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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.

Supplementary Figures and Table

Despite the recent successes of using immune modulatory Abs in patients with cancer, autoimmune pathologies resulting from the activation of self-reactive T cells preclude the dose escalations necessary to fully exploit their therapeutic potential. To reduce the observed and expected toxicities associated with immune modulation, here we describe a clinically feasible and broadly applicable approach to limit immune costimulation to the disseminated tumor lesions of the patient, whereby an agonistic 4-1BB oligonucleotide aptamer is targeted to the tumor stroma by conjugation to an aptamer that binds to a broadly expressed stromal product, VEGF. This approach was predicated on the premise that by targeting the costimulatory ligands to products secreted into the tumor stroma, the T cells will be costimulated before their engagement of the MHC–peptide complex on the tumor cell, thereby obviating the need to target the costimulatory ligands to noninternalizing cell surface products expressed on the tumor cells. Underscoring the potency of stroma-targeted costimulation and the broad spectrum of tumors secreting VEGF, in preclinical murine tumor models, systemic administration of the VEGF-targeted 4-1BB aptamer conjugates engendered potent antitumor immunity against multiple unrelated tumors in subcutaneous, postsurgical lung metastasis, methylcholantrene-induced fibrosarcoma, and oncogene-induced autochthonous glioma models, and exhibited a superior therapeutic index compared with nontargeted administration of an agonistic 4-1BB Ab or 4-1BB aptamer. Cancer Immunol Res; 2(9); 867–77. ©2014 AACR.

PDF file - 87K, Supplementary Figure 1. Sequence and secondary structure ofVEGF-4-1BB and OPN-4-1BB aptamer conjugates. Supplementary Figure 2. Biodistribution of VEGF-4-1BB aptamer conjugates. Supplementary Figure 3. OPN-targeted costimulation inhibits tumor growth.

Biodistribution of VEGF-4-1BB conjugate. Survival assay in MCA induced fibrosarcoma model. Cytokine levels in treated animals. Tumor volume studies with combinatorial therapy in Balb/c model. Histology and morphology for toxicity profiles.

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.

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

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 Foxp3, which is essential for the control of the immunosuppressive phenotype. The silencing of Foxp3 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., Graphical abstract, Here we have generated a chimeric aptamer that binds to 4-1BB receptor that is constitutively expressed in Tregs to vehiculate a transcriptional RNAi silencing molecule targeting FoxP3. Silencing FoxP3 in Tregs may inhibit immunosuppressive phenotype and potentiate antitumor response.

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.

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.

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.

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 α(v)β(5) (ITGαvβ5) 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.

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., The anti-tumour immune response greatly depends on the number of tumour neoantigens. Here the authors show in mouse models that a therapeutic strategy aimed at increasing the number of neoantigens via downregulating TAP, an antigen processing associated protein, enhances anti-tumour immunity and the efficacy of immunotherapy.

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.

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.

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.

Modulating the function of immune receptors with antibodies is ushering in a new era in cancer immunotherapy. With the notable exception of PD-1 blockade used as monotherapy, immune modulation can be associated with significant toxicities that are expected to escalate with the development of increasingly potent immune therapies. A general way to reduce toxicity is to target immune potentiating drugs to the tumor or immune cells of the patient. This Crossroads article discusses a new class of nucleic acid–based immune-modulatory drugs that are targeted to the tumor or to the immune system by conjugation to oligonucleotide aptamer ligands. Cell-free chemically synthesized short oligonucleotide aptamers represent a novel and emerging platform technology for generating ligands with desired specificity that offer exceptional versatility and feasibility in terms of development, manufacture, and conjugation to an oligonucleotide cargo. In proof-of-concept studies, aptamer ligands were used to target immune-modulatory siRNAs or aptamers to induce neoantigens in the tumor cells, limit costimulation to the tumor lesion, or enhance the persistence of vaccine-induced immunity. Using increasingly relevant murine models, the aptamer-targeted immune-modulatory drugs engendered protective antitumor immunity that was superior to that of current “gold-standard” therapies in terms of efficacy and lack of toxicity or reduced toxicity. To overcome immune exhaustion aptamer-targeted siRNA conjugates could be used to downregulate intracellular mediators of exhaustion that integrate signals from multiple inhibitory receptors. Recent advances in aptamer development and second-generation aptamer–drug conjugates suggest that we have only scratched the surface. Cancer Immunol Res; 3(11); 1195–200. ©2015 AACR.

