First-in-human Phase I Trial of TPST-1120, an Inhibitor of PPARα, as Monotherapy or in Combination with Nivolumab, in Patients with Advanced Solid Tumors

PURPOSE

TPST-1120 is a first-in-class oral inhibitor of peroxisome proliferator-activated receptor α (PPARα), a fatty acid ligand-activated transcription factor that regulates genes involved in fatty acid oxidation, angiogenesis, and inflammation, and is a novel target for cancer therapy. TPST-1120 displayed antitumor activity in xenograft models and synergistic tumor reduction in syngeneic tumor models when combined with anti-PD-1 agents.

EXPERIMENTAL DESIGN

This phase I, open-label, dose-escalation study (NCT03829436) evaluated TPST-1120 as monotherapy in patients with advanced solid tumors and in combination with nivolumab in patients with renal cell carcinoma (RCC), cholangiocarcinoma (CCA), or hepatocellular carcinoma. Objectives included evaluation of safety, pharmacokinetics, pharmacodynamics, and preliminary antitumor activity (RECIST v1.1).

RESULTS

A total of 39 patients enrolled with 38 treated (20 monotherapy, 18 combination; median 3 prior lines of therapy). The most common treatment-related adverse events (TRAE) were grade 1-2 nausea, fatigue, and diarrhea. No grade 4-5 TRAEs or dose-limiting toxicities were reported. In the monotherapy group, 53% (10/19) of evaluable patients had a best objective response of stable disease. In the combination group, 3 patients had partial responses, for an objective response rate of 20% (3/15) across all doses and 30% (3/10) at TPST-1120 ≥400 mg twice daily. Responses occurred in 2 patients with RCC, both of whom had previously progressed on anti-PD-1 therapy, and 1 patient with late-line CCA.

CONCLUSIONS

TPST-1120 was well tolerated as monotherapy and in combination with nivolumab and the combination showed preliminary evidence of clinical activity in PD-1 inhibitor refractory and immune compromised cancers.

SIGNIFICANCE

TPST-1120 is a first-in-class oral inhibitor of PPARα, whose roles in metabolic and immune regulation are implicated in tumor proliferation/survival and inhibition of anticancer immunity. This first-in-human study of TPST-1120 alone and in combination with nivolumab supports proof-of-concept of PPARα inhibition as a target of therapeutic intervention in solid tumors.

Dual Blockade of EP2 and EP4 Signaling is Required for Optimal Immune Activation and Antitumor Activity Against Prostaglandin-Expressing Tumors

While the role of prostaglandin E2 (PGE2) in promoting malignant progression is well established, how to optimally block the activity of PGE2 signaling remains to be demonstrated. Clinical trials with prostaglandin pathway targeted agents have shown activity but without sufficient significance or dose-limiting toxicities that have prevented approval. PGE2 signals through four receptors (EP1-4) to modulate tumor progression. EP2 and EP4 signaling exacerbates tumor pathology and is immunosuppressive through potentiating cAMP production. EP1 and EP3 signaling has the opposite effect through increasing IP3 and decreasing cAMP. Using available small-molecule antagonists of single EP receptors, the cyclooxygenase-2 (COX-2) inhibitor celecoxib, or a novel dual EP2/EP4 antagonist generated in this investigation, we tested which approach to block PGE2 signaling optimally restored immunologic activity in mouse and human immune cells and antitumor activity in syngeneic, spontaneous, and xenograft tumor models. We found that dual antagonism of EP2 and EP4 together significantly enhanced the activation of PGE2-suppressed mouse and human monocytes and CD8+ T cells in vitro as compared with single EP antagonists. CD8+ T-cell activation was dampened by single EP1 and EP3 antagonists. Dual EP2/EP4 PGE2 receptor antagonists increased tumor microenvironment lymphocyte infiltration and significantly reduced disease burden in multiple tumor models, including in the adenomatous polyposis coli (APC)min+/- spontaneous colorectal tumor model, compared with celecoxib. These results support a hypothesis that redundancy of EP2 and EP4 receptor signaling necessitates a therapeutic strategy of dual blockade of EP2 and EP4. Here we describe TPST-1495, a first-in-class orally available small-molecule dual EP2/EP4 antagonist.

Significance

Prostaglandin (PGE2) drives tumor progression but the pathway has not been effectively drugged. We demonstrate significantly enhanced immunologic potency and antitumor activity through blockade of EP2 and EP4 PGE2 receptor signaling together with a single molecule.

Abstract 1333: Dual blockade of the EP2 and EP4 PGE2 receptors with TPST-1495 is an optimal approach for drugging the prostaglandin pathway

Prostaglandin E2 (PGE2) is a bioactive lipid produced by tumor cells that drives disease progression through stimulating tumor proliferation, enhancing angiogenesis and suppressing immune function in the TME1, 2. PGE2 is also a mediator of adaptive resistance to immune checkpoint inhibitor therapy via the upregulation of cyclooxygenase-2 (COX-2). While the role of PGE2 signaling in cancer is clear, how best to inhibit PGE2 for cancer treatment remains under investigation. Inhibition of COX-1 and/or COX-2 has shown promising results in observational studies and meta-analyses, but inconsistent results in prospective studies. PGE2 signals through four receptors, EP1-4, that are variably expressed on tumor and immune cells and have distinct biological activities. The EP2 and EP4 receptors signal through cAMP and drive pro-tumor activities, while the EP1 and EP3 receptors signal through calcium flux and IP3 and drive immune activation and inflammation. While COX-2 and single EP inhibitors continue to be developed, the nature of PGE2 signaling supports our rationale to inhibit PGE2 by dual antagonism of the pro-tumor EP2/EP4 receptors, while sparing the pro-immune EP1/EP3 receptors. To our knowledge, TPST-1495 is the first clinical-stage dual inhibitor of both the EP2 and EP4 receptors. In mouse and human whole blood assays, dual blockade of EP2 and EP4 receptors with TPST-1495 reversed PGE2-mediated suppression of LPS-induced TNF-α, while single receptor antagonists were unable to block suppression at higher PGE2 concentrations. Similarly, in murine and human T cells in vitro, TPST-1495 inhibited PGE2-mediated suppression, resulting in a significant increase of IFN-γ production in response to stimulation with cognate peptide antigen. In vivo, TPST-1495 monotherapy significantly reduced tumor outgrowth in CT26 tumor-bearing mice and correlated with increased tumor infiltration by NK cells, CD8+ T cells, AH1-specific CD8+ T cells, and other anti-tumor myeloid and adaptive immune cell populations. The relative contribution of increased immune infiltration may be simultaneously dependent on the immunogenicity of the tumor model and on the direct antitumor effect of TPST-1495, because we also observed significant tumor regression in metastatic burden in the LS174T xenograft model in NSG mice as well as CT26 tumors in RAG2-/- animals, both of which are deficient in immune cell development. To that end, TPST- 1495 monotherapy significantly decreased the tumor burden compared to COX2 inhibition and EP2 or EP4 single antagonism in the Adenomatous Polyposis (APCmin/+) model, a model that is hypo-responsive to PD-1 monotherapy. TPST-1495 is currently being evaluated in an ongoing Phase 1 first-in-human study (NCT04344795) to characterize PK, PD, safety, and to identify a recommended phase 2 dose for expansion cohorts in key indications and biomarker-selected patients.

Citation Format: Brian Francica, Justine Lopez, Anja Holtz, Dave Freund, Dingzhi Wang, Amanda Enstrom, Raymond Dubois, Francielle Kipper, Dipak Panigrahy, Chan Whiting, Sam Whiting, Thomas W. Dubensky. Dual blockade of the EP2 and EP4 PGE2 receptors with TPST-1495 is an optimal approach for drugging the prostaglandin pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1333.

Abstract 2075: Systemic small molecule TREX1 inhibitors to selectively activate STING in the TME of metastatic disease

Genetic evidence from human disease and mouse genetic knock-out studies identify the Stimulator of Interferon Genes (STING) pathway as a critical innate immune sensor for the development of immunity. Tumor cells can evolve to avoid immune recognition through inactivating the STING pathway by diverse mechanisms, indicating that it is important to generating tumor-specific immunity. However, the clinical activity of STING agonists given by intratumoral (IT) administration has not compared well to preclinical studies. The scientific hypothesis supporting these first clinical studies is that localized CD8+ T cell priming would have activity against distal non-injected tumors, but findings that tumors in advanced malignancies have unique antigenic repertoires suggests that this approach may have limited activity against distal tumors. Global innate activation in metastases may therefore be necessary to prime a broadly active CD8+ T cell population targeting diverse antigens, in addition having the benefit of reversing the immune suppressive tumor microenvironment (TME). However, ubiquitous expression of STING presents a significant challenge to achieving a therapeutic index with systemic delivery of direct STING agonists. Selective activation of the STING pathway may be achieved through targeted inhibition of TREX1, a cytosolic DNA exonuclease that modulates cGAS/STING signaling. Expression of TREX1, in contrast to STING, is increased in tumor cells due to elevated levels of cytosolic DNA resulting from genetic instability, DNA repair mutation, inflammatory mediators or DNA-modifying anti-cancer therapies. These observations provide the principal scientific rationale to selectively activate the STING pathway in metastatic disease through targeted inhibition of TREX1. Utilizing published TREX1 X-ray crystal structures to guide medicinal chemistry, we discovered small molecule inhibitors of TREX1 and transformed these molecules from >100 µM leads into a series with drug-like physicochemical properties and picomolar potency against both human and mouse TREX1. We evaluated the activity of lead molecules in cell-based assays, in which TREX1 inhibition enhanced cGAS/STING signaling, and advanced molecules with desired pharmacokinetic profiles to mouse tumor studies. We observed significant anti-tumor activity in mice with CT26 tumors given a combined therapy of low dose doxorubicin to induce dsDNA breaks and increase TME TREX1 expression along with lead series TREX1 molecule inhibitors. Recognizing that TREX1 is a DNA repair enzyme, we also showed that TREX1 inhibitors were cytotoxic in DNA repair deficient human tumor cell lines, informing advancement of this new class of STING therapeutics as a clinical approach to both activate the cGAS/STING pathway to initiate immune recognition, as well as to inhibit DNA repair orthogonal to existing tumor-driver DNA repair mutations.

