TLR9 activation cooperates with T cell checkpoint blockade to regress poorly immunogenic melanoma

Tlr9 deficiency in B cells leads to obesity by promoting inflammation and gut dysbiosis

Toll-like receptor 9 (TLR9) recognizes bacterial, viral and self DNA and play an important role in immunity and inflammation. However, the role of TLR9 in obesity is less well-studied. Here, we generate B-cell-specific Tlr9-deficient (Tlr9fl/fl/Cd19Cre+/-, KO) B6 mice and model obesity using a high-fat diet. Compared with control mice, B-cell-specific-Tlr9-deficient mice exhibited increased fat tissue inflammation, weight gain, and impaired glucose and insulin tolerance. Furthermore, the frequencies of IL-10-producing-B cells and marginal zone B cells were reduced, and those of follicular and germinal center B cells were increased. This was associated with increased frequencies of IFNγ-producing-T cells and increased follicular helper cells. In addition, gut microbiota from the KO mice induced a pro-inflammatory state leading to immunological and metabolic dysregulation when transferred to germ-free mice. Using 16 S rRNA gene sequencing, we identify altered gut microbial communities including reduced Lachnospiraceae, which may play a role in altered metabolism in KO mice. We identify an important network involving Tlr9, Irf4 and Il-10 interconnecting metabolic homeostasis, with the function of B and T cells, and gut microbiota in obesity.

Plasmacytoid dendritic cells mediate CpG-ODN induced increase in survival in a mouse model of lymphangioleiomyomatosis

Lymphangioleiomyomatosis (LAM) is a devastating disease primarily found in women of reproductive age that leads to cystic destruction of the lungs. Recent work has shown that LAM causes immunosuppression and that checkpoint inhibitors can be used as LAM treatment. Toll-like receptor (TLR) agonists can also re-activate immunity and the TLR9 agonist, CpG-ODN, has been effective in treating lung cancer in animal models. Here we investigate the use of TLR9 agonist CpG-ODN as LAM immunotherapy in combination with checkpoint inhibitor, anti-PD1, standard of care rapamycin and determine the immune mechanisms underlying therapeutic efficacy. We used survival studies, flow cytometry, ELISA, and histology to assess immune response and survival after intranasal treatment with CpG-ODN in combination with rapamycin or anti-PD1 therapy in a mouse model of metastatic LAM. We found that local administration of CpG-ODN enhances survival in a mouse model of LAM. We found that a lower dose led to longer survival likely due to fewer local side effects but increased LAM nodule count and size compared to the higher dose. CpG-ODN treatment also reduced regulatory T cells and increased the number of Th17 helper T cells as well as cytotoxic T cells. These effects appear to be mediated in part by plasmacytoid dendritic cells (pDCs), as depletion of pDCs reduces survival and abrogates Th17 T cell response. Finally, we found that CpG-ODN treatment is effective in early stage and progressive disease and is additive with anti-PD1 therapy and rapamycin. In summary, we have found that TLR9 agonist CpG-ODN can be used as LAM immunotherapy and effectively synergizes with rapamycin and anti-PD1 therapy in LAM.

Society for Immunotherapy of Cancer (SITC) recommendations on intratumoral immunotherapy clinical trials (IICT): from premalignant to metastatic disease

BACKGROUND

Intratumorally delivered immunotherapies have the potential to favorably alter the local tumor microenvironment and may stimulate systemic host immunity, offering an alternative or adjunct to other local and systemic treatments. Despite their potential, these therapies have had limited success in late-phase trials for advanced cancer resulting in few formal approvals. The Society for Immunotherapy of Cancer (SITC) convened a panel of experts to determine how to design clinical trials with the greatest chance of demonstrating the benefits of intratumoral immunotherapy for patients with cancers across all stages of pathogenesis.

METHODS

An Intratumoral Immunotherapy Clinical Trials Expert Panel composed of international key stakeholders from academia and industry was assembled. A multiple choice/free response survey was distributed to the panel, and the results of this survey were discussed during a half-day consensus meeting. Key discussion points are summarized in the following manuscript.

RESULTS

The panel determined unique clinical trial designs tailored to different stages of cancer development-from premalignant to unresectable/metastatic-that can maximize the chance of capturing the effect of intratumoral immunotherapies. Design elements discussed included study type, patient stratification and exclusion criteria, indications of randomization, study arm determination, endpoints, biological sample collection, and response assessment with biomarkers and imaging. Populations to prioritize for the study of intratumoral immunotherapy, including stage, type of cancer and line of treatment, were also discussed along with common barriers to the development of these local treatments.

CONCLUSIONS

The SITC Intratumoral Immunotherapy Clinical Trials Expert Panel has identified key considerations for the design and implementation of studies that have the greatest potential to capture the effect of intratumorally delivered immunotherapies. With more effective and standardized trial designs, the potential of intratumoral immunotherapy can be realized and lead to regulatory approvals that will extend the benefit of these local treatments to the patients who need them the most.

TLR5 agonist in combination with anti-PD-1 treatment enhances anti-tumor effect through M1/M2 macrophage polarization shift and CD8+ T cell priming

Immune checkpoint inhibitors have revolutionized anti-tumor therapy, notably improving treatment responses in various tumors. However, many patients remain non-responsive and do not experience benefits. Given that Toll-like receptors (TLRs) can counteract tumor immune tolerance by stimulating both innate and adaptive immune responses, TLR agonists are being explored as potential immune adjuvants for cancer treatment. In this study, we assessed the potential of enhancing the efficacy of immune checkpoint inhibitors by activating innate immunity with a TLR5 agonist. In a mouse tumor model, combination therapy with TLR5 agonist and anti-PD-1 significantly inhibited tumor growth. The TLR5 agonist shifted the balance from M2-like to M1-like macrophages and upregulated the expression of co-stimulatory molecules in macrophages. Furthermore, TLR5 agonist promoted the activation and tumor infiltration of CD8+ T cells. As a result, the TLR5 agonist augmented the anti-tumor efficacy of anti-PD-1, suggesting its potential in modulating the tumor microenvironment to enhance the anti-tumor response. Our findings point toward the possibility of optimizing immune checkpoint inhibitor therapy using TLR5 agonists.

Nano-Regulator Inhibits Tumor Immune Escape via the "Two-Way Regulation" Epigenetic Therapy Strategy

Tumor immune escape caused by low levels of tumor immunogenicity and immune checkpoint-dependent suppression limits the immunotherapeutic effect. Herein, a "two-way regulation" epigenetic therapeutic strategy is proposed using a novel nano-regulator that inhibits tumor immune escape by upregulating expression of tumor-associated antigens (TAAs) to improve immunogenicity and downregulating programmed cell death 1 ligand 1 (PD-L1) expression to block programmed death-1 (PD-1)/PD-L1. To engineer the nano-regulator, the DNA methyltransferase (DNMT) inhibitor zebularine (Zeb) and the bromodomain-containing protein 4 (BRD4) inhibitor JQ1 are co-loaded into the cationic liposomes with condensing the toll-like receptor 9 (TLR9) agonist cytosine-phosphate-guanine (CpG) via electrostatic interactions to obtain G-J/ZL. Then, asparagine-glycine-arginine (NGR) modified material carboxymethyl-chitosan (CMCS) is coated on the surface of G-J/ZL to construct CG-J/ZL. CG-J/ZL is shown to target tumor tissue and disassemble under the acidic tumor microenvironment (TME). Zeb upregulated TAAs expression to improve the immunogenicity; JQ1 inhibited PD-L1 expression to block immune checkpoint; CpG promote dendritic cell (DC) maturation and reactivated the ability of tumour-associated macrophages (TAM) to kill tumor cells. Taken together, these results demonstrate that the nano-regulator CG-J/ZL can upregulate TAAs expression to enhance T-cell infiltration and downregulate PD-L1 expression to improve the recognition of tumor cells by T-cells, representing a promising strategy to improve antitumor immune response.

