Expression Of Αvβ8 Research Articles

Abstract 6349: 2MW4991, a novel ADCC-enhanced integrin αvβ8 blocker, exhibits high anti-tumor potency and was well tolerated in cynomolgus monkeys

Abstract Background: The three highly structurally related TGF-β isoforms (TGF-β1, TGF-β2, and TGF-β3) exert greatly different effects on cancer and immune cells under various physiological conditions. Efforts to target the TGF-β pathway have been hampered by systemic toxicity or limited efficacy due to challenges associated with the global inhibition of TGF-βs. Recently, TGF-β1 was proven to be a critical player in generating an immunosuppressive tumor microenvironment (TME). TGF-β1 is expressed as an inactive latent form (L-TGF-β1) and activated upon binding to integrins, and integrin αvβ8 is a key activator of TGF-β1 in TME. Here, an ADCC-enhanced αvβ8 blocking antibody, 2MW4991, was developed to specifically inhibit TGF-β1-mediated signaling for the treatment of αvβ8-expressing cancers. Methods: Binding ability, specificity, and affinity of antibodies were measured by Flow cytometry and Biacore T200. A blocking assay was performed using U251MG cells and TGF-β signaling reporter cells. Jurkat/h FcγRIIIa reporter system was used to assess the ADCC activity of 2MW4991. Mouse syngeneic tumor models were used to characterize the in vivo anti-tumor efficacy. A repeat dose administration study was performed in cynomolgus monkeys to evaluate the pharmacokinetic and toxicity profiles of 2MW4991. Results: ScRNA-seq analysis of kidney renal clear cell carcinoma (KIRC) and head and neck squamous cell carcinoma (HNSCC) clinical samples revealed that αvβ8 highly expresses in tumor and some myeloid-derived cells, suggesting the development of ADCC-enhanced αvβ8 blocking antibodies for the treatment of αvβ8-expressing cancers. 2MW4991 showed sub-nanomolar binding affinity and high specificity to αvβ8, with no cross-reactivity to other integrins. 2MW4991 could effectively block TGF-β1 release in a GARP/L-TGF-β1/αvβ8 reporter system. In an immune-excluded EMT6 syngeneic model, 2MW4991 promoted substantial tumor regression and reversed immune suppressive TME by significantly increasing tumor infiltration of CD8+ T and innate immune cells. As expected, TGF-β1 blockade significantly increased the sensitivity of anti-PD-1 therapy in a combination study. Furthermore, 2MW4991 displayed potent anti-tumor efficacy in the human αvβ8 knock-in syngeneic model mimicking αvβ8 expression in human cancers. In a repeat dose administration NHP study, 2MW4991 showed a good pharmacokinetic profile and was well tolerated at a high dose of 100 mg/kg, accompanied by significantly declined pharmacodynamic biomarker TGF-β1 in peripheral blood. Conclusion: Integrin αvβ8 is a main activator of TGF-β1 in the TME and overexpressed in some cancer types. 2MW4991 demonstrated potent anti-tumor activity by unleashing the immune cells suppressed by TGF-β1 in TME and Fc-mediated immune functions. These compelling preclinical results support further evaluation of 2MW4991 in clinical trials. Citation Format: Cuicui Guo, Zhen Han, Xiaowei Cen, Hai Wu, Jinchao Zhang, Xun Gui. 2MW4991, a novel ADCC-enhanced integrin αvβ8 blocker, exhibits high anti-tumor potency and was well tolerated in cynomolgus monkeys [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 6349.

Fungal sensing by dectin-1 directs the non-pathogenic polarization of TH17 cells through balanced type I IFN responses in human DCs

The non-pathogenic TH17 subset of helper T cells clears fungal infections, whereas pathogenic TH17 cells cause inflammation and tissue damage; however, the mechanisms controlling these distinct responses remain unclear. Here we found that fungi sensing by the C-type lectin dectin-1 in human dendritic cells (DCs) directed the polarization of non-pathogenic TH17 cells. Dectin-1 signaling triggered transient and intermediate expression of interferon (IFN)-β in DCs, which was mediated by the opposed activities of transcription factors IRF1 and IRF5. IFN-β-induced signaling led to integrin αvβ8 expression directly and to the release of the active form of the cytokine transforming growth factor (TGF)-β indirectly. Uncontrolled IFN-β responses as a result of IRF1 deficiency induced high expression of the IFN-stimulated gene BST2 in DCs and restrained TGF-β activation. Active TGF-β was required for polarization of non-pathogenic TH17 cells, whereas pathogenic TH17 cells developed in the absence of active TGF-β. Thus, dectin-1-mediated modulation of type I IFN responses allowed TGF-β activation and non-pathogenic TH17 cell development during fungal infections in humans.

