Vaccination against neoantigens induced in cross-priming cDC1 in vivo.

The conventional type 1 dendritic cells (cDC1) play a pivotal role in protective immunity against pathogens and cancer. However, their low frequency in the blood and tissues limits their use in immune therapy. We have recently described a method to vaccinate against neoantigens that are induced in tumor cells by targeted delivery of a TAP siRNA to dendritic cells using a TLR9 binding CpG oligonucleotide. Since TLR9 is also expressed in immune suppressive myeloid populations TLR9 targeting could reduce the effectiveness of this approach. Here, we describe a modular multivalent antibody platform to target the TAP siRNA to resident Clec9a expressing cDC1 and show that it leads to selective and sustained TAP downregulation in cDC1 and inhibits tumor growth in mice more effectively than CpG targeted siRNA. To induce DC maturation an agonistic CD40 antibody was administered to the siRNA treated mice. To obviate the need for a second drug formulation and reduce the risk of toxicity, we exploited the multivalent nature of this targeting platform to co-deliver the TAP siRNA and a DC maturation agent, a CpG containing oligonucleotide, to cDC1 in vivo and show that it was more effective than Clec9a targeting of TAP siRNA in combination with CD40 antibody. This study describes a way to manipulate the function of cDC1 cells in vivo using a broadly applicable antibody-based targeting platform to deliver multiple biological agents to specific cells in vivo to potentiate (immune) therapy and to probe the biology of specific cell types in their natural settings.

Remodeling of Stromal Immune Microenvironment by Urolithin A Improves Survival with Immune Checkpoint Blockade in Pancreatic Cancer.

Pancreatic ductal adenocarcinoma (PDAC) is a significant contributor to cancer-related morbidity and mortality, and it is known for its resistance to conventional treatment regimens, including chemotherapy and immune checkpoint blockade (ICB)-based therapies. We have previously shown that Urolithin A (Uro A), a gut microbial metabolite derived from pomegranates, can target and inhibit KRAS-dependent PI3K/AKT/mTOR signaling pathways to overcome therapeutic resistance and improve survival in PDAC. However, the effect of Uro A on the tumor immune microenvironment and its ability to enhance ICB efficacy has not been explored. This study demonstrates that Uro A treatment reduces stromal fibrosis and reinvigorates the adaptive T-cell immune response to overcome resistance to PD-1 blockade in a genetically engineered mouse model (GEMM) of PDAC. Flow cytometric-based analysis of Uro A-treated mouse tumors revealed a significant attenuation of immunosuppressive tumor-associated M2-like macrophages with a concurrent increase in the infiltration of CD4+ and CD8+ T cells with memory-like phenotype along with reduced expression of the exhaustion-associated protein, PD-1. Importantly, the combination of Uro A treatment with anti-PD-1 immunotherapy promoted enhancement of the antitumor response with increased infiltration of CD4+ Th1 cells, ultimately resulting in a remarkable improvement in overall survival in GEMM of PDAC. Overall, our findings provide preclinical evidence for the potential of Uro A as a novel therapeutic agent to increase sensitivity to immunotherapy in PDAC and warrant further mechanistic exploration in preclinical and clinical studies. Significance: Immunotherapeutic agents are ineffective against pancreatic cancer, mainly due to the immunosuppressive tumor microenvironment and stromal desmoplasia. Our current study demonstrates the therapeutic utility of a novel gut microbial metabolite, Uro A, to remodel the stromal-immune microenvironment and improve overall survival with anti-PD-1 therapy in pancreatic cancer.

The Quest for mRNA Vaccines.

The success of mRNA vaccines against COVID-19 is nothing short of a medical revolution. Given its chemical lability the use of mRNA as a therapeutic has been counterintuitive and met with skepticism. The development of mRNA-based COVID-19 vaccines was the culmination of long and painstaking efforts by many investigators spanning over 30 years and culminating with the seminal studies of Kariko and Weissman. This review will describe one chapter in this saga, studies that have shown that mRNA can function as a therapeutic. It started with our seminal observation that dendritic cells (DCs) transfected with mRNA in vitro administered to mice inhibits tumor growth, and led to first-in-human clinical trials with mRNA vaccines in cancer patients. The clinical development of this patient-specific DCs-mRNA approach and use on a larger scale was hindered by the challenges associated with personalized cell therapies. Confirmed and extended by many investigators, these studies did serve as impetus and motivation that led scientists to persevere, eventually leading to the development of simple, broadly applicable, and highly effective protocols of directly injecting mRNA into patients, culminating in the COVID-19 mRNA vaccines.

