Conventional Dendritic Cells Type Research Articles

Stem cells engineered to release IFNβ and scFv-PD1 target glioblastoma and alter the tumor microenvironment

Highly malignant brain tumors, glioblastomas (GBM), are immunosuppressive, thereby limiting current promising immunotherapeutic approaches. In this study, we first created interferon receptor 1 (IFNAR1) knockout allogeneic mesenchymal stem cells (MSC) to secrete dual-function pro-apoptotic and immunomodulatory Interferon (IFN) β (MSCKO-IFNβ) using a single lentiviral vector CRISPR/Cas9 system, and tested their efficacy in mouse models of immunosuppressive GBM. We show that MSCKO-IFNβ induce apoptosis in GBM cells and upregulate the cell surface expression of programmed death ligand (PDL)-1 in tumor cells. Next, we engineered MSCKO to release a secretable single-chain variable fragment (scFv) to block programmed death (PD)-1 and show the ability of MSCKO-scFv-PD1 to enhance T cell activation and T cell-mediated tumor cell killing. We further tested the effect of MSCKO-scFv-PD1 in vivo to reduce the tumor growth and improve the survival of mice bearing GBMs after tumor sensitization with MSCKO-IFNβ. To simultaneously express both immune modulators, we engineer MSCKO-IFNβ to co-express scFv-PD1 (MSCKO-IFNβ-scFv-PD1) and show the expression of both IFNβ and scFv-PD1 in vitro leads to T cell activation and lowers the viability of tumor cells. Furthermore, to mimic the clinical scenario of GBM tumor resection and subsequent treatment, we show that hyaluronic acid (HA) gel encapsulated MSCKO-IFNβ-scFv-PD1 treatment of resected tumors results in the increase of CD4+ and CD8+ T cells, mature conventional Dendritic Cells type II (cDC2) and activation of microglia as compared to the control treatment group. Overall, these results show that MSCKO-IFNβ-scFv-PD1 have the ability to shape the tumor microenvironment and enhance therapeutic outcome in GBM.

Abstract 6655: Oncolytic adenovirus dually expressing interferon beta and membrane-stable CD40 ligand increases polyfunctional CD8+T cells associated with antitumor activity

Abstract MEM-288 is a dual-transgene armed oncolytic adenovirus in phase 1 clinical development as a standalone agent and in combination with immune checkpoint inhibitors (ICI). It encodes two potent immune agonists: IFNβ and a recombinant membrane-stable chimeric form of CD40L (MEM40). We previously demonstrated this agonist combination is better than either agonist individually to activate conventional dendritic cells type 1 (cDC1) crucial for CD8+ T cell cross-priming, and to increase tumor-antigen reactive CD8+ T cells. Furthermore, first-in-human Phase 1 clinical trial (NCT05076760) results of MEM-288 for advanced non-small cell lung cancer (NSCLC) and other solid tumors showed MEM-288 tumor shrinkage was associated with systemic antitumor T cell immunity as demonstrated by cytokine, T cell clonotype, and tumor neoantigen analysis. Here, we investigated the precise nature of the localized and systemic T cell response induced by MEM40 + IFNβ in preclinical tumor models. Single-cell RNA sequencing of tumor infiltrating T lymphocytes (TILs) revealed that MEM40 + IFNβ elicited a strong increase in T cells expressing Granzyme B and PRF1, key effector cytokines and cytotoxicity mediators. We tracked the CD8+ T cell response in CD45.1 C57BL/6 mice implanted with syngeneic B16 tumor expressing the model antigen OVA. Interestingly, intratumoral treatment with adenovirus encoding MEM40 + IFNβ did not cause an appreciable increase in absolute numbers of antigen-reactive CD8+ T cells, despite tumor growth inhibition. However, MEM40 + IFNβ compared to control unarmed adenovirus induced a significant (p < 0.005) 5-fold increase in polyfunctional IFNγ+TNFα+PRF1+ and IFNγ+TNFα+Granzyme B+ CD8+ T cells. Polyfunctional CD8+ T cells have the capacity to simultaneously produce effector cytokines and cytotoxicity mediators and are known to be strongly associated with antitumor T cell activity. The robust polyfunctional CD8+ T cell response in these studies is consistent with T cell-driven antitumor activity found in both our preclinical tumor experiments and our clinical studies in advanced NSCLC patients responding to MEM-288. Overall, our findings suggest MEM40 + IFNβ generates a strong polyfunctional CD8+ T cell response in the TME that warrants continued evaluation to understand the pleiotropic mechanisms of this cancer immunotherapy. Citation Format: Mark J. Cantwell, Andreas N. Saltos, Hong Zheng, Dana Foresman, Amer A. Beg. Oncolytic adenovirus dually expressing interferon beta and membrane-stable CD40 ligand increases polyfunctional CD8+T cells associated with antitumor activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6655.

