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

Natural killer group 2D-major histocompatibility complex class I polypeptide-related sequence A activation enhances natural killer cell-mediated immunity against hepatocellular carcinoma: A review

The recent clinical introduction of immune checkpoint inhibitors has improved therapeutic outcomes in patients with advanced hepatocellular carcinoma. However, these therapies targeting CD8+ T lymphocytes have a response rate of approximately 30%. In addition to CD8+ T lymphocytes, natural killer (NK) cells represent promising therapeutic targets for hepatocellular carcinoma, because they comprise 30%-50% of all lymphocytes in the liver and contribute to antitumor immunity. A recent meta-analysis revealed that the percentage of infiltrating NK cells in hepatocellular carcinoma correlates with a better patient outcome. Similarly, our previous genome-wide association study on chronic viral hepatitis showed that a single-nucleotide polymorphism of major histocompatibility complex class I polypeptide-related sequence A (MICA), a ligand to the NK activating receptor, plays a critical role in hepatocarcinogenesis. In this review, we summarize the mechanisms underlying the regulation of MICA and NK group 2D expression in chronic hepatitis. Furthermore, we describe recent reports on MICA single-nucleotide polymorphism-driven hepatocarcinogenesis. The suppression of MICA shedding could represent a promising approach for immunosurveillance, as increased expression of membrane-bound MICA achieved through the use of a MICA shedding inhibitor also enhances NK cell-mediated cytotoxicity.

Potential targets and therapeutics for cancer stem cell-based therapy against drug resistance in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common digestive malignancyin the world, which is frequently diagnosed at late stage with a poor prognosis. For most patients with advanced HCC, the therapeutic options arelimiteddue to cancer occurrence of drug resistance. Hepatic cancer stem cells (CSCs) account for a small subset of tumor cells with the ability of self-renewal and differentiationin HCC. It is widely recognized that the presence of CSCs contributes to primary and acquired drug resistance. Therefore, hepatic CSCs-targeted therapy is considered as a promising strategy to overcome drug resistance and improve therapeutic outcome in HCC. In this article, we review drug resistance in HCC and provide a summary of potential targets for CSCs-based therapy. In addition, the development of CSCs-targeted therapeuticsagainst drug resistance in HCC is summarized in both preclinical and clinical trials. The in-depth understanding of CSCs-related drug resistance in HCC will favor optimization of the current therapeutic strategies and gain encouraging therapeutic outcomes.

Checkpoint CD24 function on tumor and immunotherapy

CD24 is a protein found on the surface of cells that plays a crucial role in the proliferation, invasion, and spread of cancer cells. It adheres to cell membranes through glycosylphosphatidylinositol (GPI) and is associated with the prognosis and survival rate of cancer patients. CD24 interacts with the inhibitory receptor Siglec-10 that is present on immune cells like natural killer cells and macrophages, leading to the inhibition of natural killer cell cytotoxicity and macrophage-mediated phagocytosis. This interaction helps tumor cells escape immune detection and attack. Although the use of CD24 as a immune checkpoint receptor target for cancer immunotherapy is still in its early stages, clinical trials have shown promising results. Monoclonal antibodies targeting CD24 have been found to be well-tolerated and safe. Other preclinical studies are exploring the use of chimeric antigen receptor (CAR) T cells, antibody-drug conjugates, and gene therapy to target CD24 and enhance the immune response against tumors. In summary, this review focuses on the role of CD24 in the immune system and provides evidence for CD24 as a promising immune checkpoint for cancer immunotherapy.

NK cells as powerful therapeutic tool in cancer immunotherapy

BACKGROUND

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

CONCLUSION

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

Enhanced antitumor and anti-metastasis by VEGFR2-targeted doxorubicin immunoliposome synergy with NK cell activation

