The bispecific immunoligand ULBP2-aCEA redirects natural killer cells to tumor cells and reveals potent anti-tumor activity against colon carcinoma

NKG2D triggering hampers DNAM-1-mediated signaling in human NK cells

Introduction

Natural Killer (NK) cells are cytotoxic innate lymphocytes able to detect transformed cells through the balanced action of inhibitory and activating receptors. NKG2D is one of the main activating receptors involved in tumor surveillance thanks to its ability to recognize stress-induced ligands. Of note, the prolonged exposure to NKG2D ligands promotes receptor down-modulation that results in defective activation of NKG2D and other unrelated activating receptors, including DNAM-1 that is also involved in tumor clearance. However, further investigations are necessary to characterize how the NKG2D/DNAM-1 interplay affects NK cell anti-tumor function.

Methods

Primary cultured human NK cells were stimulated with the natural ligand MICA or an anti-NKG2D agonist antibody. The expression of activating and inhibitory receptors as well as DNAM-1-triggered signaling events and cytotoxicity were evaluated by flow cytometry. DNAM-1-mediated granule polarization was evaluated by confocal microscopy.

Results

We showed that NKG2D crosslinking mediated by the natural ligand MICA or an agonist antibody had different consequences on primary cultured human NK cells. Indeed, MICA stimulation increases the expression of the checkpoint receptor TIGIT that is able to counteract DNAM-1 activation. Stimulation with the agonist antibody, without altering TIGIT expression, directly inhibits DNAM-1-mediated signal transduction and cytotoxic function with a mechanism that required NKG2D endocytosis.

Discussion

Our findings contribute to shed light on the functional consequences of NKG2D engagement, demonstrating that a direct impact on DNAM-1-mediated signal transduction occurs independently from the modality of NKG2D crosslinking. Understanding the molecular mechanisms responsible for suppression of NK cell activation may help the development of therapeutic anti-cancer strategies aimed to prevent NK cell dysfunction or to reinvigorate an impaired cytotoxic activity.

Bispecific killer cell engagers employing species cross-reactive NKG2D binders redirect human and murine lymphocytes to ErbB2/HER2-positive malignancies

NKG2D is an activating receptor expressed by natural killer (NK) cells and other cytotoxic lymphocytes that plays a pivotal role in the elimination of neoplastic cells through recognition of different stress-induced cell surface ligands (NKG2DL). To employ this mechanism for cancer immunotherapy, we generated NKG2D-engaging bispecific antibodies that selectively redirect immune effector cells to cancer cells expressing the tumor-associated antigen ErbB2 (HER2). NKG2D-specific single chain fragment variable (scFv) antibodies cross-reactive toward the human and murine receptors were derived by consecutive immunization of chicken with the human and murine antigens, followed by stringent screening of a yeast surface display immune library. Four distinct species cross-reactive (sc) scFv domains were selected, and reformatted into a bispecific engager format by linking them via an IgG4 Fc domain to a second scFv fragment specific for ErbB2. The resulting molecules (termed scNKAB-ErbB2) were expressed as disulfide-linked homodimers, and demonstrated efficient binding to ErbB2-positive cancer cells as well as NKG2D-expressing primary human and murine lymphocytes, and NK-92 cells engineered with chimeric antigen receptors derived from human and murine NKG2D (termed hNKAR and mNKAR). Two of the scNKAB-ErbB2 molecules were found to compete with the natural NKG2D ligand MICA, while the other two engagers interacted with an epitope outside of the ligand binding site. Nevertheless, all four tested scNKAB-ErbB2 antibodies were similarly effective in redirecting the cytotoxic activity of primary human and murine lymphocytes as well as hNKAR-NK-92 and mNKAR-NK-92 cells to ErbB2-expressing targets, suggesting that further development of these species cross-reactive engager molecules for cancer immunotherapy is warranted.

NKG2D-bispecific enhances NK and CD8+ T cell antitumor immunity

BACKGROUND

Cancer immunotherapy approaches that elicit immune cell responses, including T and NK cells, have revolutionized the field of oncology. However, immunosuppressive mechanisms restrain immune cell activation within solid tumors so additional strategies to augment activity are required.

METHODS

We identified the co-stimulatory receptor NKG2D as a target based on its expression on a large proportion of CD8+ tumor infiltrating lymphocytes (TILs) from breast cancer patient samples. Human and murine surrogate NKG2D co-stimulatory receptor-bispecifics (CRB) that bind NKG2D on NK and CD8+ T cells as well as HER2 on breast cancer cells (HER2-CRB) were developed as a proof of concept for targeting this signaling axis in vitro and in vivo.

RESULTS

HER2-CRB enhanced NK cell activation and cytokine production when co-cultured with HER2 expressing breast cancer cell lines. HER2-CRB when combined with a T cell-dependent-bispecific (TDB) antibody that synthetically activates T cells by crosslinking CD3 to HER2 (HER2-TDB), enhanced T cell cytotoxicity, cytokine production and in vivo antitumor activity. A mouse surrogate HER2-CRB (mHER2-CRB) improved in vivo efficacy of HER2-TDB and augmented NK as well as T cell activation, cytokine production and effector CD8+ T cell differentiation.

CONCLUSION

We demonstrate that targeting NKG2D with bispecific antibodies (BsAbs) is an effective approach to augment NK and CD8+ T cell antitumor immune responses. Given the large number of ongoing clinical trials leveraging NK and T cells for cancer immunotherapy, NKG2D-bispecifics have broad combinatorial potential.

Dual Targeting of Glioblastoma Cells with Bispecific Killer Cell Engagers Directed to EGFR and ErbB2 (HER2) Facilitates Effective Elimination by NKG2D-CAR-Engineered NK Cells

NKG2D is an activating receptor of natural killer cells that recognizes stress-induced ligands (NKG2DL) expressed by many tumor cells. Nevertheless, NKG2DL downregulation or shedding can still allow cancer cells to evade immune surveillance. Here, we used lentiviral gene transfer to engineer clinically usable NK-92 cells with a chimeric antigen receptor (NKAR) which contains the extracellular domain of NKG2D for target recognition, or an NKAR, together with the IL-15 superagonist RD-IL15, and combined these effector cells with recombinant NKG2D-interacting bispecific engagers that simultaneously recognize the tumor-associated antigens epidermal growth factor receptor (EGFR) or ErbB2 (HER2). Applied individually, in in vitro cell-killing assays, these NKAB-EGFR and NKAB-ErbB2 antibodies specifically redirected NKAR-NK-92 and NKAR_RD-IL15-NK-92 cells to glioblastoma and other cancer cells with elevated EGFR or ErbB2 levels. However, in mixed glioblastoma cell cultures, used as a model for heterogeneous target antigen expression, NKAR-NK cells only lysed the EGFR- or ErbB2-expressing subpopulations in the presence of one of the NKAB molecules. This was circumvented by applying NKAB-EGFR and NKAB-ErbB2 together, resulting in effective antitumor activity similar to that against glioblastoma cells expressing both target antigens. Our results demonstrate that combining NK cells carrying an activating NKAR receptor with bispecific NKAB antibodies allows for flexible targeting, which can enhance tumor-antigen-specific cytotoxicity and prevent immune escape.