CDC2 plasticity and acquisition of a DC3-like phenotype mediated by IL-6 and PGE2 in a patient-derived colorectal cancer organoids model.

Metastatic colorectal cancer (CRC) is highly resistant to therapy and prone to recur. The tumor-induced local and systemic immunosuppression allows cancer cells to evade immunosurveillance, facilitating their proliferation and dissemination. Dendritic cells (DCs) are required for the detection, processing, and presentation of tumor antigens, and subsequently for the activation of antigen-specific T cells to orchestrate an effective antitumor response. Notably, successful tumors have evolved mechanisms to disrupt and impair DC functions, underlining the key role of tumor-induced DC dysfunction in promoting tumor growth, metastasis initiation, and treatment resistance. Conventional DC type 2 (cDC2) are highly prevalent in tumors and have been shown to present high phenotypic and functional plasticity in response to tumor-released environmental cues. This plasticity reverberates on both the development of antitumor responses and on the efficacy of immunotherapies in cancer patients. Uncovering the processes, mechanisms, and mediators by which CRC shapes and disrupts cDC2 functions is crucial to restoring their full antitumor potential. In this study, we use our recently developed 3D DC-tumor co-culture system to investigate how patient-derived primary and metastatic CRC organoids modulate cDC2 phenotype and function. We first demonstrate that our collagen-based system displays extensive interaction between cDC2 and tumor organoids. Interestingly, we show that tumor-corrupted cDC2 shift toward a CD14+ population with defective expression of maturation markers, an intermediate phenotype positioned between cDC2 and monocytes, and impaired T-cell activating abilities. This phenotype aligns with the newly defined DC3 (CD14+ CD1c+ CD163+) subset. Remarkably, a comparable population was found to be present in tumor lesions and enriched in the peripheral blood of metastatic CRC patients. Moreover, using EP2 and EP4 receptor antagonists and an anti-IL-6 neutralizing antibody, we determined that the observed phenotype shift is partially mediated by PGE2 and IL-6. Importantly, our system holds promise as a platform for testing therapies aimed at preventing or mitigating tumor-induced DC dysfunction. Overall, our study offers novel and relevant insights into cDC2 (dys)function in CRC that hold relevance for the design of therapeutic approaches.

Mast cells help organize the Peyer's patch niche for induction of IgA responses.

Peyer's patches (PPs) are lymphoid structures situated adjacent to the intestinal epithelium that support B cell responses that give rise to many intestinal IgA-secreting cells. Induction of isotype switching to IgA in PPs requires interactions between B cells and TGFβ-activating conventional dendritic cells type 2 (cDC2s) in the subepithelial dome (SED). However, the mechanisms promoting cDC2 positioning in the SED are unclear. Here, we found that PP cDC2s express GPR35, a receptor that promotes cell migration in response to various metabolites, including 5-hydroxyindoleacetic acid (5-HIAA). In mice lacking GPR35, fewer cDC2s were found in the SED, and frequencies of IgA+ germinal center (GC) B cells were reduced. IgA plasma cells were reduced in both the PPs and lamina propria. These phenotypes were also observed in chimeric mice that lacked GPR35 selectively in cDCs. GPR35 deficiency led to reduced coating of commensal bacteria with IgA and reduced IgA responses to cholera toxin. Mast cells were present in the SED, and mast cell-deficient mice had reduced PP cDC2s and IgA+ cells. Ablation of tryptophan hydroxylase 1 (Tph1) in mast cells to prevent their production of 5-HIAA similarly led to reduced PP cDC2s and IgA responses. Thus, mast cell-guided positioning of GPR35+ cDC2s in the PP SED supports induction of intestinal IgA responses.

