and HER2 on tumor cells.

CONCLUSION

Monitoring immune cells along with the determination of their functional capacity provides a comprehensive assessment as a prerequisite for a personalized immunotherapeutic PDAC treatment.

Generation of BiKEs and TriKEs to Improve NK Cell-Mediated Targeting of Tumor Cells

Cancer immunotherapies have gained significant momentum over the past decade, particularly with the advent of checkpoint inhibitors and CAR T-cells. While the latter personalized targeted immunotherapy has revolutionized the field, a need for off-the-shelf therapies remains. The ability of NK cells to quickly lyse antibody-coated tumors and potently secrete cytokines without prior priming has made NK cells ideal candidates for antigen-specific immunotherapy. NK cells have been targeted to tumors through two main strategies: mono-specific antibodies and bi/tri-specific antibodies. Mono-specific antibodies drive NK cell antibody-dependent cell-mediated cytotoxicity (ADCC) of tumor cells. Bi/tri-specific antibodies drive re-directed lysis of tumor cells through binding of a tumor antigen and direct binding and crosslinking of the CD16 receptor on NK cells, thus bypassing the need for binding of the Fc portion of mono-specific antibodies. This chapter focuses on the generation of bi- and tri-specific killer engagers (BiKEs and TriKEs) meant to target NK cells to tumors. BiKEs and TriKEs are smaller molecules composed of 2-3 variable portions of antibodies with different specificities, and represent a novel and more versatile strategy compared to traditional bi- and tri-specific antibody platforms.

NK Cell-Mediated Antibody-Dependent Cellular Cytotoxicity in Cancer Immunotherapy

Natural killer (NK) cells play a major role in cancer immunotherapies that involve tumor-antigen targeting by monoclonal antibodies (mAbs). NK cells express a variety of activating and inhibitory receptors that serve to regulate the function and activity of the cells. In the context of targeting cells, NK cells can be "specifically activated" through certain Fc receptors that are expressed on their cell surface. NK cells can express FcγRIIIA and/or FcγRIIC, which can bind to the Fc portion of immunoglobulins, transmitting activating signals within NK cells. Once activated through Fc receptors by antibodies bound to target cells, NK cells are able to lyse target cells without priming, and secrete cytokines like interferon gamma to recruit adaptive immune cells. This antibody-dependent cell-mediated cytotoxicity (ADCC) of tumor cells is utilized in the treatment of various cancers overexpressing unique antigens, such as neuroblastoma, breast cancer, B cell lymphoma, and others. NK cells also express a family of receptors called killer immunoglobulin-like receptors (KIRs), which regulate the function and response of NK cells toward target cells through their interaction with their cognate ligands that are expressed on tumor cells. Genetic polymorphisms in KIR and KIR-ligands, as well as FcγRs may influence NK cell responsiveness in conjunction with mAb immunotherapies. This review focuses on current therapeutic mAbs, different strategies to augment the anti-tumor efficacy of ADCC, and genotypic factors that may influence patient responses to antibody-dependent immunotherapies.

γδ T cell activation by bispecific antibodies

Bispecific antibodies have been successfully introduced into clinical application. γδ T cells are of special interest for tumor immunotherapy, due to their recognition of pyrophosphates that are overproduced by many tumor cells resulting in HLA-nonrestricted tumor cell killing. Here we describe in detail a [(Her2)2 × Vγ9] tribody construct that targets human Vγ9 T cells to HER2-expressing tumor cells. The direct comparison with other selective Vγ9 T cell agonists including phosphoantigens and nitrogen-containing bisphosphonates revealed the superiority of the [(Her2)2 × Vγ9] tribody in triggering γδ T cell-mediated tumor cell killing with negligible induction of γδ T cell death. In contrast, phosphoantigens and bisphosphonates are potent inducers of γδ T cell proliferation but less efficient enhancers of γδ T cell-mediated tumor cell killing. Collectively, our data identify unique properties of a γδ T cell-targeting [(Her2)2 × Vγ9] tribody which make it an attractive candidate for clinical application in γδ T cell-based tumor immunotherapy.