Bispecific NK-cell engager targeting BCMA elicits stronger antitumor effects and produces less proinflammatory cytokines than T-cell engager

Bispecific antibodies have attracted more attention in recent years for the treatment of tumors, in which most of them target CD3, which mediates the killing of tumor cells by T cells. However, T-cell engager may cause serious side effects, including neurotoxicity and cytokine release syndrome. More safe treatments are still needed to address unmet medical needs, and NK cell-based immunotherapy is a safer and more effective way to treat tumors. Our study developed two IgG-like bispecific antibodies with the same configuration: BT1 (BCMA×CD3) attracted T cells and tumor cells, while BK1 (BCMA×CD16) attracted NK cells and tumor cells. Our study showed that BK1 mediated NK cell activation and upregulated the expression of CD69, CD107a, IFN-γ and TNF. In addition, BK1 elicited a stronger antitumor effect than BT1 both in vitro and in vivo. Combinatorial treatment (BK1+BT1) showed a stronger antitumor effect than either treatment alone, as indicated by in vitro experiments and in vivo murine models. More importantly, BK1 induced fewer proinflammatory cytokines than BT1 both in vitro and in vivo. Surprisingly, BK1 reduced cytokine production in the combinatorial treatment, suggesting the indispensable role of NK cells in the control of cytokine secretion by T cells. In conclusion, our study compared NK-cell engagers and T-cell engagers targeting BCMA. The results indicated that NK-cell engagers were more effective with less proinflammatory cytokine production. Furthermore, the use of NK-cell engagers in combinatorial treatment helped to reduce cytokine secretion by T cells, suggesting a bright future for NK-cell engagers in clinical settings.

Engaging natural killer cells for cancer therapy via NKG2D, CD16A and other receptors

The field of immuno-oncology has revolutionized cancer patient care and improved survival and quality of life for patients. Much of the focus in the field has been on exploiting the power of the adaptive immune response through therapeutic targeting of T cells. While these approaches have markedly advanced the field, some challenges remain, and the clinical benefit of T cell therapies does not extend to all patients or tumor indications. Alternative strategies, such as engaging the innate immune system, have become an intense area of focus in the field. In particular, the engagement of natural killer (NK) cells as potent effectors of the innate immune response has emerged as a promising modality in immunotherapy. Here, we review therapeutic approaches for selective engagement of NK cells for cancer therapy, with a particular focus on targeting the key activating receptors NK Group 2D (NKG2D) and cluster of differentiation 16A (CD16A).

Natural killer cell immunotherapy in glioblastoma

Glioblastoma (GBM) is one of the most difficult cancers to treat because GBM has the high therapeutic resistance. Recently, immunotherapies for GBM have been used instead of conventional treatments. Among them, Natural killer (NK) cell-based immunotherapy has the potential to treat GBM due to its properties such as the absence of restriction by antigen-antibody reaction and deep penetration into the tumor microenvironment. Especially, genetically engineered NK cells, such as chimeric antigen receptor (CAR)-NK cells, dual antigen-targeting CAR NK cells, and adapter chimeric antigen receptor NK cells are considered to be an important tool for GBM immunotherapy. Therefore, this review describes the recent efforts of NK cell-based immunotherapy in GBM patients. We also describe key receptors expressing on NK cells such as killer cell immunoglobulin-like receptor, CD16, and natural killer group 2, member D (NKG2DL) receptor and discuss the function and importance of these molecules.

The application of the natural killer cells, macrophages and dendritic cells in treating various types of cancer

Innate immune cells such as natural killer (NK) cells, macrophages and dendritic cells (DCs) are involved in the surveillance and clearance of tumor. Intensive research has exposed the mechanisms of recognition and elimination of tumor cells by these immune cells as well as how cancers evade immune response. Hence, harnessing the immune cells has proven to be an effective therapy in treating a variety of cancers. Strategies aimed to harness and augment effector function of these cells for cancer therapy have been the subject of intense researches over the decades. Different immunotherapeutic possibilities are currently being investigated for anti-tumor activity. Pharmacological agents known to influence immune cell migration and function include therapeutic antibodies, modified antibody molecules, toll-like receptor agonists, nucleic acids, chemokine inhibitors, fusion proteins, immunomodulatory drugs, vaccines, adoptive cell transfer and oncolytic virus–based therapy. In this review, we will focus on the preclinical and clinical applications of NK cell, macrophage and DC immunotherapy in cancer treatment.

Immunotherapeutic targeting of activating natural killer cell receptors and their ligands in cancer

Natural killer (NK) cells exert an important role in cancer immune surveillance. Recognition of malignant cells and controlled activation of effector functions are facilitated by the expression of activating and inhibitory receptors, which is a complex interplay that allows NK cells to discriminate malignant cells from healthy tissues. Due to their unique profile of effector functions, the recruitment of NK cells is attractive in cancer treatment and a key function of NK cells in antibody therapy is widely appreciated. In recent years, besides the low-affinity fragment crystallizable receptor for immunoglobulin G (FcγRIIIA), the activating natural killer receptors p30 (NKp30) and p46 (NKp46), as well as natural killer group 2 member D (NKG2D), have gained increasing attention as potential targets for bispecific antibody-derivatives to redirect NK cell cytotoxicity against tumors. Beyond modulation of the receptor activity on NK cells, therapeutic targeting of the respective ligands represents an attractive approach. Here, novel therapeutic approaches to unleash NK cells by engagement of activating NK-cell receptors and alternative strategies targeting their tumor-expressed ligands in cancer therapy are summarized.

Baseline soluble MICA levels act as a predictive biomarker for the efficacy of regorafenib treatment in colorectal cancer

Background

To evaluate the effect of regorafenib on soluble MHC class I polypeptide-related sequence A (MICA) (sMICA) level in vitro. In addition, we clinically examined whether its plasma levels were associated with regorafenib activity in terms of progression-free survival (PFS) in patients with CRC.

Methods

Human CRC cell line HCT116 and HT29 cells were treated with regorafenib and its pharmacologically active metabolites, M2 or M5 at the same concentrations as those in sera of patients. We also examined the sMICA levels and the area under the plasma concentration–time curve of regorafenib, M2 and M5.