Clec12A, CD301b, and FcγRIIB/III define the heterogeneity of murine DC2s and DC3s

Over the last decade, multiple studies have investigated the heterogeneity of murine conventional dendritic cells type 2 (cDC2s). However, their phenotypic similarity with monocytes and macrophages renders their clear identification challenging. By creating a protein atlas utilizing multiparameter flow cytometry, we show that ESAM+ cDC2s are a specialized feature of the spleen strongly differing in their proteome from other cDC2s. In contrast, all other tissues are populated by Clec12A+ cDC2s or Clec12A- cDC2s (high or low for Fcγ receptors, C-type lectin receptors, and CD11b, respectively), rendering Clec12A+ cDC2s classical sentinels. Further, expression analysis of CD301b, Clec12A, and FcγRIIB/III provides a conserved definition of cDC2 heterogeneity, including the discovery of putative FcγRIIB/III+ DC3s across tissues. Finally, our data reveal that cell identity (ontogeny) dictates the proteome that is further fine-tuned by the tissue environment on macrophages and dendritic cells (DCs), while monocytes and plasmacytoid DCs (pDCs) display subset intrinsic default settings.

RWTC-MBTA Vaccine Induces Potent Adaptive Immune Responses Against Glioblastomas via Dynamic Activation of Dendritic Cells.

Despite strides in immunotherapy, glioblastoma multiforme (GBM) remains challenging due to low inherent immunogenicity and suppressive tumor microenvironment. Converting "cold" GBMs to "hot" is crucial for immune activation and improved outcomes. This study comprehensively characterized a therapeutic vaccination strategy for preclinical GBM models. The vaccine consists of Mannan-BAM-anchored irradiated whole tumor cells, Toll-like receptor ligands [lipoteichoic acid (LTA), polyinosinic-polycytidylic acid (Poly (I:C)), and resiquimod (R-848)], and anti-CD40 agonistic antibody (rWTC-MBTA). Intracranial GBM models (GL261, SB28 cells) are used to evaluate the vaccine efficacy. A substantial number of vaccinated mice exhibited complete regression of GBM tumors in a T-cell-dependent manner, with no significant toxicity. Long-term tumor-specific immune memory is confirmed upon tumor rechallenge. In the vaccine-draining lymph nodes of the SB28 model, rWTC-MBTA vaccination triggered a major rise in conventional dendritic cell type 1 (cDC1) 12h post-treatment, followed by an increase in conventional dendritic cell type 2 (cDC2), monocyte-derived dendritic cell (moDC), and plasmacytoid dendritic cell (pDC) on Day 5 and Day 13. Enhanced cytotoxicity of CD4+ and CD8+ T cells in vaccinated mice is verified in co-culture with tumor cells. Analyses of immunosuppressive signals (T-cell exhaustion, myeloid-derived suppressor cells (MDSC), M2 macrophages) in the GBM microenvironment suggest potential combinations with other immunotherapies for enhanced efficacy. In conclusion, the authors findings demonstrate that rWTC-MBTA induces potent and long-term adaptive immune responses against GBM.

PGE2-EP4 signaling steers cDC2 maturation toward the induction of suppressive T-cell responses.

Dendritic cells (DCs) shape adaptive immunity in response to environmental cues such as cytokines or lipid mediators, including prostaglandin E2 (PGE2). In cancer, tumors are known to establish an enriched PGE2 microenvironment. Tumor-derived PGE2 primes regulatory features across immune cells, including DCs, facilitating tumor progression. PGE2 shapes DC function by providing signaling via its two so-called E-prostanoid receptors (EPs) EP2 and EP4. Although studies with monocyte-derived DCs have shown the importance of PGE2 signaling, the role of PGE2-EP2/EP4 on conventional DCs type 2 (cDC2s), is still poorly defined. In this study, we investigated the function of EP2 and EP4 using specific EP antagonists on human cDC2s. Our results show that EP2 and EP4 exhibit different functions in cDC2s, with EP4 modulating the upregulation of activation markers (CD80, CD86, CD83, MHC class II) and the production of IL-10 and IL-23. Furthermore, PGE2-EP4 boosts CCR type 7-based migration as well as a higher T-cell expansion capacity, characterized by the enrichment of suppressive rather than pro-inflammatory T-cell populations. Our findings are relevant to further understanding the role of EP receptors in cDC2s, underscoring the benefit of targeting the PGE2-EP2/4 axis for therapeutic purposes in diseases such as cancer.