Citation Format: Brian Francica, Dara Burdette, Ryan Clark, Jamie Cope, David Freund, Anja Holtz, Peppi Prasit, Chan Whiting, Thomas W. Dubensky. Systemic small molecule TREX1 inhibitors to selectively activate STING in the TME of metastatic disease [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2075.

STING-Activating Adjuvants Elicit a Th17 Immune Response and Protect against Mycobacterium tuberculosis Infection

There are a limited number of adjuvants that elicit effective cell-based immunity required for protection against intracellular bacterial pathogens. Here, we report that STING-activating cyclic dinucleotides (CDNs) formulated in a protein subunit vaccine elicit long-lasting protective immunity to Mycobacterium tuberculosis in the mouse model. Subcutaneous administration of this vaccine provides equivalent protection to that of the live attenuated vaccine strain Bacille Calmette-Guérin (BCG). Protection is STING dependent but type I IFN independent and correlates with an increased frequency of a recently described subset of CXCR3-expressing T cells that localize to the lung parenchyma. Intranasal delivery results in superior protection compared with BCG, significantly boosts BCG-based immunity, and elicits both Th1 and Th17 immune responses, the latter of which correlates with enhanced protection. Thus, a CDN-adjuvanted protein subunit vaccine has the capability of eliciting a multi-faceted immune response that results in protection from infection by an intracellular pathogen.

Cyclic Dinucleotide-Adjuvanted Dengue Virus Nonstructural Protein 1 Induces Protective Antibody and T Cell Responses

Endothelial dysfunction and vascular leak, pathogenic hallmarks of severe dengue disease, are directly triggered by dengue virus (DENV) nonstructural protein 1 (NS1). Previous studies have shown that immunization with NS1, as well as passive transfer of NS1-immune serum or anti-NS1 mAb, prevent NS1-mediated lethality in vivo. In this study, we evaluated the immunogenicity and protective capacity of recombinant DENV NS1 administered with cyclic dinucleotides (CDNs), potent activators of innate immune pathways and highly immunogenic adjuvants. Using both wild-type C57BL/6 mice and IFN-α/β receptor-deficient mice, we show that NS1-CDN immunizations elicit serotype-specific and cross-reactive Ab and T cell responses. Furthermore, NS1-CDN vaccinations conferred significant homotypic and heterotypic protection from DENV2-induced morbidity and mortality. In addition, we demonstrate that high anti-NS1 Ab titers are associated with protection, supporting the role of humoral responses against DENV NS1 as correlates of protection. These findings highlight the potential of CDN-based adjuvants for inducing Ab and T cell responses and validate NS1 as an important candidate for dengue vaccine development.

Combining STING-based neoantigen-targeted vaccine with checkpoint modulators enhances antitumor immunity in murine pancreatic cancer

Tumor neoantigens arising from somatic mutations in the cancer genome are less likely to be subject to central immune tolerance and are therefore attractive targets for vaccine immunotherapy. We utilized whole-exome sequencing, RNA sequencing (RNASeq), and an in silico immunogenicity prediction algorithm, NetMHC, to generate a neoantigen-targeted vaccine, PancVAX, which was administered together with the STING adjuvant ADU-V16 to mice bearing pancreatic adenocarcinoma (Panc02) cells. PancVAX activated a neoepitope-specific T cell repertoire within the tumor and caused transient tumor regression. When given in combination with two checkpoint modulators, namely anti-PD-1 and agonist OX40 antibodies, PancVAX resulted in enhanced and more durable tumor regression and a survival benefit. The addition of OX40 to vaccine reduced the coexpression of T cell exhaustion markers, Lag3 and PD-1, and resulted in rejection of tumors upon contralateral rechallenge, suggesting the induction of T cell memory. Together, these data provide the framework for testing personalized neoantigen-based combinatorial vaccine strategies in patients with pancreatic and other nonimmunogenic cancers.

Abstract 631: Intratumoral activation of STING with a synthetic cyclic dinucleotide elicits antitumor CD8 T-cell immunity that effectively combines with checkpoint inhibitors

Activation of the STING pathway by intratumoral (IT) injection of synthetic cyclic dinucleotides (CDNs) induces stable tumor regression in preclinical models, yet the underlying immune correlates are not fully understood. ADU-S100, a CDN under clinical evaluation, was administered IT with an optimized dosing regimen to explore the immune requirements for antitumor efficacy in mouse syngeneic tumor models. We show that CD8+ T cells are necessary and sufficient for durable antitumor immunity elicited by ADU-S100 and that activation of STING in hematopoietic cells mediates CD8+ T cell induction. Both type I IFN and TNFα, which are induced by STING pathway activation, influence the antitumor immune response. The combination of ADU-S100 and anti-PD1 treatment enhances CD8+ T cell-dependent, noninjected tumor control that correlates with an enhanced effector profile of CD8+ T cells in the tumor. Combination of ADU-S100 with checkpoint inhibition also enhances durable immunity in a poorly immunogenic tumor model. Together, these results elucidate the immune correlates to STING-mediated antitumor efficacy and highlight the potential of combining STING agonists with checkpoint inhibition in the clinic.

Citation Format: Anthony L. Desbien, Kelsey Sivick Gauthier, Leticia Corrales, Gabrielle Reiner, Laura Hix Glickman, George Katibah, Thomas E. Hudson, Uyen Vu, Natalie H. Surh, Brian Francica, Weiwen Deng, David B. Kanne, Justin J. Leong, Chudi Ndubaku, Ken Metchette, Jeffery M. McKenna, Steven L. Bender, Meredith L. Leong, Thomas W. Dubensky Jr., Andrea van Elsas, Sarah M. McWhirter. Intratumoral activation of STING with a synthetic cyclic dinucleotide elicits antitumor CD8 T-cell immunity that effectively combines with checkpoint inhibitors [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 631.

TNFα and Radioresistant Stromal Cells Are Essential for Therapeutic Efficacy of Cyclic Dinucleotide STING Agonists in Nonimmunogenic Tumors

The cGAS-STING cytosolic DNA sensing pathway may play an integral role in the initiation of antitumor immune responses. Studies evaluating the immunogenicity of various cyclic dinucleotide (CDN) STING agonists administered by intratumoral (i.t.) injection showed potent induction of inflammation, tumor necrosis, and, in some cases, durable tumor-specific adaptive immunity. However, the specific immune mechanisms underlying these responses remain incompletely defined. The majority of these studies have focused on the effect of CDNs on immune cells but have not conclusively interrogated the role of stromal cells in the acute rejection of the CDN-injected tumor. Here, we revealed a mechanism of STING agonist-mediated tumor response that relied on both stromal and immune cells to achieve tumor regression and clearance. Using knockout and bone marrow chimeric mice, we showed that although bone marrow-derived TNFα was necessary for CDN-induced necrosis, STING signaling in radioresistant stromal cells was also essential for CDN-mediated tumor rejection. These results provide evidence for crosstalk between stromal and hematopoietic cells during CDN-mediated tumor collapse after i.t. administration. These mechanistic insights may prove critical in the clinical development of STING agonists. Cancer Immunol Res; 6(4); 422-33. ©2018 AACR.

Abstract 1695: Exploiting the pancreatic cancer mutome for immune interception

This study aims to translate tumor-specific mutations identified by next-generation sequencing techniques into an effective anti-tumor vaccine for a classically non-immunogenic tumor, pancreatic ductal adenocarcinoma (PDA). Pancreatic ductal adenocarcinomas develop an average of 63 mutations during tumorigenesis, collectively referred to as the “mutome.” Of these, approximately 45 are amino acid point mutations. These mutations are not present in normal cells and provide a source of tumor-specific neoepitopes for targeted immunotherapy. Next-generation sequencing technologies allow for rapid identification of mutations present in patient tumors; however, methods for rapid identification of immunogenic neoepitopes which can be effectively targeted for tumor clearance, and optimized vaccination strategies for targeting them, still need to be developed.

In this study, we are using a transplantable murine PDA model, Panc02, to develop vaccination strategies for inducing neoepitope-specific T cell antitumor responses, and to define parameters for selecting appropriate targets. Exome sequencing identified 878 nonsynonymous mutations in the Panc02 cell line. Three immunological epitope prediction servers identified 878 potentially immunogenic peptides in the Panc02 model, 29 of which were strong candidates (scores <50) and another 240 candidate epitopes within the limits of prediction (scores <1000). Panc02 neoepitope peptide vaccinations in mice confirmed 14% of the predicted epitopes to be immunogenic by IFNγ ELISPOT, which may include both CD8+ and CD4+ T cell responses. Tumor transplant experiments demonstrate that therapeutic vaccination against neoepitopes in combination with a human STING-activating cyclic dinucleotide adjuvant is capable of inducing a temporary regression of implanted tumors. After tumor escape and regrowth, flow cytometry reveals a large population of infiltrating lymphocytes, the majority of which are co-expressing the checkpoint molecules PD-1, Tim3, and Lag3, indicating that treatment of vaccinated animals with checkpoint blockade therapy may potentiate infiltrating lymphocytes and ultimately result in permanent tumor regression. Thus, a broad and unbiased approach for screening vaccine targets will allow for the evaluation of predictive algorithms and ultimately the development of more effective vaccination approaches for targeting the tumor mutome.

