Impact of checkpoint blockade on cancer vaccine-activated CD8+ T cell responses

Current status of vaccine immunotherapy for gastrointestinal cancers

Recent advances in tumor immunology and molecular drug development have ushered in a new era of cancer immunotherapy. Immunotherapy has shown promising results for several types of tumors, such as advanced melanoma, non-small cell lung cancer, renal cell carcinoma, bladder cancers, and refractory Hodgkin's lymphoma. Similarly, efforts have been made to develop immunotherapies such as adoptive T-cell transplantation, peptide vaccines, and dendritic cell vaccines, specifically for gastrointestinal tumors. However, before the advent of immune checkpoint inhibitors, immunotherapy did not work as well as expected. In this article, we review immunotherapy, focusing on cancer vaccines for gastrointestinal tumors, which generally target eliciting tumor-specific CD8 + cytotoxic T lymphocytes (CTLs). We also review various vaccine therapies and describe the relationship between vaccines and adjuvants. Finally, we discuss prospects for the combination of immunotherapy with immune checkpoint inhibitors.

Soluble immune checkpoint molecules in cancer risk, outcomes prediction, and therapeutic applications

Immunotherapy has emerged as a pivotal modality in cancer treatment, with immune checkpoint inhibitors effectively combating malignancies by impeding crucial pathways within the immune system and stimulating patients' immune responses. Soluble forms of immune checkpoints exhibit a remarkable diversity and can be readily tracked in circulation, holding immense potential as biomarkers for cancer treatment. An increasing number of studies focused on soluble immune checkpoints in cancer have emerged thanks to technological advancements. In this systematic review, we comprehensively summarized the recent studies on soluble immune checkpoints in human cancer risk prediction, outcome prediction, therapeutic applications, and potential molecular mechanisms, which demonstrated the promising future of soluble immune checkpoints in clinical applications. The clinical relevance of soluble immune checkpoints has been recognized in multiple cancers, yet the therapeutic applications and mechanisms remain obscure. Interpreting the impacts and mechanisms of soluble immune checkpoints could shed a light on the novel strategies of cancer screening, treatments, and outcome prediction.

Immunotherapy combination approaches: mechanisms, biomarkers and clinical observations

The approval of the first immune checkpoint inhibitors provided a paradigm shift for the treatment of malignancies across a broad range of indications. Whereas initially, single-agent immune checkpoint inhibition was used, increasing numbers of patients are now treated with combination immune checkpoint blockade, where non-redundant mechanisms of action of the individual agents generally lead to higher response rates. Furthermore, immune checkpoint therapy has been combined with various other therapeutic modalities, including chemotherapy, radiotherapy and other immunotherapeutics such as vaccines, adoptive cellular therapies, cytokines and others, in an effort to maximize clinical efficacy. Currently, a large number of clinical trials test combination therapies with an immune checkpoint inhibitor as a backbone. However, proceeding without inclusion of broad, if initially exploratory, biomarker investigations may ultimately slow progress, as so far, few combinations have yielded clinical successes based on clinical data alone. Here, we present the rationale for combination therapies and discuss clinical data from clinical trials across the immuno-oncology spectrum. Moreover, we discuss the evolution of biomarker approaches and highlight the potential new directions that comprehensive biomarker studies can yield.

Personalizing Oncolytic Immunovirotherapy Approaches

Development of successful cancer therapeutics requires exploration of the differences in genetics, metabolism, and interactions with the immune system among malignant and normal cells. The clinical observation of spontaneous tumor regression following natural infection with microorganism has created the premise of their use as cancer therapeutics. Oncolytic viruses (OVs) originate from viruses with attenuated virulence in humans, well-characterized vaccine strains of known human pathogens, or engineered replication-deficient viral vectors. Their selectivity is based on receptor expression level and post entry restriction factors that favor replication in the tumor, while keeping the normal cells unharmed. Clinical trials have demonstrated a wide range of patient responses to virotherapy, with subgroups of patients significantly benefiting from OV administration. Tumor-specific gene signatures, including antiviral interferon-stimulated gene (ISG) expression profile, have demonstrated a strong correlation with tumor permissiveness to infection. Furthermore, the combination of OVs with immunotherapeutics, including anticancer vaccines and immune checkpoint inhibitors [ICIs, such as anti-PD-1/PD-L1 or anti-CTLA-4 and chimeric antigen receptor (CAR)-T or CAR-NK cells], could synergistically improve the therapeutic outcome. Creating response prediction algorithms represents an important step for the transition to individualized immunovirotherapy approaches in the clinic. Integrative predictors could include tumor mutational burden (TMB), inflammatory gene signature, phenotype of tumor-infiltrating lymphocytes, tumor microenvironment (TME), and immune checkpoint receptor expression on both immune and target cells. Additionally, the gut microbiota has recently been recognized as a systemic immunomodulatory factor and could further be used in the optimization of individualized immunovirotherapy algorithms.