Immunogenic chemotherapy: great potential for improving response rates

The activation of anti-tumor immunity is critical in treating cancers. Recent studies indicate that several chemotherapy agents can stimulate anti-tumor immunity by inducing immunogenic cell death and durably eradicate tumors. This suggests that immunogenic chemotherapy holds great potential for improving response rates. However, chemotherapy in practice has only had limited success in inducing long-term survival or cure of cancers when used either alone or in combination with immunotherapy. We think that this is because the importance of dose, schedule, and tumor model dependence of chemotherapy-activated anti-tumor immunity is under-appreciated. Here, we review immune modulation function of representative chemotherapy agents and propose a model of immunogenic chemotherapy-induced long-lasting responses that rely on synergetic interaction between killing tumor cells and inducing anti-tumor immunity. We comb through several chemotherapy treatment schedules, and identify the needs for chemotherapy dose and schedule optimization and combination therapy with immunotherapy when chemotherapy dosage or immune responsiveness is too low. We further review tumor cell intrinsic factors that affect the optimal chemotherapy dose and schedule. Lastly, we review the biomarkers indicating responsiveness to chemotherapy and/or immunotherapy treatments. A deep understanding of how chemotherapy activates anti-tumor immunity and how to monitor its responsiveness can lead to the development of more effective chemotherapy or chemo-immunotherapy, thereby improving the efficacy of cancer treatment.

PD-1 blockade in combination with dasatinib potentiates induction of anti-acute lymphocytic leukemia immunity

Immunotherapy, in the form of hematopoietic stem cell transplantation (HSCT), has been part of the standard of care in the treatment of acute leukemia for over 40 years. Trials evaluating novel immunotherapeutic approaches, such as targeting the programmed death-1 (PD-1) pathway, have unfortunately not yielded comparable results to those seen in solid tumors. Major histocompatibility complex (MHC) proteins are cell surface proteins essential for the adaptive immune system to recognize self versus non-self. MHC typing is used to determine donor compatibility when evaluating patients for HSCT. Recently, loss of MHC class II (MHC II) was shown to be a mechanism of immune escape in patients with acute myeloid leukemia after HSCT. Here we report that treatment with the tyrosine kinase inhibitor, dasatinib, and an anti-PD-1 antibody in preclinical models of Philadelphia chromosome positive B-cell acute lymphoblastic leukemia is highly active. The dasatinib and anti-PD-1 combination reduces tumor burden, is efficacious, and extends survival. Mechanistically, we found that treatment with dasatinib significantly increased MHC II expression on the surface of antigen-presenting cells (APC) in a tumor microenvironment-independent fashion and caused influx of APC cells into the leukemic bone marrow. Finally, the induction of MHC II may potentiate immune memory by impairing leukemic engraftment in mice previously cured with dasatinib, after re-inoculation of leukemia cells. In summary, our data suggests that anti-PD-1 therapy may enhance the killing ability of dasatinib via dasatinib driven APC growth and expansion and upregulation of MHC II expression, leading to antileukemic immune rewiring.

Construction of CpG Delivery Nanoplatforms by Functionalized MoS2 Nanosheets for Boosting Antitumor Immunity in Head and Neck Squamous Cell Carcinoma

Despite the promising achievements of immune checkpoint blockade (ICB) therapy for tumor treatment, its therapeutic effect against solid tumors is limited due to the suppressed tumor immune microenvironment (TIME). Herein, a series of polyethyleneimine (Mw = 0.8k, PEI0.8k )-covered MoS2 nanosheets with different sizes and charge densities are synthesized, and the CpG, a toll-like receptor-9 agonist, is enveloped to construct nanoplatforms for the treatment of head and neck squamous cell carcinoma (HNSCC). It is proved that functionalized nanosheets with medium size display similar CpG loading capacity regardless of low or high PEI0.8k coverage owing to the flexibility and crimpability of 2D backbone. CpG-loaded nanosheets with medium size and low charge density (CpG@MM -PL ) could promote the maturation, antigen-presenting capacity, and proinflammatory cytokines generation of bone marrow-derived dendritic cells (DCs). Further analysis reveals that CpG@MM -PL effectively boosts the TIME of HNSCC in vivo including DC maturation and cytotoxic T lymphocyte infiltration. Most importantly, the combination of CpG@MM -PL and ICB agents anti-programmed death 1 hugely improves the tumor therapeutic effect, inspiring more attempts for cancer immunotherapy. In addition, this work uncovers a pivotal feature of the 2D sheet-like materials in nanomedicine development, which should be considered for the design of future nanosheet-based therapeutic nanoplatforms.

Enhanced systemic tumor suppression by in situ vaccine combining radiation and OX40 agonist with CpG therapy

BACKGROUND

In situ tumor vaccine has been gradually becoming a hot research field for its advantage of achieving personalized tumor therapy without prior antigen identification. Various in situ tumor vaccine regimens have been reported to exert considerable antitumor efficacy in preclinical and clinical studies. However, the design of in situ tumor vaccines still needs further optimization and the underlying immune mechanism also waits for deeper investigation.

METHODS

A novel triple in situ vaccine strategy that combining local radiation with intratumoral injection of TLR9 agonist CpG and OX40 agonist was established in this sturdy. Local and abscopal antitumor efficacy as well as survival benefit were evaluated in the bilateral tumors and pulmonary metastasis model of B16F10 melanoma. In situ vaccine-induced immune responses and immune-associated variation in tumor environment were further investigated using multiparameter flow cytometry and RNA sequencing. Base on the analysis, the RT + CpG + αOX40 triple in situ vaccine was combined with checkpoint blockade therapy to explore the potential synergistic antitumor efficacy.

RESULTS

Enhanced tumor suppression was observed with minimal toxicity in both treated and untreated abscopal tumors after receiving RT + CpG + αOX40 triple vaccine. The introduction of local radiation and OX40 agonist benefit more to the inhibition of local and abscopal lesions respectively, which might be partially attributed to the increase of effector memory T cells in the tumor microenvironment. Further analysis implied that the triple in situ vaccine did not only activate the microenvironment of treated tumors, with the upregulation of multiple immune-associated pathways, but also enhanced systemic antitumor responses, thus achieved superior systemic tumor control and survival benefit. Moreover, the triple in situ vaccine synergized with checkpoint blockade therapy, and significantly improved the therapeutic effect of anti-programmed cell death protein (PD)-1 antibody.

CONCLUSION

This triple combining in situ vaccine induced intensive antitumor responses, mediated effective systemic tumor control and survival benefit, and displayed impressive synergistic antitumor effect with checkpoint blockade therapy. These data preliminary confirmed the efficacy, feasibility and safety of the triple combining in situ vaccine, suggesting its great application potential as both monotherapy and a part of combined immunotherapeutic regimens in clinical scenario.

Local CpG- Stat3 siRNA treatment improves antitumor effects of immune checkpoint inhibitors

Immune checkpoint blockade (ICB) therapy has significantly benefited patients with several types of solid tumors and some lymphomas. However, many of the treated patients do not have durable clinical response. It has been demonstrated that rescuing exhausted CD8 + T cells is required for ICB-mediated antitumor effects. We recently developed an immunostimulatory strategy based on silencing STAT3 while stimulating immune responses by CpG, ligand for Toll-like receptor 9 (TLR9). The CpG-small interfering RNA (siRNA) conjugates efficiently enter immune cells, silencing STAT3 and activating innate immunity to enhance T-cell mediated antitumor immune responses. In the present study, we demonstrate that blocking STAT3 through locally delivered CpG- Stat3 siRNA enhances the efficacies of the systemic PD-1 and CTLA4 blockade against mouse A20 B cell lymphoma. In addition, locally delivered CpG- Stat3 siRNA combined with systemic administration of PD-1 antibody significantly augmented both local and systemic antitumor effects against mouse B16 melanoma tumors, with enhanced tumor-associated T cell activation. Overall, our studies in both B cell lymphoma and melanoma mouse models demonstrate the potential of combinatory immunotherapy with CpG- Stat3 siRNA and checkpoint inhibitors as a therapeutic strategy for B cell lymphoma and melanoma.

