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

Suppression of the primary T cell response is antigen-independent.

<p>(A) Mice were infected with the indicated combinations of 1×10⁵ CFU ActA-Lm, 1×10⁵ CFU ActA-Lm–OVA, 1×10⁸ CFU LLO-Lm, and 1×10⁸ CFU LLO-Lm-OVA. 7 days later, the frequency of OVA_257–264 -specific CD8 and LLO_190–201 -specific CD4 T cells was determined by IFN-γ intracellular cytokine staining. (B) ActA-Lm and LLO-Lm <i>L. monocytogenes</i> were engineered to express 4 defined epitopes from vaccinia virus. Mice were infected intravenously with the indicated combinations of ActA-Lm-QuadVacc and LLO-Lm-QuadVacc. 7 days later, spleens were harvested and the frequency of CD8 T cells specific for each epitope was determined by IFN-γ intracellular cytokine staining. Total splenocyte number and absolute CD8 T cells per spleen were consistent between all groups. Values in each plot represent the mean±SEM of IFN-γ+ cells within the CD4 or CD8 population from 5 animals per group.</p

<i>L. monocytogenes</i> within a phagosome impairs protective immunity.

<p>Mice were infected with 1×10⁵ CFU ActA-Lm–OVA alone, or in combination with increasing doses of phagosome-confined LLO-Lm-OVA. (A) Mice were challenged 60 days later with a lethal dose of wt <i>L. monocytogenes</i>-OVA. Spleens were harvested 3 days later and CFU per spleen determined. (B) Mice were infected with 1×10⁵ CFU ActA-Lm-Erm^R alone, or in combination with 1×10⁸ CFU LLO-Lm. Erythromycin-resistant colonies were enumerated from the spleen and liver over 96 hours. Each data point represents the mean and standard error of 5 mice per group. (C) Mice were infected with 1×10⁵ CFU ActA-Lm-Erm^R alone, or in combination with 1×10⁸ CFU LLO-Lm. Erythromycin-resistant colonies were enumerated from the spleen and liver at 1 and 6 hours post infection. Each data point represents the mean and standard error of 5 mice per group from one representative experiment of two. (D) Bone marrow-derived macrophages were infected with ActA-Lm-Erm^R alone (at 1∶10,000), or in combination with 1×10⁸ CFU LLO-Lm (at 1∶200). Erythromycin-resistant colonies were enumerated at the indicated timepoints. Each data point represents the mean and standard error of 3 independent coverslips per timepoint from one representative experiment of two. (E) Mice were infected with the indicated combinations of 1×10⁵ CFU ActA-Lm–OVA and 1×10⁸ heat-killed ActA-Lm–OVA. 30 days later, mice were challenged with 1×10⁵ CFU of wt <i>L. monocytogenes</i>-OVA. Spleens were harvested 3 days later and CFU per spleen determined. (F) Mice were infected with 1×10⁵ CFU ActA-Lm, 1×10⁵ CFU <i>B. subtilis</i>, or the combination of both strains. 30 days post infection, mice were challenged and CFU determined. (G) Mice were infected with the indicated combinations of 1×10³ CFU wild-type and 1×10⁶ CFU LLO-Lm. 58 days later, mice were challenged with 1×10⁵ CFU of wild-type <i>L. monocytognes</i>. Spleens were harvested 3 days later and CFU per spleen determined. In all panels, each point represents a single animal with † indicating animals that died before CFU were determined. Lines indicate the median of each group.</p

IL-10 receptor blockade during T cell priming prevents the suppressive effects of <i>L. monocytogenes</i> within a phagosome.

<p>Mice were infected with ActA-Lm–OVA, LLO-Lm-OVA, or the combination of both strains in combination with αIL-10R antibody. (A) 30 days post infection mice were challenged with a lethal dose of wt <i>L. monocytogenes</i>-OVA. Spleens were harvested 3 days later and CFU per spleen determined. Each bar represents the mean and standard error of 5 mice per group. (B) B6.MyD88−/− mice were infected with 1×10⁵ CFU ActA-Lm-OVA, 1×10⁸ CFU LLO-Lm-OVA, or the combination of both strains. 16 weeks later, mice were challenged with 1×10³ CFU wt <i>L. monocytogenes</i>-OVA. Spleens and livers were harvested 3 days later and CFU per organ determined. Each bar represents the mean and standard error of 3–5 mice per group. Data are from one representative experiment of two.</p

<i>L. monocytogenes</i> within a phagosome suppress the host inflammatory response to bacteria within the cytosol.