Citation Format: Heather Kinkead, Eric Lutz, Thomas W. Dubensky, Elizabeth Jaffee. Exploiting the pancreatic cancer mutome for immune interception [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1695. doi:10.1158/1538-7445.AM2017-1695

Abstract 2993: STING signaling in breast tumor microenvironment modulates immune checkpoint blockade efficacy in the neu-N mouse model of breast cancer

Background: The presence of tumor infiltrating T cells (TILs) is associated with improved clinical outcomes in multiple tumor types and is also necessary for response to immune checkpoint blockade. While T cell responses to some tumors occur spontaneously, the majority of cancers are not naturally recognized by the immune system. The lack of response is attributed primarily to insufficient T cell infiltration into the tumor microenvironment (TME). Activating the STING pathway represents one strategy for increasing infiltration of T cells into the TME. This induces interferon-β (IFN-β) production, leading to dendritic cell (DC) activation and priming of tumor antigen specific CD8+ T cells that mediate tumor regression. The intratumoral injection (IT) of ML-RR-S2-CDA (ADU-S100), a synthetic cyclic dinucleotide STING agonist, has antitumor efficacy in several aggressive mouse tumor models, including B16 melanoma, CT26 colon carcinoma, Panc02 pancreatic carcinoma, and 4T1 triple negative breast cancer. However, the impact of antigen-specific tolerance on tumor regression associated with STING-activation remains poorly understood. Therefore, we evaluated the efficacy of IT ADU-S100 in both non-tolerant parental FVB/N and the immune tolerant neu/N transgenic mice bearing established HER-2+ breast tumors.

Methods: First we first evaluated the impact of IT ADU-S100 on tumor regression, survival, innate sensing, and priming of HER-2 specific CD8+ T cells in both tumor-bearing non-tolerant FVB/N control and tolerant neu/N mice. Then we determined whether modulating the most highly expressed immune checkpoints on tumor infiltrating CD8+ T cells enhanced intratumoral STING activation with ADU-S100 in the tolerant neu/N mouse model of HER-2+ breast cancer.

Results: ADU S-100 induced HER-2-specific CD8+ T cell priming and durable tumor clearance in 100% of non-tolerant, FVB/N mice. In contrast, ADU S-100 failed to sufficiently prime HER-2-specific CD8+ T cells in tolerant neu/N mice, delaying tumor growth and clearing tumors in only 10% of mice. No differences in IFN-β production, DC priming, or HER-2-specific CD8+ T cell trafficking were detected between FVB/N and neu/N mice. However, activation and expansion of HER-2-specific CD8+ T cells was defective in neu/N mice. Immune cell infiltrates of untreated tumor-bearing neu/N mice expressed high levels of PD1 and OX40 on CD8+ T cells, and high levels of PD-L1 on both myeloid and tumor cells. Modulating PD-L1 and OX40 signaling combined with IT ADU S-100 enhanced HER-2-specific CD8+ T cell activity, clearing tumors from 40% of neu/N mice.

Conclusions: Intratumoral STING activation synergizes with PD1 pathway-blockade and OX40 receptor stimulation to overcome immune tolerance and prime tumor antigen-specific CD8+ T cell responses that mediate effective tumor regression.

Citation Format: Jeremy B. Foote, Marlene Kok, James M. Leatherman, Todd D. Armstrong, Bridget Marcinkowski, David B. Kanne, Elizabeth M. Jaffee, Thomas W. Dubensky, Leisha A. Emens. STING signaling in breast tumor microenvironment modulates immune checkpoint blockade efficacy in the neu-N mouse model of breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2993. doi:10.1158/1538-7445.AM2017-2993

New Cancer Immunotherapy Agents in Development: a report from an associated program of the 31stAnnual Meeting of the Society for Immunotherapy of Cancer, 2016

This report is a summary of ‘New Cancer Immunotherapy Agents in Development’ program, which took place in association with the 31st Annual Meeting of the Society for Immunotherapy of Cancer (SITC), on November 9, 2016 in National Harbor, Maryland. Presenters gave brief overviews of emerging clinical and pre-clinical immune-based agents and combinations, before participating in an extended panel discussion with multidisciplinary leaders, including members of the FDA, leading academic institutions and industrial drug developers, to consider topics relevant to the future of cancer immunotherapy.

A STING Agonist Given with OX40 Receptor and PD-L1 Modulators Primes Immunity and Reduces Tumor Growth in Tolerized Mice

Stimulator of interferon genes (STING) signaling induces IFNβ production by intratumoral dendritic cells (DC), driving T-cell priming and recruitment into the tumor microenvironment (TME). We examined to what extent preexisting antigen-specific tolerance influenced the efficacy of in situ delivery of a potent STING-activating cyclic dinucleotide (CDN), ADU S-100, against established HER-2⁺ breast tumors. ADU S-100 induced HER-2-specific CD8⁺ T-cell priming and durable tumor clearance in 100% of nontolerant parental FVB/N mice. In contrast, ADU S-100 did not sufficiently prime HER-2-specific CD8⁺ T cells in tolerant neu/N mice, resulting in only delayed tumor growth and tumor clearance in 10% of the mice. No differences in IFNβ production, DC priming, or HER-2-specific CD8⁺ T-cell trafficking were detected between FVB/N and neu/N mice. However, activation and expansion of HER-2-specific CD8⁺ T cells were defective in neu/N mice. Immune cell infiltrates of untreated tumor-bearing neu/N mice expressed high numbers of PD1 and OX40 receptors on their CD8⁺ T cells, and PD-L1 was highly expressed on both myeloid and tumor cells. Modulating PD-L1 and OX40 receptor signaling combined with intratumoral ADU S-100 administration enhanced HER-2-specific CD8⁺ T-cell activity, clearing tumors in 40% of neu/N mice. Thus, intratumoral STING agonists could potently prime tumor antigen-specific CD8⁺ T-cell responses, and adding PD-L1 blockade and OX40 receptor activation can overcome antigen-enforced immune tolerance to induce tumor regression. Cancer Immunol Res; 5(6); 468-79. ©2017 AACR.

Abstract B50: Synergistic antitumor efficacy in mice with immunotherapy regimens combining recombinant live-attenuated Listeria with immune checkpoint inhibitors

Development of effective and durable antitumor immunity requires the activation, expansion and maintenance of function of tumor antigen-specific effector T cells. The mechanism of action of recently FDA approved monoclonal antibody (mAb) therapies which target immune checkpoints such as PD-1 and CTLA-4 and uncouple inhibitory pathways from the activation of antigen-specific T cells underlines the critical requirement for antigen-specific priming to elicit potent and long-lasting anti-tumor immunity. However, immune checkpoint blockade results in significant clinical benefit largely in malignancies with high mutational burden, where the tumor itself can initiate T cell priming, but is less effective when used as a single agent among cancers with lower mutational burden, associated typically with a low level of lymphocyte infiltration into the tumor microenvironment (TME). We are evaluating clinical immunotherapy regimens combining immune checkpoint blockade with recombinant live-attenuated double-deleted strains of the intracellular bacterium Listeria monocytogenes (LADD), based on a hypothesis that effective immunotherapy will result from agents that in combination re-polarize the TME to facilitate immune effector cell function, prime functional tumor-specific T cells in the appropriate context, and block inhibitory signaling pathways. Here we show that tumor antigen-expressing LADD therapy enhanced CD8+ T cell effector function, resulting in significant tumor eradication in several preclinical mouse models. LADD treatment in addition induced favorable changes in the TME, as shown by enhanced CD8+ T effector function, recruitment of antigen presenting cells and reduction of regulatory T cells. Treatment regimens combining LADD-based immunotherapy with PD-1 immune checkpoint blockade significantly enhanced antitumor efficacy in CT26, 4T1 and MC38 tumor models. Together these data support the rationale for integrating LADD-based immunotherapy into clinical regimens with immune checkpoint blockade on the basis that TME modification and priming of tumor Ag-specific T cells significantly enhances the activity of mAb therapies blocking T cell inhibitory pathways.

Citation Format: Weiwen Deng, Weiqun Liu, Thomas Hudson, Chris S. Rae, Ed Lemmens, Anthony Desbien, Bill Hanson, Pete Lauer, Thomas W. Dubensky, Jr., Meredith Leong. Synergistic antitumor efficacy in mice with immunotherapy regimens combining recombinant live-attenuated Listeria with immune checkpoint inhibitors. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2016 Oct 20-23; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2017;5(3 Suppl):Abstract nr B50.

Abstract A013: Favorable changes in tumor microenvironment following intravenous dosing with live attenuated Listeria monocytogenes-based immunotherapy

Modification of the tumor microenvironment (TME) to promote immune-mediated tumor cell destruction is considered to be an essential step for effective immunotherapy. We are evaluating recombinant live-attenuated, double deleted Listeria monocytogenes (LADD) as an immunotherapy platform for the treatment of cancer in several clinical trials in diverse indications. One LADD strain, known as CRS-207, has been engineered to express the tumor-associated antigen mesothelin and is being tested in pancreatic, ovarian and mesothelioma malignancies. Using multi-dimensional immunohistochemistry of paired biopsies from three patients with mesothelioma, we demonstrate the recruitment and expansion of effector tumor-infiltrating lymphocytes, including CD8+ T cells, mature DCs, CD163− macrophages and NK cells, following two prime infusions of CRS-207. In several different syngeneic mouse tumor models, we demonstrate that treatment with LADD engineered to express endogenous tumor antigens also induced significant changes in the TME that were consistent with changes observed in cancer patients, including enhanced CD8+ T cell effector function, recruitment of critical antigen presenting cells and reduction of regulatory T cells, and these changes correlated with significant therapeutic benefit in the mouse. LADD-induced changes to the TME were required for synergistic therapeutic antitumor efficacy combined with immune checkpoint blockade, including targeting MC38 tumor-specific neoantigens. Together, these findings demonstrate that intravenous administration of recombinant LADD therapy induces favorable changes in the tumor microenvironment in mice and humans with promise for effective outcomes in human clinical trials.