Introduction of an Ultraviolet C-Irradiated 4T1 Murine Breast Cancer Whole-Cell Vaccine Model

The advent of immunotherapy has revolutionized cancer treatments. However, the application of immune checkpoint inhibitors may entail severe side effects, with the risk of therapeutic resistance. The generation of chimeric antigen receptor (CAR) T-cells or CAR-NK cells requires specialized molecular laboratories, is costly, and is difficult to adapt to the rapidly growing number of cancer patients. To provide a simpler but effective immune therapy, a whole-cell tumor vaccine protocol was established based on ultraviolet C (UCV)-irradiated 4T1 triple-negative breast cancer cells. The apoptosis of tumor cells after UVC irradiation was verified using resazurin and Annexin V/propidium iodide flow cytometric assays. Protective immunity was achieved in immunized BALB/c mice, showing partial remission. Adoptive transfer of splenocytes or plasma from the mice in remission showed a protective effect in the naive BALB/c mice that received a living 4T1 tumor cell injection. 4T1-specific IgG antibodies were recorded in the plasma of the mice following immunization with the whole-cell vaccine. Interleukin-2 (IL-2) and oligonucleotide 2006 (ODN2006) adjuvants were used for the transfer of splenocytes from C57BL/6 mice into cyclophosphamide-treated BALB/c mice, resulting in prolonged survival, reduced tumor growth, and remission in 33% of the cases, without the development of the graft-versus-host disease. Our approach offers a simple, cost-effective whole-cell vaccine protocol that can be administered to immunocompetent healthy organisms. The plasma or the adoptive transfer of HLA-matching immunized donor-derived leukocytes could be used as an immune cell therapy for cancer patients.

Regulating tumor microenvironments by a lymph node-targeting adjuvant via tumor-specific CTL-derived IFNγ

Inducing tumor-specific T cell responses and regulating suppressive tumor microenvironments have been a challenge for effective tumor therapy. CpG (ODN), the Toll-like receptor 9 agonist, has been widely used as adjuvants of cancer vaccines to induce T cell responses. We developed a novel adjuvant to improve the targeting of lymph nodes. CpG were modified with lipid and glycopolymers by the combination of photo-induced RAFT polymerization and click chemistry, and the novel adjuvant was termed as lipid-glycoadjuvant@AuNPs (LCpG). OVA protein was used as model antigen and melanoma model was established to test the immunotherapy effect of the adjuvant. In tumor model, the antitumor effect and mechanism of LCpG on the response of CTLs were examined by flow cytometry and cell cytotoxicity assay. The effects of LCpG on macrophage polarization and Tregs differentiation in tumor microenvironment were also studied by cell depletion assay and cytokine neutralization assay. We also tested the therapeutic effect of the combination of the adjuvant and anti-PD-1 treatment. LCpG could be rapidly transported to and retained longer in the lymphoid nodes than unmodified CpG. In melanoma model, LCpG controlled both primary tumor and its metastasis, and established long-term memory. In spleen and tumor draining lymphoid nodes, LCpG activated tumor-specific Tc1 responses, with increased CD8+ T-cell proliferation, antigen-specific Tc1 cytokine production and specific-tumor killing capacity. In tumor microenvironments, antigen-specific Tc1 induced by the LCpG promoted CTL infiltration, skewed tumor associated macrophages to M1 phenotype, regulated Treg and induced proinflammatory cytokines production in a CTL-derived IFN-γ-dependent manner. In vivo cell depletion and adoptive transfer experiments confirmed that antitumor activity of LCpG included vaccine was mainly dependent on CTL-derived IFN-γ. The anti-tumor efficacy of LCpG was dramatically enhanced when combined with anti-PD1 immunotherapy. LCpG was a promising adjuvant for vaccine formulation which could augment tumor-specific Tc1 activity, and regulate tumor microenvironments.

Neutrophils in Cancer and Potential Therapeutic Strategies Using Neutrophil-Derived Exosomes

Neutrophils are the most abundant immune cells and make up about 70% of white blood cells in human blood and play a critical role as the first line of defense in the innate immune response. They also help regulate the inflammatory environment to promote tissue repair. However, in cancer, neutrophils can be manipulated by tumors to either promote or hinder tumor growth depending on the cytokine pool. Studies have shown that tumor-bearing mice have increased levels of neutrophils in peripheral circulation and that neutrophil-derived exosomes can deliver various cargos, including lncRNA and miRNA, which contribute to tumor growth and degradation of extracellular matrix. Exosomes derived from immune cells generally possess anti-tumor activities and induce tumor-cell apoptosis by delivering cytotoxic proteins, ROS generation, H2O2 or activation of Fas-mediated apoptosis in target cells. Engineered exosome-like nanovesicles have been developed to deliver chemotherapeutic drugs precisely to tumor cells. However, tumor-derived exosomes can aggravate cancer-associated thrombosis through the formation of neutrophil extracellular traps. Despite the advancements in neutrophil-related research, a detailed understanding of tumor-neutrophil crosstalk is still lacking and remains a major barrier in developing neutrophil-based or targeted therapy. This review will focus on the communication pathways between tumors and neutrophils, and the role of neutrophil-derived exosomes (NDEs) in tumor growth. Additionally, potential strategies to manipulate NDEs for therapeutic purposes will be discussed.

Clinical and molecular overview of immunotherapeutic approaches for malignant skin melanoma: Past, present and future

Traditional therapeutic approaches for malignant melanoma, have proved to be limited and/or ineffective, especially with respect to their role in improving patient survival and tumor recurrence. In this regard, immunotherapy has been demonstrated to be a promising therapeutic alternative, boosting antitumor responses through the modulation of cell signaling pathways involved in the effector mechanisms of the immune system, particularly, the so-called "immunological checkpoints". Clinical studies on the efficacy and safety of immunotherapeutic regimens, alone or in combination with other antitumor approaches, have increased dramatically in recent decades, with very encouraging results. Hence, this review will discuss the current immunotherapeutic regimens used to treat malignant melanoma, as well as the molecular and cellular mechanisms involved. In addition, current clinical studies that have investigated the use, efficacy, and adverse events of immunotherapy in melanoma will also be discussed.

PD-L1 antibody enhanced β-glucan antitumor effects via blockade of the immune checkpoints in a melanoma model

In the tumor microenvironment (TME), one of the major functions of tumor-recruited CD11b⁺ cells are the suppression of the T-cell-mediated anti-tumor immune response. β-glucan could convert the phenotype of tumor-recruited CD11b⁺ cells from the suppressive to the promotive, and enhanced their anti-tumor effects. However, β-glucan could enhance the PD-1/PD-L1 expression on CD11b⁺ cells, while PD-1 could inhibit macrophage phagocytosis and PD-L1 could induce a co-inhibitory signal in T-cells and lead to T-cell apoptosis and anergy. These protumor effects may be reversed by PD-1/PD-L1 block therapy. In the present study, we focused on the efficacy of β-glucan anti-tumor therapy combined with anti-PD-L1 mAb treatment, and the mechanism of their synergistic effects could be fully verified. We verified the effect of β-glucan (i.e., inflammatory cytokine secretion of TNF-α, IL-12, IL-6, IL-1β and the expression of immune checkpoint PD-1/PD-L1) in naïve mouse peritoneal exudate CD11b⁺ cells. In our mouse melanoma model, treatment with a PD-L1 blocking antibody with β-glucan synergized tumor regression. After treatment with β-glucan and anti-PD-L1 mAb antibody, tumor infiltrating leukocyte (TILs) not only showed a competent T-cell function (CD107a, perforin, IL-2, IFN-γ and Ki67) and CTL population, but also showed enhanced tumor-recruited CD11b⁺ cell activity (IL-12, IL-6, IL-1β and PD-1). This effect was also verified in the peritoneal exudate CD11b⁺ cells of tumor-bearing mice. PD-1/PD-L1 blockade therapy enhanced the β-glucan antitumor effects via the blockade of tumor-recruited CD11b⁺ cell immune checkpoints in the melanoma model.

Programmed cell death-1 blockade therapy in melanoma: Resistance mechanisms and combination strategies

Melanoma is a highly aggressive tumor derived from melanocytes. In recent years, the incidence and mortality of melanoma have gradually increased, seriously threatening human health. Classic treatments like surgery, chemotherapy, and radiotherapy show very limited efficacy. Due to the high immunogenicity of melanoma cells, immune checkpoint inhibitors have received considerable attention as melanoma treatments. One such therapy is blockade of programmed cell death-1 (PD-1), which is one of the most important negative immune regulators and is mainly expressed on activated T cells. Disruption of the interactions between PD-1 and its ligands, programmed death-ligand 1 (PD-L1) or programmed death-ligand 2 (PD-L2) rejuvenates exhausted T cells and enhances antitumor immunity. Although PD-1 blockade therapy is widely used in melanoma, a substantial proportion of patients still show no response or short durations of remission. Recent researches have focused on revealing the underlying mechanisms for resistance to this treatment and improving its efficacy through combination therapy. Here, we will introduce the resistance mechanisms associated with PD-1 blockade therapy in melanoma and review the combination therapies available.