Results

Regorafenib, M2, and M5 significantly suppressed shedding of MICA in human CRC cells without toxicity. This resulted in the reduced production of sMICA. In the clinical examination, patients with CRC who showed long median PFS (3.7 months) had significantly lower sMICA levels than those with shorter median PFS (1.2 months) (p = 0.045).

Conclusions

MICA is an attractive agent for manipulating the immunological control of CRC and baseline sMICA levels could be a predictive biomarker for the efficacy of regorafenib treatment.

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.

Investigation and verification of the clinical significance and perspective of natural killer group 2 member D ligands in colon adenocarcinoma

This study investigated and verified the diagnostic and prognostic values of natural killer group 2 member D ligand (NKG2DL) genes in colon adenocarcinoma (COAD). We downloaded NKG2DLs expression data and corresponding clinical parameters from The Cancer Genome Atlas (TCGA) and used bioinformatics techniques to investigate the values of NKG2DLs in COAD. Then, we used the GSE40967 cohort to verify the prognostic value of NKG2DLs. Finally, we verified the ULBP2 expression level in tissues, and also investigated the diagnostic and prognostic values of ULBP2 in COAD. The diagnostic receiver operating characteristic curves showed that ULBP1, ULBP2, ULBP3, and RAET1L had high diagnostic values in COAD [Area Under Curve (AUC) > 0.9]. In TCGA cohort, the univariate and multivariate survival analyses suggested that ULBP2 was correlated with the prognosis of COAD recurrence-free survival (RFS) and overall survival (OS). In GSE40967 cohort, ULBP2 was associated with CC RFS and OS. Reverse transcription-quantitative polymerase chain reaction and immunohistochemistry results showed that ULBP2 was highly expressed in COAD tumor tissues (P < 0.05) and both had diagnostic values (AUC > 0.7). Validated survival analysis showed that the high expression of ULBP2 had a worse prognosis in COAD OS and RFS. Thus, ULBP2 might be an independent diagnostic and prognostic biomarker of COAD.

Immune cell engagers in solid tumors: promises and challenges of the next generation immunotherapy

In the landscape of cancer immunotherapy, immune cell engagers (ICEs) are rapidly emerging as a feasible and easy-to-deliver alternative to adoptive cell therapy for the antitumor redirection of immune effector cells. Even if in hematological malignancies this class of new therapeutics already hit the clinic, the development of ICEs in solid tumors still represents a challenge. Considering that ICEs are a rapidly expanding biotechnology in cancer therapy, we designed this review as a primer for clinicians, focusing on the major obstacles for the clinical implementation and the most translatable approaches proposed to overcome the limitations in solid tumors.

The role of natural killer cell in gastrointestinal cancer: killer or helper

Gastrointestinal cancer is one of the leading health problems worldwide, with a high morbidity and mortality. To date, harnessing both the innate and adaptive immune system against cancer provides a selective and effective therapeutic strategy for patients. As a first line defense against cancer, natural killer (NK) cells can swiftly target and lyse tumor cells without prior activation. In addition to its pivotal role in innate immunity, NK cells also play unique roles in the adaptive immune system as it enhance anti-tumor adaptive immune responses through secretion of cytokines and retaining an immunological memory. All these characteristics make NK cell a promising anti-cancer agent for patients. In spite of scarce infiltration and impaired function of NK cells in tumors, and the fact that tumors easily develop resistant mechanisms to evade the attacks from endogenous NK cells, multiple strategies have been developed to boost anti-tumor effect of NK cells and abolish tumor resistance. Some examples include adoptive transfer of NK cells after ex vivo activation and expansion; restoration of NK cell function using immune checkpoint inhibitors, and monoclonal antibody or cytokine treatment. Preclinical data have shown encouraging results, suggesting that NK cells hold great potential in cancer therapy. In this review, we discuss NK cells' cytotoxicity and modulation function in GI cancer and the current application in clinical therapy.

Anti-NKG2D single domain-based antibodies for the modulation of anti-tumor immune response

The natural killer group 2 member D (NKG2D) receptor is a C-type lectin-like activating receptor mainly expressed by cytotoxic immune cells including NK, CD8⁺ T, γδ T and NKT cells and in some pathological conditions by a subset of CD4⁺ T cells. It binds a variety of ligands (NKG2DL) whose expressions is finely regulated by stress-related conditions. The NKG2DL/NKG2D axis plays a central and complex role in the regulation of immune responses against diverse cellular threats such as oncogene-mediated transformations or infections. We generated a panel of seven highly specific anti-human NKG2D single-domain antibodies targeting various epitopes. These single-domain antibodies were integrated into bivalent and bispecific antibodies using a versatile plug-and-play Fab-like format. Depending on the context, these Fab-like antibodies exhibited activating or inhibitory effects on the immune response mediated by the NKG2DL/NKG2D axis. In solution, the bivalent anti-NKG2D antibodies that compete with NKG2DL potently blocked the activation of NK cells seeded on immobilized MICA, thus constituting antagonizing candidates. Bispecific anti-NKG2DxHER2 antibodies that concomitantly engage HER2 on tumor cells and NKG2D on NK cells elicited cytotoxicity of unstimulated NK in a tumor-specific manner, regardless of their apparent affinities and epitopes. Importantly, the bispecific antibodies that do not compete with ligands binding retained their full cytotoxic activity in the presence of ligands, a valuable property to circumvent immunosuppressive effects induced by soluble ligands in the microenvironment.

Recent developments in antibody derivatives against colorectal cancer; A review

Colorectal cancer (CRC) is the fourth most common cause of cancer and mortality worldwide and is the third most common cancer in men and women. Surgery, radiotherapy, and chemotherapy are conventionally used for the treatment of colorectal cancer. However, these methods are associated with various side effects on normal cells. Thus, new studies are moving towards more effective and non-invasive methods for treatment of colorectal cancer. Targeted therapy of CRC is a promising new approach to enhance the efficiency and decrease the toxicity of the treatment. In targeted therapy of CRC, antibody fragments can directly inhibit tumor cell growth and proliferation. They also can act as an ideal carrier for targeted delivery of anticancer drugs. In the present study, the structure and function of different formats of antibody fragments, immune-targeted therapy of CRC using antibody fragments will be discussed.