High-Throughput (HT) SELEX combines SELEX (Systematic Evolution of Ligands by EXponential Enrichment), a method for aptamer discovery, with massively parallel sequencing technologies. This emerging technology provides data for a global analysis of the selection process and for simultaneous discovery of a large number of candidates but currently lacks dedicated computational approaches for their analysis. To close this gap, we developed novel in-silico methods to analyze HT-SELEX data and utilized them to study the emergence of polymerase errors during HT-SELEX. Rather than considering these errors as a nuisance, we demonstrated their utility for guiding aptamer discovery. Our approach builds on two main advancements in aptamer analysis: AptaMut-a novel technique allowing for the identification of polymerase errors conferring an improved binding affinity relative to the 'parent' sequence and AptaCluster-an aptamer clustering algorithm which is to our best knowledge, the only currently available tool capable of efficiently clustering entire aptamer pools. We applied these methods to an HT-SELEX experiment developing aptamers against Interleukin 10 receptor alpha chain (IL-10RA) and experimentally confirmed our predictions thus validating our computational methods.

TGFβ 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 TGFβ pathway exhibited at best a modest therapeutic benefit. A likely reason, a common limitation of many cancer drugs, is that the physiologic roles of TGFβ 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 TGFβ may be sufficient to inhibit tumor growth. Here we describe an approach to render vaccine-activated CD8+ T cells transiently resistant to TGFβ inhibition using an siRNA against Smad4 to inhibit a key step in the canonical TGFβ 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 TGFβ 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 TGFβ to tumor-specific T cells will not interfere with its multiple physiologic roles and hence reduce the risk of toxicity.

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.

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 β-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.

The paucity of costimulation at the tumor site compromises the ability of tumor-specific T cells to eliminate the tumor. The recent U.S. Food and Drug Administration approval of ipilumimab, an antibody that blocks the inhibitory action of CTLA-4, and clinical trials targeting 4-1BB and PD-1 or PD-L1, have underscored the therapeutic potential of using immunomodulatory antibodies to stimulate protective immunity in human patients. Nonetheless, systemic administration of immunomodulatory antibodies has been associated with dose-limiting autoimmune pathologies, conceivably reflecting also the activation of resident autoreactive T cells. Arguably, targeting immunomodulatory ligands to the disseminated tumor lesions of the patient would reduce such drug-associated toxicities. We have recently developed a new class of inhibitory (CTLA-4) and agonistic (4-1BB and OX-40) ligands composed of short oligonucleotide (ODN) aptamers that exhibited bioactivities comparable or superior to that of antibodies. To reduce toxicity, the immunomodulatory aptamers were targeted to the tumor by conjugation to a second aptamer that bound to a product expressed on the surface of the tumor cell, the targeting aptamer, generating a bispecific aptamer conjugate analogous to bispecific antibodies. In a proof-of-concept study in mice, we have shown that an agonistic 4-1BB–binding aptamer conjugated to a prostate-specific membrane antigen (PSMA)–binding aptamer led to the inhibition of PSMA-expressing tumors, was more effective than, and synergized with, vaccination, and exhibited a superior therapeutic index compared with nontargeted costimulation with 4-1BB antibodies or 4-1BB aptamers. The cell-free chemically synthesized ODN aptamers offer significant advantages over antibodies in terms of synthesis, cost, as well as conjugation chemistry needed to generate bispecific ligand fusions. Clin Cancer Res; 19(5); 1054–62. ©2012 AACR.

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.