Advances in Intralesional Therapy for Locoregionally Advanced and Metastatic Melanoma: Five Years of Progress

Locoregionally advanced and metastatic melanoma are complex diagnoses with a variety of available treatment options. Intralesional therapy for melanoma has been under investigation for decades; however, it has advanced precipitously in recent years. In 2015, the Food and Drug Administration (FDA) approved talimogene laherparepvec (T-VEC), the only FDA-approved intralesional therapy for advanced melanoma. There has been significant progress since that time with other oncolytic viruses, toll-like receptor agonists, cytokines, xanthene dyes, and immune checkpoint inhibitors all under investigation as intralesional agents. Further to this, there has been exploration of numerous combinations of intralesional therapies and systemic therapies as various lines of therapy. Several of these combinations have been abandoned due to their lack of efficacy or safety concerns. This manuscript presents the various types of intralesional therapies that have reached phase 2 or later clinical trials in the past 5 years, including their mechanism of action, therapeutic combinations under investigation, and published results. The intention is to provide an overview of the progress that has been made, discuss ongoing trials worth following, and share our opinions on opportunities for further advancement.

DSP-0509, a systemically available TLR7 agonist, exhibits combination effect with immune checkpoint blockade by activating anti-tumor immune effects

TLR7 is an innate immune receptor that recognizes single-stranded RNAs, and its activation leads to anti-tumor immune effects. Although it is the only approved TLR7 agonist in cancer therapy, imiquimod is allowed to be administered with topical formulation. Thus, systemic administrative TLR7 agonist is expected in terms of expanding applicable cancer types. Here, we demonstrated the identification and characterization of DSP-0509 as a novel small-molecule TLR7 agonist. DSP-0509 is designed to have unique physicochemical features that could be administered systemically with a short half-life. DSP-0509 activated bone marrow-derived dendritic cells (BMDCs) and induced inflammatory cytokines including type I interferons. In the LM8 tumor-bearing mouse model, DSP-0509 reduced tumor growth not only in subcutaneous primary lesions but also in lung metastatic lesions. DSP-0509 inhibited tumor growth in several syngeneic tumor-bearing mouse models. We found that the CD8⁺ T cell infiltration of tumor before treatment tended to be positively correlated with anti-tumor efficacy in several mouse tumor models. The combination of DSP-0509 with anti-PD-1 antibody significantly enhanced the tumor growth inhibition compared to each monotherapy in CT26 model mice. In addition, the effector memory T cells were expanded in both the peripheral blood and tumor, and rejection of tumor re-challenge occurred in the combination group. Moreover, synergistic anti-tumor efficacy and effector memory T cell upregulation were also observed for the combination with anti-CTLA-4 antibody. The analysis of the tumor-immune microenvironment by using the nCounter assay revealed that the combination of DSP-0509 with anti-PD-1 antibody enhanced infiltration by multiple immune cells including cytotoxic T cells. In addition, the T cell function pathway and antigen presentation pathway were activated in the combination group. We confirmed that DSP-0509 enhanced the anti-tumor immune effects of anti-PD-1 antibody by inducing type I interferons via activation of dendritic cells and even CTLs. In conclusion, we expect that DSP-0509, a new TLR7 agonist that synergistically induces anti-tumor effector memory T cells with immune checkpoint blockers (ICBs) and can be administered systemically, will be used in the treatment of multiple cancers.

Genetic dysregulation of immunologic and oncogenic signaling pathways associated with tumor-intrinsic immune resistance: a molecular basis for combination targeted therapy-immunotherapy for cancer

Since the turn of the century, advances in targeted therapy and immunotherapy have revolutionized the treatment of cancer. Although these approaches have far outperformed traditional therapies in various clinical settings, both remain plagued by mechanisms of innate and acquired resistance that limit therapeutic efficacy in many patients. With a focus on tumor-intrinsic resistance to immunotherapy, this review highlights our current understanding of the immunologic and oncogenic pathways whose genetic dysregulation in cancer cells enables immune escape. Emphasis is placed on genomic, epigenomic, transcriptomic, and proteomic aberrations that influence the activity of these pathways in the context of immune resistance. Specifically, the role of pathways that govern interferon signaling, antigen processing and presentation, and immunologic cell death as determinants of tumor immune susceptibility are discussed. Likewise, mechanisms of tumor immune resistance mediated by dysregulated RAS-MAPK, WNT, PI3K-AKT-mTOR, and cell cycle pathways are described. Finally, this review highlights the ways in which recent insight into genetic dysregulation of these immunologic and oncogenic signaling pathways is informing the design of combination targeted therapy-immunotherapy regimens that aim to restore immune susceptibility of cancer cells by overcoming resistance mechanisms that often limit the success of monotherapies.

Toll-like receptor 9 agonists and combination therapies: strategies to modulate the tumour immune microenvironment for systemic anti-tumour immunity

Over the past decade, tremendous progress has taken place in tumour immunotherapy, relying on the fast development of combination therapy strategies that target multiple immunosuppressive signaling pathways in the immune system of cancer patients to achieve a high response rate in clinical practice. Toll-like receptor 9 (TLR9) agonists have been extensively investigated as therapeutics in monotherapy or combination therapies for the treatment of cancer, infectious diseases and allergies. TLR9 agonists monotherapy shows limited efficacy in cancer patients; whereas, in combination with other therapies including antigen vaccines, radiotherapies, chemotherapies and immunotherapies exhibit great potential. Synthetic unmethylated CpG oligodeoxynucleotide (ODN), a commonly used agonist for TLR9, stimulate various antigen-presenting cells in the tumour microenvironment, which can initiate innate and adaptive immune responses. Novel combination therapy approaches, which co-deliver immunostimulatory CpG-ODN with other therapeutics, have been tested in animal models and early human clinical trials to induce anti-tumour immune responses. In this review, we describe the basic understanding of TLR9 signaling pathway; the delivery methods in most studies; discuss the key challenges of each of the above mentioned TLR9 agonist-based combination immunotherapies and provide an overview of the ongoing clinical trial results from CpG-ODN based combination therapies in cancer patients.

Contribution of T- and B-cell intrinsic toll-like receptors to the adaptive immune response in viral infectious diseases

Toll-like receptors (TLRs) comprise a class of highly conserved molecules that recognize pathogen-associated molecular patterns and play a vital role in host defense against multiple viral infectious diseases. Although TLRs are highly expressed on innate immune cells and play indirect roles in regulating antiviral adaptive immune responses, intrinsic expression of TLRs in adaptive immune cells, including T cells and B cells, cannot be ignored. TLRs expressed in CD4 + and CD8 + T cells play roles in enhancing TCR signal-induced T-cell activation, proliferation, function, and survival, serving as costimulatory molecules. Gene knockout of TLR signaling molecules has been shown to diminish antiviral adaptive immune responses and affect viral clearance in multiple viral infectious animal models. These results have highlighted the critical role of TLRs in the long-term immunological control of viral infection. This review summarizes the expression and function of TLR signaling pathways in T and B cells, focusing on the in vitro and vivo mechanisms and effects of intrinsic TLR signaling in regulating T- and B-cell responses during viral infection. The potential clinical use of TLR-based immune regulatory drugs for viral infectious diseases is also explored.

Tripartite antigen-agnostic combination immunotherapy cures established poorly immunogenic tumors

BACKGROUND

Single-agent immunotherapy has shown remarkable efficacy in selected cancer entities and individual patients. However, most patients fail to respond. This is likely due to diverse immunosuppressive mechanisms acting in a concerted way to suppress the host anti-tumor immune response. Combination immunotherapy approaches that are effective in such poorly immunogenic tumors mostly rely on precise knowledge of antigenic determinants on tumor cells. Creating an antigen-agnostic combination immunotherapy that is effective in poorly immunogenic tumors for which an antigenic determinant is not known is a major challenge.