Exploiting innate immunity for cancer immunotherapy

Immunotherapies have revolutionized the treatment paradigms of various types of cancers. However, most of these immunomodulatory strategies focus on harnessing adaptive immunity, mainly by inhibiting immunosuppressive signaling with immune checkpoint blockade, or enhancing immunostimulatory signaling with bispecific T cell engager and chimeric antigen receptor (CAR)-T cell. Although these agents have already achieved great success, only a tiny percentage of patients could benefit from immunotherapies. Actually, immunotherapy efficacy is determined by multiple components in the tumor microenvironment beyond adaptive immunity. Cells from the innate arm of the immune system, such as macrophages, dendritic cells, myeloid-derived suppressor cells, neutrophils, natural killer cells, and unconventional T cells, also participate in cancer immune evasion and surveillance. Considering that the innate arm is the cornerstone of the antitumor immune response, utilizing innate immunity provides potential therapeutic options for cancer control. Up to now, strategies exploiting innate immunity, such as agonists of stimulator of interferon genes, CAR-macrophage or -natural killer cell therapies, metabolic regulators, and novel immune checkpoint blockade, have exhibited potent antitumor activities in preclinical and clinical studies. Here, we summarize the latest insights into the potential roles of innate cells in antitumor immunity and discuss the advances in innate arm-targeted therapeutic strategies.

Immuno-metabolic dendritic cell vaccine signatures associate with overall survival in vaccinated melanoma patients

Efficacy of cancer vaccines remains low and mechanistic understanding of antigen presenting cell function in cancer may improve vaccine design and outcomes. Here, we analyze the transcriptomic and immune-metabolic profiles of Dendritic Cells (DCs) from 35 subjects enrolled in a trial of DC vaccines in late-stage melanoma (NCT01622933). Multiple platforms identify metabolism as an important biomarker of DC function and patient overall survival (OS). We demonstrate multiple immune and metabolic gene expression pathway alterations, a functional decrease in OCR/OXPHOS and increase in ECAR/glycolysis in patient vaccines. To dissect molecular mechanisms, we utilize single cell SCENITH functional profiling and show patient clinical outcomes (OS) correlate with DC metabolic profile, and that metabolism is linked to immune phenotype. With single cell metabolic regulome profiling, we show that MCT1 (monocarboxylate transporter-1), a lactate transporter, is increased in patient DCs, as is glucose uptake and lactate secretion. Importantly, pre-vaccination circulating myeloid cells in patients used as precursors for DC vaccine generation are significantly skewed metabolically as are several DC subsets. Together, we demonstrate that the metabolic profile of DC is tightly associated with the immunostimulatory potential of DC vaccines from cancer patients. We link phenotypic and functional metabolic changes to immune signatures that correspond to suppressed DC differentiation.

What’s next for cancer vaccines

Cancer vaccines have been shown clinically to drive tumor-reactive cell activation, proliferation, and effector function. Unfortunately, tumor eradication by treatment with cancer vaccines has been unsuccessful in many patients. Critical steps are under way to improve vaccine efficacy and combine them with immunotherapy and standard-of-care treatments.

Immunosuppressive cells in cancer: mechanisms and potential therapeutic targets

Immunotherapies like the adoptive transfer of gene-engineered T cells and immune checkpoint inhibitors are novel therapeutic modalities for advanced cancers. However, some patients are refractory or resistant to these therapies, and the mechanisms underlying tumor immune resistance have not been fully elucidated. Immunosuppressive cells such as myeloid-derived suppressive cells, tumor-associated macrophages, tumor-associated neutrophils, regulatory T cells (Tregs), and tumor-associated dendritic cells are critical factors correlated with immune resistance. In addition, cytokines and factors secreted by tumor cells or these immunosuppressive cells also mediate the tumor progression and immune escape of cancers. Thus, targeting these immunosuppressive cells and the related signals is the promising therapy to improve the efficacy of immunotherapies and reverse the immune resistance. However, even with certain success in preclinical studies or in some specific types of cancer, large perspectives are unknown for these immunosuppressive cells, and the related therapies have undesirable outcomes for clinical patients. In this review, we comprehensively summarized the phenotype, function, and potential therapeutic targets of these immunosuppressive cells in the tumor microenvironment.