B7-H3 confers resistance to Vγ9Vδ2 T cell-mediated cytotoxicity in human colon cancer cells via the STAT3/ULBP2 axis

Immunotherapy based on γδT cells has limited efficiency in solid tumors, including colon cancer (CC). The immune evasion of tumor cells may be the main cause of the difficulties of γδT cell-based treatment. In the present study, we explored whether and how B7-H3 regulates the resistance of CC cells to the cytotoxicity of Vγ9Vδ2 (Vδ2) T cells. We observed that B7-H3 overexpression promoted, while B7-H3 knockdown inhibited, CC cell resistance to the killing effect of Vδ2 T cells in vitro and in vivo. Mechanistically, we showed that B7-H3-mediated CC cell resistance to the cytotoxicity of Vδ2 T cells involved a molecular pathway comprising STAT3 activation and decreased ULBP2 expression. ULBP2 blockade or knockdown abolished the B7-H3 silencing-induced increase in the cytotoxicity of Vδ2 T cells to CC cells. Furthermore, cryptotanshinone, a STAT3 phosphorylation inhibitor, reversed the B7-H3 overexpression-induced decrease in ULBP2 expression and attenuated the killing effect of Vδ2 T cells on CC cells. Moreover, there was a negative correlation between the expression of B7-H3 and ULBP2 in the tumor tissues of CC patients. Our results suggest that the B7-H3-mediated STAT3/ULBP2 axis may be a potential candidate target for improving the efficiency of γδT cell-based immunotherapy in CC.

Arming cytotoxic lymphocytes for cancer immunotherapy by means of the NKG2D/NKG2D-ligand system

INTRODUCTION

The activating NKG2D receptor plays a central role in the immune recognition and elimination of abnormal self-cells by cytotoxic lymphocytes. NKG2D binding to cell stress-inducible ligands (NKG2DL) up-regulated on cancer cells facilitates their immunorecognition. Yet tumor cells utilize various escape mechanisms to avert NKG2D-based immunosurveillance. Hence, therapeutic strategies targeting the potent NKG2D/NKG2DL axis and such immune escape mechanisms become increasingly attractive in cancer therapy.

AREAS COVERED

This perspective provides a brief introduction into the NKG2D/NKG2DL axis and its relevance for cancer immune surveillance. Subsequently, the most advanced therapeutic approaches targeting the NKG2D system are presented focusing on NKG2D-CAR engineered immune cells and antibody-mediated strategies to inhibit NKG2DL shedding by tumors.

EXPERT OPINION

Thus far, NKG2D-CAR engineered lymphocytes represent the most advanced therapeutic approach utilizing the NKG2D system. Similarly to other tumor-targeting CAR approaches, NKG2D-CAR cells demonstrate powerful on-target activity, but may also cause off-tumor toxicities or lose efficacy, if NKG2DL expression by tumors is reduced. However, NKG2D-CAR cells also act on the tumor microenvironment curtailing its immunosuppressive properties, thus providing an independent therapeutic benefit. The potency of tumoricidal NKG2D-expressing lymphocytes can be further boosted by enhancing NKG2DL expression through small molecules and therapeutic antibodies inhibiting tumor-associated shedding of NKG2DL.

Progression or suppression: Two sides of the innate lymphoid cells in cancer

Innate lymphoid cells (ILCs) as key players in innate immunity have been shown to be significantly associated with inflammation, lymphoid neogenesis, tissue remodeling, mucosal immunity and lately have been considered a remarkable nominee for either tumor-promoting or tumor-inhibiting functions. This dual role of ILCs, which is driven by intrinsic and extrinsic factors like plasticity of ILCs and the tumor microenvironment, respectively, has aroused interest in ILCs subsets in past decade. So far, numerous studies in the cancer field have revealed ILCs to be key players in the initiation, progression and inhibition of tumors, therefore providing valuable insights into therapeutic approaches to utilize the immune system against cancer. Herein, the most recent achievements regarding ILCs subsets including new classifications, their transcription factors, markers, cytokine release and mechanisms that led to either progression or inhibition of many tumors have been evaluated. Additionally, the available data regarding ILCs in most prevalent cancers and new therapeutic approaches are summarized.

Strategies to Augment Natural Killer (NK) Cell Activity against Solid Tumors

The immune system plays a crucial role to prevent local growth and dissemination of cancer. Therapies based on activating the immune system can result in beneficial responses in patients with metastatic disease. Treatment with antibodies targeting the immunological checkpoint axis PD-1 / PD-L1 can result in the induction of anti-tumor T cell activation leading to meaningful long-lasting clinical responses. Still, many patients acquire resistance or develop dose-limiting toxicities to these therapies. Analysis of tumors from patients who progress on anti-PD-1 treatment reveal defective interferon-signaling and antigen presentation, resulting in immune escape from T cell-mediated attack. Natural killer (NK) cells are innate lymphocytes that can kill tumor cells without prior sensitization to antigens and can be activated to kill tumor cells that have an impaired antigen processing and presentation machinery. Thus, NK cells may serve as useful effectors against tumor cells that have become resistant to classical immune checkpoint therapy. Various approaches to activate NK cells are being increasingly explored in clinical trials against cancer. While clinical benefit has been demonstrated in patients with acute myeloid leukemia receiving haploidentical NK cells, responses in patients with solid tumors are so far less encouraging. Several hurdles need to be overcome to provide meaningful clinical responses in patients with solid tumors. Here we review the recent developments to augment NK cell responses against solid tumors with regards to cytokine therapy, adoptive infusion of NK cells, NK cell engagers, and NK cell immune checkpoints.

CD24 targeting bi-specific antibody that simultaneously stimulates NKG2D enhances the efficacy of cancer immunotherapy

PURPOSE

Bi-specific antibody (BsAb) is an emerging novel format of antibody. We aimed to develop the natural killer (NK) cell receptor NK group 2, member D (NKG2D)-mediated, immune surveillance system. In this system, the NKG2D ligand MHC class I-related chain A (MICA) was fused with BsAb, which targeted a cluster of differentiation 24 (CD24), a tumor-initiating cell marker that is over-expressed on hepatocellular carcinoma (HCC).

METHODS

The Homo MICA extracellular domains (hMICA) were fused to the end of the heavy chain of cG7 with the flexible pentapeptide (Gly-Gly-Gly-Gly-Ser; G4S), which formed the cG7-MICA that was further identified using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and western blotting (WB). The targeting specificity was characterized using the Surface Plasmon Resonance (SPR) technology and a flow cytometry assay. Furthermore, the design of BsAb cG7-MICA that targeted CD24 and NKG2D was proven to enhance antibody-dependent, cell-mediated cytotoxicity (ADCC) in vitro by the CytoTox 96 Nonradioactive Cytotoxicity assay. Degranulation and a cytokine production assay of NK cells demonstrated that NK cells were activated effectively by cG7-MICA. Further, in HCC-bearing nude mice, the anti-tumor effects of cG7-MICA combined with sorafenib were verified again.

RESULTS

We purified cG7-MICA successfully, and it has a high affinity. In vivo, cG7-MICA recruited NK cells to the tumor site and improved the anti-tumor efficacy of sorafenib. cG7-MICA also activated NK cells to release interferon γ (IFN-γ) and tumor necrosis factor α (TNF-α), and it increased the CD107a expression on the surface of the NK cells in vitro.