SYK ubiquitination by CBL E3 ligases restrains cross-presentation of dead cell-associated antigens by type 1 dendritic cells

Cross-presentation of dead cell-associated antigens by conventional dendritic cells type 1 (cDC1s) is critical for CD8+ Tcells response against many tumors and viral infections. It is facilitated by DNGR-1 (CLEC9A), an SYK-coupled cDC1 receptor that detects dead cell debris. Here, we report that DNGR-1 engagement leads to rapid activation of CBL and CBL-B E3 ligases to cause K63-linked ubiquitination of SYK and terminate signaling. Genetic deletion of CBL E3 ligases or charge-conserved mutation of target lysines within SYK abolishes SYK ubiquitination and results in enhanced DNGR-1-dependent antigen cross-presentation. We also find that cDC1 deficient in CBL E3 ligases are more efficient at cross-priming CD8+ Tcells to dead cell-associated antigens and promoting host resistance to tumors. Our findings reveal a role for CBL-dependent ubiquitination in limiting cross-presentation of dead cell-associated antigens and highlight an axis of negative regulation of cDC1 activity that could be exploited to increase anti-tumor immunity.

XCR1 expression distinguishes human conventional dendritic cell type 1 with full effector functions from their immediate precursors

Dendritic cells (DCs) are major regulators of innate and adaptive immune responses. DCs can be classified into plasmacytoid DCs and conventional DCs (cDCs) type 1 and 2. Murine and human cDC1 share the mRNA expression of XCR1. Murine studies indicated a specific role of the XCR1-XCL1 axis in the induction of immune responses. Here, we describe that human cDC1 can be distinguished into XCR1- and XCR1+ cDC1 in lymphoid as well as nonlymphoid tissues. Steady-state XCR1+ cDC1 display a preactivated phenotype compared to XCR1- cDC1. Upon stimulation, XCR1+ cDC1, but not XCR1- cDC1, secreted high levels of inflammatory cytokines as well as chemokines. This was associated with enhanced activation of NK cells mediated by XCR1+ cDC1. Moreover, XCR1+ cDC1 excelled in inhibiting replication of Influenza A virus. Further, under DC differentiation conditions, XCR1- cDC1 developed into XCR1+ cDC1. After acquisition of XCR1 expression, XCR1- cDC1 secreted comparable level of inflammatory cytokines. Thus, XCR1 is a marker of terminally differentiated cDC1 that licenses the antiviral effector functions of human cDC1, while XCR1- cDC1 seem to represent a late immediate precursor of cDC1.

Complement C1q essential for aeroallergen sensitization via CSF1R+ conventional dendritic cells type 2

Dendritic cells (DCs) are heterogeneous, comprising multiple subsets with unique functional specifications. Our previous work has demonstrated that the specific conventional type 2 DC subset, CSF1R+cDC2s, plays a critical role in sensing aeroallergens. It remains to be understood how CSF1R+cDC2s recognize inhaled allergens. We sought to elucidate the transcriptomic programs and receptor-ligand interactions essential for function of this subset in allergen sensitization. We applied single-cell RNA sequencing to mouse lung DCs. Conventional DC-selective knockout mouse models were employed, and mice were subjected to inhaled allergen sensitization with multiple readouts of asthma pathology. Under the clinical arm of this work, human lung transcriptomic data were integrated with mouse data, and bronchoalveolar lavage (BAL) specimens were collected from subjects undergoing allergen provocation, with samples assayed for C1q. We found that C1q is selectively enriched in lung CSF1R+cDC2s, but not in other lung cDC2 or cDC1 subsets. Depletion of C1q in conventional DCs significantly attenuates allergen sensing and features of asthma. Additionally, we found that C1q binds directly to human dust mite allergen, and the C1q receptor CD91 (LRP1) is required for lung CSF1R+cDC2s to recognize the C1q-allergen complex and induce allergic lung inflammation. Lastly, C1q is enriched in human BAL samples following subsegmental allergen challenge, and human RNA sequencing data demonstrate close homology between lung IGSF21+DCs and mouse CSF1R+cDC2s. C1q is secreted from the CSF1R+cDC2 subset among conventional DCs. Our data indicate that the C1q-LRP1 axis represents a candidate for translational therapeutics in the prevention and suppression of allergic lung inflammation.

Conventional dendritic cells type 1 are strongly enriched, quiescent and relatively tolerogenic in local inflammatory arthritis.