The "Great Debate" at Immunotherapy Bridge 2021, December 1st-2nd, 2021

As part of the 2021 Immunotherapy Bridge virtual congress (December 1–2, Naples, Italy), the Great Debate sessions featured experts who were assigned counter opposing views on four important questions in immunotherapy today. The first topic was whether oncolytic viruses or other specific immunomodulators were the more promising approach for intralesional therapy. The second was whether early surrogate endpoints, such as response rate or progression-free survival, correlate with long-term overall survival was considered. Thirdly, whether vaccines can transform cold into hot tumors was discussed and, finally, broad versus deep analytic profiling approaches to gain insights into immune-oncology development were compared. As with previous Bridge congresses, presenters were invited by the meeting Chairs and positions taken during the debates may not have reflected their respective personal view. In addition, the views summarised in this article are based on available evidence but may reflect personal interpretation of these data, clinical experience and subjective opinion of the speaker.

Plasma extracellular vesicle derived protein profile predicting and monitoring immunotherapeutic outcomes of gastric cancer

Immune checkpoint inhibitor (ICI)-based immunotherapy brought new hope for gastric cancer (GC) treatment. However, due to the lack of proper biomarkers, patient selection and outcome prediction for GC's immunotherapy remain unsatisfying. In this study, through applying an extracellular vesicle (EV) protein expression array, we assessed the correlation of plasma EV-derived protein spectrum with outcomes of ICI-related therapeutic combinations. Plasma from 112 GC patients received ICI-related therapies were investigated retrospectively/prospectively as three cohorts. We identified four plasma EV-derived proteins (ARG1/CD3/PD-L1/PD-L2) from 42 crucial candidate proteins and combined them as an EV-score that robustly predicting immunotherapeutic outcomes at baseline and dynamically monitoring disease progression along with treatment. High EV-score reflected microenvironmental features of stronger antitumour immunity, characterized by more activated CD8+ T/NK cells, higher TH1/TH2 ratio and higher expressions of IFN-γ/perforin/granzymes in paired peripheral blood, which were verified by dataset analysis and in vivo experiments. EV-score≥1 GC received more therapeutic benefits from ICIs, while EV-score < 1 GC potentially benefited more from ICIs combining HER2-targeted therapies. Collectively, through proposing a plasma EV-score on protein level that powerfully predicting and monitoring GC's immunotherapeutic outcomes, our work facilitated clinical patient selection and decision-makings, and provided mechanistical insights for immunotherapy-related microenvironmental changes and improvements for current ICI-regimens.

Advanced Pancreatic Cancer Patient Benefit From Personalized Neoantigen Nanovaccine Based Immunotherapy: A Case Report

Personal neoantigen vaccines are considered to be effective methods for inducing, amplifying and diversifying antitumor T cell responses. We recently conducted a clinical study that combined neoantigen nanovaccine with anti-PD-1 antibody. Here, we reported a case with a clear beneficial outcome from this treatment. We established a process that includes comprehensive identification of individual mutations, computational prediction of new epitopes, and design and manufacture of unique nanovaccines for this patient. Nanovaccine started after a relapse in third-line treatment. We assessed the patient's clinical outcome and circulating immune response. In this advanced pancreatic cancer patient, the OS associated with the vaccine treatment was 10.5 months. A peptide-specific T-cell response against 9 of the 12 vaccine peptides could be detected sequentially. Robust neoantigen-specific T cell responses were also detected by IFN-γ ELISPOT and intracellular cytokine staining. In conclusion, sustained functional neoantigen-specific T cell therapy combined with immune checkpoint targeting may be well suited to help control progressive metastatic pancreatic cancer.

Immunobiology of Melanoma

Despite the ability of immune-based interventions to dramatically increase the survival of patients with melanoma, a significant subset fail to benefit from this treatment, underscoring the need for accurate means to identify the patient population likely to respond to immunotherapy. Understanding how melanoma evades natural or manipulated immune responses could provide the information needed to identify such resistant individuals. Efforts to address this challenge are hampered by the vast immune diversity characterizing tumor microenvironments that remain largely understudied. It is thus important to more clearly elucidate the complex interactions that take place between the tumor microenvironment and host immune system.

The "Great Debate" at Immunotherapy Bridge 2020, December 3rd, 2020

As part of the 2020 Immunotherapy Bridge virtual congress (December 2nd–3rd, Italy), the Great Debate session featured counterpoint views from leading experts on three clinical questions in immunotherapy today. The first of these was whether antitumoral vaccination is still a treatment option. The second topic debated whether anti-programmed death (PD)-1/PD-ligand (L)1 blockade should be the backbone for immunotherapy combination. Finally, the use of innovative study designs and surrogate endpoints was considered from both an academic and industry perspective. For each topic, two experts presented the argument and counter-argument in support of two different points of view. As with previous Bridge congresses, the debates were assigned by meeting Chairs and positions taken by experts during the debates may not have necessarily reflected their respective personal view. The views summarised in this article are based on available evidence but may reflect personal interpretation of these data, clinical experience and subjective opinion of the speaker.