Citation Format: Weiwen Deng, Takahiro Tsujikawa, Nitya Nair, Thomas Hudson, Weiqun Liu, Chris S. Rae, Edward E. Lemmens, Anthony W. Desbien, William Hanson, Peter Lauer, Lisa M. Coussens, Dirk G. Brockstedt, Thomas W. Dubensky, Jr., Meredith L. Leong. Favorable changes in tumor microenvironment following intravenous dosing with live attenuated Listeria monocytogenes-based immunotherapy [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A013.

Abstract B020: STING activation in the tumor microenvironment using a synthetic human STING-activating cyclic dinucleotide induces potent antitumor immunity

Stimulator of Interferon Genes (STING) is a critical component of the cytosolic DNA sensing pathway of the innate immune system. STING is activated by cyclic dinucleotides (CDNs), a product of the intracellular enzyme, cyclic GMP-AMP synthase (cGAS), in response to presence of cytosolic DNA, including tumor-derived DNA. Production of type I interferon within the tumor microenvironment (TME), mediated by the STING pathway, leads to the priming and activation of systemic tumor antigen-specific CD8+ T-cell immunity and tumor regression. Therapeutic activation of STING through intratumoral (IT) administration of CDNs results in anti-tumor efficacy and long-lived survival in several mouse syngeneic tumor models. Rational design of synthetic CDN derivatives has shown that certain modifications alter STING binding, increase cellular potency, enhance maturation of human dendritic cells to promote in vitro T cell expansion, and are able to broadly activate all human STING haplotypes. Mechanistic studies in mouse tumor models demonstrate that CDNs mediate anti-tumor immunity by inducing an acute innate immune response, leading to collapse of the injected tumor, and promoting a tumor-specific CD8+ T cell response that protects against tumor re-challenge. Anti-tumor efficacy is enhanced by combination with immune checkpoint inhibitors, informing future clinical development. The ability to elicit innate and adaptive anti-tumor immunity via activation of STING in the TME demonstrates that CDNs have high translational potential for the treatment of patients with advanced/metastatic solid tumors. The design of an ongoing Phase 1 first-in-human clinical study to evaluate the safety, tolerability and possible antitumor activity of ADU-S100 in subjects with cutaneously accessible tumors and lymphomas will also be presented.

Citation Format: Sarah M. McWhirter, Laura Hix Glickman, Tony Desbien, Kelsey Sivick Gauthier, David Kanne, Shailaja Kasibhatla, Jie Li, AnneMarie Culazzo Pferdekamper, George Katibah, Ed Lemmens, Leticia Corrales, Meredith Leong, Chudi Ndubaku, Justin Leong, Leonard Sung, Lianxing Zheng, Charles Cho, Yan Feng, Jeffery M. McKenna, John A. Tallarico, Steven L. Bender, Thomas W. Dubensky, Jr.. STING activation in the tumor microenvironment using a synthetic human STING-activating cyclic dinucleotide induces potent antitumor immunity [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr B020.

Abstract SY39-02: Direct activation of STING in the tumor microenvironment leads to potent and systemic tumor regression and immunity

Recent reports have provided the mechanistic insight of how innate immune activation promotes priming of anti-tumor immunity and inform the development of clinical approaches to facilitate this process. Spontaneous T cell infiltration of melanoma lesions in humans is correlated with a type I interferon (IFN) transcriptional profile in the tumor microenvironment (TME) and infiltration of lymphocytes, indicative of ongoing innate immune recognition within the tumor. Substantial evidence indicates that tumor infiltrating lymphocytes (TILs), including activated CD8+ T cells, is predictive of a positive clinical outcome in response to several immunotherapy strategies. Similarly, in mice bearing melanoma, there is a correlation between expression of IFN-β by tumor-resident dendritic cells (DCs), and spontaneous priming of tumor-specific immunity. Induction of IFN-β expression and co-regulated IFN-responsive genes and pro-inflammatory chemokines is dependent upon activation of the STING (Stimulator of Interferon Genes) pathway, mediated through sensing of tumor dsDNA in TME-resident CD8α+ DCs by cyclic GMP-AMP (cGAMP) synthase (cGAS), which in turn synthesizes cGAMP. The cyclic dinucleotide (CDN) cGAMP produced by cGAS is the natural STING agonist ligand. Thus, the cGAS-STING signaling axis has emerged as a central node for sensing damage in the host. We hypothesized that direct activation of the STING pathway in the TME by intratumoral (IT) injection of specific CDNs would be an effective therapeutic strategy to promote broad tumor-initiated T cell priming against an individual's tumor antigen repertoire. There are five variant human STING alleles that exist at varying frequencies. While the natural STING ligand cGAMP activates signaling in all variants, other natural CDNs, including those produced by bacteria, have structural differences and are unable to activate particular STING variants, such as the REF (R232H) allele, informing the development of compounds that activate all human STING alleles. We sought to develop synthetic CDN compounds with increased activity in human cells as well as the ability to engage all known polymorphic human STING molecules. Using human 293T cell lines engineered to express the various STING proteins, we screened a large panel of CDN derivatives that varied in purine nucleotide base, structure of the phosphate bridge linkage, and substitution of the non-bridging oxygen atoms at the phosphate bridge with sulfur atoms. ADU-S100 is composed of two adenosine monophosphate (AMP) analogues cyclized via a 2’-5’ (non-canonical) and a 3’-5’ (canonical) phosphodiester bond, and was selected for clinical translation based on properties of enhanced cellular uptake, human STING activation, stability and anti-tumor efficacy, as compared to bacterial and mammalian derived CDNs. Induced cytokine expression from a panel of donor human peripheral blood mononuclear cells (PBMCs) expressing a variety of STING haplotypes, including donors with a homozygous haplotype for the refractory human REF allele, indicates that ADU-S100 activates STING across a diverse human population. Direct engagement of STING through IT administration of ADU-S100 results in effective anti-tumor therapy and long-term survival in various mouse syngeneic tumor models. IT injection of ADU-S100 also generates substantial systemic immune responses capable of rejecting distant metastases and provided long-lived immunologic memory.

A bell-shaped ADU-S100 dose response curve (which varied based on tumor model) delineated regression of injected tumor, induction of tumor-specific CD8+ T cell immunity, and regression of distal non-injected tumors (abscopal effect), and/or protection against autologous tumor challenge. At low dose levels, regression of the treated tumor was suboptimal. At optimal doses, regression of the treated and distal untreated tumors, or protection against tumor re-challenge was observed, and correlated with induction of a robust tumor Ag-specific CD8+ T cell response. At higher dose levels there was a loss of protection against tumor re-challenge which correlated with increases in acute systemic cytokines and reduction in CD8+ T cell responses even though growth of the treated tumor was inhibited. These results suggest that the mechanism of ADU-S100-induced tumor regression is due to both an acute pro-inflammatory cytokine response and also tumor-specific CD8+ T cell immunity. The local anti-tumor effect without systemic immunity is consistent with well-established data in which excessive innate immune stimulation and induction of pro-inflammatory cytokines such as TNF-α are known to inhibit both priming of CD8+ T cell immunity and establishment of a stable and self-renewing memory CD8+ T cell population. In addition, anti-tumor efficacy was enhanced by combination with immune checkpoint inhibitors, for example α-PD1, informing future clinical development. By virtue of the ability to elicit innate and T cell-mediated anti-tumor immunity in the TME, these results demonstrate that CDNs have high translational potential for the treatment of patients with advanced/metastatic solid tumors. A Phase 1 clinical study to evaluate the safety and tolerability and possible anti-tumor effects in subjects with cutaneously accessible non UV-induced and UV-induced malignancies or lymphomas given repeated IT doses of ADU-S100 is planned.

Citation Format: Laura Hix Glickman, Leticia Corrales, David B. Kanne, Shailaja Kasibhatla, Jie Li, Anne Marie Culazzo Pferdekamper, Kelsey Sivick Gauthier, George E. Katibah, Justin J. Leong, Leonard Sung, Ken Metchette, Weiwen Deng, Anthony L. Desbien, Chudi Ndubaku, Lianxing Zheng, Charles Cho, Yan Feng, Jeffery M. McKenna, John A. Tallarico, Steven L. Bender, Sarah M. McWhirter, Thomas F. Gajewski, Thomas W. Dubensky. Direct activation of STING in the tumor microenvironment leads to potent and systemic tumor regression and immunity. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr SY39-02.

The host STING pathway at the interface of cancer and immunity

A major subset of human cancers shows evidence for spontaneous adaptive immunity, which is reflected by the presence of infiltrating CD8+ T cells specific for tumor antigens within the tumor microenvironment. This observation has raised the question of which innate immune sensing pathway might detect the presence of cancer and lead to a natural adaptive antitumor immune response in the absence of exogenous infectious pathogens. Evidence for a critical functional role for type I IFNs led to interrogation of candidate innate immune sensing pathways that might be triggered by tumor presence and induce type I IFN production. Such analyses have revealed a major role for the stimulator of IFN genes pathway (STING pathway), which senses cytosolic tumor-derived DNA within the cytosol of tumor-infiltrating DCs. Activation of this pathway is correlated with IFN-β production and induction of antitumor T cells. Based on the biology of this natural immune response, pharmacologic agonists of the STING pathway are being developed to augment and optimize STING activation as a cancer therapy. Intratumoral administration of STING agonists results in remarkable therapeutic activity in mouse models, and STING agonists are being carried forward into phase I clinical testing.