Immune Modulatory Short Noncoding RNAs Targeting the Glioblastoma Microenvironment.

Glioblastomas are heterogeneous and have a poor prognosis. Glioblastoma cells interact with their neighbors to form a tumor-permissive and immunosuppressive microenvironment. Short noncoding RNAs are relevant mediators of the dynamic crosstalk among cancer, stromal, and immune cells in establishing the glioblastoma microenvironment. In addition to the ease of combinatorial strategies that are capable of multimodal modulation for both reversing immune suppression and enhancing antitumor immunity, their small size provides an opportunity to overcome the limitations of blood-brain-barrier (BBB) permeability. To enhance glioblastoma delivery, these RNAs have been conjugated with various molecules or packed within delivery vehicles for enhanced tissue-specific delivery and increased payload. Here, we focus on the role of RNA therapeutics by appraising which types of nucleotides are most effective in immune modulation, lead therapeutic candidates, and clarify how to optimize delivery of the therapeutic RNAs and their conjugates specifically to the glioblastoma microenvironment.

Aptamer-mediated transcriptional gene silencing of Fox p 3 inhibits regulatory T cells and potentiates antitumor response.

The inhibition of immunosuppressive mechanisms may switch the balance between tolerance and surveillance, leading to an increase in antitumor activity. Regulatory T cells play an important role in the control of immunosuppression, exhibiting the unique property of inhibiting T cell proliferation. These cells migrate to tumor sites or may be generated at the tumor site itself from the conversion of lymphocytes exposed to tumor microenvironment signaling. Because of the high similarity between regulatory T cells and other lymphocytes, the available approaches to inhibit this population are nonspecific and may antagonize antitumor response. In this work we explore a new strategy for inhibition of regulatory T cells based on the use of a chimeric aptamer targeting a marker of immune activation harboring a small antisense RNA molecule for transcriptional gene silencing of Fox p 3, which is essential for the control of the immunosuppressive phenotype. The silencing of Fox p 3 inhibits the immunosuppressive phenotype of regulatory T cells and potentiates the effect of the GVAX antitumor vaccine in immunocompetent animals challenged with syngeneic tumors. This novel approach highlights an alternative method to antagonize regulatory T cell function to augment antitumor immune responses.

Vaccination against Nonmutated Neoantigens Induced in Recurrent and Future Tumors.

Vaccination of patients against neoantigens expressed in concurrent tumors, recurrent tumors, or tumors developing in individuals at risk of cancer is posing major challenges in terms of which antigens to target and is limited to patients expressing neoantigens in their tumors. Here, we describe a vaccination strategy against antigens that were induced in tumor cells by downregulation of the peptide transporter associated with antigen processing (TAP). Vaccination against TAP downregulation-induced antigens was more effective than vaccination against mutation-derived neoantigens, was devoid of measurable toxicity, and inhibited the growth of concurrent and future tumors in models of recurrence and premalignant disease. Human CD8+ T cells stimulated with TAPlow dendritic cells elicited a polyclonal T-cell response that recognized tumor cells with experimentally reduced TAP expression. Vaccination against TAP downregulation-induced antigens overcomes the main limitations of vaccinating against mostly unique tumor-resident neoantigens and could represent a simpler vaccination strategy that will be applicable to most patients with cancer.

Tumor-targeted silencing of the peptide transporter TAP induces potent antitumor immunity.