Liposomal doxorubicin exhibits stronger drug accumulation at the tumor site due to the Enhanced Permeability and Retention (EPR) effect. However, the prognosis for the patient is poor due to this drug's lack of targeting and tumor metastasis during treatment. Vascular epidermal growth factor receptor (VEGFR2) plays an important role in angiogenesis and cancer metastasis. To enhance antitumor efficacy of PEGylated liposomal doxorubicin, we constructed a VEGFR2-targeted and doxorubicin-loaded immunoliposome (Lipo-DOX-C00) by conjugating a VEGFR2-specific, single chain antibody fragment to DSPE-PEG2000-MAL, and then we inserted the antibody-conjugated polymer into liposomal doxorubicin (Lipo-DOX). The immunoliposome was formed uniformly with high affinity for VEGFR2. In vitro, Lipo-DOX-C00 enhanced doxorubicin internalization into LLC and 4T1 cells compared with non-conjugated, liposomal doxorubicin. In vivo, Lipo-DOX-C00 delivered DOX to tumor tissues effectively, which exhibited an improved antitumor and anti-metastasis efficacy in both LLC subcutaneous tumor models and 4T1 tumor models. In addition, the combined therapy of a VEGFR2-MICA bispecific antibody (JZC01) and Lipo-DOX-C00 achieved enhanced inhibition of cancer growth and metastasis due to activation of the immune system. Our study provides a promising approach to clinical application of liposomal doxorubicin.

CD24 blockade as a novel strategy for cancer treatment

The CD24 protein is a heat-stable protein with a small core that undergoes extensive glycosylation. It is expressed on the surface of various normal cells, including lymphocytes, epithelial cells, and inflammatory cells. CD24 exerts its function by binding to different ligands. Numerous studies have demonstrated the close association of CD24 with tumor occurrence and progression. CD24 not only facilitates tumor cell proliferation, metastasis, and immune evasion but also plays a role in tumor initiation, thus, serving as a marker on the surface of cancer stem cells (CSCs). Additionally, CD24 induces drug resistance in various tumor cells following chemotherapy. To counteract the tumor-promoting effects of CD24, several treatment strategies targeting CD24 have been explored, such as the use of CD24 monoclonal antibodies (mAb) alone, the combination of CD24 and chemotoxic drugs, or the combination of these drugs with other targeted immunotherapeutic techniques. Regardless of the approach, targeting CD24 has demonstrated significant anti-tumor effects. Therefore, the present study focuses on anti-tumor therapy and provides a comprehensive review of the structure and fundamental physiological function of CD24 and its impact on tumor development, and suggests that targeting CD24 may represent an effective strategy for treating malignant tumors.

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.

αVEGFR2-MICA fusion antibodies enhance immunotherapy effect and synergize with PD-1 blockade

Antiangiogenic therapy has shown significant clinical benefits in gastric cancer (GC) and non-small cell lung cancer (NSCLC). However, their effectiveness is limited by the immunosuppressive tumor microenvironment. The MHC class I chain-related molecules A and B (MICA/B) are expressed in many human cancers, enabling elimination of cancer cells by cytotoxic lymphocytes through natural killer group 2D (NKG2D) receptor activation. To improve antiangiogenic therapy and prolong its efficacy, we generated a bi-specific fusion protein (mAb04-MICA). This was comprised of an antibody targeting VEGFR2 fused to a MICA α1-α2 ectodomain. mAb04-MICA inhibited proliferation of GC and NSCLC cells through specific binding to VEGFR2 and had superior anti-tumor efficacy in both GC and NSCLC-bearing mouse models compared with ramucirumab. Further investigation revealed that the mAb04-MICA promoted NKG2D⁺ NK cell activation and induced the tumor-associated macrophage (TAM) polarization from M2 type to M1 type both in vitro and in vivo. The polarization of TAMs upon NKG2D and MICA mediated activation has not yet been reported. Moreover, given the up-regulation of PD-L1 in tumors during anti-angiogenesis therapy, anti-PD-1 antibody enhanced the anti-tumoral activity of mAb04-MICA through stimulating infiltration and activation of NKs and CD8⁺T cells in responding tumors. Our findings demonstrate that dual targeting of angiogenesis and NKG2D, or in combination with the PD-1/PD-L1 blockade, is a promising anti-tumor therapeutic strategy. This is accomplished through maintaining or reinstating tumor immunosurveillance during treatment, which expands the repertoire of anti-angiogenesis-based cancer immunotherapies.