METHODS

We use multiple cell line and poorly immunogenic syngeneic, autochthonous, and autologous mouse models to evaluate the efficacy of a novel combination immunotherapy named tripartite immunotherapy (TRI-IT). To elucidate TRI-ITs mechanism of action we use immune cell depletions and comprehensive tumor and immune infiltrate characterization by flow cytometry, RNA sequencing and diverse functional assays.

RESULTS

We show that combined adoptive cellular therapy (ACT) with lymphokine-activated killer cells, cytokine-induced killer cells, Vγ9Vδ2-T-cells (γδ-T-cells) and T-cells enriched for tumor recognition (CTLs) display synergistic antitumor effects, which are further enhanced by cotreatment with anti-PD1 antibodies. Most strikingly, the full TRI-IT protocol, a combination of this ACT with anti-PD1 antibodies, local immunotherapy of agonists against toll-like receptor 3, 7 and 9 and pre-ACT lymphodepletion, eradicates and induces durable anti-tumor immunity in a variety of poorly immunogenic syngeneic, autochthonous, as well as autologous humanized patient-derived models. Mechanistically, we show that TRI-IT coactivates adaptive cellular and humoral, as well as innate antitumor immune responses to mediate its antitumor effect without inducing off-target toxicity.

CONCLUSIONS

Overall, TRI-IT is a novel, highly effective, antigen-agnostic, non-toxic combination immunotherapy. In this study, comprehensive insights into its preclinical efficacy, even in poorly immunogenic tumors, and mode of action are given, so that translation into clinical trials is the next step.

Orthotopic and Heterotopic Murine Models of Pancreatic Cancer Exhibit Different Immunological Microenvironments and Different Responses to Immunotherapy

For decades, tumor-bearing murine models established using tumor cell lines have been the most commonly used models to study human cancers. Even though there are several studies reported that implant sites caused disparities in tumor behaviors, few of them illuminated the positional effect on immunotherapy. Herein, we describe surgical techniques for a novel orthotopic implantation of syngeneic pancreatic ductal adenocarcinoma (PDAC) tissue slices. This method has a high success modeling rate and stable growth kinetics, which makes it useful for testing novel therapeutics. Pathological examination indicated that the orthotopic tumor displayed poor vascularization, desmoplastic stromal reaction, and a highly immunosuppressive tumor microenvironment. This unique microenvironment resulted in limited response to PD1/CTLA4 blockade therapy and anti-MUC1 (αMUC1) CAR-T transfer treatment. To reverse the suppressive tumor microenvironment, we developed gene modified T-cells bearing a chimeric receptor in which activating receptor NKG2D fused to intracellular domains of 4-1BB and CD3ζ (NKG2D CAR). The NKG2D CAR-T cells target myeloid-derived suppressor cells (MDSCs), which overexpress Rae1 (NKG2D ligands) within the TME. Results indicated that NKG2D CAR-T cells eliminated MDSCs and improved antitumor activity of subsequently infused CAR-T cells. Moreover, we generated a bicistronic CAR-T, including αMUC1 CAR and NKG2D CAR separated by a P2A element. Treatment with the dual targeted bicistronic CAR-T cells also resulted in prolonged survival of orthotopic model mice. In summary, this study describes construction of a novel orthotopic PDAC model through implantation of tissue slices and discusses resistance to immunotherapy from the perspective of a PDAC microenvironment. Based on the obtained results, it is evident that elimination MDSCs by NKG2D CAR could rescue the impaired CAR-T cell activity.

Innate and Adaptive Responses of Intratumoral Immunotherapy with Endosomal Toll-Like Receptor Agonists

Toll-like receptors (TLRs) are natural initial triggers of innate and adaptive immune responses. With the advent of cancer immunotherapy, nucleic acids engineered as ligands of endosomal TLRs have been investigated for the treatment of solid tumors. Despite promising results, their systemic administration, similarly to other immunotherapies, raises safety issues. To overcome these problems, recent studies have applied the direct injection of endosomal TLR agonists in the tumor and/or draining lymph nodes, achieving high local drug exposure and strong antitumor response. Importantly, intratumoral delivery of TLR agonists showed powerful effects not only against the injected tumors but also often against uninjected lesions (abscopal effects), resulting in some cases in cure and antitumoral immunological memory. Herein, we describe the structure and function of TLRs and their role in the tumor microenvironment. Then, we provide our vision on the potential of intratumor versus systemic delivery or vaccination approaches using TLR agonists, also considering the use of nanoparticles to improve their targeting properties. Finally, we collect the preclinical and clinical studies applying intratumoral injection of TLR agonists as monotherapies or in combination with: (a) other TLR or STING agonists; (b) other immunotherapies; (c) radiotherapy or chemotherapy; (d) targeted therapies.

The Role of Toll-like Receptor Agonists and Their Nanomedicines for Tumor Immunotherapy

Toll-like receptors (TLRs) are a class of pattern recognition receptors that play a critical role in innate and adaptive immunity. Toll-like receptor agonists (TLRa) as vaccine adjuvant candidates have become one of the recent research hotspots in the cancer immunomodulatory field. Nevertheless, numerous current systemic deliveries of TLRa are inappropriate for clinical adoption due to their low efficiency and systemic adverse reactions. TLRa-loaded nanoparticles are capable of ameliorating the risk of immune-related toxicity and of strengthening tumor suppression and eradication. Herein, we first briefly depict the patterns of TLRa, followed by the mechanism of agonists at those targets. Second, we summarize the emerging applications of TLRa-loaded nanomedicines as state-of-the-art strategies to advance cancer immunotherapy. Additionally, we outline perspectives related to the development of nanomedicine-based TLRa combined with other therapeutic modalities for malignancies immunotherapy.

Engaging Pattern Recognition Receptors in Solid Tumors to Generate Systemic Antitumor Immunity

Malignant tumors frequently exploit innate immunity to evade immune surveillance. The priming, function, and polarization of antitumor immunity fundamentally depends upon context provided by the innate immune system, particularly antigen presenting cells. Such context is determined in large part by sensing of pathogen specific and damage associated features by pathogen recognition receptors (PRRs). PRR activation induces the delivery of T cell priming cues (e.g. chemokines, co-stimulatory ligands, and cytokines) from antigen presenting cells, playing a decisive role in the cancer immunity cycle. Indeed, endogenous PRR activation within the tumor microenvironment (TME) has been shown to generate spontaneous antitumor T cell immunity, e.g., cGAS-STING mediated activation of antigen presenting cells after release of DNA from dying tumor cells. Thus, instigating intratumor PRR activation, particularly with the goal of generating Th1-promoting inflammation that stokes endogenous priming of antitumor CD8⁺ T cells, is a growing area of clinical investigation. This approach is analogous to in situ vaccination, ultimately providing a personalized antitumor response against relevant tumor associated antigens. Here I discuss clinical stage intratumor modalities that function via activation of PRRs. These approaches are being tested in various solid tumor contexts including melanoma, colorectal cancer, glioblastoma, head and neck squamous cell carcinoma, bladder cancer, and pancreatic cancer. Their mechanism (s) of action relative to other immunotherapy approaches (e.g., antigen-defined cancer vaccines, CAR T cells, dendritic cell vaccines, and immune checkpoint blockade), as well as their potential to complement these approaches are also discussed. Examples to be reviewed include TLR agonists, STING agonists, RIG-I agonists, and attenuated or engineered viruses and bacterium. I also review common key requirements for effective in situ immune activation, discuss differences between various strategies inclusive of mechanisms that may ultimately limit or preclude antitumor efficacy, and provide a summary of relevant clinical data.

ApoE-mediated systemic nanodelivery of granzyme B and CpG for enhanced glioma immunotherapy

The response of malignant glioma to immunotherapy remains gloomy due to its discrete immunological environment and poor brain penetration of immunotherapeutic agents. Here, we disclose that ApoE peptide-mediated systemic nanodelivery of granzyme B (GrB) and CpG ODN co-stimulates enhanced immunotherapy of murine malignant LCPN glioma model. ApoE peptide-functionalized polymersomes encapsulating GrB (ApoE-PS-GrB) could effectively penetrate the blood-brain barrier-mimicking endothelial cell monolayer in vitro and further be taken up by LCPN cells, inducing strong immunogenic cell death (ICD). The co-administration of ApoE-PS-GrB and ApoE-PS-CpG in orthotopic LCPN glioma-bearing mice co-stimulated cytokine production, maturation of dendritic cells (DCs), infiltration of cytotoxic T lymphocytes (CTLs) while reduction of regulatory T lymphocytes (T_reg) and M2 phenotype macrophages in the tumor microenvironment, leading to greatly delayed tumor progression and significantly prolonged survival time compared with all controls. The ApoE-mediated systemic nanodelivery of GrB and CpG ODN opens a new pathway for potent immunotherapy of malignant glioma.