STING Pathway Activation Stimulates Potent Immunity against Acute Myeloid Leukemia

Type I interferon (IFN), essential for spontaneous T cell priming against solid tumors, is generated through recognition of tumor DNA by STING. Interestingly, we observe that type I IFN is not elicited in animals with disseminated acute myeloid leukemia (AML). Further, survival of leukemia-bearing animals is not diminished in the absence of type I IFN signaling, suggesting that STING may not be triggered by AML. However, the STING agonist, DMXAA, induces expression of IFN-β and other inflammatory cytokines, promotes dendritic cell (DC) maturation, and results in the striking expansion of leukemia-specific T cells. Systemic DMXAA administration significantly extends survival in two AML models. The therapeutic effect of DMXAA is only partially dependent on host type I IFN signaling, suggesting that other cytokines are important. A synthetic cyclic dinucleotide that also activates human STING provided a similar anti-leukemic effect. These data demonstrate that STING is a promising immunotherapeutic target in AML.

Antagonism of the STING Pathway via Activation of the AIM2 Inflammasome by Intracellular DNA

Recent evidence has indicated that innate immune sensing of cytosolic DNA in dendritic cells via the host STING pathway is a major mechanism leading to spontaneous T cell responses against tumors. However, the impact of the other major pathway triggered by intracellular DNA, the absent in melanoma 2 (AIM2) inflammasome, on the functional output from the stimulator of IFN genes (STING) pathway is poorly understood. We found that dendritic cells and macrophages deficient in AIM2, apoptosis-associated specklike protein, or caspase-1 produced markedly higher IFN-β in response to DNA. Biochemical analyses showed enhanced generation of cyclic GMP-AMP, STING aggregation, and TANK-binding kinase 1 and IFN regulatory factor 3 phosphorylation in inflammasome-deficient cells. Induction of pyroptosis by the AIM2 inflammasome was a major component of this effect, and inhibition of caspase-1 reduced cell death, augmenting phosphorylation of TANK-binding kinase 1/IFN regulatory factor 3 and production of IFN-β. Our data suggest that in vitro activation of the AIM2 inflammasome in murine macrophages and dendritic cells leads to reduced activation of the STING pathway, in part through promoting caspase-1-dependent cell death.

STING agonist formulated cancer vaccines can cure established tumors resistant to PD-1 blockade

Stimulator of interferon genes (STING) is a cytosolic receptor that senses both exogenous and endogenous cytosolic cyclic dinucleotides (CDNs), activating TBK1/IRF3 (interferon regulatory factor 3), NF-κB (nuclear factor κB), and STAT6 (signal transducer and activator of transcription 6) signaling pathways to induce robust type I interferon and proinflammatory cytokine responses. CDN ligands were formulated with granulocyte-macrophage colony-stimulating factor (GM-CSF)-producing cellular cancer vaccines--termed STINGVAX--that demonstrated potent in vivo antitumor efficacy in multiple therapeutic models of established cancer. We found that rationally designed synthetic CDN derivative molecules, including one with an Rp,Rp dithio diastereomer and noncanonical c[A(2',5')pA(3',5')p] phosphate bridge structure, enhanced antitumor efficacy of STINGVAX in multiple aggressive therapeutic models of established cancer in mice. Antitumor activity was STING-dependent and correlated with increased activation of dendritic cells and tumor antigen-specific CD8(+) T cells. Tumors from STINGVAX-treated mice demonstrated marked PD-L1 (programmed death ligand 1) up-regulation, which was associated with tumor-infiltrating CD8(+)IFNγ(+) T cells. When combined with PD-1 (programmed death 1) blockade, STINGVAX induced regression of palpable, poorly immunogenic tumors that did not respond to PD-1 blockade alone.

Radiotherapy Combined with Novel STING-Targeting Oligonucleotides Results in Regression of Established Tumors

Cytotoxic therapies prime adaptive immune responses to cancer by stimulating the release of tumor-associated antigens. However, the tumor microenvironment into which these antigens are released is typically immunosuppressed, blunting the ability to initiate immune responses. Recently, activation of the DNA sensor molecule STING by cyclic dinucleotides was shown to stimulate infection-related inflammatory pathways in tumors. In this study, we report that the inflammatory pathways activated by STING ligands generate a powerful adjuvant activity for enhancing adaptive immune responses to tumor antigens released by radiotherapy. In a murine model of pancreatic cancer, we showed that combining CT-guided radiotherapy with a novel ligand of murine and human STING could synergize to control local and distant tumors. Mechanistic investigations revealed T-cell-independent and TNFα-dependent hemorrhagic necrosis at early times, followed by later CD8 T-cell-dependent control of residual disease. Clinically, STING was found to be expressed extensively in human pancreatic tumor and stromal cells. Our findings suggest that this novel STING ligand could offer a potent adjuvant for leveraging radiotherapeutic management of pancreatic cancer.

Systemic Tolerance Mediated by Melanoma Brain Tumors Is Reversible by Radiotherapy and Vaccination

PURPOSE

Immune responses to antigens originating in the central nervous system (CNS) are generally attenuated, as collateral damage can have devastating consequences. The significance of this finding for the efficacy of tumor-targeted immunotherapies is largely unknown.

EXPERIMENTAL DESIGN

The B16 murine melanoma model was used to compare cytotoxic responses against established tumors in the CNS and in the periphery. Cytokine analysis of tissues from brain tumor-bearing mice detected elevated TGFβ secretion from microglia and in the serum and TGFβ signaling blockade reversed tolerance of tumor antigen-directed CD8 T cells. In addition, a treatment regimen using focal radiation therapy and recombinant Listeria monocytogenes was evaluated for immunologic activity and efficacy in this model.

RESULTS

CNS melanomas were more tolerogenic than equivalently progressed tumors outside the CNS as antigen-specific CD8 T cells were deleted and exhibited impaired cytotoxicity. Tumor-bearing mice had elevated serum levels of TGFβ; however, blocking TGFβ signaling with a small-molecule inhibitor or a monoclonal antibody did not improve survival. Conversely, tumor antigen-specific vaccination in combination with focal radiation therapy reversed tolerance and improved survival. This treatment regimen was associated with increased polyfunctionality of CD8 T cells, elevated T effector to T regulatory cell ratios, and decreased TGFβ secretion from microglia.

CONCLUSIONS

These data suggest that CNS tumors may impair systemic antitumor immunity and consequently accelerate cancer progression locally as well as outside the CNS, whereas antitumor immunity may be restored by combining vaccination with radiation therapy. These findings are hypothesis-generating and warrant further study in contemporary melanoma models as well as human trials.

Abstract IA10: Effective immunotherapy regimens incorporating highly active human STING-activating cyclic dinucleotide derivatives

Innate immune sensing in the tumor microenvironment is a critical step in promoting tumor infiltrating lymphocytes (TILs) and spontaneous anti-tumor T cell priming. Transcriptional profiling analysis of melanoma patients has revealed that tumors with a T cell-inflamed immunophenotype are characterized by a type I IFN (IFN) transcriptional signature. Studies in mice support the notion that IFN produced by tumor-resident dendritic cells (DCs) plays a critical role in spontaneous T cell priming against tumor antigens, which is dependent upon the host Stimulator of Interferon Genes (STING) pathway. STING mediates host innate defense by responding to cytosolic nucleic acids, either through direct binding of cyclic dinucleotides (CDNs) produced by bacteria, or through binding of a structurally distinct CDN produced by host cyclic GMP-AMP synthetase in response to cytosolic double-stranded DNA. While CDN adjuvants have been explored previously in mice, we sought to develop compounds that activate human STING. We therefore synthesized a panel of cyclic dinucleotides (CDNs) that varied by purine nucleotide base, internucleotide phosphate bridge linkage, or by substitution of non-bridging oxygen atoms in the phosphate bridge with sulfur. We screened and selected from among these compounds based on their capacity to activate all known human STING alleles expressed in stably transformed reporter cell lines, stimulate the activation of human PBMCs, and impact significant antitumor efficacy in several mouse tumor models, without significant local or systemic toxicity. Strikingly, direct IT injection of particular CDN derivative molecules into two-week established flank B16 melanoma, CT26 colon, or 4T1 breast tumors profoundly inhibited tumor growth that was durable and correlated with induction of lasting systemic antigen-specific CD8+ T cell immunity that conferred complete protection against tumor re-challenge, or significantly inhibited the growth of distal untreated tumors. Induction of cytokines, tumor antigen-specific immunity, and antitumor efficacy was entirely STING-dependent. We selected dithio-[Rp,Rp]-c[A(2',5')pA(3',5')p], a synthetic CDN molecule that has significantly higher activity than natural STING ligands, as the lead molecule for continued development. We next tested whether direct activation of STING within the tumor microenvironment would enhance the absocopal effect resulting from irradiating the CDN-treated tumor. Treatment of one tumor in mice bearing established bilateral Panc02 flank tumors, with a suboptimal dose of 10 Gy of radiotherapy (RT) in combination with IT CDN injection resulted in rapid local and systemic induction of inflammatory mediators, and vascular damage that spread through the injected tumor without causing detectable damage to normal tissues. Compared to RT alone, CDN injection resulted in significantly enhanced adaptive-immune mediated control of the contralateral tumor. The synthetic CDN molecule described here was significantly more potent than IT TLR ligands, indicating its high translational potential as an approach to elicit effective unbiased T cell priming against an individual's unique tumor antigen repertoire.