Weaponizing natural killer cells for solid cancer immunotherapy

Enhancing natural killer (NK) cell-based innate immunity has become a promising strategy for immunotherapy against hard-to-cure solid cancers. Monoclonal antibody (mAb) therapy has been used to activate NK-cell-mediated antibody-dependent cellular cytotoxicity (ADCC) towards solid cancers. Cancer cells, however, can subvert immunosurveillance using multiple immunosuppressive mechanisms, which may hamper NK cell ADCC. Mechanisms to safely enhance ADCC by NK cells, such as utilizing temporary inhibition of receptor endocytosis to increase antibody presentation from target to effector cells can now be used to enhance NK-cell-mediated ADCC against solid tumors. This review summarizes and discusses the recent advances in the field and highlights current and potential future use of immunotherapies to maximize the therapeutic efficacy of innate anticancer immunity.

The role of NLRP3 inflammasome in hepatocellular carcinoma

Inflammasomes play an important role in innate immunity. As a signal platform, they deal with the excessive pathogenic products and cellular products related to stress and injury. So far, the best studied and most characteristic inflammasome is the NLR-family pyrin domain-containing protein 3(NLRP3) inflammasome, which is composed of NLRP3, apoptosis associated speck like protein (ASC) and pro-caspase-1. The formation of NLRP3 inflammasome complexes results in the activation of caspase-1, the maturation of interleukin (IL)-1β and IL-18, and pyroptosis. Many studies have demonstrated that NLRP3 inflammasome not only participates in tumorigenesis, but also plays a protective role in some cancers. Hepatocellular carcinoma (HCC) is a major cause of cancer-related mortality. Currently, due to the lack of effective treatment methods for HCC, the therapeutic effect of HCC has not been ideal. Therefore, it is particularly urgent to explore the pathogenesis of HCC and find its effective treatment methods. The increasing evidences indicate that NLRP3 inflammasome plays a vital role in HCC, however, the related mechanisms are not fully understood. Hence, we focused on the recent progress about the role of NLRP3 inflammasome in HCC, and analyzed the relevant mechanisms in detail to provide reference for the future in-depth researches.

Multifunctional NK Cell–Engaging Antibodies Targeting EGFR and NKp30 Elicit Efficient Tumor Cell Killing and Proinflammatory Cytokine Release

In this work, we have generated novel Fc-comprising NK cell engagers (NKCEs) that bridge human NKp30 on NK cells to human epidermal growth factor receptor (EGFR) on tumor cells. Camelid-derived VHH single-domain Abs specific for human NKp30 and a humanized Fab derived from the EGFR-specific therapeutic Ab cetuximab were used as binding arms. By combining camelid immunization with yeast surface display, we were able to isolate a diverse panel of NKp30-specific VHHs against different epitopes on NKp30. Intriguingly, NKCEs built with VHHs that compete for binding to NKp30 with B7-H6, the natural ligand of NKp30, were significantly more potent in eliciting tumor cell lysis of EGFR-positive tumor cells than NKCEs harboring VHHs that target different epitopes on NKp30 from B7-H6. We demonstrate that the NKCEs can be further improved with respect to killing capabilities by concomitant engagement of FcγRIIIa and that soluble B7-H6 does not impede cytolytic capacities of all scrutinized NKCEs at significantly higher B7-H6 concentrations than observed in cancer patients. Moreover, we show that physiological processes requiring interactions between membrane-bound B7-H6 and NKp30 on NK cells are unaffected by noncompeting NKCEs still eliciting tumor cell killing at low picomolar concentrations. Ultimately, the NKCEs generated in this study were significantly more potent in eliciting NK cell–mediated tumor cell lysis than cetuximab and elicited a robust release of proinflammatory cytokines, both features which might be beneficial for antitumor therapy.

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.

CD24: A Novel Target for Cancer Immunotherapy

Cluster of differentiation 24 (CD24) is a small, highly glycosylated cell adhesion protein that is normally expressed by immune as well as epithelial, neural, and muscle cells. Tumor CD24 expression has been linked with alterations in several oncogenic signaling pathways. In addition, the CD24/Siglec-10 interaction has been implicated in tumor immune evasion, inhibiting macrophage-mediated phagocytosis as well as natural killer (NK) cell cytotoxicity. CD24 blockade has shown promising results in preclinical studies. Although there are limited data on efficacy, monoclonal antibodies against CD24 have demonstrated clinical safety and tolerability in two clinical trials. Other treatment modalities evaluated in the preclinical setting include antibody–drug conjugates and chimeric antigen receptor (CAR) T cell therapy. In this review, we summarize current evidence and future perspectives on CD24 as a potential target for cancer immunotherapy.