Dendritic cells (DC) are crucial for initiating and shaping immune responses. So far, little is known about the functional specialization of human DC subsets in (local) inflammatory conditions. We profiled conventional (c)DC1, cDC2 and monocytes based on phenotype, transcriptome and function from a local inflammatory site, namely synovial fluid (SF) from patients suffering from a chronic inflammatory condition, Juvenile Idiopathic Arthritis (JIA) as well as patients with rheumatoid arthritis (RA). Paired PB and SF samples from 32 JIA and 4 RA patients were collected for mononuclear cell isolation. Flow cytometry was done for definition of antigen presenting cell (APC) subsets. Cell sorting was done on the FACSAria II or III. RNA sequencing was done on SF APC subsets. Proliferation assays were done on co-cultures after CD3 magnetic activated cell sorting (MACS). APC Toll-like receptor (TLR) stimulation was done using Pam3CSK4, Poly(I:C), LPS, CpG-A and R848. Cytokine production was measured by Luminex. cDC1, a relatively small DC subset in blood, are strongly enriched in SF, and showed a quiescent immune signature without a clear inflammatory profile, low expression of pathogen recognition receptors (PRRs), chemokine and cytokine receptors, and poor induction of T cell proliferation and cytokine production, but selective production of IFNλ upon polyinosinic:polycytidylic acid exposure. In stark contrast, cDC2 and monocytes from the same environment, showed a pro-inflammatory transcriptional profile, high levels of (spontaneous) pro-inflammatory cytokine production, and strong induction of T cell proliferation and cytokine production, including IL-17. Although the cDC2 and monocytes showed an overlapping transcriptional core profile, there were clear differences in the transcriptional landscape and functional features, indicating that these cell types retain their lineage identity in chronic inflammatory conditions. Our findings suggest that at the site of inflammation, there is specific functional programming of human DCs, especially cDC2. In contrast, the enriched cDC1 remain relatively quiescent and seemingly unchanged under inflammatory conditions, pointing to a potentially more regulatory role.

Reprogramming Cancer Cells to Antigen-presenting Cells.

Cancer cells evade the immune system by downregulating antigen presentation. Although immune checkpoint inhibitors (ICI) and adoptive T-cell therapies revolutionized cancer treatment, their efficacy relies on the intrinsic immunogenicity of tumor cells and antigen presentation by dendritic cells. Here, we describe a protocol to directly reprogram murine and human cancer cells into tumor-antigen-presenting cells (tumor-APCs), using the type 1 conventional dendritic cell (cDC1) transcription factors PU.1, IRF8, and BATF3 delivered by a lentiviral vector. Tumor-APCs acquire a cDC1 cell-like phenotype, transcriptional and epigenetic programs, and function within nine days (Zimmermannova et al., 2023). Tumor-APCs express the hematopoietic marker CD45 and acquire the antigen presentation complexes MHC class I and II as well as co-stimulatory molecules required for antigen presentation to T cells, but do not express high levels of negative immune checkpoint regulators. Enriched tumor-APCs present antigens to Naïve CD8+ and CD4+ T cells, are targeted by activated cytotoxic T lymphocytes, and elicit anti-tumor responses in vivo. The tumor-APC reprogramming protocol described here provides a simple and robust method to revert tumor evasion mechanisms by increasing antigen presentation in cancer cells. This platform has the potential to prime antigen-specific T-cell expansion, which can be leveraged for developing new cancer vaccines, neoantigen discovery, and expansion of tumor-infiltrating lymphocytes. Key features • This protocol describes the generation of antigen-presenting cells from cancer cells by direct reprogramming using lineage-instructive transcription factors of conventional dendritic cells type I. • Verification of reprogramming efficiency by flow cytometry and functional assessment of tumor-APCs by antigen presentation assays.