Interleukin-10 (IL-10) is a key suppressor of inflammation in chronic infections and in cancer. In mice, the inability of the immune system to clear viral infections or inhibit tumor growth can be reversed by antibody-mediated blockade of IL-10 action. We used a modified selection protocol to isolate RNA-based, nuclease-resistant, aptamers that bind to the murine IL-10 receptor. After 5 rounds of selection high-throughput sequencing (HTS) was used to analyze the library. Using distribution statistics on about 11 million sequences, aptamers were identified which bound to IL-10 receptor in solution with low K(d). After 12 rounds of selection the predominant IL-10 receptor-binding aptamer identified in the earlier rounds remained, whereas other high-affinity aptamers were not detected. Prevalence of certain nucleotide (nt) substitutions in the sequence of a high-affinity aptamer present in round 5 was used to deduce its secondary structure and guide the truncation of the aptamer resulting in a shortened 48-nt long aptamer with increased affinity. The aptamer also bound to IL-10 receptor on the cell surface and blocked IL-10 function in vitro. Systemic administration of the truncated aptamer was capable of inhibiting tumor growth in mice to an extent comparable to that of an anti- IL-10 receptor antibody.

Development of therapeutic strategies to prevent recurrence in cancer patients, or tumor progression in individuals at high risk of developing cancer, has been challenging given the long and often unpredictable time to the emergence of the malignant tumors. Mutation-generated neoantigens represent the most potent antigens to induce antitumor immunity, yet the ability to predict which neoantigens will be expressed in future tumors is at present not an option.To overcome the limitations of targeting mutated neoantigens, we have developed a simple and broadly applicable approach to induce neoantigens in tumor cells in situ by reducing the expression of peptide transporter TAP, whereby a TAP-specific siRNA is targeted to tumor cells in mice by conjugation to a broad-range nucleolin-binding aptamer. Nucleolin, normally expressed in the cytoplasm and nucleolus of all somatic cells, is translocated to the cell surface of most murine and human tumors and hence could serve as an almost universal target to deliver therapeutics to tumors in vivo. Previous results have demonstrated that genetic ablation of TAP not only inhibits the canonical antigen processing pathway but also upregulates alternative pathways presenting new epitopes, essentially neoantigens, that can be recognized by the immune system to elicit effective CD8+ T-cell responses. Such epitopes are shared among all (tumor) cells in which TAP is downregulated, corresponding to the functional equivalent of clonal mutation-generated neoantigens. Our study shows that transiently increasing the neoantigen burden of tumor cells in situ by targeted downregulation of TAP represent a potent way of generating antitumor immunity in the absence of measurable toxicity.Exploiting the ability to induce neoantigens in situ, we are developing a novel vaccination strategy targeting potent neoantigens to control the growth of the future tumors—whereby mice in remission or with premalignant lesions are first vaccinated against TAP downregulation-induced neoantigens, and when or if tumor develops the same antigens are induced in the tumor, termed prorapeutic vaccination (prophylactic + therapeutic). To induce an immune response against TAP downregulation-induced neoantigens, mice were vaccinated with TAP siRNAs that are targeted to DC in situ by conjugation to a short CpG oligonucleotide leading to the downregulation of TAP, expression of neoantigens, as well as activation of the DC, and thereby priming of a potent T-cell response. To induce neoantigens in the future tumors, the TAP siRNA is targeted to the developing tumor lesion by conjugation to the nucleolin (Nucl) aptamer. Both Nucl and CpG targeted siRNA are administered systemically via intraperitoneal injection to reach the disseminated tumor lesions and resident DC present throughout the body. In murine models of recurrence and premalignant disease, prorapeutic vaccination elicited an adaptive and innate antitumor immune response and inhibited tumor growth. The prorapeutic vaccination approach was more effective than vaccinating against prototypic mutated neoantigens, and did not elicit measurable autoimmune toxicity, in stark contrast to a comparatively therapeutic dose of CTLA-4.The ability to vaccinate against experimentally induced neoantigens using a broadly applicable procedure with two chemically synthesized reagents, introduces a new paradigm in cancer immunotherapy of vaccinating against neoantigens induced in future tumors, to prevent recurrence in patients in remission or preventing tumor development in individuals at high risk of developing cancer. Citation Format: Greta Garrido Hidalgo, Brett Schrand, Ailem Rabasa, Agata Levay, Tal Gefen, Giri Bhuwan Bhuwan, Anthony R. Ferrantella, Vikas Dudeja, Koen Marijt, Thorbald T. van Hall, Eli Gilboa. Vaccination against TAP downregulation-induced neoantigens to prevent future tumor development in the setting of recurrence or premalignancy [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr B111.