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.

Cancer stem cells in hepatocellular carcinoma - from origin to clinical implications

Hepatocellular carcinoma (HCC) is an aggressive disease with a poor clinical outcome. The cancer stem cell (CSC) model states that tumour growth is powered by a subset of tumour stem cells within cancers. This model explains several clinical observations in HCC (as well as in other cancers), including the almost inevitable recurrence of tumours after initial successful chemotherapy and/or radiotherapy, as well as the phenomena of tumour dormancy and treatment resistance. The past two decades have seen a marked increase in research on the identification and characterization of liver CSCs, which has encouraged the design of novel diagnostic and treatment strategies for HCC. These studies revealed novel aspects of liver CSCs, including their heterogeneity and unique immunobiology, which are suggestive of opportunities for new research directions and potential therapies. In this Review, we summarize the present knowledge of liver CSC markers and the regulators of stemness in HCC. We also comprehensively describe developments in the liver CSC field with emphasis on experiments utilizing single-cell transcriptomics to understand liver CSC heterogeneity, lineage-tracing and cell-ablation studies of liver CSCs, and the influence of the CSC niche and tumour microenvironment on liver cancer stemness, including interactions between CSCs and the immune system. We also discuss the potential application of liver CSC-based therapies for treatment of HCC.

The interactions between major immune effector cells and Hepatocellular Carcinoma: A systematic review

BACKGROUND

Hepatocellular carcinoma (HCC) is the most common liver neoplasm with high morbidity and mortality. Tumor immunotherapy might be promising adjuvant therapy for HCC after surgery. To better develop HCC immunotherapy, comprehensive understanding of cell-cell interactions between immune effector cells and HCC cells remains crucial.

AIM

To review the existing studies to summarize the cell-cell interactions between major immune effector cells and HCC cells providing new data for HCC immunotherapy.

METHODS

A systematic review was conducted by searching PubMed database covering all papers published in recent five years up to January 2020. The guidelines of the preferred reporting items for systematic reviews were firmly followed.

RESULTS

There are 9 studies researching the interactions between CD8⁺ T lymphocytes and HCC cells and 22 studies researching that between natural killer (NK) cells and HCC cells. Among the 9 studies, 6 studies reported that CD8⁺ T lymphocytes showed cytotoxicity towards HCC cells while 3 studies found CD8⁺ T lymphocytes were impaired by HCC cells. Among the 22 studies, 20 studies presented that NK cells could inhibit HCC cells. Two studies were found to report NK cell dysfunction in HCC.

CONCLUSION

Based on the systematic analysis, we concluded that CD8⁺ T lymphocytes and NK cells can inhibit HCC cells. While in turn, HCC cells can also result in the dysfunction of those effector cells through various mechanisms. Organoids and direct contact cell co-culture with primary HCC cells and TILs should be the most innovative way to investigate the interactions and develop novel immunotherapy.

CD24, A Review of its Role in Tumor Diagnosis, Progression and Therapy

CD24, is a mucin-like GPI-anchored molecules. By immunohistochemistry, it is widely detected in many solid tumors, such as breast cancers, genital system cancers, digestive system cancers, neural system cancers and so on. The functional roles of CD24 are either fulfilled by combination with ligands or participate in signal transduction, which mediate the initiation and progression of neoplasms. However, the character of CD24 remains to be intriguing because there are still opposite voices about the impact of CD24 on tumors. In preclinical studies, CD24 target therapies, including monoclonal antibodies, target silencing by RNA interference and immunotherapy, have shown us brighten futures on the anti-tumor application. Nevertheless, evidences based on clinical studies are urgently needed. Here, with expectancy to spark new ideas, we summarize the relevant studies about CD24 from a tumor perspective.