CONCLUSION

NK cells play a major role in the natural, innate immune system, and they have the function of identifying and killing target cells. cG7-MICA remodels the function of MICA molecules to activate NK cells, which provides a possible strategy for HCC-targeting immunotherapy.

Transcriptomic changes associated with PCK1 overexpression in hepatocellular carcinoma cells detected by RNA-seq

Phosphoenolpyruvate carboxykinase 1 (PCK1), a step limiting enzyme of gluconeogenesis, is downregulated in hepatocellular carcinoma (HCC). Overexpression of PCK1 has been shown to suppress hepatoma cell growth, but the underlying mechanism remains unclear. We used recombinant adenovirus overexpressing PCK1 or GFP in Huh7 cells, and the differentially expressed genes (DEGs) were identified by RNA-Seq. 180 were upregulated by PCK1 overexpression, whereas 316 were downregulated. Pathway analysis illustrated that PCK1 was closely correlated with Wnt signaling pathway and TGF-beta signaling pathway. Hence, Wnt signaling pathway and its downstream component, FZD2, FZD6, FZD7 and β-catenin were confirmed by qRT-PCR and Western blot. In vivo we also observed that PCK1 had restrained tumor growth as a result of decreasing expression of β-catenin. Whole-transcriptomic profile analysis discovered that overexpression of PCK1 downregulates several oncogenic signaling pathways in HCC, providing potential therapeutic targets for improving HCC therapy.

Adoptive Cell Transfer: Is it a Promising Immunotherapy for Colorectal Cancer?

The last decade has witnessed significant advances in the adoptive cell transfer (ACT) technique, which has been appreciated as one of the most promising treatments for patients with cancer. Utilization of ACT can enhance the function of the immune system or improve the specificity and persistence of transferred cells. Various immune cells including T lymphocytes, natural killer cells, dendritic cells, and even stem cells can be used in the ACT despite their different functional mechanisms. Colorectal cancer (CRC) is among the most common malignancies and causes millions of deaths worldwide every year. In this review, we discuss the status and perspective of the ACT in the treatment of CRC.

NK cell-mediated anti-leukemia cytotoxicity is enhanced using a NKG2D ligand MICA and anti-CD20 scfv chimeric protein

NK cells are important innate cytotoxic lymphocytes that have potential in treatment of leukemia. Engagement of NKG2D receptor on NK cells enhances the target cytotoxicity. Here, we produced a fusion protein consisting of the extracellular domain of the NKG2D ligand MICA and the anti-CD20 single-chain variable fragment (scfv). This recombinant protein is capable of binding both NK cells and CD20⁺ tumor cells. Using a human NKG2D reporter cell system we developed, we showed that this fusion protein could decorate CD20⁺ tumor cells with MICA extracellular domain and activate NK through NKG2D. We further demonstrated that this protein could specifically induce the ability of a NK cell line (NKL) and primary NK cells to lyse CD20⁺ leukemia cells. Moreover, we found that downregulation of surface HLA class I expression in the target cells improved NKL-mediated killing. Our results demonstrated that this recombinant protein specifically lyses leukemia cells by NK cells, which may lead to development of a novel strategy for treating leukemia and other tumors.

Genetic alterations detected by comparative genomic hybridization in BRCAX breast and ovarian cancers of Brazilian population

Background

About 5–10% of breast/ovarian cancers are hereditary. However, for a large proportion of cases (around 50%), the genetic cause remains unknown. These cases are grouped in a separated BRCAX category. The aim of this study was to identify genomic alterations in BRCA1/BRCA2 wild-type tumor samples from women with family history strongly suggestive of hereditary breast/ovarian cancer.

Results

A cohort of 31 Brazilian women was included in the study. Using the GISTIC algorithm, we identified 20 regions with genomic gains and 31 with losses. The most frequent altered regions were 1q21.2, 6p22.1 and 8p23.3 in breast tumors and Xq26 and Xp22.32-22.31 among the ovarian cancer cases. An interesting association identified was the loss of 22q13.31-13.32 and the presence of ovarian cancer cases. Among the genes present in the frequently altered regions, we found FGFR1, NSMCE2, CTTN, CRLF2, ERBB2, STARD3, MIR3201 and several genes of RAET and ULBP family.

Conclusions

In conclusion, our results suggest that alterations on chromosomes 1, 6, 8 and X are common on BRCAX tumors and that the loss on 22q can be associated with the presence of ovarian cancer.

Methods

DNA copy number alterations were analyzed by 60K array comparative genomic hybridization in breast and ovarian FFPE tumors.

Gemcitabine inhibits immune escape of pancreatic cancer by down regulating the soluble ULBP2 protein

Due to early onset of local invasion and distant metastasis, pancreatic cancer is the most lethal human malignant tumor, with a 5 year survival rate of less than 5%. As a effective chemotherapy drug for pancreatic cancer patients, gemcitabine is reported to inhibit cell proliferation as a nucleotide analog. In this study, we investigated the role of gemcitabine in immune regulation of pancreatic cancer. Our data showed that the level of soluble ULBP2 (sULBP2), a ligand of NKG2D receptor, decreased in the supernatants of pancreatic cancer cell lines when gemcitabine was added, and sULBP2 level correlated with NK92 cells cytotoxicity to pancreatic cancer cell lines. Importantly, our data showed that gemcitabine promoted PANC-1 cells and MIA PaCa-2 immune evasion by reducing ADAM10 expression, a metalloproteinase involved in sULBP2 shedding from cell membrane. Knockdown of ADAM10 clearly downregulated sULBP2 levels in the culture supernatants and cells became more susceptible to NK92 cytotoxicity. Serum samples and tumor samples were obtained from 45 patients with pancreatic ductal adenocarcinoma (PDAC). Statistical analysis showed a significant correlation between the serum level of sULBP2 with ADAM10 expression in PDAC tissues. In conclusion, our data demostrated that gemcitabine inhibits ULBP2 ectodomain shedding through the suppression of ADAM10 and enhance NK cells cytotoxicity by NKG2D-ULBP2 interaction. The results extends our understanding of gemcitabine in the treatment of pancreatic cancer from cell proliferation inhibition to immune regulation.

Fusion Proteins of NKG2D/NKG2DL in Cancer Immunotherapy

NKG2D (natural killer group 2, member D) is an important activating receptor in natural killer (NK) cells and some T cells. NKG2D ligands (NKG2DLs) are specifically expressed on most tumor cells. The engagement of these ligands on tumor cells to NKG2D on NK cells will induce cell-mediated cytotoxicity and have target cells destroyed. This gives NKG2D/NKG2DLs great potential in cancer therapeutic application. The creation of NKG2D/NKG2DL-based multi-functional fusion proteins is becoming one of the most promising strategies in immunotherapy for cancer. Antibodies, cytokines, and death receptors have been fused with NKG2D or its ligands to produce many powerful fusion proteins, including NKG2D-based chimeric antigen receptors (CARs). In this article, we review the recent developments of the fusion proteins with NKG2D/NKG2DL ligands in cancer immunotherapy.