Abstract C018: Co-activation of myeloid signaling pathways for pancreatic cancer immunotherapy

Abstract Pancreatic ductal adenocarcinoma (PDA) is characterized by a robust myeloid cell infiltrate. Although myeloid cells in PDA most commonly associate with immunosuppression, they also show plasticity and possess the capacity to engage productive anti-tumor immunity, thereby providing a potential therapeutic vulnerability. Here, we show that distinct myeloid cell subsets infiltrating human PDA express non-redundant activating receptors. Among the most highly expressed receptors was the pattern recognition receptor CLEC7A, which was expressed by macrophages, monocytes, and immature myeloid cells. In contrast, the TNF superfamily member CD40, was expressed by dendritic cells (DC) and SPP1+ macrophages. We hypothesized that combinatory targeting of myeloid activating receptors might be needed to restore productive immunosurveillance in PDA. In immune checkpoint blockade-resistant mouse models of PDA, pharmacologic activation of CLEC7A, using beta glucan (BG) therapy was associated with upregulation of the CXCL2/3-CXCR2 axis and triggered increases in intra-tumoral macrophages and granulocytes. Conversely, CD40 agonist therapy induced activity of the CXCL9-CXCR3 axis and drove conventional DC type 1-dependent infiltration of CD4+ and CD8+ T cells into tumors. Neither myeloid agonist alone, though, was sufficient to trigger durable anti-tumor immunity. By contrast, induction of both myeloid and lymphoid immunosurveillance by co-activation of CLEC7A/CD40 pathways caused tumor eradication, durable tumor control and T cell dependent immunological memory. Depletion of CSF1R+ myeloid cells or T cells significantly reduced the anti-tumor activity of treatment thereby highlighting the cooperativity of innate and adaptive immunity for anti-tumor activity. Moreover, the efficacy of CLEC7A and CD40 co-activation was independent of immune checkpoint blockade. Thus, beyond inhibitory checkpoint molecules on T cells, combinatory activation of non-redundant myeloid signaling pathways can be leveraged to trigger durable anti-tumor immunity, suggesting a new immunotherapy paradigm. A clinical trial of CLEC7A and CD40 agonist therapy for the treatment of patients with PDA is under development. Citation Format: Max M. Wattenberg, Heather Coho, Veronica M. Herrera, Kathleen Graham, Meredith L. Stone, Yuqing Xue, Renee B. Chang, Christopher Cassella, Mingen Liu, Shaanti Choi-Bose, Stacy K. Thomas, Hana Choi, Yan Li, Lauren Melendez, Michael Giannone, Nandita Bose, Gregory L. Beatty. Co-activation of myeloid signaling pathways for pancreatic cancer immunotherapy [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr C018.

A Machine Learning Workflow of Multiplexed Immunofluorescence Images to Interrogate Activator and Tolerogenic Profiles of Conventional Type 1 Dendritic Cells Infiltrating Melanomas of Disease-Free and Metastatic Patients.

Melanoma is the deadliest form of skin cancer. Due to its high mutation rates, melanoma is a convenient model to study antitumor immune responses. Dendritic cells (DCs) play a key role in activating cytotoxic CD8+ T lymphocytes and directing them to kill tumor cells. Although there is evidence that DCs infiltrate melanomas, information about the profile of these cells, their activity states, and potential antitumor function remains unclear, particularly for conventional DCs type 1 (cDC1). Approaches to profiling tumor-infiltrating DCs are hindered by their diversity and the high number of signals that can affect their state of activation. Multiplexed immunofluorescence (mIF) allows the simultaneous analysis of multiple markers, but image-based analysis is time-consuming and often inconsistent among analysts. In this work, we evaluated several machine learning (ML) algorithms and established a workflow of nine-parameter image analysis that allowed us to study cDC1s in a reproducible and accessible manner. Using this workflow, we compared melanoma samples between disease-free and metastatic patients at diagnosis. We observed that cDC1s are more abundant in the tumor infiltrate of the former. Furthermore, cDC1s in disease-free patients exhibit an expression profile more congruent with an activator function: CD40highPD-L1low CD86+IL-12+. Although disease-free patients were also enriched with CD40−PD-L1+ cDC1s, these cells were also more compatible with an activator phenotype. The opposite was true for metastatic patients at diagnosis who were enriched for cDC1s with a more tolerogenic phenotype (CD40lowPD-L1highCD86−IL-12−IDO+). ML-based workflows like the one developed here can be used to analyze complex phenotypes of other immune cells and can be brought to laboratories with standard expertise and computer capacity.