Citation Format: Laura Hix Glickman, Leticia Corrales, Sarah M. McWhirter, David B. Kanne, Kelsey E. Sivick, Jason R. Baird, Edward Lemmens, Justin J. Leong, Ken Metchette, Mark Crittenden, Michael Gough, Thomas F. Gajewski, Thomas W. Dubensky, Jr.. Effective immunotherapy regimens incorporating highly active human STING-activating cyclic dinucleotide derivatives. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr IA10.

Abstract 4272: Potent in situ cancer immunotherapy with synthetic human STING-activating cyclic dinucleotides

Spontaneous tumor-initiated T cell priming is dependent on IFN-β production by tumor-resident dendritic cells. Based on recent observations indicating that IFN-β expression was dependent upon activation of the host STING (Stimulator of Interferon Genes) pathway, we hypothesized that direct engagement of STING through intratumoral administration of specific agonists would result in effective anti-tumor therapy. To this end, we generated novel synthetic cyclic dinucleotide (CDN) derivatives with superior STING-activating and anti-tumor properties. The most potent molecule contains a 2′-5′ and 3′-5′ phosphate bridge that increases its affinity for STING at least 10-fold. Additionally, sulfur atoms at the non-bridging oxygens of the internucleotide phosphate bridge enable both superior STING binding affinity, as well as resistance to host cell phosphodiesterases. Importantly, the lead molecule activates PBMCs from a panel of human donors representing all known STING alleles, including homozygotes for the most refractory allele. Intratumoral injection of the lead CDN molecule induced profound regression of established B16 melanoma tumors, generated substantial systemic immune responses capable of rejecting distant metastases and provided long-lived immunologic memory. Cures in entire cohorts of mice bearing well-established 4T1 mammary and CT26 colon carcinoma models correlated with induction of cytokine-mediated innate and adaptive antigen-specific T cell immunity, both systemically and in the tumor microenvironment. Immune activation and anti-tumor efficacy was lost in mice encoding non-functional STING. In vivo activation of STING with the lead CDN administered by multiple routes demonstrated a high safety and tolerability margin in preclinical toxicology studies. In addition, pharmacokinetic analysis indicates that the lead CDN compound was rapidly cleared from systemic circulation, consistent with pulsatile STING activation and transient systemic cytokine and hematological changes. These results demonstrate that CDNs have high translation potential for treatment strategies to induce activation of the tumor microenvironment, leading to effective tumor-initiated T cell priming and anti-tumor immunity.

Citation Format: Laura Hix Glickman, David B. Kanne, Kelsey E. Gauthier, George E. Katibah, Justin J. Leong, Ken Metchette, Thomas W. Dubensky, Sarah M. McWhirter. Potent in situ cancer immunotherapy with synthetic human STING-activating cyclic dinucleotides. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4272. doi:10.1158/1538-7445.AM2015-4272

Direct Activation of STING in the Tumor Microenvironment Leads to Potent and Systemic Tumor Regression and Immunity

Spontaneous tumor-initiated T cell priming is dependent on IFN-β production by tumor-resident dendritic cells. On the basis of recent observations indicating that IFN-β expression was dependent upon activation of the host STING pathway, we hypothesized that direct engagement of STING through intratumoral (IT) administration of specific agonists would result in effective anti-tumor therapy. After proof-of-principle studies using the mouse STING agonist DMXAA showed a potent therapeutic effect, we generated synthetic cyclic dinucleotide (CDN) derivatives that activated all human STING alleles as well as murine STING. IT injection of STING agonists induced profound regression of established tumors in mice and generated substantial systemic immune responses capable of rejecting distant metastases and providing long-lived immunologic memory. Synthetic CDNs have high translational potential as a cancer therapeutic.

Attenuated Listeria monocytogenes vectors overcome suppressive plasma factors during HIV infection to stimulate myeloid dendritic cells to promote adaptive immunity and reactivation of latent virus

HIV-1 infection is characterized by myeloid dendritic cell (DC) dysfunction, which blunts the responsiveness to vaccine adjuvants. We previously showed that nonviral factors in HIV-seropositive plasma are partially responsible for mediating this immune suppression. In this study we investigated recombinant Listeria monocytogenes (Lm) vectors, which naturally infect and potently activate DCs from seronegative donors, as a means to overcome DC dysfunction associated with HIV infection. Monocyte-derived DCs were cocultured with plasma from HIV-infected donors (HIV-moDCs) to induce a dysregulated state and infected with an attenuated, nonreplicative vaccine strain of Lm expressing full length clade B consensus gag (KBMA Lm-gag). Lm infection stimulated cytokine secretion [interleukin (IL)-12p70, tumor necrosis factor (TNF)-α, and IL-6] and Th-1 skewing of allogeneic naive CD4 T cells by HIV-moDCs, in contrast to the suppressive effects observed by HIV plasma on moDCs on toll-like receptor ligand stimulation. Upon coculture of "killed" but metabolically active (KBMA) Lm-gag-infected moDCs from HIV-infected donors with autologous cells, expansion of polyfunctional, gag-specific CD8(+) T cells was observed. Reactivation of latent proviruses by moDCs following Lm infection was also observed in models of HIV latency in a TNF-α-dependent manner. These findings reveal the unique ability of Lm vectors to contend with dysregulation of HIV-moDCs, while simultaneously possessing the capacity to activate latent virus. Concurrent stimulation of innate and adaptive immunity and disruption of latency may be an approach to reduce the pool of latently infected cells during HIV infection. Further study of Lm vectors as part of therapeutic vaccination and eradication strategies may advance this evolving field.

Abstract 2566: Activation of tumor-initiated T cell priming and tumor destruction with potent STING-activating cyclic dinucleotide derivatives

Cyclic dinucleotides (CDNs) are bacterial messengers that are sensed by the host cytosolic surveillance pathway receptor, STING (Stimulator of Interferon Genes). CDN binding to STING initiates a TLR-independent signaling cascade through the TBK-1/IRF-3 axis, inducing type I interferon (IFN) and other co-regulated genes central to host innate defense. In response to binding cytosolic double-stranded DNA, a recently discovered mammalian enzyme, cyclic GMP-AMP synthase (cGAS), synthesizes CDNs that are structurally distinct from CDNs produced by bacteria. The mammalian CDN has a phosphate bridge with 2′-5′ and 3′-5′ linkages that increases its affinity for STING at least 10-fold. We show that mixed linkage (ML) CDNs were more potent activators of human PBMCs as compared to CDNs with canonical 3′-5′ phosphate linkages. Additionally, particular ML CDN derivatives with sulfur atoms at non-bridging oxygens of the internucleotide phosphate bridge were resistant to digestion by host cell phosphodiesterases, and R,R di-thio CDN diastereomers demonstrated increased potency in vitro and in vivo, as compared to either the R,S di-thio CDN diastereomer, or unmodified CDNs. Strikingly, direct injection of 2-week established flank B16 melanoma tumors with ML R,R dithio-CDN derivatives significantly and profoundly inhibited tumor growth, correlated with cytokine-mediated activation of NK and T lymphocytes, induction of antigen-specific T cell immunity and long-term survival. Anti-tumor efficacy was lost in mice encoding non-functional STING. Similar results were observed in other tumor models. These results demonstrate that CDNs have high translation potential for treatment strategies to induce activation of the tumor microenvironment, leading to effective tumor-initiated CD8+ T cell priming and anti-tumor efficacy.

Citation Format: Laura Hix Glickman, David B. Kanne, Sarah M. McWhirter, Meredith L. Leong, Edward E. Lemmens, Ken Metchette, Russell E. Vance, Drew M. Pardoll, Thomas W. Dubensky. Activation of tumor-initiated T cell priming and tumor destruction with potent STING-activating cyclic dinucleotide derivatives. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2566. doi:10.1158/1538-7445.AM2014-2566

Rationale, progress and development of vaccines utilizing STING-activating cyclic dinucleotide adjuvants

A principal barrier to the development of effective vaccines is the availability of adjuvants and formulations that can elicit both effector and long-lived memory CD4 and CD8 T cells. Cellular immunity is the presumptive immune correlate of protection against intracellular pathogens: a group composed of bacteria, viruses and protozoans that is responsible for a staggering level of morbidity and mortality on a global scale. T-cell immunity is also correlated with clinical benefit in cancer, and the development of therapeutic strategies to harness the immune system to treat diverse malignancies is currently undergoing a renaissance. Cyclic dinucleotides (CDNs) are ubiquitous small molecule second messengers synthesized by bacteria that regulate diverse processes and are a relatively new class of adjuvants that have been shown to increase vaccine potency. CDNs activate innate immunity by directly binding the endoplasmic reticulum-resident receptor STING (stimulator of interferon genes), activating a signaling pathway that induces the expression of interferon-β (IFN-β) and also nuclear factor-κB (NF-κB) dependent inflammatory cytokines. The STING signaling pathway has emerged as a central Toll-like receptor (TLR) independent mediator of host innate defense in response to sensing cytosolic nucleic acids, either through direct binding of CDNs secreted by bacteria, or, as shown recently, through binding of a structurally distinct CDN produced by a host cell receptor in response to binding cytosolic double-stranded (ds)DNA. Although this relatively new class of adjuvants has to date only been evaluated in mice, newly available CDN-STING cocrystal structures will likely intensify efforts in this field towards further development and evaluation in human trials both in preventive vaccine and immunotherapy settings.

A Listeria vaccine and depletion of T-regulatory cells activate immunity against early stage pancreatic intraepithelial neoplasms and prolong survival of mice

BACKGROUND & AIMS

Premalignant lesions and early stage tumors contain immunosuppressive microenvironments that create barriers for cancer vaccines. Kras(G12D/+);Trp53(R172H/+);Pdx-1-Cre (KPC) mice, which express an activated form of Kras in pancreatic tissues, develop pancreatic intraepithelial neoplasms (PanIN) that progress to pancreatic ductal adenocarcinoma (PDA). We used these mice to study immune suppression in PDA.