Neoantigen burden is a major determinant of tumor immunogenicity, underscored by recent clinical experience with checkpoint blockade therapy. Yet the majority of patients do not express, or express too few, neoantigens, and hence are less responsive to immune therapy. Here we describe an approach whereby a common set of new antigens are induced in tumor cells in situ by transient downregulation of the transporter associated with antigen processing (TAP). Administration of TAP siRNA conjugated to a broad-range tumor-targeting nucleolin aptamer inhibited tumor growth in multiple tumor models without measurable toxicity, was comparatively effective to vaccination against prototypic mutation-generated neoantigens, potentiated the antitumor effect of PD-1 antibody or Flt3 ligand, and induced the presentation of a TAP-independent peptide in human tumor cells. Treatment with the chemically-synthesized nucleolin aptamer-TAP siRNA conjugate represents a broadly-applicable approach to increase the antigenicity of tumor lesions and thereby enhance the effectiveness of immune potentiating therapies.

Osteopontin mediates glioblastoma-associated macrophage infiltration and is a potential therapeutic target.

Glioblastoma is highly enriched with macrophages, and osteopontin (OPN) expression levels correlate with glioma grade and the degree of macrophage infiltration; thus, we studied whether OPN plays a crucial role in immune modulation. Quantitative PCR, immunoblotting, and ELISA were used to determine OPN expression. Knockdown of OPN was achieved using complementary siRNA, shRNA, and CRISPR/Cas9 techniques, followed by a series of in vitro functional migration and immunological assays. OPN gene-deficient mice were used to examine the roles of non-tumor-derived OPN on survival of mice harboring intracranial gliomas. Patients with mesenchymal glioblastoma multiforme (GBM) show high OPN expression, a negative survival prognosticator. OPN is a potent chemokine for macrophages, and its blockade significantly impaired the ability of glioma cells to recruit macrophages. Integrin αvß5 (ITGαvß5) is highly expressed on glioblastoma-infiltrating macrophages and constitutes a major OPN receptor. OPN maintains the M2 macrophage gene signature and phenotype. Both tumor-derived and host-derived OPN were critical for glioma development. OPN deficiency in either innate immune or glioma cells resulted in a marked reduction in M2 macrophages and elevated T cell effector activity infiltrating the glioma. Furthermore, OPN deficiency in the glioma cells sensitized them to direct CD8+ T cell cytotoxicity. Systemic administration in mice of 4-1BB-OPN bispecific aptamers was efficacious, increasing median survival time by 68% (P < 0.05). OPN is thus an important chemokine for recruiting macrophages to glioblastoma, mediates crosstalk between tumor cells and the innate immune system, and has the potential to be exploited as a therapeutic target.

An RNA toolbox for cancer immunotherapy.

Cancer immunotherapy has revolutionized oncology practice. However, current protein and cell therapy tools used in cancer immunotherapy are far from perfect, and there is room for improvement regarding their efficacy and safety. RNA-based structures have diverse functions, ranging from gene expression and gene regulation to pro-inflammatory effects and the ability to specifically bind different molecules. These functions make them versatile tools that may advance cancer vaccines and immunomodulation, surpassing existing approaches. These technologies should not be considered as competitors of current immunotherapies but as partners in synergistic combinations and as a clear opportunity to reach more efficient and personalized results. RNA and RNA derivatives can be exploited therapeutically as a platform to encode protein sequences, provide innate pro-inflammatory signals to the immune system (such as those denoting viral infection), control the expression of other RNAs (including key immunosuppressive factors) post-transcriptionally and conform structural scaffoldings binding proteins that control immune cells by modifying their function. Nascent RNA immunotherapeutics include RNA vaccines encoding cancer neoantigens, mRNAs encoding immunomodulatory factors, viral RNA analogues, interference RNAs and protein-binding RNA aptamers. These approaches are already in early clinical development with promising safety and efficacy results.

Hapten-mediated recruitment of polyclonal antibodies to tumors engenders antitumor immunity.