MICA-G129R: A bifunctional fusion protein increases PRLR-positive breast cancer cell death in co-culture with natural killer cells

Breast cancer cells were reported to up-regulate human prolactin receptor (PRLR) to assist their growth through the utilization of prolactin (PRL) as the growth factor, which makes PRLR a potential therapeutic target for breast cancer. On the other hand, advanced cancer cells tend to down-regulate or shed off stress signal proteins to evade immune surveillance and elimination. In this report, we created a fusion protein consisting of the extracellular domain of MHC class I chain-related protein (MICA), a stress signal protein and ligand of the activating receptor NKG2D of natural killer (NK) cells, and G129R, an antagonistic variant of PRL. We hypothesize that the MICA portion of the fusion protein binds to NKG2D to activate NK cells and the G129R portion binds to PRLR on breast cancer cells, so that the activated NK cells will kill the PRLR-positive breast cancer cells. We demonstrated that the MICA-G129R fusion protein not only binds to human natural killer NK-92 cells and PRLR-positive human breast cancer T-47D cells, but also promotes NK cells to release granzyme B and IFN-γ and enhances the cytotoxicity of NK cells specifically on PRLR-positive cells. The fusion protein, therefore, represents a new approach for the development of breast cancer specific immunotherapy.

Major Histocompatibility Complex Class I-Related Chain A Alleles and Histology of Nonalcoholic Fatty Liver Disease

Major histocompatibility complex class I-related chain A (MICA) is a highly polymorphic gene that modulates immune surveillance by binding to its receptor on natural killer cells, and its genetic polymorphisms have been associated with chronic immune-mediated diseases. The progressive form of nonalcoholic fatty liver disease (NAFLD), nonalcoholic steatohepatitis (NASH), is characterized by accumulation of fat and inflammatory cells in the hepatic parenchyma, potentially leading to liver cell injury and fibrosis. To date, there are no data describing the potential role of MICA in the pathogenesis of NAFLD. Therefore, our aim was to assess the association between MICA polymorphism and NASH and its histologic features. A total of 134 subjects were included. DNA from patients with biopsy-proven NAFLD were genotyped using polymerase chain reaction-sequence-specific oligonucleotide for MICA alleles. Liver biopsies were assessed for histologic diagnosis of NASH and specific pathologic features, including stage of fibrosis and grade of inflammation. Multivariate analysis was performed to draw associations between MICA alleles and the different variables; P ≤ 0.05 was considered significant. Univariate analysis showed that MICA*011 (odds ratio [OR], 7.14; 95% confidence interval [CI], 1.24-41.0; P = 0.04) was associated with a higher risk for histologic NASH. Multivariate analysis showed that MICA*002 was independently associated with a lower risk for focal hepatocyte necrosis (OR, 0.24; 95% CI, 0.08-0.74; P = 0.013) and advanced fibrosis (OR, 0.11; 95% CI, 0.02-0.70; P = 0.019). MICA*017 was independently associated with a higher risk for lymphocyte-mediated inflammation (OR, 5.12; 95% CI, 1.12-23.5; P = 0.035). Conclusion: MICA alleles may be associated with NASH and its histologic features of inflammation and fibrosis. Additional research is required to investigate the potential role of MICA in increased risk or protection against NAFLD.

Role of cellular, molecular and tumor microenvironment in hepatocellular carcinoma: Possible targets and future directions in the regorafenib era

Hepatocellular carcinoma (HCC) remains as one of the major causes of cancer-related mortality, despite the recent development of new therapeutic options. Regorafenib, an oral multikinase inhibitor, is the first systemic therapy that has a survival benefit for patients with advanced HCC that have a poor response to sorafenib. Even though regorafenib has been approved by the FDA, the clinical trial for regorafenib treatment does not show significant improvement in overall survival. The impaired efficacy of regorafenib caused by various resistance mechanisms, including epithelial-mesenchymal transitions, inflammation, angiogenesis, hypoxia, oxidative stress, fibrosis and autophagy, still needs to be resolved. In this review, we provide insight on regorafenib microenvironmental, molecular and cellular mechanisms and interactions in HCC treatment. The aim of this review is to help physicians select patients that would obtain the maximal benefits from regorafenib in HCC therapy.