Managing Metastatic Melanoma in 2022: A Clinical Review

Cutaneous melanoma remains the most lethal of the primary cutaneous neoplasms, and although the incidence of primary melanoma continues to rise, the mortality from metastatic disease remains unchanged, in part through advances in treatment. Major developments in immunomodulatory and targeted therapies have provided robust improvements in response and survival trends that have transformed the clinical management of patients with metastatic melanoma. Additional advances in immunologic and cancer cell biology have contributed to further optimization in (1) risk stratification, (2) prognostication, (3) treatment, (4) toxicity management, and (5) surveillance approaches for patients with an advanced melanoma diagnosis. In this review, we provide a comprehensive overview of the historical and future advances regarding the translational and clinical implications of advanced melanoma and share multidisciplinary recommendations to aid clinicians in the navigation of current treatment approaches for a variety of patient cohorts.

In situ targeting nanoparticles-hydrogel hybrid system for combined chemo-immunotherapy of glioma

It is well known that glioma is currently the most malignant brain tumor. Because of the existence of blood-brain barrier (BBB) and tumor cell heterogeneity, systemic chemotherapy exerts unsatisfied therapeutic effect for the treatment of glioma after surgical resection and may even damage the body's immune system. Here, we developed an in situ sustained-release hydrogel delivery system for combined chemo-immunotherapy of glioma by combined chemotherapy drug and immunoadjuvant through the resection cavity local delivery. Briefly, glioma homing peptide modified paclitaxel targeting nanoparticles (PNP_PTX) and mannitolated immunoadjuvant CpG targeting nanoparticles (MNP_CpG) were embedded into PLGA₁₇₅₀-PEG₁₅₀₀-PLGA₁₇₅₀ thermosensitive hydrogel framework (PNP_PTX&MNP_CpG@Gel). The in vitro and in vivo results showed that the targeting nanoparticles-hydrogel hybrid system could cross-link into a gel drug reservoir when injected into the resection cavity of glioma. And then, the sustained-release PNP_PTX could target the residual infiltration glioma cells and produce tumor antigens. Meanwhile, MNP_CpG targeted and activated the antigen-presenting cells, which enhanced the tumor antigen presentation ability and activated CD8⁺T and NK cells to reverse immunosuppression of glioma microenvironment. This study indicated that the PNP_PTX&MNP_CpG@Gel system could enhance the therapeutic effect of glioma by chemo-immunotherapy.

Type I interferon-mediated tumor immunity and its role in immunotherapy

Immune checkpoint blockade (ICB) therapies have achieved remarkable clinical responses in patients with many different types of cancer; however, most patients who receive ICB monotherapy fail to achieve long-term responses, and some tumors become immunotherapy-resistant and even hyperprogressive. Type I interferons (IFNs) have been demonstrated to inhibit tumor growth directly and indirectly by acting upon tumor and immune cells, respectively. Furthermore, accumulating evidence indicates that endo- and exogenously enhancing type I IFNs have a synergistic effect on anti-tumor immunity. Therefore, clinical trials studying new treatment strategies that combine type I IFN inducers with ICB are currently in progress. Here, we review the cellular sources of type I IFNs and their roles in the immune regulation of the tumor microenvironment. In addition, we highlight immunotherapies based on type I IFNs and combination therapy between type I IFN inducers and ICBs.

The treatment of advanced melanoma: a review of systemic and local therapies in combination with immune checkpoint inhibitors in phase 1 and 2 clinical trials

INTRODUCTION

While the incidence of melanoma continues to rise, the mortality of the disease appears to have stabilized. This may, in part, be due to the development and application of immune checkpoint inhibitors as standard of care in advanced melanoma. However, many patients do not respond to these therapies alone. Combining immune checkpoint inhibitors with other classes of therapeutics appears to be a promising direction to improve response and survival in advanced melanoma.

AREAS COVERED

This review article aims to discuss phase 1 and 2 clinical trials examining immune checkpoint inhibitors in combination therapy for the treatment of advanced, unresectable melanoma. In particular, these regimens include various kinase inhibitors, tumor-infiltrating lymphocytes, toll-like receptor agonists, cytokines, and oncolytic viral therapies. The combinations under discussion include both systemic and combination systemic/local therapies.

EXPERT OPINION

Drug combinations discussed here appear to be promising therapeutic regimens for advanced melanoma. Improved understanding of the mechanisms of primary, adaptive, and acquired resistance to immune checkpoint inhibitors may guide the development of future combination regimens.

Gut microbiota: impacts on gastrointestinal cancer immunotherapy

The association of gut microbiota with gastrointestinal carcinogenesis has been heavily investigated since the recent advance in sequencing technology. Accumulating evidence has revealed the critical roles of commensal microbes in cancer progression. Given by its importance, emerging studies have focussed on targeting microbiota to ameliorate therapeutic effectiveness. It is now clear that the microbial community is closely related to the efficacy of chemotherapy, while the correlation of microbiota with immunotherapy is much less studied. Herein, we review the up-to-date findings on the influence of gut microbiota on three common immunotherapies including adoptive cell transfer, immune checkpoint blockade, and CpG-oligodeoxynucleotide therapy. We then explore three microbiota-targeted strategies that may improve treatment efficacy, involving dietary intervention, probiotics supplementation, and fecal microbiota transplantation.

Regional infusion of a class C TLR9 agonist enhances liver tumor microenvironment reprogramming and MDSC reduction to improve responsiveness to systemic checkpoint inhibition

Myeloid-derived suppressor cells (MDSCs) expand in response to malignancy and suppress responsiveness to immunotherapy, including checkpoint inhibitors (CPIs). Within the liver, MDSCs have unique immunosuppressive features. While TLR9 agonists have shown promising activities in enhancing CPI responsiveness in superficial tumors amenable to direct needle injection, clinical success for liver tumors with TLR9 agonists has been limited by delivery challenges. Here, we report that regional intravascular infusion of ODN2395 into mice with liver metastasis (LM) partially eliminated liver MDSCs and reprogrammed residual MDSC. TLR9 agonist regional infusion also induced an increase in the M1/M2 macrophage ratio. Enhanced TLR9 signaling was demonstrated by an increased activation of in NFκB (pP65) and production of IL6 compared with systemic infusion. Further, PBMC-derived human MDSCs express TLR9, and treatment with class C TLR9 agonists (ODN2395 and SD101) reduced the expansion of MDSC population. TLR9 stimulation induced MDSC apoptosis and increased the M1/M2 macrophage ratio. Regional TLR9 agonist infusion along with systemic anti-PD-1 therapy improved control of LM. With effective delivery, TLR9 agonists have the potential to favorably reprogram the liver TME through reduction of MDSCs and favorable macrophage polarization, which may improve responsiveness to systemic CPI therapy.

Tilsotolimod: an investigational synthetic toll-like receptor 9 (TLR9) agonist for the treatment of refractory solid tumors and melanoma

INTRODUCTION

Cancer immunotherapy has seen tremendous strides in the past 15 years, with the introduction of several novel immunotherapeutic agents. Nevertheless, as clinical practice has shown, significant challenges remain with a considerable number of patients responding sub-optimally to available therapeutic options. Research has demonstrated the important immunoregulatory role of the tumor microenvironment (TME), with the potential to either hinder or promote an effective anti-tumor immune response. As such, scientific efforts have focused on investigating novel candidate immunomodulatory agents with the potential to alter the TME toward a more immunopotentiating composition.

AREAS COVERED

Herein, we discuss the novel investigational toll-like receptor 9 agonist tilsotolimod currently undergoing phase II and III clinical trials for advanced refractory cancer, highlighting its mode of action, efficacy, tolerability, and potential future applications in the treatment of cancer. To this effect, we conducted an exhaustive Web of Science and PubMed search to evaluate available research on tilsotolimod as of August 2021.