Indirubin regulates T cell differentiation by promoting αVβ8 expression in bone marrow-derived dendritic cells to alleviate inflammatory bowel disease.

Inflammatory bowel disease is a disease that can invade the whole digestive tract and is accompanied by immune abnormalities. Immune dysfunction involving dendritic cells (DCs) and T cells is recognized as a key factor in diseases. Indirubin (IDRB) exerts antiinflammatory effects and can help in treating immune diseases. This study aimed to isolate bone marrow-derived dendritic cells (BMDCs) using lipopolysaccharide(LPS) to obtain mature DCs (mDCs). The expression of CD80, CD86, CD40, and MHC-II was detected using flow cytometry after treatment with IDRB. αVβ8 siRNA was used to knock down αVβ8 in mDCs, and the expression of CD80, CD86, CD40, and MHC-II was detected. Meanwhile, DCs were co-cultured with T cells. Then, T cell differentiation was detected using flow cytometry, and the cytokine levels were detected using enzyme-linked immunosorbent assay. The animal model of dextran sulfate sodium (DSS)-induced inflammatory bowel disease was established in mice. After intervention with IDRB and αVβ8 shRNA, the intestinal tissues were evaluated using H&E staining, disease activity index (DAI) score, and histological damage index, and the corresponding factors and cytokines to regulatory T cells (Treg) and Th17 were measured. The results showed that αVβ8 was expressed in immature DCs and mDCs. CD80, CD86, CD40, and MHC-II expression decreased after IDRB treatment in mDCs. Meanwhile, the expression of TNF-α and TGF-β also decreased after IDRB treatment. The effect of IDRB on the expression of CD80, CD86, CD40, MHC-II, TNF-α, and TGF-β in mDCs was reversed by αVβ8 siRNA. The Treg differentiation increased after IDRB treatment, while the differentiation of Th17 cells was inhibited. This effect of IDRB was reversed by mDCs after treatment with αVβ8 siRNA. In vivo experiments showed that IDRB alleviated the symptoms of inflammatory bowel disease in animals. Enteritis significantly reduced, and the effect of IDRB was reversed by αVβ8 shRNA. The results suggested that IDRB regulated the differentiation of T cells by mediating the maturation of BMDCs through αVβ8. This study confirmed the therapeutic effect of IDRB in inflammatory bowel disease and suggested that IDRB might serve as a potential drug.

Abstract 1559: Inhibition of integrin αvβ8 enhances immune checkpoint induced anti-tumor immunity by acting across immunologic synapse in syngeneic models of breast cancer

Abstract Introduction We explored whether integrin αvβ8 inhibition potentiates immune checkpoint blockade (ICB) in syngeneic orthotopic models of breast cancer. Integrin αvβ8 mediates cell type specific and tissue localized activation of TGFβ1/3 to regulate the immune system. For example, αvβ8 expressed on dendritic cells (DC) in the intestine has been shown to be a key mediator of tolerance, maintaining gut immunologic homeostasis. Methods Efficacy was evaluated in combination with anti-PD-1 in EMT6 and PyMT breast cancer syngeneic mouse models. A potent αvβ8 inhibitor was orally administered at 60mg/kg BID for 21 days. Anti-αvβ8 or non-isoform specific anti-TGFβ mAbs were dosed TIWx3 at 7 and 10mg/kg, respectively. Tumor volumes are presented as mean±SEM. Statistics were performed by t test, one-way ANOVA, or log-rank test. Flow cytometry and transcriptome analysis on bulk and single-cell levels were used to assess the mechanism of action in EMT6. Results A similar αvβ8 expression pattern on DC, macrophages and regulatory T cells (Treg) was observed in mouse models and human tumors. Combination of oral αvβ8 inhibitor with anti-PD-1 was efficacious in the primary ICB resistant EMT6 model and resulted in superior tumor regression during treatment (p=0.0003) and improved survival with 5/12 complete responders relative to 0/12 in anti-PD-1 alone. Across studies the αvβ8 inhibitor phenocopied the results obtained with αvβ8 and TGFβ mAbs (n=3 independent studies). Complete responders re-challenged 89 days after treatment with EMT6 or 4T1 tumors showed no EMT6 tumor growth, suggesting the combination induced long-term immunologic memory. Analysis of tumors by flow cytometry showed combination resulted in increased CD8 T cell infiltrates (p=0.0006), T cell activation (CD8+CD69+, p=0.0194) and IFN-γ expression (CD8+IFN-γ+, p=0.0021). Single cell transcriptomic analysis of lymph nodes showed that αvβ8 inhibition potentiated DC co-stimulation (Cd40, Cd83/6) and migration (Ccr7, Cxcl16, Ccl22). Moreover, combination treatment led to tumor infiltrated Treg dysfunction including downregulation of Ctla4, Il10 and Tigit, and upregulation of Ifn-γ. The observation of these anti-tolerance and pro-inflammatory signatures in DC and Treg has not been described previously. Anti-tumor efficacy was driven by immune-mediated mechanisms as confirmed by a CD8 depletion study. Efficacy was confirmed in PyMT breast cancer model. Conclusions An αvβ8 inhibitor in combination with anti-PD-1 showed efficacy in syngeneic mouse models, supported by increased T cell infiltrates and evidence of reduced tumor tolerance. These results show that an orally administered αvβ8 targeted inhibitor is a potent modulator of anti-tumor immune response acting across the immunologic synapse, and is a promising therapeutic approach to ICB refractory tumors. Citation Format: Natalia J. Reszka-Blanco, Vinod Yadav, Megan Krumpoch, Laura Cappellucci, Dan Cui, James E. Dowling, Elizabeth Gwara, Bryce Harrison, Dooyoung Lee, Fu-Yang Lin, Lia Luus, Meghan Monroy, Terence I. Moy, Eugene Nebelitsky, Qi Qiao, Andrew Sullivan, Dawn Troast, Blaise Lippa, Bruce Rogers, Adrian S. Ray. Inhibition of integrin αvβ8 enhances immune checkpoint induced anti-tumor immunity by acting across immunologic synapse in syngeneic models of breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1559.