Development of therapeutic strategies to prevent recurrence in cancer patients, or tumor progression in at risk individuals has been challenging given the long and often unpredictable time to the emergence of the malignant tumors. Neoantigens represent the most potent antigens to induce antitumor immunity, yet the ability to predict which neoantigens will be expressed in future tumors is at present not an option. We have developed a simple and broadly applicable approach to induce neoantigens in tumor cells in situ by reducing the expression of antigen processing mediators like TAP, ERAAP, or invariant chain (Ii), using siRNAs that were targeted to tumor cells by conjugation to a nucleolin-binding aptamer. Exploiting the ability to induce neoantigens in situ, we describe a novel vaccination strategy targeting potent neoantigens to control the growth of the future tumors whereby patients in remission or individuals at risk are first vaccinated against the antigen processing downregulation-induced neoantigens and when or if tumor develops the same antigens are induced in the tumor, termed prorapeutic vaccination (prophylactic + therapeutic). Mice were vaccinated against the TAP downregulation-induced neoantigens by targeting the corresponding siRNAs to dendritic cells (DC) in situ via conjugation to a short CpG oligonucleotide (ODN); the CpG ODN also activated the targeted DC to avoid induction of tolerance against the neoantigens. Vaccination with CpG ODN-TAP siRNA conjugates inhibited subsequently implanted or autochthonous tumors in several tumor models, provided the said neoantigens were also induced in the tumor by nucleolin aptamer-targeted siRNA inhibition of TAP. The CpG-siRNA and nucleolin aptamer-siRNA conjugates are simple, chemically- synthesized, off-the-shelf, and broadly applicable reagents to vaccinate against neoantigens and control the growth of future tumors irrespective of their origin. Citation Format: Greta Garrido Hidalgo, Brett Schrand, Ailem Rabasa, Agata Levay, Alexey Berezhnoy, Shrey Modi, Giri Bhuwan Bhuwan, Vikas Dudeja, Elien Doorduijn, Thorbald van Hall, Eli Gilboa. Vaccination against neoantigens induced in future tumors in the setting of recurrence and premalignancy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 264.

Introduction: Pancreatic ductal adenocarcinoma, one of the most aggressive malignancies and is refractory to Immunotherapy. This, in part, is mediated by the fibrotic stroma, creating an immune-suppressive microenvironment. CXCL12/SDF-1 has been shown to act as a chemo-repellant in several cancers. Therefore, we evaluated the role of stromal CXCL-12 in mediating an immunosuppressive phenotype within the pancreatic tumor. Methods: Pancreatic cancer cells harvested from KPC, a genetically engineered mouse model for PDAC, were either injected or alone or co-injected with pancreatic stellate cells (PSCs) extracted from WT (C57/BL6) mice to induce tumors. SDF-1 expression levels were detected by IF and q-RT PCR in tumor sections. An SDF-1 inhibitor, AMD3100 (2mg/kg), or vehicle was administered i.p for 21 days in tumor bearing mice and tumor growth and immune infiltration were assessed as an end point by flow cytometry. To evaluate the T cell migration in vitro, PSCs were pre-treated with SDF-1 neutralizing antibody, educated with KPC cancer cells and further co-cultured with splenic CD3+ T cells extracted from KPC mice. Results: In vitro results showed markedly increased secretion of SDF-1 by PSCs and neutralization of SDF-1 led to increased T-cell migration when cultured with cancer cells alone. We also evaluated the effect of inhibition of SDF-CXCR4 axis on tumor growth. Co-injection of KPC with WT PSC formed larger tumors with increased section of CXCL-12 as compared to when KPC cells were injected alone. Interestingly, Inhibition of SDF-1-CXCR4 interaction with AMD3100 led to reduced tumor growth with increased infiltration of activated CD8+ cytotoxic T cells as compared to the saline-treated mice. Conclusion: Our results indicate that stromal cells contribute to tumor progression by blocking the infiltration of cytotoxic T cells via secretion of CXCL-12. Targeting CXCL-12 could pave the way for designing better therapeutic interventions against pancreatic cancer. Citation Format: Bharti Garg, Anthony Ferrantella, Bhuwan Giri, Shrey Modi, Vrisketan Sethi, Saba Kurtom, Sulagna Banerjee, Ramakrishnan Sundaram, Eli Gilboa, Ashok Saluja, Vikas Dudeja. Cxcl-12-cxcr4 inhibition enhances immune response in pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4502.