EXPERT OPINION

With encouraging early clinical results demonstrating extensive TME immunomodulation and abscopal effects on distant tumor lesions, tilsotolimod has emerged as a potential candidate immunomodulatory agent with the possibility to augment currently available immunotherapy and provide novel avenues of treatment for patients with advanced refectory cancer.

Signal pathways of melanoma and targeted therapy

Melanoma is the most lethal skin cancer that originates from the malignant transformation of melanocytes. Although melanoma has long been regarded as a cancerous malignancy with few therapeutic options, increased biological understanding and unprecedented innovations in therapies targeting mutated driver genes and immune checkpoints have substantially improved the prognosis of patients. However, the low response rate and inevitable occurrence of resistance to currently available targeted therapies have posed the obstacle in the path of melanoma management to obtain further amelioration. Therefore, it is necessary to understand the mechanisms underlying melanoma pathogenesis more comprehensively, which might lead to more substantial progress in therapeutic approaches and expand clinical options for melanoma therapy. In this review, we firstly make a brief introduction to melanoma epidemiology, clinical subtypes, risk factors, and current therapies. Then, the signal pathways orchestrating melanoma pathogenesis, including genetic mutations, key transcriptional regulators, epigenetic dysregulations, metabolic reprogramming, crucial metastasis-related signals, tumor-promoting inflammatory pathways, and pro-angiogenic factors, have been systemically reviewed and discussed. Subsequently, we outline current progresses in therapies targeting mutated driver genes and immune checkpoints, as well as the mechanisms underlying the treatment resistance. Finally, the prospects and challenges in the development of melanoma therapy, especially immunotherapy and related ongoing clinical trials, are summarized and discussed.

Distinct roles but cooperative effect of TLR3/9 agonists and PD-1 blockade in converting the immunotolerant microenvironment of irreversible electroporation-ablated tumors

Irreversible electroporation (IRE) is a new cancer ablation technology, but methods to improve IRE-induced therapeutic immunity are only beginning to be investigated. We developed a mouse model bearing large primary (300 mm³) and medium distant (100 mm³) EG7 lymphomas engineered to express ovalbumin (OVA) as a nominal tumor antigen. We established experimental protocols including IRE alone and IRE combined with Toll-like receptor (TLR)3/9 agonists (poly I:C/CpG) (IRE + pIC/CpG), PD-1 blockade (IRE + PD-1 blockade), or both (IRE + Combo) to investigate therapeutic effects on primary and distant EG7 tumors and conversion-promoting effects on the immunotolerant tumor microenvironment (TME). We demonstrated that IRE alone simulated very weak OVA-specific CD8⁺ T cell responses and did not inhibit primary tumor growth. IRE + pIC/CpG synergistically stimulated more efficient OVA-specific CD8⁺ T cell responses and primary tumor growth inhibition than IRE + PD-1 blockade. IRE + pIC/CpG played a major role in the modulation of immune cell profiles but a minor role in the downregulation of PD-L1 expression in the TME and vice versa for IRE + PD-1 blockade. IRE + Combo cooperatively induced potent OVA-specific CD8⁺ T cell immunity and rescued exhausted intratumoral CD8⁺ T cells, leading to eradication of not only primary tumors but also untreated concomitant distant tumors and lung metastases. IRE + Combo efficiently modulated immune cell profiles, as evidenced by reductions in immunotolerant type-2 (M2) macrophages, myeloid-derived suppressor-cells, plasmacytoid dendritic cells, and regulatory T cells and by increases in immunogenic M1 macrophages, CD169⁺ macrophages, type-1 conventional dendritic cells, and CD8⁺ T cells, leading to conversion of immunotolerance in not only primary TMEs but also untreated distant TMEs. IRE + Combo also showed effective therapeutic effects in two breast cancer models. Therefore, our results suggest that IRE + Combo is a promising strategy to improve IRE ablation therapy in cancer.

The oncolytic virus VT09X optimizes immune checkpoint therapy in low immunogenic melanoma

Tumors with a low level of pre-existing immune cell infiltration respond poorly to immune checkpoint therapies. Oncolytic viruses optimize immunotherapies by modulating the tumor microenvironment and affecting multiple steps in the cancer-immunity cycle, making them an attractive agent for combination strategies. We engineered an HSV-1-based oncolytic virus and investigated its antitumor effects in combination with the marketed PD-1 antibody Keytruda (pembrolizumab) in hPD-1 knock-in mice bearing non-immunogenic B16-F10 melanoma. Our results showed enhanced CD8⁺ and CD4⁺ T cell infiltration, IFN-γ secretion and PD-L1 expression in tumors, subsequently leading to the prolonged overall survival of mice. Systemic changes in lymphocyte cell proportions were also observed in the peripheral blood. In summary, these findings provide evidence that oncolytic viruses can be engineered as a potential platform for combination therapies, especially to treat tumors that are poorly responsive to immune checkpoint therapy.

Macrophages Impair TLR9 Agonist Antitumor Activity through Interacting with the Anti-PD-1 Antibody Fc Domain

Simple Summary

We evaluated the contribution of macrophages to the effect of combinatorial immunotherapeutic treatments based on TLR9 stimulation (with CpG-ODNs) and PD-1 blockade in an ovarian cancer preclinical model. We observed a strong reduction in the antitumor efficacy of a TLR9 agonist upon anti-PD-1 antibody administration. Specifically, we found that TLR9-stimulated macrophages, through interacting with the fragment crystallizable (Fc) domain of the anti-PD-1 antibody, acquire an immunoregulatory phenotype leading to dampening of CpG-ODN antitumor effect. Since the stimulation of macrophage TLRs can be achieved not only by synthetic agonists but also by molecules present in the tumor microenvironment, the data we are presenting may represent another possible mechanism of anti-PD-1 antibody therapy resistance. Indeed, it is possible that when delivered as a monotherapy, anti-PD-1 antibody Fc domain may interact with macrophages in which TLR signaling has already been triggered by endogenous ligands, mirroring the biological effects described in the present study.

Abstract

Background. A combination of TLR9 agonists and an anti-PD-1 antibody has been reported to be effective in immunocompetent mice but the role of innate immunity has not yet been completely elucidated. Therefore, we investigated the contribution of the innate immune system to this combinatorial immunotherapeutic regimens using an immunodeficient mouse model in which the effector functions of innate immunity can clearly emerge without any interference from T lymphocytes. Methods. Athymic mice xenografted with IGROV-1 human ovarian cells, reported to be sensitive to TLR9 agonist therapy, were treated with cytosine–guanine (CpG)-oligodeoxynucleotides (ODNs), an anti-PD-1 antibody or their combination. Results. We found that PD-1 blockade dampened CpG-ODN antitumor activity. In vitro studies indicated that the interaction between the anti-PD-1 antibody fragment crystallizable (Fc) domain and macrophage Fc receptors caused these immune cells to acquire an immunoregulatory phenotype, contributing to a decrease in the efficacy of CpG-ODNs. Accordingly, in vivo macrophage depletion abrogated the detrimental effect exerted by the anti-PD-1 antibody. Conclusion. Our data suggest that if TLR signaling is active in macrophages, coadministration of an anti-PD-1 antibody can reprogram these immune cells towards a polarization state able to negatively affect the immune response and eventually promote tumor growth.

Tilsotolimod with Ipilimumab Drives Tumor Responses in Anti-PD-1 Refractory Melanoma

Many patients with advanced melanoma are resistant to immune checkpoint inhibition. In the ILLUMINATE-204 phase I/II trial, we assessed intratumoral tilsotolimod, an investigational Toll-like receptor 9 agonist, with systemic ipilimumab in patients with anti-PD-1- resistant advanced melanoma. In all patients, 48.4% experienced grade 3/4 treatment-emergent adverse events. The overall response rate at the recommended phase II dose of 8 mg was 22.4%, and an additional 49% of patients had stable disease. Responses in noninjected lesions and in patients expected to be resistant to ipilimumab monotherapy were observed. Rapid induction of a local IFNα gene signature, dendritic cell maturation and enhanced markers of antigen presentation, and T-cell clonal expansion correlated with clinical response. A phase III clinical trial with this combination (NCT03445533) is ongoing. SIGNIFICANCE: Despite recent developments in advanced melanoma therapies, most patients do not experience durable responses. Intratumoral tilsotolimod injection elicits a rapid, local type 1 IFN response and, in combination with ipilimumab, activates T cells to promote clinical activity, including in distant lesions and patients not expected to respond to ipilimumab alone.This article is highlighted in the In This Issue feature, p. 1861.