METHODS

We immunized KPC and Kras(G12D/+);Pdx-1-Cre mice with attenuated intracellular Listeria monocytogenes (which induces CD4(+) and CD8(+) T-cell immunity) engineered to express Kras(G12D) (LM-Kras). The vaccine was given alone or in sequence with an anti-CD25 antibody (PC61) and cyclophosphamide to deplete T-regulatory (Treg) cells. Survival times were measured; pancreatic and spleen tissues were collected and analyzed by histologic, flow cytometry, and immunohistochemical analyses.

RESULTS

Interferon γ-mediated, CD8(+) T-cell responses were observed in KPC and Kras(G12D/+);Pdx-1-Cre mice given LM-Kras, but not in unvaccinated mice. Administration of LM-Kras to KPC mice 4-6 weeks old (with early stage PanINs), depleted of Treg cells, significantly prolonged survival and reduced PanIN progression (median survival, 265 days), compared with unvaccinated mice (median survival, 150 days; P = .002), mice given only LM-Kras (median survival, 150 days; P = .050), and unvaccinated mice depleted of Treg cells (median survival, 170 days; P = .048). In 8- to 12-week-old mice (with late-stage PanINs), LM-Kras, alone or in combination with Treg cell depletion, did not increase survival time or slow PanIN progression. The combination of LM-Kras and Treg cell depletion reduced numbers of Foxp3(+)CD4(+) T cells in pancreatic lymph nodes, increased numbers of CD4(+) T cells that secrete interleukin 17 and interferon γ, and caused CD11b(+)Gr1(+) cells in the pancreas to acquire an immunostimulatory phenotype.

CONCLUSIONS

Immunization of KPC mice with Listeria monocytogenes engineered to express Kras(G12D), along with depletion of Treg cells, reduces progression of early stage, but not late-stage, PanINs. This approach increases infiltration of the lesion with inflammatory cells. It might be possible to design immunotherapies against premalignant pancreatic lesions to slow or prevent progression to PDA.

Abstract 4573: STINGVAX - A novel tumor vaccine with cyclic dinucleotides - can induce potent anti-tumor responses in vivo

Cyclic dinucleotides (CDN) are ubiquitous bacterial intracellular messengers, and they have recently been shown to also function as a pathogen associated molecular pattern (PAMP) molecules that are sensed by eukaryotic host Stimulator of Interferon Genes (STING) that can activate the TBK-1/IRF-3 signaling pathway to induce type I interferon and other co-regulated genes. CDN was found to induce STING dependent augmentation of T-cell priming in multiple vaccination models, potentially by activating dendritic cells. We formulated CDN with a GM-CSF secreting tumor cell vaccine (STINGVAX) to mobilize and as well as activate dendritic cells both in vitro and in vivo. STINGVAX was tested in a stringent B16 melanoma treatment model, and we demonstrated significant reduction of tumor growth rate in vivo. STINGVAX's anti-tumor response was correlated with increased tumor infiltrating CD8 T-cells as well as increased number of p15E tumor-specific cytotoxic T-cells. STINGVAX's in vivo anti-tumor response was T-cell dependent as well as STING dependent. When we combined STINGVAX with multiple TLR 4/7/8 agonists signaling through the MyD88/TRIF pathway that is distinct from CDN/STING/TBK-1 signaling treatment of palpable B16 tumor resulted in regression of 30-60% of these non-immunogenic tumors. When the STINGVAX treated tumor microenvironment was examined, both IFNγ+CD8+ and PD-L1 was upregulated, potentially demonstrating an adaptive immune resistance mechanism which would render STINGVAX an excellent candidate to be combined with anti-PD-1 blockade. Cumulatively, STINGVAX is a novel tumor vaccine with a high potential for translation in clinical oncology.

Citation Format: Thomas W. Dubensky, Meredith L. Leong, David B. Kanne, Edward E. Lemmens, Ken Metchette, Weiqun Liu, Marcella Fasso, Juan Fu, Joshua J. Woodward, Drew Pardoll, Daniel A. Portnoy, Young J. Kim. STINGVAX - A novel tumor vaccine with cyclic dinucleotides - can induce potent anti-tumor responses in vivo. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4573. doi:10.1158/1538-7445.AM2013-4573

Killed but metabolically active vaccines

Beginning in the 20th century and continuing into the new millennia, vaccines against numerous diseases have had an unquestioned principal role of both enhancing the quality of life and increasing life expectancy (Rappuoli R, Mandl CW, Black S, De Gregorio E: Vaccines for the twenty-first century society. Nat Rev Immunol 2011, 11:865-872). Despite this success and the development of sophisticated new vaccine technologies, there remain multiple infectious diseases including tuberculosis, malaria and AIDS that await an effective prophylactic vaccine. In addition, there have been recent clinical successes among individuals with cancer using vaccine treatment strategies-so-called therapeutic vaccines-that stimulate tumor specific immunity and increase survival (Kantoff PW, Higano CS, Shore ND, Berger ER, Small EJ, Penson DF, Redfern CH, Ferrari AC, Dreicer R, Sims RB, et al.: Sipuleucel-T immunotherapy for castration-resistant prostate cancer. New Engl J Med 2010, 363:411-422). Here we summarize a new class of vaccines termed Killed But Metabolically Active (KBMA). KBMA vaccines are whole pathogenic or attenuated organisms killed through photochemical inactivation and cannot cause disease, yet retain sufficient metabolic activity to initiate a potent immune response. KBMA vaccines have two broad applications. First, recombinant KBMA vaccines encoding selected antigens relevant to infectious disease or cancer can be used to elicit a desired immune response. In the second application, KBMA vaccines can be derived from attenuated forms of a targeted pathogen, allowing for the presentation of the entire antigenic repertoire to the immune system, of particular importance when the correlates of protection are unknown.

A live-attenuated Listeria vaccine (ANZ-100) and a live-attenuated Listeria vaccine expressing mesothelin (CRS-207) for advanced cancers: phase I studies of safety and immune induction

PURPOSE

Listeria monocytogenes (Lm)-based vaccines stimulate both innate and adaptive immunity. ANZ-100 is a live-attenuated Lm strain (Lm ΔactA/ΔinlB). Uptake by phagocytes in the liver results in local inflammatory responses and activation and recruitment of natural killer (NK) and T cells, in association with increased survival of mice bearing hepatic metastases. The Lm ΔactA/ΔinlB strain, engineered to express human mesothelin (CRS-207), a tumor-associated antigen expressed by a variety of tumors, induces mesothelin-specific T-cell responses against mesothelin-expressing murine tumors. These two phase I studies test ANZ-100 and CRS-207 in subjects with liver metastases and mesothelin-expressing cancers, respectively.

EXPERIMENTAL DESIGN

A single intravenous injection of ANZ-100 was evaluated in a dose escalation study in subjects with liver metastases. Nine subjects received 1 × 10(6), 3 × 10(7), or 3 × 10(8) colony-forming units (cfu). CRS-207 was evaluated in a dose-escalation study in subjects with mesothelioma, lung, pancreatic, or ovarian cancers. Seventeen subjects received up to 4 doses of 1 × 10(8), 3 × 10(8), 1 × 10(9), or 1 × 10(10) cfu.

RESULTS

A single infusion of ANZ-100 was well tolerated to the maximum planned dose. Adverse events included transient laboratory abnormalities and symptoms associated with cytokine release. Multiple infusions of CRS-207 were well tolerated up to 1 × 10(9) cfu, the determined maximum tolerated dose. Immune activation was observed for both ANZ-100 and CRS-207 as measured by serum cytokine/chemokine levels and NK cell activation. In the CRS-207 study, listeriolysin O and mesothelin-specific T-cell responses were detected and 37% of subjects lived ≥15 months.

CONCLUSIONS

ANZ-100 and CRS-207 administration was safe and resulted in immune activation.

Adjuvants for cancer vaccines

The recent FDA approval of sipuleucel-T (Provenge), a patient-specific immunotherapy for androgen-independent prostate cancer developed by Dendreon Corporation, has provided support for the concept of cellular immunotherapy as an approach to cancer treatment. Adjuvants are compounds that enhance the potency of the antigen-specific immune response and can be an essential component of an efficacious vaccine. Cervarix is a prophylactic vaccine against human papilloma virus (HPV) types 16 and 18, which can cause cervical cancer, and recently received approval from the FDA, due in part to the protective immunity it conferred against not only HPV types contained in the vaccine but in addition to oncogenic HPV strains that were not contained in the vaccine. Cervarix is formulated with MPL (monophosphoryl lipid A), a TLR-4 targeted adjuvant shown to promote immune response broadening. The recent FDA approvals of these pioneering vaccines are landmark events, and will likely usher in renewed interest and investment in the development of new therapeutic cancer vaccine candidates. In this review, we examine new molecularly defined adjuvants and formulations and its application to cancer vaccines under development.

Suppression of cell-mediated immunity following recognition of phagosome-confined bacteria

Listeria monocytogenes is a facultative intracellular pathogen capable of inducing a robust cell-mediated immune response to sub-lethal infection. The capacity of L. monocytogenes to escape from the phagosome and enter the host cell cytosol is paramount for the induction of long-lived CD8 T cell–mediated protective immunity. Here, we show that the impaired T cell response to L. monocytogenes confined within a phagosome is not merely a consequence of inefficient antigen presentation, but is the result of direct suppression of the adaptive response. This suppression limited not only the adaptive response to vacuole-confined L. monocytogenes, but negated the response to bacteria within the cytosol. Co-infection with phagosome-confined and cytosolic L. monocytogenes prevented the generation of acquired immunity and limited expansion of antigen-specific T cells relative to the cytosolic L. monocytogenes strain alone. Bacteria confined to a phagosome suppressed the production of pro-inflammatory cytokines and led to the rapid MyD88-dependent production of IL-10. Blockade of the IL-10 receptor or the absence of MyD88 during primary infection restored protective immunity. Our studies demonstrate that the presence of microbes within a phagosome can directly impact the innate and adaptive immune response by antagonizing the signaling pathways necessary for inflammation and the generation of protective CD8 T cells.