<p>(A) Mice were infected with 1×10⁵ CFU ActA-Lm–OVA alone, or in combination with increasing doses of LLO-Lm-OVA. Serum was collected 24 hours later and assayed for IFN-γ, IL-12p70, IL-6, and MCP-1. (B) C57Bl/6 and B6.MyD88−/− mice were infected with 1×10⁵ CFU ActA-Lm–OVA, 1×10⁸ CFU LLO-Lm-OVA, or the combination of both strains. Serum was collected 4 hours later and assayed for IL-10 and IL-12p40. Bars represent the mean and standard error of 5 mice per group.</p

<i>L. monocytogenes</i> within a phagosome impairs the primary T cell response.

<p>Mice were infected with 1×10⁵ CFU ActA-Lm–OVA alone, or in combination with increasing doses of LLO-Lm-OVA. 7 days later, the frequency of OVA_257–264-specific CD8 T cells and LLO_190–201-specific CD4 T cells was determined by pentamer and IFN-γ intracellular cytokine staining. Total splenocyte number and absolute CD8 T cells per spleen were consistent between all groups. Values in each plot represent the mean±SEM of antigen-specific cells within the CD4 or CD8 population from 5 animals per group.</p

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

Summary: 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. : Van Dis et al. demonstrate that STING-activating cyclic dinucleotides provide significant protection when used as adjuvants in a protein subunit vaccine against Mycobacterium tuberculosis and show that mucosal administration of this vaccine elicits a Th17 immune response that correlates with enhanced protection. Keywords: Mycobacterium tuberculosis, vaccine adjuvant, cyclic dinucleotides, Th1

Magnitude of Therapeutic STING Activation Determines CD8+ T Cell-Mediated Anti-tumor Immunity

Summary: Intratumoral (IT) STING activation results in tumor regression in preclinical models, yet factors dictating the balance between innate and adaptive anti-tumor immunity are unclear. Here, clinical candidate STING agonist ADU-S100 (S100) is used in an IT dosing regimen optimized for adaptive immunity to uncover requirements for a T cell-driven response compatible with checkpoint inhibitors (CPIs). In contrast to high-dose tumor ablative regimens that result in systemic S100 distribution, low-dose immunogenic regimens induce local activation of tumor-specific CD8+ effector T cells that are responsible for durable anti-tumor immunity and can be enhanced with CPIs. Both hematopoietic cell STING expression and signaling through IFNAR are required for tumor-specific T cell activation, and in the context of optimized T cell responses, TNFα is dispensable for tumor control. In a poorly immunogenic model, S100 combined with CPIs generates a survival benefit and durable protection. These results provide fundamental mechanistic insights into STING-induced anti-tumor immunity. : Intratumoral STING pathway activation is a promising therapeutic approach to treat cancer. While high doses of STING agonist are effective at clearing injected tumors, Sivick et al. find that lower doses of STING agonist are optimal for generating robust systemic tumor-specific T cell responses and durable anti-tumor immunity. Keywords: STING, cyclic dinucleotide, intratumoral, ImmunoOncology, anti-tumor immunity, CD8+ T cell, checkpoint inhibitor, ADU-S100, type I interferon, abscopal immunit

Interferon-producing killer dendritic cells provide a link between innate and adaptive immunity

Natural killer (NK) cells and dendritic cells (DCs) are, respectively, central components of innate and adaptive immune responses 1,2. We describe here a third DC lineage, termed interferon-producing killer DCs (IKDCs), distinct from conventional DCs and plasmacytoid DCs and with the molecular expression profile of both NK cells and DCs. They produce substantial amounts of type I interferons (IFN) and interleukin (IL)-12 or IFN-γ, depending on activation stimuli. Upon stimulation with CpG oligodeoxynucleotides, ligands for Toll-like receptor (TLR)-9, IKDCs kill typical NK target cells using NK-activating receptors. Their cytolytic capacity subsequently diminishes, associated with the loss of NKG2D receptor (also known as Klrk1) and its adaptors, Dap10 and Dap12. As cytotoxicity is lost, DC-like antigen-presenting activity is gained, associated with upregulation of surface major histocompatibility complex class II (MHC II) and costimulatory molecules, which formally distinguish them from classical NK cells. In vivo, splenic IKDCs preferentially show NK function and, upon systemic infection, migrate to lymph nodes, where they primarily show antigen-presenting cell activity. By virtue of their capacity to kill target cells, followed by antigen presentation, IKDCs provide a link between innate and adaptive immunity. © 2006 Nature Publishing Group.link_to_subscribed_fulltex