Programmed death 1 (PD-1) and its ligand PD-L1 provide inhibitory signals that affect the balance of T cell activation, playing major roles in tumor immune escape. Inhibition of negative regulators of T cell activation effectively remove signals that restrain T cell proliferation and gain of effector function. Hence, disruption of the PD-1/PD-L1 signaling pathway by the use of monoclonal antibodies (mAbs) can improve tumor control by enhancement of the endogenous antitumor immune responses. Toll-like receptors (TLR) are a specialized set of pathogen recognition receptors found in innate and adaptive immune system cells. Activation of these receptors by danger-associated molecules such as bacterial DNA or RNA, initiate signaling cascades leading to protective immune responses. Synthetic oligodeoxynucleotides (ODNs) containing unmethylated CpG motifs can mimic bacterial DNA and therefore function as ligands for intracellular TLR9, prompting consequential activation of immune responses. The purpose of this study was to assess the feasibility of using PD-1/PD-L1 mAbs conjugated to TLR9 agonists (ODNs) as a novel strategy for tumor-targeting immune checkpoint signaling and activation of immune cells. Antibodies recognizing PD-1 and PDL-1 were covalently modified with a 21mer ssDNA oligonucleotide linker sequence that served as an anchor site for the ODNs synthesized with a 3' extension. Annealing of complementary strands formed mAb-ODN conjugates. Quantification of ODNs per PD-1 or PDL-1 mAbs was verified by flow cytometry. Functionality of PD-1 and PDL-1-ODN conjugates was analyzed in vitro using splenocyte cultures and cell proliferation was evaluated by incorporation of radiolabeled H3 Thymidine. In vivo experiments were carried out using Balb/c mice bearing 4T1 subcutaneous tumors. Flow cytometry analysis confirmed each modified mAb had 5 linker sequences available to bind ODNs, and also defined the binding capability of mAb portion of the conjugate to epitope target. Splenocytes proliferation at day 5 after treatment revealed that PD-1 and PDL-1 conjugated to ODNs have significantly increased proliferation in comparison to non-conjugated mAb and ODN controls. These results indicate that conjugation of mAb-ODN is feasible and that conjugation does not affect PD-1 and PDL-1 antibody functionality. Interestingly, in vivo experiments demonstrated PDL-1-ODN but not PD1-ODN conjugate affects 4T1 tumor growth. Use of this approach to improve the therapeutic index of immunotherapeutic mAbs requires further study and validation in different murine tumor models. Citation Format: Ana Paula Benaduce, Tal Gefen, Sergio Rodriguez, Brian Marples, Eli Gilboa, Adrian Ishkanian. Upgrading cancer immunotherapy: Checkpoint blockade mAb-ODN conjugate [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4702.

Whereas tumor progression in cancer patients can elicit a weak immune response which keeps the tumor in check, albeit transiently, the weak antigenicity of the tumor provides the time and opportunity for the tumor to elaborate immune evasion mechanisms. Weak antigenicity is, therefore, the root cause why tumors escape immune control. We have recently described a way to activate the antitumor immune response that is fundamentally different from current strategies collectively referred to as “cancer vaccination,” because instead of stimulating immune responses against existing and mostly weak, tumor antigens, novel, and thereby potent, antigens are induced de novo in the disseminated tumor lesions of the patient. The approach is to inhibit a process in the tumor cells known as nonsense-mediated mRNA decay (NMD). The physiological role of NMD is to eliminate defective products generated in the cells, and therefore inhibiting the NMD process will lead to the accumulation of defective products, some of which will encode novel, and thereby potent, antigens to which the immune system has not been tolerized. Inhibition of NMD was accomplished using chemically synthesized siRNAs to downregulate key mediators of the NMD process such as Smg-1 or Upf-2. However, since NMD is a constitutive process that operates in all the somatic cells of the body, global inhibition of NMD could lead to system-wide autoimmune pathology. To obviate the risk of autoimmunity, NMD inhibition was limited to the disseminated tumor lesions by targeted delivery of siRNAs conjugated to oligonucleotide aptamer ligands that bind to receptors expressed preferentially, if not exclusively, on the tumor cells. We have shown that in subcutaneous and metastatic murine tumor models, the tumor-targeted delivery of NMD factor siRNAs led to significant inhibition of tumor growth which was superior to that of a gold standard “conventional” cancer vaccination protocol. Tumor-targeted NMD inhibition forms the basis of a simple, broadly useful, and clinically feasible approach to enhance the antigenicity of disseminated tumors leading to their immune recognition and rejection. The cell-free chemically synthesized oligonucleotide backbone of aptamer–siRNAs reduces the risk of immunogenicity and enhances the feasibility of generating reagents suitable for clinical use.