Tumor immunotherapy: New aspects of natural killer cells

A group of impressive immunotherapies for cancer treatment, including immune checkpoint-blocking antibodies, gene therapy and immune cell adoptive cellular immunotherapy, have been established, providing new weapons to fight cancer. Natural killer (NK) cells are a component of the first line of defense against tumors and virus infections. Studies have shown dysfunctional NK cells in patients with cancer. Thus, restoring NK cell antitumor functionality could be a promising therapeutic strategy. NK cells that are activated and expanded ex vivo can supplement malfunctional NK cells in tumor patients. Therapeutic antibodies, chimeric antigen receptor (CAR), or bispecific proteins can all retarget NK cells precisely to tumor cells. Therapeutic antibody blockade of the immune checkpoints of NK cells has been suggested to overcome the immunosuppressive signals delivered to NK cells. Oncolytic virotherapy provokes antitumor activity of NK cells by triggering antiviral immune responses. Herein, we review the current immunotherapeutic approaches employed to restore NK cell antitumor functionality for the treatment of cancer.

VEGFR2 targeted antibody fused with MICA stimulates NKG2D mediated immunosurveillance and exhibits potent anti-tumor activity against breast cancer

Binding of MHC class I-related chain molecules A and B (MICA/B) to the natural killer (NK) cell receptor NK group 2, member D (NKG2D) is thought critical for activating NK-mediated immunosurveillance. Angiogenesis is important for tumor growth and interfering with angiogenesis using the fully human IgG1 anti-VEGFR2 (vascular endothelial growth factor receptor 2) antibody (mAb04) can be effective in treating malignancy. In an effort to make mAb04 more effective we have generated a novel antibody fusion protein (mAb04-MICA) consisting of mAb04 and MICA. We found that mAb04-MICA maintained the anti-angiogenic and antineoplastic activities of mAb04, and also enhanced immunosurveillance activated by the NKG2D pathway. Moreover, in human breast tumor-bearing nude mice, mAb04-MICA demonstrated superior anti-tumor efficacy compared to combination therapy of mAb04 + Docetaxel or Avastin + Docetaxel, highlighting the immunostimulatory effect of MICA. In conclusion, mAb04-MICA provided new inspiration for anti-tumor treatment and had prospects for clinical application.

Triplebody Mediates Increased Anti-Leukemic Reactivity of IL-2 Activated Donor Natural Killer (NK) Cells and Impairs Viability of Their CD33-Expressing NK Subset

Natural killer cells (NK) are essential for the elimination of resistant acute myeloid and acute lymphoblastic leukemia (AML and ALL) cells. NK cell-based immunotherapies have already successfully entered for clinical trials, but limitations due to immune escape mechanisms were identified. Therefore, we extended our established NK cell protocol by integration of the previously investigated powerful trispecific immunoligand ULBP2-aCD19-aCD33 [the so-called triplebodies (TBs)] to improve the anti-leukemic specificity of activated NK cells. IL-2-driven expansion led to strongly elevated natural killer group 2 member D (NKG2D) expressions on donor NK cells which promote the binding to ULBP2⁺ TBs. Similarly, CD33 expression on these NK cells could be detected. Dual-specific targeting and elimination were investigated against the B-cell precursor leukemia cell line BV-173 and patient blasts, which were positive for myeloid marker CD33 and B lymphoid marker CD19 exclusively presented on biphenotypic B/myeloid leukemia’s. Cytotoxicity assays demonstrated improved killing properties of NK cells pre-coated with TBs compared to untreated controls. Specific NKG2D blocking on those NK cells in response to TBs diminished this killing activity. On the contrary, the observed upregulation of surface CD33 on about 28.0% of the NK cells decreased their viability in response to TBs during cytotoxic interaction of effector and target cells. Similar side effects were also detected against CD33⁺ T- and CD19⁺ B-cells. Very preliminary proof of principle results showed promising effects using NK cells and TBs against primary leukemic cells. In summary, we demonstrated a promising strategy for redirecting primary human NK cells in response to TBs against leukemia, which may lead to a future progress in NK cell-based immunotherapies.

Control of Tumor Initiation by NKG2D Naturally Expressed on Ovarian Cancer Cells

Cancer cells may co-opt the NKG2D lymphocyte receptor to complement the presence of its ligands for autonomous stimulation of oncogenic signaling. Previous studies raise the possibility that cancer cell NKG2D may induce high malignancy traits, but its full oncogenic impact is unknown. Using epithelial ovarian cancer as model setting, we show here that ex vivo NKG2D⁺ cancer cells have stem-like capacities, and provide formal in vivo evidence linking NKG2D stimulation with the development and maintenance of these functional states. NKG2D⁺ ovarian cancer cell populations harbor substantially greater capacities for self-renewing in vitro sphere formation and in vivo tumor initiation in immunodeficient (NOD scid gamma) mice than NKG2D⁻ controls. Sphere formation and tumor initiation are impaired by NKG2D silencing or ligand blockade using antibodies or a newly designed pan ligand-masking NKG2D multimer. In further support of pathophysiological significance, a prospective study of 47 high-grade serous ovarian cancer cases revealed that the odds of disease recurrence were significantly greater and median progression-free survival rates higher among patients with above and below median NKG2D⁺ cancer cell frequencies, respectively. Collectively, our results define cancer cell NKG2D as an important regulator of tumor initiation in ovarian cancer and presumably other malignancies and thus challenge current efforts in immunotherapy aimed at enhancing NKG2D function.

The swinging pendulum of cancer immunotherapy personalization

Cancer immunotherapy has long offered the promise of producing cancer treatments that are more effective and less toxic than traditional chemotherapy and radiotherapy. That potential has only begun to be realized in the last 5 years with the first US FDA-approved cancer vaccine (sipuleucel-T), checkpoint inhibitors and adoptive cell therapy. While these therapies have been remarkably more effective than previous cancer immunotherapeutics, they are often limited by their inherently personalized nature. Indeed, each patient’s immune system and cancer are unique, limiting the scalability and generalizability of new approaches. However, emerging solutions may overcome these limitations, producing ‘off-the-shelf’ cancer immunotherapies that transform patient outcomes.