Uptake of tumor antigens by tumor-infiltrating dendritic cells is limiting step in the induction of tumor immunity, which can be mediated through Fc receptor (FcR) triggering by antibody-coated tumor cells. Here we describe an approach to potentiate tumor immunity whereby hapten-specific polyclonal antibodies are recruited to tumors by coating tumor cells with the hapten. Vaccination of mice against dinitrophenol (DNP) followed by systemic administration of DNP targeted to tumors by conjugation to a VEGF or osteopontin aptamer elicits potent FcR dependent, T cell mediated, antitumor immunity. Recruitment of αGal-specific antibodies, the most abundant naturally occurring antibodies in human serum, inhibits tumor growth in mice treated with a VEGF aptamer-αGal hapten conjugate, and recruits antibodies from human serum to human tumor biopsies of distinct origin. Thus, treatment with αGal hapten conjugated to broad-spectrum tumor targeting ligands could enhance the susceptibility of a broad range of tumors to immune elimination.

NFκB in Pancreatic Stellate Cells Reduces Infiltration of Tumors by Cytotoxic T Cells and Killing of Cancer Cells, via Up-regulation of CXCL12.

BACKGROUND & AIMS: Immunotherapies are ineffective against pancreatic cancer. We investigated whether the activity of nuclear factor (NF)κB in pancreatic stromal cells contributes to an environment that suppresses antitumor immune response. METHODS: Pancreata of C57BL/6 or Rag1-/- mice were given pancreatic injections of a combination of KrasG12D/+; Trp53 R172H/+; Pdx-1cre (KPC) pancreatic cancer cells and pancreatic stellate cells (PSCs) extracted from C57BL/6 (control) or mice with disruption of the gene encoding the NFκB p50 subunit (Nfkb1 or p50-/- mice). Tumor growth was measured as an endpoint. Other mice were given injections of Lewis lung carcinoma (LLC) lung cancer cells or B16-F10 melanoma cells with control or p50-/- fibroblasts. Cytotoxic T cells were depleted from C57BL/6 mice by administration of antibodies against CD8 (anti-CD8), and growth of tumors from KPC cells, with or without control or p50-/- PSCs, was measured. Some mice were given an inhibitor of CXCL12 (AMD3100) and tumor growth was measured. T-cell migration toward cancer cells was measured using the Boyden chamber assay. RESULTS: C57BL/6 mice coinjected with KPC cells (or LLC or B16-F10 cells) and p50-/- PSCs developed smaller tumors than mice given injections of the cancer cells along with control PSCs. Tumors that formed when KPC cells were injected along with p50-/- PSCs had increased infiltration by activated cytotoxic T cells along with decreased levels of CXCL12, compared with tumors grown from KPC cells injected along with control PSCs. KPC cells, when coinjected with control or p50-/- PSCs, developed the same-size tumors when CD8+ T cells were depleted from C57BL/6 mice or in Rag1-/- mice. The CXCL12 inhibitor slowed tumor growth and increased tumor infiltration by cytotoxic T cells. In vitro expression of p50 by PSCs reduced T-cell migration toward and killing of cancer cells. When cultured with cancer cells, control PSCs expressed 10-fold higher levels of CXCL12 than p50-/- PSCs. The CXCL12 inhibitor increased migration of T cells toward KPC cells in culture. CONCLUSIONS: In studies of mice and cell lines, we found that NFκB activity in PSCs promotes tumor growth by increasing expression of CXCL12, which prevents cytotoxic T cells from infiltrating the tumor and killing cancer cells. Strategies to block CXCL12 in pancreatic tumor cells might increase antitumor immunity.

Potentiating tumor immunity using aptamer-targeted RNAi to render CD8+ T cells resistant to TGFß inhibition.

TGFß secreted by tumor cells and/or tumor infiltrating stromal cells is a key mediator of tumor growth and immune suppression at the tumor site. Nonetheless, clinical trials in cancer patients targeting the TGFß pathway exhibited at best a modest therapeutic benefit. A likely reason, a common limitation of many cancer drugs, is that the physiologic roles of TGFß in tissue homeostasis, angiogenesis, and immune regulation precluded the dose escalation necessary to achieve a profound clinical response. Murine studies have suggested that countering immune suppressive effects of TGFß may be sufficient to inhibit tumor growth. Here we describe an approach to render vaccine-activated CD8+ T cells transiently resistant to TGFß inhibition using an siRNA against Smad4 to inhibit a key step in the canonical TGFß signaling pathway. The siRNA was targeted to vaccine activated CD8+ T cells in the mouse by conjugation to a 4-1BB binding oligonucleotide (ODN) aptamer ligand (4-1BB-Smad4 conjugate). In vitro the 4-1BB-Smad4 conjugate rendered T cells partially resistant to TGFß inhibition, and treatment of tumor bearing mice with systemically administered 4-1BB-Smad4 conjugate enhanced vaccine- and irradiation-induced antitumor immunity. Limiting the inhibitory effects of TGFß to tumor-specific T cells will not interfere with its multiple physiologic roles and hence reduce the risk of toxicity.