Direct Reprogramming of Mouse and Human Fibroblasts into Conventional Dendritic Cells Type 1

Cell fate reprogramming of adult cells towards pluripotency or unrelated somatic cell-types has been explored in the context of regenerative medicine. Dendritic cells (DCs) are professional antigen presenting cells (APCs) specialized in the recognition, processing and presentation of antigens to T-cells, inducing adaptive immunity. In particular, the mouse conventional DCs type 1 (cDC1) subset or DC1 human equivalent excel on the ability to perform antigen cross-presentation, a critical step for inducing cytotoxic responses. We hypothesized that the unique properties of cDC1s could be induced in unrelated cell-types, allowing the direct control of immune responses with cell reprogramming. Here, the requirements to induce cDC1s were investigated using combinatorial overexpression of Transcription Factors (TFs) in Clec9a-tdTomato mouse fibroblasts. In the hematopoietic system, Clec9a specifically marks the DC lineage, including all conventional dendritic cells type 1 (cDC1). We have identified PU.1, IRF8 and BATF3 (PIB) as sufficient and necessary to induce Clec9a reporter activation, establish DC morphology and activate a cDC1 transcriptional program in mouse fibroblasts. The over- expression of PIB ignites the expression of DC markers including CD103, XCR1, MHC-I, MHC-II and co-stimulatory molecules. Functionally, Induced DCs (iDCs) secrete inflammatory cytokines and engulf, process, present and cross-present antigens to CD4+ and CD8+ T cells, respectively. Additionally, we have demonstrated that combined expression of PIB factors induces DC1 reprogramming in human fibroblasts. Human iDC1s acquire DC morphology, express DC1 markers, including Clec9a, CD141 and the co-stimulatory molecules CD40, CD80 and CD86, and acquire a DC1 transcriptional signature at the single cell level. Interestingly, DC1 reprogramming efficiency can be enhanced 70-fold by supplementing culture media with inflammatory cytokines, suggesting a regulatory role of inflammation during DC1 reprogramming. Hence, we provide evidence that antigen presentation and cross-presentation can be dynamically programmed by a small combination of TFs. These findings provide insights into cDC1 specification and a platform for developing cancer immunotherapies based on cell reprogramming.

Who on IRF are you? IRF8 deficiency redirects cDC1 lineage commitment

Interferon regulatory factor 8 (IRF8) has long been associated with conventional dendritic cell type I (cDC1) development. In a recent study, Lança et al. demonstrate that IRF8 is also crucial in cells already committed to the cDC1 lineage. Here, deletion of IRF8 from the XCR1-expressing pre-cDC1 stage onward leads to a loss of commitment and reprogramming of the cells toward a cDC2-like phenotype.

PEG Spacer Length Substantially Affects Antibody-Based Nanocarrier Targeting of Dendritic Cell Subsets.

Successful cell targeting depends on the controlled positioning of cell-type-specific antibodies on the nanocarrier’s (NC) surface. Uncontrolled antibody immobilization results in unintended cell uptake due to Fc-mediated cell interaction. Consequently, precise immobilization of the Fc region towards the nanocarrier surface is needed with the Fab regions staying freely accessible for antigen binding. Moreover, the antibody needs to be a certain distance from the nanocarrier surface, influencing the targeting performance after formation of the biomolecular corona. This can be achieved by using PEG linker molecules. Here we demonstrate cell type-specific targeting for dendritic cells (DC) as cellular key regulators of immune responses. However, to date, dendritic cell targeting experiments using different linker lengths still need to be conducted. Consequently, we focused on the surface modification of nanocarriers with different molecular weight PEG linkers (0.65, 2, and 5 kDa), and their ability to reduce undesired cell uptake, while achieving efficient DC targeting via covalently immobilized antibodies (stealth targeting). Our findings demonstrate that the PEG linker length significantly affects active dendritic cell targeting from cell lines (DC2.4) to primary cells (BMDCs, splenocytic conventional DCs type 1 (cDC1)). While antibody-functionalized nanocarriers with a shorter PEG length (0.65 kDa) showed the best targeting in DC2.4, a longer PEG length (5 kDa) was required to specifically accumulate in BMDCs and splenocytic cDC1. Our study highlights that these crucial aspects must be considered when targeting dendritic cell subsets, which are of great importance in the fields of cancer immunotherapy and vaccine development.

BATF3 Protects Against Metabolic Syndrome and Maintains Intestinal Epithelial Homeostasis.