A Combined ULBP2 and SEMA5A Expression Signature as a Prognostic and Predictive Biomarker for Colon Cancer

Background: Prognostic biomarkers for cancer have the power to change the course of disease if they add value beyond known prognostic factors, if they can help shape treatment protocols, and if they are reliable. The aim of this study was to identify such biomarkers for colon cancer and to understand the molecular mechanisms leading to prognostic stratifications based on these biomarkers. Methods and Findings: We used an in house R based script (SSAT) for the in silico discovery of stage-independent prognostic biomarkers using two cohorts, GSE17536 and GSE17537, that include 177 and 55 colon cancer patients, respectively. This identified 2 genes, ULBP2 and SEMA5A, which when used jointly, could distinguish patients with distinct prognosis. We validated our findings using a third cohort of 48 patients ex vivo. We find that in all cohorts, a combined ULBP2/SEMA5A classification (SU-GIB) can stratify distinct prognostic sub-groups with hazard ratios that range from 2.4 to 4.5 (p≤0.01) when overall- or cancer-specific survival is used as an end-measure, independent of confounding prognostic parameters. In addition, our preliminary analyses suggest SU-GIB is comparable to Oncotype DX colon(®) in predicting recurrence in two different cohorts (HR: 1.5-2; p≤0.02). SU-GIB has potential as a companion diagnostic for several drugs including the PI3K/mTOR inhibitor BEZ235, which are suitable for the treatment of patients within the bad prognosis group. We show that tumors from patients with worse prognosis have low EGFR autophosphorylation rates, but high caspase 7 activity, and show upregulation of pro-inflammatory cytokines that relate to a relatively mesenchymal phenotype. Conclusions: We describe two novel genes that can be used to prognosticate colon cancer and suggest approaches by which such tumors can be treated. We also describe molecular characteristics of tumors stratified by the SU-GIB signature.

Antigen Loss Variants: Catching Hold of Escaping Foes

Since mid-1990s, the field of cancer immunotherapy has seen steady growth and selected immunotherapies are now a routine and preferred therapeutic option of certain malignancies. Both active and passive cancer immunotherapies exploit the fact that tumor cells express specific antigens on the cell surface, thereby mounting an immune response specifically against malignant cells. It is well established that cancer cells typically lose surface antigens following natural or therapy-induced selective pressure and these antigen-loss variants are often the population that causes therapy-resistant relapse. CD19 and CD20 antigen loss in acute lymphocytic leukemia and chronic lymphocytic leukemia, respectively, and lineage switching in leukemia associated with mixed lineage leukemia (MLL) gene rearrangements are well-documented evidences in this regard. Although increasing number of novel immunotherapies are being developed, majority of these do not address the control of antigen loss variants. Here, we review the occurrence of antigen loss variants in leukemia and discuss the therapeutic strategies to tackle the same. We also present an approach of dual-targeting immunoligand effectively retargeting NK cells against antigen loss variants in MLL-associated leukemia. Novel immunotherapies simultaneously targeting more than one tumor antigen certainly hold promise to completely eradicate tumor and prevent therapy-resistant relapses.

Mechanisms of Acute Toxicity in NKG2D Chimeric Antigen Receptor T Cell-Treated Mice

Targeting cancer through the use of effector T cells bearing chimeric Ag receptors (CARs) leads to elimination of tumors in animals and patients, but recognition of normal cells or excessive activation can result in significant toxicity and even death. CAR T cells based on modified NKG2D receptors are effective against many types of tumors, and their efficacy is mediated through direct cytotoxicity and cytokine production. Under certain conditions, their ligands can be expressed on nontumor cells, so a better understanding of the potential off-tumor activity of these NKG2D CAR T cells is needed. Injection of very high numbers of activated T cells expressing CARs based on murine NKG2D or DNAM1 resulted in increased serum cytokines (IFN-γ, IL-6, and MCP-1) and acute toxicity similar to cytokine release syndrome. Acute toxicity required two key effector molecules in CAR T cells-perforin and GM-CSF. Host immune cells also contributed to this toxicity, and mice with severe immune cell defects remained healthy at the highest CAR T cell dose. These data demonstrate that specific CAR T cell effector mechanisms and the host immune system are required for this cytokine release-like syndrome in murine models.

Mono- and dual-targeting triplebodies activate natural killer cells and have anti-tumor activity in vitro and in vivo against chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is the most common form of leukemia that affects B lymphocytes in adults. Natural killer (NK) cells in CLL patients are intrinsically potent but display poor in situ effector functions. NKG2D is an activating receptor found on NK and CD8⁺ T cells and plays a role in immunosurveillance of CLL. In this study, we developed mono- and dual-targeting triplebodies utilizing a natural ligand for human NKG2D receptor (ULBP2) to retarget NK cells against tumor cells. Triplebodies in both formats showed better ability to induce NK-cell-dependent killing of target cells compared to bispecific counterparts. A mono-targeting triplebody ULBP2-aCD19-aCD19 successfully triggered NK cell effector functions against CLL cell line MEC1 and primary tumor cells in allogenic and autologous settings. Additionally, a dual-targeting triplebody ULBP2-aCD19-aCD33 specific for two distinct tumor-associated antigens was developed to target antigen loss variants, such as mixed lineage leukemia (MLL). Of note, this triplebody exhibited cytotoxic activity against CD19/CD33 double positive cells and retained its binding features even in the absence of one of the tumor antigens. Further, ULBP2-aCD19-aCD19 showed significant in vivo activity in immune-deficient (NSG) mouse model transplanted with CLL cell line as target cells and human immune cells as an effector population providing a proof-of-principle for this therapeutic concept.

Designing multivalent proteins based on natural killer cell receptors and their ligands as immunotherapy for cancer

INTRODUCTION

Natural killer (NK) cells are an important component of the innate immune system that play a key role in host immunity against cancer. NK cell recognition and activation is based on cell surface receptors recognizing specific ligands that are expressed on many types of tumor cells. Some of these receptors are capable of activating NK cell function while other receptors inhibit NK cell function. Therapeutic approaches to treat cancer have been developed based on preventing NK cell inhibition or using NK cell receptors and their ligands to activate NK cells or T cells to destroy tumor cells.

AREAS COVERED

This article describes the various strategies for targeting NK cell receptors and NK cell receptor ligands using multivalent proteins to activate immunity against cancer.

EXPERT OPINION

NK cell receptors work in synergy to activate NK cell effector responses. Effective anti-cancer strategies will need to not only kill tumor cells but must also lead to the destruction of the tumor microenvironment. Immunotherapy based on NK cells and their receptors has the capacity to accomplish this through triggering lymphocyte cytotoxicity and cytokine production.