A TIM-3 Oligonucleotide Aptamer Enhances T Cell Functions and Potentiates Tumor Immunity in Mice.

T cell immunoglobulin-3 (TIM-3) is a negative regulator of interferon-γ (IFN-γ) secreting CD4+ T cells and CD8+ T cytotoxic cells. Recent studies have highlighted the role of TIM-3 as an important mediator of CD8+ T cell exhaustion in the setting of chronic viral infections and cancer. In murine tumor models, antibody blockade of TIM-3 with anti-TIM-3 antibodies as monotherapy has no or minimal antitumor activity, suggesting that TIM-3 signaling exerts an accessory or amplifying effect in keeping immune responses in check. Using a combined bead and cell-based systemic evolution of ligands by exponential enrichment (SELEX) protocol, we have isolated nuclease-resistant oligonucleotide aptamer ligands that bind to cell-associated TIM-3 with high affinity and specificity. A trimeric form of the TIM-3 aptamer blocked the interaction of TIM-3 with Galectin-9, reduced cell death, and enhanced survival, proliferation, and cytokine secretion in vitro. In tumor-bearing mice, the aptamer delayed tumor growth as monotherapy and synergized with PD-1 antibody in prolonging the survival of the tumor-bearing mice. Both in vitro and in vivo, the trimeric aptamer displayed superior activity compared to the currently used RMT3-23 monoclonal antibody. This study suggests that multi-valent aptamers could represent an alternative platform to generate potent ligands to manipulate the function of TIM-3 and other immune modulatory receptors.

Aptamer-Targeted Attenuation of IL-2 Signaling in CD8+ T Cells Enhances Antitumor Immunity.

Immune responses elicited against cancer using existing therapies such as vaccines or immune stimulatory antibodies are often not curative. One way to potentiate antitumor immunity is to enhance the long-term persistence of anti-tumor CD8+ T cells. Studies have shown that the persistence of activated CD8+ T cells is negatively impacted by the strength of interleukin 2 (IL-2) signaling. Here, we used small interfering RNAs (siRNAs) against CD25 (IL-2Rα) to attenuate IL-2 signaling in CD8+ T cells. The siRNAs were targeted to 4-1BB-expressing CD8+ T cells by conjugation to a 4-1BB-binding oligonucleotide aptamer. Systemic administration of the 4-1BB aptamer-CD25 siRNA conjugate downregulated CD25 mRNA only in 4-1BB-expressing CD8+ T cells promoting their differentiation into memory cells. Treatment with the 4-1BB aptamer-CD25 siRNA conjugates enhanced the antitumor response of a cellular vaccine or local radiation therapy. Indicative of the generality of this approach, 4-1BB aptamer-targeted delivery of an Axin-1 siRNA, a rate-limiting component of the ß-catenin destruction complex, enhanced CD8+ T cell memory development and antitumor activity. These findings show that aptamer-targeted siRNA therapeutics can be used to modulate the function of circulating CD8+ T cells, skewing their development into long-lasting memory CD8+ T cells, and thereby potentiating antitumor immunity.

Radiation-Induced Enhancement of Antitumor T-cell Immunity by VEGF-Targeted 4-1BB Costimulation.