Objective Regulatory T cells are crucial for immune homeostasis and an impaired regulatory T cell function results in many pathological conditions. Regulatory T cells have already been described to be protective in atherosclerosis. However the exact contribution of Foxp3-expressing natural regulatory T cells in atherosclerosis has not been elucidated yet. Methods and results In this study we vaccinated LDL receptor deficient mice with dendritic cells which are transfected with Foxp3 encoding mRNA and studied the effect on initial atherosclerosis. Vaccination against Foxp3 resulted in a reduction of Foxp3 + regulatory T cells in several organs and in an increase in initial atherosclerotic lesion formation. Furthermore we observed an increase in plaque cellularity and increased T cell proliferation in the Foxp3 vaccinated mice. Conclusion We further establish the protective role of Tregs in atherosclerosis. The results illustrate the important role for Foxp3-expressing regulatory T cells in atherosclerosis, thereby providing a potential opportunity for therapeutic intervention against this disease.

Antibodies are natural nanomaterials and have been widely used for targeted cell labeling. However, the applications of antibodies are often limited by their large size and instability. The purpose of this study is to develop a new type of multifunctional nanomaterial that is comprised of a nucleic acid aptamer and a dendrimer, both of which are stable. This nanomaterial is approximately 8 nm in size. Moreover, it could not only carry multiple signal molecules, but also bind to target cancer cells with high affinity and specificity. This sub-10 nm multifunctional nanomaterial is expected to be useful in basic biomedical research and clinical medicine.

SummaryWe show that a molecular scaffold can be utilized to convert a receptor binding aptamer into a receptor agonist. Many receptors (including tumor necrosis receptor family members) are activated when they are multimerized on the cell surface. Molecular scaffolds have been utilized to assemble multiple receptor binding peptide ligands to generate activators of such receptors. We demonstrate that an RNA aptamer that recognizes OX40, a member of the tumor necrosis factor receptor superfamily, can be converted into a receptor-activating aptamer by assembling two copies on an olignucleotide-based scaffold. The OX40 receptor-activating aptamer is able to induce nuclear localization of nuclear factor-κB, cytokine production, and cell proliferation, as well as enhance the potency of dendritic cell-based tumor vaccines when systemically delivered to mice.

4-1BB is a major costimulatory receptor that promotes the survival and expansion of activated T cells. Administration of agonistic anti–4-1BB Abs has been previously shown to enhance tumor immunity in mice. Abs are cell-based products posing significant cost, manufacturing, and regulatory challenges. Aptamers are oligonucleotide-based ligands that exhibit specificity and avidity comparable to, or exceeding, that of Abs. To date, various aptamers have been shown to inhibit the function of their cognate target. Here, we have described the development of an aptamer that binds 4-1BB expressed on the surface of activated mouse T cells and shown that multivalent configurations of the aptamer costimulated T cell activation in vitro and mediated tumor rejection in mice. Because aptamers can be chemically synthesized, manufacturing and the regulatory approval process should be substantially simpler and less costly than for Abs. Agonistic aptamers could therefore represent a superior alternative to Abs for the therapeutic manipulation of the immune system.

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.