A VEGFR2-MICA bispecific antibody activates tumor-infiltrating lymphocytes and exhibits potent anti-tumor efficacy in mice

MHC class I-related chain A (MICA) is one of the major ligands for natural killer group 2 member D (NKG2D), which is an activating NK receptor. MICA is expressed on the surface of human epithelial tumor cells, and its shedding from tumor cells leads to immunosuppression. To activate immune response in the tumor microenvironment, we designed an anti-VEGFR2-MICA bispecific antibody (JZC01), consisting of MICA and an anti-VEGFR2 single chain antibody fragment (JZC00) and explored its potential anti-tumor activity. JZC01 targeted vascular endothelial growth factor receptor 2 (VEGFR2) and inhibited tumorigenesis by blocking the VEGFR2 signaling pathway. Additionally, JZC01 promoted NK and CD8⁺ T cells to release IFN-γ and engaged activated lymphocytes to lysis of VEGFR2-expressing tumor cells. The in vivo anti-tumor activity of JZC01 was investigated by establishing a Lewis lung cancer cell-transplanted mouse model. It effectively reduced the tumor vascular density and increased the infiltration and activation of NK and CD8⁺ T cells in the tumor microenvironment. Thus, JZC01 functions in anti-tumor angiogenesis and anti-tumor immune activation, and showed improved anti-tumor efficacy combined with docetaxel, which provides a new insight into anti-tumor therapy.

Anti-CD24 Antibody-Nitric Oxide Conjugate Selectively and Potently Suppresses Hepatic Carcinoma

Nitric oxide (NO) has a wide range of potential applications in tumor therapy. However, a targeted delivery system for NO donors has remained elusive, creating a bottleneck that limits its druggability. The antibody-drug conjugate (ADC) is a targeted drug delivery system composed of an antibody linked to an active cytotoxic drug. This design may compensate for the weak targeting ability and various biological functions of the NO donor. In this study, we designed the NO donor HL-2, which had a targeted, cleaved disulfide bond and an attachable maleimide terminal. We conjugated HL-2 with an antibody that targeted CD24 through a thioether bond to generate an ADC-like immunoconjugate, antibody-nitric oxide conjugate (ANC), which we named HN-01. HN-01 showed efficient internalization and significantly increased the release of NO in hepatic carcinoma cells in vitro. HN-01 induced apoptosis of tumor cells and suppressed tumor growth in hepatic carcinoma-bearing nude mice through antibody-dependent co-toxicity; HN-01 also increased NO levels in tumor cells. Collectively, this study expands the concept of ADC and provides an innovative NO donor and ANC to address current challenges in targeted delivery of NO. This new inspiration for an ANC design can also be used in future studies for other molecules with intracellular targets. SIGNIFICANCE: This study is the first to expand the concept of ADC with an antibody-nitric oxide conjugate that suppresses hepatic carcinoma in vitro and in vivo.

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.

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.

Anti-hepatocarcinoma activity of TT-1, an analog of melittin, combined with interferon-α via promoting the interaction of NKG2D and MICA

Hepatocarcinoma is one of the malignant cancers with significant morbidity and mortality. Immunotherapy has emerged in clinical treatment, owing to the limitation and severe side effects of chemotherapy. In the immune system, natural killer (NK) cells are important effectors required to eliminate malignant tumor cells without the limitation of major histocompatibility complex (MHC) molecule issues. Hence, treatment which could stimulate NK cells is of great interest. Here, we investigated the efficacy of the combined therapy of TT-1 (a mutant of melittin) and interferon-α (IFN-α) on NK cells and human liver cancer HepG-2/Huh7 cells in vitro and in vivo, as well as the mechanism involved. The combination therapy significantly inhibited the growth of HepG-2/Huh7 cells in vivo, but this effect was impaired after depleting NK cells. TT-1 not only up-regulated MHC class I-related chain molecules A (MICA) expression, but also prevented the secretion of soluble MICA (sMICA). Both the mRNA and protein of a disintegrin and metallopeptidase 10 (ADAM 10) in HepG-2/Huh7 cells were decreased after TT-1 treatment. The combined therapy of TT-1 and IFN-α could suppress the growth of HepG-2/Huh7 xenografted tumor effectively via promoting the interaction of NK group 2, member D (NKG2D) and MICA, indicating that TT-1+IFN-α would be a potential approach in treating liver cancer.