Immune mechanisms orchestrate tertiary lymphoid structures in tumors via cancer-associated fibroblasts

Tumor-associated tertiary lymphoid structures (TA-TLS) are associated with enhanced patient survival and responsiveness to cancer therapies, but the mechanisms underlying their development are unknown. We show here that TA-TLS development in murine melanoma is orchestrated by cancer-associated fibroblasts (CAF) with characteristics of lymphoid tissue organizer cells that are induced by tumor necrosis factor receptor signaling. CAF organization into reticular networks is mediated by CD8 T cells, while CAF accumulation and TA-TLS expansion depend on CXCL13-mediated recruitment of B cells expressing lymphotoxin-α1β2. Some of these elements are also overrepresented in human TA-TLS. Additionally, we demonstrate that immunotherapy induces more and larger TA-TLS that are more often organized with discrete T and B cell zones, and that TA-TLS presence, number, and size are correlated with reduced tumor size and overall response to checkpoint immunotherapy. This work provides a platform for manipulating TA-TLS development as a cancer immunotherapy strategy.

Toll-Like Receptor-Based Strategies for Cancer Immunotherapy

Toll-like receptors (TLRs) are expressed and play multiple functional roles in a variety of immune cell types involved in tumor immunity. There are plenty of data on the pharmacological targeting of TLR signaling using agonist molecules that boost the antitumor immune response. A recent body of research has also demonstrated promising strategies for improving the cell-based immunotherapy methods by inducing TLR signaling. These strategies include systemic administration of TLR antagonist along with immune cell transfer and also genetic engineering of the immune cells using TLR signaling components to improve the function of genetically engineered immune cells such as chimeric antigen receptor-modified T cells. Here, we explore the current status of the cancer immunotherapy approaches based on manipulation of TLR signaling to provide a perspective of the underlying rationales and potential clinical applications. Altogether, reviewed publications suggest that TLRs make a potential target for the immunotherapy of cancer.

Molecular Chaperone GRP94/GP96 in Cancers: Oncogenesis and Therapeutic Target

During tumor development and progression, intrinsic and extrinsic factors trigger endoplasmic reticulum (ER) stress and the unfolded protein response, resulting in the increased expression of molecular chaperones to cope with the stress and maintain tumor cell survival. Heat shock protein (HSP) GRP94, also known as GP96, is an ER paralog of HSP90 and has been shown to promote survival signaling during tumor-induced stress and modulate the immune response through its multiple clients, including TLRs, integrins, LRP6, GARP, IGF, and HER2. Clinically, elevated expression of GRP94 correlates with an aggressive phenotype and poor clinical outcome in a variety of cancers. Thus, GRP94 is a potential molecular marker and therapeutic target in malignancies. In this review, we will undergo deep molecular profiling of GRP94 in tumor development and summarize the individual roles of GRP94 in common cancers, including breast cancer, colon cancer, lung cancer, liver cancer, multiple myeloma, and others. Finally, we will briefly review the therapeutic potential of selectively targeting GRP94 for the treatment of cancers.

T cell infiltration on local CpG-B delivery in early-stage melanoma is predominantly related to CLEC9A+CD141+ cDC1 and CD14+ antigen-presenting cell recruitment

Background

We previously reported CpG-B injection at the primary tumor excision site prior to re-excision and sentinel node biopsy to result in immune activation of the sentinel lymph node (SLN), increased melanoma-specific CD8⁺ T cell rates in peripheral blood, and prolonged recurrence-free survival. Here, we assessed recruitment and activation of antigen-presenting cell (APC) subsets in the SLN and at the injection site in relation to T cell infiltration.

Methods

Re-excision skin specimens from patients with clinical stage I-II melanoma, collected 7 days after intradermal injection of either saline (n=10) or 8 mg CpG-B (CPG7909, n=12), were examined by immunohistochemistry, quantifying immune subsets in the epidermis, papillary, and reticular dermis. Counts were related to flow cytometric data from matched SLN samples. Additional in vitro cultures and transcriptional analyses on peripheral blood mononuclear cells (PBMCs) were performed to ascertain CpG-induced APC activation and chemokine profiles.

Results

Significant increases in CD83⁺, CD14⁺, CD68⁺, and CD123⁺ APC were observed in the reticular dermis of CpG-B-injected skin samples. Fluorescent double/triple staining revealed recruitment of both CD123⁺BDCA2⁺ plasmacytoid dendritic cells (DCs) and BDCA3/CD141⁺CLEC9A⁺ type-1 conventional DC (cDC1), of which only the cDC1 showed considerable levels of CD83 expression. Simultaneous CpG-B-induced increases in T cell infiltration were strongly correlated with both cDC1 and CD14 counts. Moreover, cDC1 and CD14⁺ APC rates in the reticular dermis and matched SLN suspensions were positively correlated. Flow cytometric, transcriptional, and chemokine release analyses of PBMC, on in vitro or in vivo exposure to CpG-B, indicate a role for the activation and recruitment of both cDC1 and CD14⁺ monocyte-derived APCs in the release of CXCL10 and subsequent T cell infiltration.

Conclusion

The CpG-B-induced concerted recruitment of cDC1 and CD14⁺ APC to the injection site and its draining lymph nodes may allow for both the (cross-)priming of T cells and their subsequent homing to effector sites.

Advanced Melanoma: Resistance Mechanisms to Current Therapies

Novel therapeutic agents introduced over the past decade, including immune checkpoint inhibitors and targeted therapies, have revolutionized the management of metastatic melanoma and significantly improved patient outcomes. Although robust and durable responses have been noted in some cases, treatment is often limited by innate or acquired resistance to these agents. This article provides an overview of known and suspected mechanisms involved with acquired resistance to BRAF/MEK inhibitors as well as developing insights into innate and acquired resistance to checkpoint inhibitors in patients with melanoma.

TLRs as a Promise Target Along With Immune Checkpoint Against Gastric Cancer

Gastric cancer (GC) is one of the most common cancers in the world, and the incidence of gastric cancer in Asia appears to increase in recent years. Although there is a lot of improvement in treatment approaches, the prognosis of GC is poor. So it is urgent to search for a novel and more effective treatment to improve the survival rate of patients. Both innate immunity and adaptive immunity are important in cancer. In the innate immune system, pattern recognition receptors (PRRs) activate immune responses by recognizing pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). Toll-like receptors (TLRs) are a class of pattern recognition receptors (PRRs). Many studies have reported that TLRs are involved in the occurrence, development, and treatment of GC. Therefore, TLRs are potential targets for immunotherapy to gastric cancer. However, gastric cancer is a heterogeneous disorder, and TLRs function in GC is complex. TLRs agonists can be potentially used not only as therapeutic agents to treat gastric cancer but also as adjuvants in conjunction with other immunotherapies. They might provide a promising new target for GC treatment. In the review, we sort out the mechanism of TLRs involved in tumor immunity and summarize the current progress in TLRs-based therapeutic approaches and other immunotherapies in the treatment of GC.

Modulating the Tumour Microenvironment by Intratumoural Injection of Pattern Recognition Receptor Agonists

Signalling through pattern recognition receptors (PRRs) leads to strong proinflammatory responses, enhancing the activity of antigen presenting cells and shaping adaptive immune responses against tumour associated antigens. Unfortunately, toxicities associated with systemic administration of these agonists have limited their clinical use to date. Direct injection of PRR agonists into the tumour can enhance immune responses by directly modulating the cells present in the tumour microenvironment. This can improve local antitumour activity, but importantly, also facilitates systemic responses that limit tumour growth at distant sites. As such, this form of therapy could be used clinically where metastatic tumour lesions are accessible, or as neoadjuvant therapy. In this review, we summarise current preclinical data on intratumoural administration of PRR agonists, including new strategies to optimise delivery and impact, and combination studies with current and promising new cancer therapies.