Radiotherapy can elicit systemic immune control of local tumors and distant nonirradiated tumor lesions, known as the abscopal effect. Although this effect is enhanced using checkpoint blockade or costimulatory antibodies, objective responses remain suboptimal. As radiotherapy can induce secretion of VEGF and other stress products in the tumor microenvironment, we hypothesized that targeting immunomodulatory drugs to such products will not only reduce toxicity but also broaden the scope of tumor-targeted immunotherapy. Using an oligonucleotide aptamer platform, we show that radiation-induced VEGF-targeted 4-1BB costimulation potentiated both local tumor control and abscopal responses with equal or greater efficiency than 4-1BB, CTLA-4, or PD1 antibodies alone. Although 4-1BB and CTLA-4 antibodies elicited organ-wide inflammatory responses and tissue damage, VEGF-targeted 4-1BB costimulation produced no observable toxicity. These findings suggest that radiation-induced tumor-targeted immunotherapy can improve the therapeutic index and extend the reach of immunomodulatory agents. Cancer Res; 77(6); 1310-21. ©2017 AACR.

4-1BB Aptamer-Based Immunomodulation Enhances the Therapeutic Index of Radiation Therapy in Murine Tumor Models.

PURPOSE: To report a novel strategy using oligonucleotide aptamers to 4-1BB as an alternate method for costimulation, and show that combinatorial therapy with radiation improves the therapeutic ratio over equivalent monoclonal antibodies. METHODS AND MATERIALS: Subcutaneous 4T1 (mouse mammary carcinoma) tumors were established (approximately 100 mm(3)), and a radiation therapy (RT) dose/fractionation schedule that optimally synergizes with 4-1BB monoclonal antibody (mAb) was identified. Comparable tumor control and animal survival was observed when either 4-1BB antibody or aptamer were combined with RT using models of breast cancer and melanoma (4T1 and B16-F10). Off-target CD8(+) T-cell toxicity was evaluated by quantification of CD8(+) T cells in livers and spleens of treated animals. RESULTS: When combined with 4-1BB mAb, significant differences in tumor control were observed by varying RT dose and fractionation schedules. Optimal synergy between RT and 4-1BB mAb was observed at 5 Gy × 6. Testing 4-1BB mAb and aptamer independently using the optimal RT (5 Gy × 6 for 4T1/Balb/c and 12 Gy × 1 for B16/C57BL6J mouse models) revealed equivalent tumor control using 4-1BB aptamer and 4-1BB mAb. 4-1BB mAb, but not 4-1BB aptamer-treated animals, exhibited increased lymphocytic liver infiltrates and increased splenic and liver CD8(+) T cells. CONCLUSIONS: Radiation therapy synergizes with 4-1BB mAb, and this effect is dependent on RT dose and fractionation. Tumor control by 4-1BB aptamer is equivalent to 4-1BB mAb when combined with optimal RT dose, without eliciting off-target liver and spleen CD8(+) expansion. 4-1BB aptamer-based costimulation affords a comparable and less toxic strategy to augment RT-mediated tumor control.

Tipping a favorable CNS intratumoral immune response using immune stimulation combined with inhibition of tumor-mediated immune suppression.

High-grade gliomas are notoriously heterogeneous regarding antigen expression, effector responses, and immunosuppressive mechanisms. Therefore, combinational immune therapeutic approaches are more likely to impact a greater number of patients and result in longer, durable responses. We have previously demonstrated the monotherapeutic effects of miR-124, which inhibits the signal transducer and activator of transcription 3 (STAT3) immune suppressive pathway, and immune stimulatory 4-1BB aptamers against a variety of malignancies, including genetically engineered immune competent high-grade gliomas. To evaluate potential synergy, we tested an immune stimulatory aptamer together with microRNA-124 (miRNA-124), which blocks tumor-mediated immune suppression, and found survival to be markedly enhanced, including beyond that produced by monotherapy. The synergistic activity appeared to be not only secondary to enhanced CD3(+) cell numbers but also to reduced macrophage immune tumor trafficking, indicating that a greater therapeutic benefit can be achieved with approaches that both induce immune activation and inhibit tumor-mediated immune suppression within the central nervous system (CNS) tumors.

The Human Vaccines Project: A roadmap for cancer vaccine development.

Cancer vaccine development has been vigorously pursued for 40 years. Immunity to tumor antigens can be elicited by most vaccines tested, but their clinical efficacy remains modest. We argue that a concerted international effort is necessary to understand the human antitumor immune response and achieve clinically effective cancer vaccines.