Depletion of CD4+CD25+ regulatory T cells (Treg) by treatment with αCD25 antibody synergizes with vaccination protocols to engender protective immunity in mice. The effectiveness of targeting CD25 to eliminate Treg is limited by the fact that CD25, the low-affinity interleukin-2 receptor, is up-regulated on conventional T cells. At present, foxp3 is the only product known to be exclusively expressed in Treg of mice. However, foxp3 is not expressed on the cell surface and hence cannot be targeted with antibodies. In this study, we tested the hypothesis that vaccination of mice against foxp3, a self-antigen expressed also in the thymus, is capable of stimulating foxp3-specific CTL that will cause the depletion of Treg and enhanced antitumor immunity. Vaccination of mice with foxp3 mRNA-transfected dendritic cells elicited a robust foxp3-specific CTL response and potentiated vaccine-induced protective immunity comparably with that of αCD25 antibody administration. In contrast to αCD25 antibody treatment, repeated foxp3 vaccination did not interfere with vaccine-induced protective immunity. Importantly, foxp3 vaccination led to the preferential depletion of foxp3-expressing Treg in the tumor but not in the periphery, whereas αCD25 antibody treatment led to depletion of Treg in both the tumor and the periphery. Targeting foxp3 by vaccination offers a specific and simpler protocol for the prolonged control of Treg that may be associated with reduced risk of autoimmunity, introducing an approach whereby specific depletion of cells is not limited to targeting products expressed on the cell surface. [Cancer Res 2006;67(1):371–80]

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.

Purpose: Elevated proportions of regulatory T cells (Treg) are present in patients with a variety of cancers, including malignant glioma, yet recapitulative murine models are wanting. We therefore examined Tregs in mice bearing malignant glioma and evaluated anti-CD25 as an immunotherapeutic adjunct.Experimental Design: CD4+CD25+Foxp3+GITR+ Tregs were quantified in the peripheral blood, spleens, cervical lymph nodes, and bone marrow of mice bearing malignant glioma. The capacities for systemic anti-CD25 therapy to deplete Tregs, enhance lymphocyte function, and generate antiglioma CTL responses were assessed. Lastly, survival and experimental allergic encephalitis risks were evaluated when anti-CD25 was combined with a dendritic cell–based immunization targeting shared tumor and central nervous system antigens.Results: Similar to patients with malignant glioma, glioma-bearing mice show a CD4 lymphopenia. Additionally, CD4+CD25+Foxp3+GITR+ Tregs represent an increased fraction of the remaining peripheral blood CD4+ T cells, despite themselves being reduced in number. Similar trends are observed in cervical lymph node and spleen, but not in bone marrow. Systemic anti-CD25 administration hinders detection of CD25+ cells but fails to completely eliminate Tregs, reducing their number only moderately, yet eliminating their suppressive function. This elimination of Treg function permits enhanced lymphocyte proliferative and IFN-γ responses and up to 80% specific lysis of glioma cell targets in vitro. When combined with dendritic cell immunization, anti-CD25 elicits tumor rejection in 100% of challenged mice without precipitating experimental allergic encephalitis.Conclusions: Systemic anti-CD25 administration does not entirely eliminate Tregs but does prevent Treg function. This leads to safe enhancement of tumor immunity in a murine glioma model that recapitulates the tumor-induced changes to the CD4 and Treg compartments seen in patients with malignant glioma.

Transfection with synthetic mRNA is a safe and efficient method of delivering antigens to dendritic cells for immunotherapy. Targeting antigens to the lysosome can sometimes enhance the CD4+ T-cell response. We transfected antigen-presenting cells (APCs) with mRNA encoding Gag-p24 and cytoplasmic, lysosomal, and secreted forms of Nef. Antigen-specific cytotoxic T cells were able to lyse the majority of transfected targets, indicating that transfection was efficient. Transfection of APCs with a Nef construct bearing lysosomal targeting signals produced rapid and prolonged antigen presentation to CD4+ and CD8+ T cells. Polyclonal CD4+ and CD8+ T-cell lines recognizing multiple distinct epitopes were expanded by coculture of transfected dendritic cells with peripheral blood mononuclear cells from viremic and aviremic HIV-infected subjects. Importantly, lysosome-targeted antigen drove a significantly greater expansion of Nef-specific CD4+ T cells than cytoplasmic antigen. The frequency of recognition of CD8 but not CD4 epitopes by mRNA-expanded T cells was inversely proportional to sequence entropy and was similar to ex vivo responses from a large chronic cohort. Thus human dendritic cells transfected with mRNA encoding lysosome-targeted HIV antigen can expand a broad, polyclonal repertoire of antiviral T cells, offering a promising approach to HIV immunotherapy.