Dendritic cell vaccine therapy for colorectal cancer

Colorectal cancer (CRC) remains a leading cause of cancer-related deaths in the United States despite an array of available treatment options. Current standard-of-care interventions for this malignancy include surgical resection, chemotherapy, and targeted therapies depending on the disease stage. Specifically, infusion of anti-vascular endothelial growth factor agents in combination with chemotherapy was an important development in improving the survival of patients with advanced colorectal cancer, while also helping give rise to other forms of anti-angiogenic therapies. Yet, one approach by which tumor angiogenesis may be further disrupted is through the administration of a dendritic cell (DC) vaccine targeting tumor-derived blood vessels, leading to cytotoxic immune responses that decrease tumor growth and synergize with other systemic therapies. Early generations of such vaccines exhibited protection against various forms of cancer in pre-clinical models, but clinical results have historically been disappointing. Sipuleucel-T (Provenge®) was the first, and to-date, only dendritic cell-based therapy to receive FDA approval after significantly increasing overall survival in prostate cancer patients. The unparalleled success of Sipuleucel-T has helped revitalize the clinical development of dendritic cell vaccines, which will be examined in this review. We also highlight the promise of these vaccines to instill anti-angiogenic immunity for individuals with advanced colorectal cancer.

Perspectives in immunotherapy: meeting report from the "Immunotherapy Bridge" (December 4th-5th, 2019, Naples, Italy)

Over the last few years, numerous clinical trials and real-world experience have provided a large amount of evidence demonstrating the potential for long-term survival with immunotherapy agents across various malignancies, beginning with melanoma and extending to other tumours. The clinical success of immune checkpoint blockade has encouraged increasing development of other immunotherapies. It has been estimated that there are over 3000 immuno-oncology trials ongoing, targeting hundreds of disease and immune pathways. Evolving topics on cancer immunotherapy, including the state of the art of immunotherapy across various malignancies, were the focus of discussions at the Immunotherapy Bridge meeting (4-5 December, 2019, Naples, Italy), and are summarised in this report.

Dysregulated NF-κB-Dependent ICOSL Expression in Human Dendritic Cell Vaccines Impairs T-cell Responses in Patients with Melanoma

Therapeutic cancer vaccines targeting melanoma-associated antigens are commonly immunogenic but are rarely effective in promoting objective clinical responses. To identify critical molecules for activation of effective antitumor immunity, we have profiled autologous dendritic cell (DC) vaccines used to treat 35 patients with melanoma. We showed that checkpoint molecules induced by ex vivo maturation correlated with in vivo DC vaccine activity. Melanoma patient DCs had reduced expression of cell surface inducible T-cell costimulator ligand (ICOSL) and had defective intrinsic NF-κB signaling. Chromatin immunoprecipitation assays revealed NF-κB-dependent transcriptional regulation of ICOSL expression by DCs. Blockade of ICOSL on DCs reduced priming of antigen-specific CD8⁺ and CD4⁺ T cells from naïve donors in vitro Concentration of extracellular/soluble ICOSL released from vaccine DCs positively correlated with patient clinical outcomes, which we showed to be partially regulated by ADAM10/17 sheddase activity. These data point to the critical role of canonical NF-κB signaling, the regulation of matrix metalloproteinases, and DC-derived ICOSL in the specific priming of cognate T-cell responses in the cancer setting. This study supports the implementation of targeted strategies to augment these pathways for improved immunotherapeutic outcomes in patients with cancer.

Combining therapeutic vaccines with chemo- and immunotherapies in the treatment of cancer

INTRODUCTION

Breakthroughs in cancer immunotherapy have spurred interest in the development of vaccines to mediate prophylactic protection and therapeutic efficacy against primary tumors or to prevent relapse. However, immunosuppressive mechanisms employed by cancer cells to generate effective resistance have hampered clinical translation of therapeutic cancer vaccines. To enhance vaccine efficacy, the immunomodulatory properties of cytoreductive therapies could amplify a cancer-specific immune response.

AREAS COVERED

Herein, the authors discuss therapeutic cancer vaccines that harness whole cells and antigen-targeted vaccines. First, recent advancements in both autologous and allogeneic whole-cell vaccines and combinations with checkpoint blockade and chemotherapy are reviewed. Next, tumor antigen-targeted vaccines using peptide-based vaccines and DNA-vaccines are discussed. Finally, combination therapies using antigen-targeted vaccines are reviewed.

EXPERT OPINION

A deeper understanding of the immunostimulatory properties of cytoreductive therapies has supported their utility in combination therapies involving cancer vaccines as a potential strategy to induce a durable anti-tumor immune response for multiple types of cancers. Based on current evidence, combination therapies may have synergies that depend on the identity of the cytotoxic agent, vaccine target, dosing schedule, and cancer type. Together, these observations suggest that combining cancer vaccines with immunomodulatory cytoreductive therapy is a promising strategy for cancer therapy.