Little is understood about how the immune system distinguishes between pathogenic and non-pathogenic microbes. Limiting or preventing infections by intracellular pathogens requires the activation of innate immunity and the consequent generation of effector and memory T cells, which recognize and kill infected cells. Investigators are currently testing attenuated versions of pathogenic microbes as vaccines in an attempt to generate pathogen-specific T cells without causing disease. Unfortunately, attenuated microbes often fail to elicit long-lived protective immunity. We hypothesized that attenuated bacterial vaccines do not immunize because they fail to activate a stimulatory arm of host innate immune receptors. However, we found that these attenuated bacterial vaccines are not simply prevented from activating immunity, but rather generate a negative signal that inhibits the desired immune response. These studies may explain why the addition of an adjuvant to ineffective vaccines does not necessarily improve immunogenicity. Furthermore, these studies provide a framework for the development of attenuated vaccines that do not inhibit the desired immune responses.

KBMA Listeria monocytogenes is an effective vector for DC-mediated induction of antitumor immunity

Vaccine strategies that utilize human DCs to enhance antitumor immunity have yet to realize their full potential. Approaches that optimally target a spectrum of antigens to DCs are urgently needed. Here we report the development of a platform for loading DCs with antigen. It is based on killed but metabolically active (KBMA) recombinant Listeria monocytogenes and facilitates both antigen delivery and maturation of human DCs. Highly attenuated KBMA L. monocytogenes were engineered to express an epitope of the melanoma-associated antigen MelanA/Mart-1 that is recognized by human CD8+ T cells when presented by the MHC class I molecule HLA-A*0201. The engineered KBMA L. monocytogenes induced human DC upregulation of costimulatory molecules and secretion of pro-Th1 cytokines and type I interferons, leading to effective priming of Mart-1-specific human CD8+ T cells and lysis of patient-derived melanoma cells. KBMA L. monocytogenes expressing full-length NY-ESO-1 protein, another melanoma-associated antigen, delivered the antigen for presentation by MHC class I and class II molecules independent of the MHC haplotype of the DC donor. A mouse therapeutic tumor model was used to show that KBMA L. monocytogenes efficiently targeted APCs in vivo to induce protective antitumor responses. Together, our data demonstrate that KBMA L. monocytogenes may be a powerful platform that can both deliver recombinant antigen to DCs for presentation and provide a potent DC-maturation stimulus, making it a potential cancer vaccine candidate.

Promises and challenges for the development of Listeria monocytogenes-based immunotherapies

Active immunotherapy has shown great promise in preclinical models for the treatment of infectious and malignant disease. Yet, these promising results have not translated into approved therapies. One of the major deficits of active immunotherapies tested to date in advanced clinical studies has been their inability to stimulate both arms of the immune system appropriately. The interest in using recombinant bacteria as vaccine vectors for active immunotherapy derives in part from their ability to stimulate multiple innate immune pathways and, at the same time, to deliver antigen for presentation to the adaptive immune system. This review will focus on the development of live-attenuated and killed strains of the intracellular bacterium Listeria monocytogenes for treatment of chronic infections and cancer. Early clinical trials intended to demonstrate safety as well as proof of concept have recently been initiated in several indications. Advances in molecular engineering as well as successes and challenges for clinical development of L. monocytogenes-based vaccines will be discussed.

Activation of immature hepatic NK cells as immunotherapy for liver metastatic disease

NK cells can identify and eliminate emerging tumors due to altered expression of activating and inhibitory ligands on aberrant cells, a process that is greatly enhanced following NK cell activation. As a principal site of both tumor metastases and immature NK cells, the liver represents a unique anatomic location in which activation of the innate immune system could provide substantial therapeutic benefit. We describe here the NK cell-dependent destruction of a primary hepatic tumor following infection with an attenuated intracellular bacterium derived from Listeria monocytogenes. NK cell-mediated immunity correlated with the ordered migration and maturation of NK cells within the liver. Cytolytic activity was partially dependent on NKG2D-mediated tumor cell recognition, but surprisingly was still effective in the absence of type I IFN. Significantly, NK cell-mediated destruction of a primary hepatic tumor in infected mice led to long-lived CD4- and CD8 T cell-dependent tumor-specific adaptive immunity. These findings establish that activation and differentiation of immature NK cells using complex microbial stimuli can elicit potent anti-tumor activity within the liver, promote cross-presentation of tumor-derived Ags leading to long-lived systemic anti-tumor immunity, and suggests a paradigm for clinical intervention of liver metastatic carcinoma.

Inactivation of parvovirus B19 in human platelet concentrates by treatment with amotosalen and ultraviolet A illumination

BACKGROUND

The human erythrovirus B19 (B19) is a small (18- to 26-nm) nonenveloped virus with a single-stranded DNA genome of 5.6 kb. B19 is clinically significant and is also generally resistant to pathogen inactivation methods. Photochemical treatment (PCT) with amotosalen and ultraviolet A (UVA) inactivates viruses, bacteria, and protozoa in platelets (PLTs) and plasma prepared for transfusion. In this study, the capacity of PCT to inactivate B19 in human PLT concentrates was evaluated.

STUDY DESIGN AND METHODS

B19 inactivation was measured by a novel enzyme-linked immunosorbent spot (ELISPOT) erythroid progenitor cell infectivity assay and by inhibition of long-range (up to 4.3 kb) polymerase chain reaction (PCR), under conditions where the whole coding region of the viral genome was amplified. B19-infected plasma was used to test whether incubation of amotosalen with virus before PCT enhanced inactivation compared to immediate PCT.

RESULTS

Inactivation of up to 5.8 log of B19 as measured by the infectivity assay, or up to 6 logs as measured by PCR inhibition can be achieved under non-limiting conditions. Inactivation efficacy was found to increase with incubation prior to UVA illumination. Without incubation prior to illumination 2.1 +0.4 log was inactivated as determined by infectivity assay. When measured by PCR inhibition, inactivation varied inversely with amplicon size. When primers that spanned the entire coding region of the B19 genome were used, maximum inhibition of PCR amplification was demonstrated.

CONCLUSION

Under defined conditions, PCT with amotosalen combined with UVA light can be used to inactivate B19, a clinically significant virus that can be transmitted through blood transfusion, and heretofore has been demonstrated to be refractory to inactivation.

Role of PD-1 and its ligand, B7-H1, in early fate decisions of CD8 T cells

Expression of the PD-1 receptor on T cells has been shown to provide an important inhibitory signal that down-modulates peripheral effector responses in normal tissues and tumors. Furthermore, PD-1 up-regulation on chronically activated T cells can maintain them in a partially reversible inactive state. The function of PD-1 in the very early stages of T-cell response to antigen in vivo has not been fully explored. In this study, we evaluate the role of PD-1 and its 2 B7 family ligands, B7-H1 (PD-L1) and B7-DC (PD-L2), in early fate decisions of CD8 T cells. We show that CD8 T cells specific for influenza hemagglutinin (HA) expressed as a self-antigen become functionally tolerized and express high levels of surface PD-1 by the time of their first cell division. Blockade of PD-1 or B7-H1, but not B7-DC, at the time of self-antigen encounter mitigates tolerance induction and results in CD8 T-cell differentiation into functional cytolytic T lymphocytes (CTLs). These findings demonstrate that, in addition to modulating effector functions in the periphery, B7-H1:PD-1 interactions regulate early T-cell-fate decisions.

Cytosolic entry controls CD8+-T-cell potency during bacterial infection

Interaction with host immunoreceptors during microbial infection directly impacts the magnitude of the ensuing innate immune response. How these signals affect the quality of the adaptive T-cell response remains poorly understood. Utilizing an engineered strain of the intracellular pathogen Listeria monocytogenes that infects cells but fails to escape from the phagosome, we demonstrate the induction of long-lived memory T cells that are capable of secondary expansion and effector function but are incapable of providing protective immunity. We demonstrate that microbial invasion of the cytosol is required for dendritic cell activation and integration of CD40 signaling, ultimately determining the ability of the elicited CD8+-T-cell pool to protect against lethal wild-type L. monocytogenes challenge. These results reveal a crucial role for phagosomal escape, not for delivery of antigen to the class I major histocompatibility complex pathway but for establishing the appropriate cellular context during CD8+-T-cell priming.

Selective targeting of antitumor immune responses with engineered live-attenuated Listeria monocytogenes

Improved immunization and ex vivo T-cell culture strategies can generate larger numbers and more potent tumor-specific effector cells than previously possible. Nonetheless, the capacity of these cells to eliminate established tumors is limited by their ability to efficiently enter tumor-bearing organs and mediate their effector function. In the current study, we show that the administration of an engineered organ-homing microbe selectively targets tumor-specific immune responses to metastases within that organ. Specifically, an attenuated Listeria monocytogenes strain, which preferentially infects the liver following systemic administration, dramatically enhances the activity of a cancer vaccine against liver metastases but not metastases in the lung. This enhanced activity results from both local recruitment of innate immune effectors as well as concentration and increased activation of vaccine-induced antitumor T cells within the liver. These findings show a general approach to focus systemic cancer immunotherapies to specific organs bearing tumor metastases by taking advantage of differential tropisms and the proinflammatory nature of microbes.