The intestinal immune system and microbiota are emerging as important contributors to the development of metabolic syndrome, but the role of intestinal dendritic cells (DCs) in this context is incompletely understood. BATF3 is a transcription factor essential in the development of mucosal conventional DCs type 1 (cDC1). We show that Batf3-/- mice developed metabolic syndrome and have altered localization of tight junction proteins in intestinal epithelial cells leading to increased intestinal permeability. Treatment with the glycolysis inhibitor 2-deoxy-D-glucose reduced intestinal inflammation and restored barrier function in obese Batf3-/- mice. High-fat diet further enhanced the metabolic phenotype and susceptibility to dextran sulfate sodium colitis in Batf3-/- mice. Antibiotic treatment of Batf3-/- mice prevented metabolic syndrome and impaired intestinal barrier function. Batf3-/- mice have altered IgA-coating of fecal bacteria and displayed microbial dysbiosis marked by decreased obesity protective Akkermansia muciniphila, and Bifidobacterium. Thus, BATF3 protects against metabolic syndrome and preserves intestinal epithelial barrier by maintaining beneficial microbiota.

Mobilization of innate and adaptive antitumor immune responses by the RNP-targeting antibody ATRC-101

Immunotherapy approaches focusing on T cells have provided breakthroughs in treating solid tumors. However, there remains an opportunity to drive anticancer immune responses via other cell types, particularly myeloid cells. ATRC-101 was identified via a target-agnostic process evaluating antibodies produced by the plasmablast population of B cells in a patient with non-small cell lung cancer experiencing an antitumor immune response during treatment with checkpoint inhibitor therapy. Here, we describe the target, antitumor activity in preclinical models, and data supporting a mechanism of action of ATRC-101. Immunohistochemistry studies demonstrated tumor-selective binding of ATRC-101 to multiple nonautologous tumor tissues. In biochemical analyses, ATRC-101 appears to target an extracellular, tumor-specific ribonucleoprotein (RNP) complex. In syngeneic murine models, ATRC-101 demonstrated robust antitumor activity and evidence of immune memory following rechallenge of cured mice with fresh tumor cells. ATRC-101 increased the relative abundance of conventional dendritic cell (cDC) type 1 cells in the blood within 24 h of dosing, increased CD8+ T cells and natural killer cells in blood and tumor over time, decreased cDC type 2 cells in the blood, and decreased monocytic myeloid-derived suppressor cells in the tumor. Cellular stress, including that induced by chemotherapy, increased the amount of ATRC-101 target in tumor cells, and ATRC-101 combined with doxorubicin enhanced efficacy compared with either agent alone. Taken together, these data demonstrate that ATRC-101 drives tumor destruction in preclinical models by targeting a tumor-specific RNP complex leading to activation of innate and adaptive immune responses.

Triggering receptor expressed on myeloid cells (Trem)-1 plays important roles in UVB induced immune suppression and cutaneous carcinogenesis

Abstract American Cancer Society acknowledges that most skin cancers result from exposure to ultraviolet (UV) rays in sunlight. UVB radiation induces mutant cells as well as immune suppression. Tumors only occur when mutant cells are in an immune suppressive environment. The mechanisms for UVB induced immune suppression are yet to be fully elucidated. The goal of this work is to explore new mechanisms for UVB induced immune suppression and skin carcinogenesis by using advanced technology. Analysis of UVB exposed mouse (Nanostring) and human (RNAseq) skin shows that triggering receptor expressed on myeloid cells (TREM)-1 signal pathway is the top canonic pathway increased by UVB. TREM-1 has roles in inflammatory diseases and cancers. However, its role in UVB induced immune suppression and skin cancers is not understood. We have found by using multi-color flow cytometry that UVB induces TREM-1 expression in a subset of conventional dendritic cell type 2 (cDC2) in the draining lymph nodes (LN). TREM-1+ cDC2 cells are barely detected in normal LN and express a high level of the co-inhibitory molecule PD-L1. In functional assays, treatment of mice with a specific TREM-1 blocking peptide LP-17 significantly diminishes UVB-induced suppression of contact hypersensitivity responses that are mediated by T cells. Further, mice treated with this peptide show decreased incidence of photocarcinogenesis and reduced number of tumors. In summary, our findings demonstrate that UVB induces the development of a novel TREM-1+ cDC2 cell subset and that TREM-1 has an important role in UVB induced immune suppression and skin carcinogenesis. Importantly, our study implies new strategies for targeting TREM-1 in the prevention and treatment of UVB induced skin cancers. Supported by grants from NIH (R01AR072213 and R01AI154842)