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.

Selective targeted delivery of doxorubicin via conjugating to anti-CD24 antibody results in enhanced antitumor potency for hepatocellular carcinoma both in vitro and in vivo

PURPOSE

Antibody-drug conjugates (ADCs) represent a promising therapeutic approach for clinical application. Cluster of differentiation 24 (CD24) is over-expressed in several human malignancies, especially in hepatocellular carcinoma (HCC). We aimed to develop a new class of CD24-targeted ADCs for HCC.

METHODS

DOX was conjugated with G7mAb by a heterobifunctional cross-linker GMBS (N-[gamma-maleimido butyryloxy] succinimide ester) and further analyzed using HPLC. The targeting specificity and endocytosis of the newly generated ADC, G7mAb-DOX, were characterized using flow cytometry assay, near-infrared fluorescence imaging and laser scanning confocal microscope. The antitumor effects were evaluated in nude mice bearing HCC xenografts.

RESULTS

G7mAb-DOX with average two drug molecules per antibody was selectively captured and endocytosed by CD24 (+) tumor cells in vitro. In vivo, the ADC was proved to target tumor tissues, suppress tumor growth and prolong the survival of HCC-bearing nude mice with improved efficacy and less systemic toxicity compared with either G7mAb or DOX single-agent treatment.

CONCLUSION

These studies provide proof of concept for development of DOX-based ADCs which provide a novel approach for HCC-targeted immune therapy in clinical application.

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.

Engineering a high-affinity humanized anti-CD24 antibody to target hepatocellular carcinoma by a novel CDR grafting design

Cluster of differentiation 24 (CD24) is a specific surface marker involved in the tumorigenesis and progression of hepatocellular carcinoma (HCC). However, all reported anti-CD24 antibodies are murine ones with inevitable immunogenicity. To address this, a method using both molecular structure and docking-based complementarity determining region (CDR) grafting was employed for humanization. After xenogeneic CDR grafting into a human antibody, three types of canonical residues (in the VL/VH interface core, in the loop foundation, and interaction with loop residues) that support loop conformation and residues involved in the antigen-binding interface were back-mutated. Four engineered antibodies were produced, among which hG7-BM3 has virtually identical 3-D structure and affinity parameters with the parental chimeric antibody cG7. In vitro, hG7-BM3 demonstrated superior immunogenicity and serum stability to cG7. Antibody-dependent cellular cytotoxicity (ADCC), tumor cell internalization and in vivo targeting assays indicate that hG7-BM3 has the potential for development as an antibody-drug conjugate (ADC). We therefore generated the hG7-BM3-VcMMAE conjugate, which was shown to induce tumor cell apoptosis and effectively suppress nude mice bearing HCC xenografts. In conclusion, our study provides new inspiration for antibody humanization and an ADC candidate for laboratory study and clinical applications.

Bispecific Antibodies as a Development Platform for New Concepts and Treatment Strategies

With the development of molecular cloning technology and the deep understanding of antibody engineering, there are diverse bispecific antibody formats from which to choose to pursue the optimal biological activity and clinical purpose. The single-chain-based bispecific antibodies usually bridge tumor cells with immune cells and form an immunological synapse because of their relatively small size. Bispecific antibodies in the IgG format include asymmetric bispecific antibodies and homodimerized bispecific antibodies, all of which have an extended blood half-life and their own crystalline fragment (Fc)-mediated functions. Besides retargeting effector cells to the site of cancer, new applications were established for bispecific antibodies. Bispecific antibodies that can simultaneously bind to cell surface antigens and payloads are a very ideal delivery system for therapeutic use. Bispecific antibodies that can inhibit two correlated signaling molecules at the same time can be developed to overcome inherent or acquired resistance and to be more efficient angiogenesis inhibitors. Bispecific antibodies can also be used to treat hemophilia A by mimicking the function of factor VIII. Bispecific antibodies also have broad application prospects in bone disorders and infections and diseases of the central nervous system. The latest developments of the formats and application of bispecific antibodies will be reviewed. Furthermore, the challenges and perspectives are summarized in this review.

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.