The biology of NK cells and their receptors affects clinical outcomes after hematopoietic cell transplantation (HCT)

Natural killer (NK) cells were first identified for their capacity to reject bone marrow allografts in lethally irradiated mice without prior sensitization. Subsequently, human NK cells were detected and defined by their non-major histocompatibility complex (MHC)-restricted cytotoxicity toward transformed or virally infected target cells. Karre et al. later proposed 'the missing self hypothesis' to explain the mechanism by which self-tolerant cells could kill targets that had lost self MHC class I. Subsequently, the receptors that recognize MHC class I to mediate tolerance in the host were identified on NK cells. These class I-recognizing receptors contribute to the acquisition of function by a dynamic process known as NK cell education or licensing. In the past, NK cells were assumed to be short lived, but more recently NK cells have been shown to mediate immunologic memory to secondary exposures to cytomegalovirus infection. Because of their ability to lyse tumors with aberrant MHC class I expression and to produce cytokines and chemokines upon activation, NK cells may be primed by many stimuli, including viruses and inflammation, to contribute to a graft-versus-tumor effect. In addition, interactions with other immune cells support the therapeutic potential of NK cells to eradicate tumor and to enhance outcomes after hematopoietic cell transplantation.

Novel bispecific antibodies increase γδ T-cell cytotoxicity against pancreatic cancer cells

The ability of human γδ T cells from healthy donors to kill pancreatic ductal adenocarcinoma (PDAC) in vitro and in vivo in immunocompromised mice requires the addition of γδ T-cell-stimulating antigens. In this study, we demonstrate that γδ T cells isolated from patients with PDAC tumor infiltrates lyse pancreatic tumor cells after selective stimulation with phosphorylated antigens. We determined the absolute numbers of γδ T-cell subsets in patient whole blood and applied a real-time cell analyzer to measure their cytotoxic effector function over prolonged time periods. Because phosphorylated antigens did not optimally enhance γδ T-cell cytotoxicity, we designed bispecific antibodies that bind CD3 or Vγ9 on γδ T cells and Her2/neu (ERBB2) expressed by pancreatic tumor cells. Both antibodies enhanced γδ T-cell cytotoxicity with the Her2/Vγ9 antibody also selectively enhancing release of granzyme B and perforin. Supporting these observations, adoptive transfer of γδ T cells with the Her2/Vγ9 antibody reduced growth of pancreatic tumors grafted into SCID-Beige immunocompromised mice. Taken together, our results show how bispecific antibodies that selectively recruit γδ T cells to tumor antigens expressed by cancer cells illustrate the tractable use of endogenous γδ T cells for immunotherapy.

Mimicking an induced self phenotype by coating lymphomas with the NKp30 ligand B7-H6 promotes NK cell cytotoxicity

Induced self expression of the NKp30 ligand B7-H6 facilitates NK cell-mediated elimination of stressed cells. A fusion protein consisting of the ectodomain of B7-H6 and the CD20 single-chain fragment variable 7D8 was generated to mimic an induced self phenotype required for NK cell-mediated target cell elimination. B7-H6:7D8 had bifunctional properties as reflected by its ability to simultaneously bind to the CD20 Ag and to the NKp30 receptor. B7-H6:7D8 bound by CD20(+) lymphoma cells activated human NK cells and triggered degranulation. Consequently, the immunoligand B7-H6:7D8 induced killing of lymphoma-derived cell lines as well as fresh tumor cells from chronic lymphocytic leukemia or lymphoma patients. B7-H6:7D8 was active at nanomolar concentrations in a strictly Ag-specific manner and required interaction with both CD20 and NKp30. Remarkably, NK cell cytotoxicity was further augmented by concomitant activation of Fcγ receptor IIIa or NK group 2 member D. Thus, B7-H6:7D8 acted synergistically with the CD20 Ab rituximab and the immunoligand ULBP2:7D8, which was similarly designed as B7-H6:7D8 but engaging the NK group 2 member D receptor. In conclusion, to our knowledge, B7-H6:7D8 represents the first Ab-based molecule stimulating NKp30-mediated NK cell cytotoxicity for therapeutic purposes and provides proof of concept that Ag-specific NKp30 engagement may represent an innovative strategy to enhance antitumoral NK cell cytotoxicity.