A Novel Recombinant Anti-CD22 Immunokinase Delivers Proapoptotic Activity of Death-Associated Protein Kinase (DAPK) and Mediates Cytotoxicity in Neoplastic B Cells

The serine/threonine death-associated protein kinases (DAPK) provide pro-death signals in response to (oncogenic) cellular stresses. Lost DAPK expression due to (epi)genetic silencing is found in a broad spectrum of cancers. Within B-cell lymphomas, deficiency of the prototypic family member DAPK1 represents a predisposing or early tumorigenic lesion and high-frequency promoter methylation marks more aggressive diseases. On the basis of protein studies and meta-analyzed gene expression profiling data, we show here that within the low-level context of B-lymphocytic DAPK, particularly CLL cells have lost DAPK1 expression. To target this potential vulnerability, we conceptualized B-cell-specific cytotoxic reconstitution of the DAPK1 tumor suppressor in the format of an immunokinase. After rounds of selections for its most potent cytolytic moiety and optimal ligand part, a DK1KD-SGIII fusion protein containing a constitutive DAPK1 mutant, DK1KD, linked to the scFv SGIII against the B-cell-exclusive endocytic glyco-receptor CD22 was created. Its high purity and large-scale recombinant production provided a stable, selectively binding, and efficiently internalizing construct with preserved robust catalytic activity. DK1KD-SGIII specifically and efficiently killed CD22-positive cells of lymphoma lines and primary CLL samples, sparing healthy donor- or CLL patient-derived non-B cells. The mode of cell death was predominantly PARP-mediated and caspase-dependent conventional apoptosis as well as triggering of an autophagic program. The notoriously high apoptotic threshold of CLL could be overcome by DK1KD-SGIII in vitro also in cases with poor prognostic features, such as therapy resistance. The manufacturing feasibility of the novel CD22-targeting DAPK immunokinase and its selective antileukemic efficiency encourage intensified studies towards specific clinical application. Mol Cancer Ther; 15(5); 971-84. ©2016 AACR.

A bispecific protein rG7S-MICA recruits natural killer cells and enhances NKG2D-mediated immunosurveillance against hepatocellular carcinoma

MHC class I-related chain A (MICA) is a principal immunoligand of the natural killer (NK) cell receptor NK group 2, member D (NKG2D) and plays a key role in NK cell-mediated immune recognition. Shedding of MICA from tumor cells leads to immunosuppression. To reconstitute the immunosurveilance function of NK cells, we constructed a fusion protein rG7S-MICA and explored its potential anti-tumor activity against hepatocellular carcinoma (HCC). rG7S-MICA consists of human MICA and a single-chain antibody fragment (scFv) targeting the tumor-associated antigen cluster of differentiation 24 (CD24). In vitro, rG7S-MICA engaged both NK cells and CD24(+) human HCC cells, and triggered NK cell-mediated cytolysis. Furthermore, in CD24(+) HCC-bearing nude mice, rG7S-MICA specifically targeted to the tumor tissue, where it effectively recruited NK cells and induced the release of cytokines, and showed superior anti-tumor activity. In conclusion, rG7S-MICA provides a new approach for HCC-targeting immunotherapy and has attracting potentials for clinical applications.

NK cells and cancer: you can teach innate cells new tricks

Natural killer (NK) cells are the prototype innate lymphoid cells endowed with potent cytolytic function that provide host defence against microbial infection and tumours. Here, we review evidence for the role of NK cells in immune surveillance against cancer and highlight new therapeutic approaches for targeting NK cells in the treatment of cancer.

Natural killer (NK) cells and anti-tumor therapeutic mAb: unexplored interactions

Tumor-targeting mAb are widely used in the treatment of a variety of solid and hematopoietic tumors and represent the first immunotherapeutic approach successfully arrived to the clinic. Nevertheless, the role of distinct immune mechanisms in contributing to their therapeutic efficacy is not completely understood and may vary depending on tumor- or antigen/antibody-dependent characteristics. Availability of next-generation, engineered, tumor-targeting mAb, optimized in their capability to recruit selected immune effectors, re-enforces the need for a deeper understanding of the mechanisms underlying anti-tumor mAb functionality. NK cells participate with a major role to innate anti-tumor responses, by exerting cytotoxic activity and producing a vast array of cytokines. As the CD16 (low-affinity FcγRIIIA)-activating receptor is expressed on the majority of NK cells, its effector functions can be ideally recruited against therapeutic mAb-opsonized tumor cells. The exact role of NK cells in determining therapeutic efficacy of tumor-targeting mAb is still unclear and much sought after. This knowledge will be instrumental to design innovative combination schemes with newly validated immunomodulatory agents. We will summarize what is known about the role of NK cells in therapeutic anti-tumor mAb therapy, with particular emphasis on RTX chimeric anti-CD20 mAb, the first one used in clinical practice for treating B cell malignancies.

Multi-specific antibodies for cancer immunotherapy

Targeted treatment of cancer with monoclonal antibodies has added to the beneficial outcome of patients. In an attempt to improve anti-tumor activity of monoclonal antibodies, multi-specific antibodies have entered the research arena. To date, only a few multi-specific constructs have entered phase III clinical trials, in contrast to classical monoclonal antibodies, which are the standard first-line therapy in several tumor entities. In this review, we will assess selected multi-specific antibodies in pre-clinical and clinical development that may be new treatment options for cancer patients in the very near future. We will further evaluate therapy modalities including the timely distribution or the combination of various therapeutic approaches and assess the potential role of multi-specific antibodies in cancer treatment.

DNA damage response and evasion from immunosurveillance in CLL: new options for NK cell-based immunotherapies

Chronic lymphocytic leukemia (CLL) is the most prominent B cell malignancy among adults in the Western world and characterized by a clonal expansion of B cells. The patients suffer from severe immune defects resulting in increased susceptibility to infections and failure to generate an antitumor immune response. Defects in both, DNA damage response (DDR) pathway and crosstalk with the tissue microenvironment have been reported to play a crucial role for the survival of CLL cells, therapy resistance and impaired immune response. To this end, major advances over the past years have highlighted several T cell immune evasion mechanisms in CLL. Here, we discuss the consequences of an impaired DDR pathway for detection and elimination of CLL cells by natural killer (NK) cells. NK cells are considered to be a major component of the immunosurveillance in leukemia but NK cell activity is impaired in CLL. Restoration of NK cell activity using immunoligands and immunoconstructs in combination with the conventional chemotherapy may provide a future perspective for CLL treatment.

Bispecific antibody platforms for cancer immunotherapy

Over the past decades advances in bioengineering and expanded insight in tumor immunology have resulted in the emergence of novel bispecific antibody (bsAb) constructs that are capable of redirecting immune effector cells to the tumor microenvironment. (Pre-) clinical studies of various bsAb constructs have shown impressive results in terms of immune effector cell retargeting, target dependent activation and the induction of anti-tumor responses. This review summarizes recent advances in the field of bsAb-therapy and limitations that were encountered. Furthermore, we will discuss potential future developments that can be expected to take the bsAb approach successfully forward.