A tumor-specific mechanism of Treg enrichment mediated by the integrin αvβ8.

Regulatory T cells (Tregs) that promote tumor immune evasion are enriched in certain tumors and correlate with poor prognosis. However, mechanisms for Treg enrichment remain incompletely understood. We described a mechanism for Treg enrichment in mouse and human tumors mediated by the αvβ8 integrin. Tumor cell αvβ8 bound to latent transforming growth factor-β (L-TGF-β) presented on the surface of T cells, resulting in TGF-β activation and immunosuppressive Treg differentiation in vitro. In vivo, tumor cell αvβ8 expression correlated with Treg enrichment, immunosuppressive Treg gene expression, and increased tumor growth, which was reduced in mice by αvβ8 inhibition or Treg depletion. Structural modeling and cell-based studies suggested a highly geometrically constrained complex forming between αvβ8-expressing tumor cells and L-TGF-β-expressing T cells, facilitating TGF-β activation, independent of release and diffusion, and providing limited access to TGF-β inhibitors. These findings suggest a highly localized tumor-specific mechanism for Treg enrichment.

The differentiation and maintenance of RORγt+ Tregs respectively require integrin αvβ8 expression by dendritic cells and commensal microbiota

Abstract The generation of RORγt+ regulatory T cells (Tregs), which regulate type 2 immune respond, is dependent on dendritic cells and microbiota, but mechanisms are poorly understood. Here we show that the differentiation of RORγt+ Tregs was critically dependented on integrin αvβ8 expressed in DCs. In mice, lack of αvβ8 in DCs resulted in loss of RORγt+ Tregs in the small intestine and mesenteric lymph nodes. Moreover, we also report that the maintenance of RORγt+ Tregs needs the existence of commensal bacteria but not DCs in small intestine. The percentage and the proliferation of RORγt+ Tregs were decreased after treated with antibiotic while these were unaffected by the absence of DCs in a short time. These date demonstrate that αvβ8 expressed in small intestinal DCs play a critical role in the induction of RORγt+ Tregs and microbiota act as a key factor on maintenance of RORγt+ Tregs, respectively. Our results may help to explain the mechanisms of oral tolerance via αvβ8 in DCs and commensal microbiota regulate the generation of RORγt+ Tregs to suppress type 2 immune respond.

069 Expression of αvβ8 by Langerhans cells is required for Th17 differentiation and tethering of LC in the epidermis

069 Expression of αvβ8 by Langerhans cells is required for Th17 differentiation and tethering of LC in the epidermis

β8 Integrin Expression and Activation of TGF-β by Intestinal Dendritic Cells Are Determined by Both Tissue Microenvironment and Cell Lineage

Activation of TGF-β by dendritic cells (DCs) expressing αvβ8 integrin is essential for the generation of intestinal regulatory T cells (Tregs) that in turn promote tolerance to intestinal Ags. We have recently shown that αvβ8 integrin is preferentially expressed by CD103(+) DCs and confers their ability to activate TGF-β and generate Tregs. However, how these DCs become specialized for this vital function is unknown. In this study, we show that β8 expression is controlled by a combination of factors that include DC lineage and signals derived from the tissue microenvironment and microbiota. Specifically, our data demonstrate that TGF-β itself, along with retinoic acid and TLR signaling, drives expression of αvβ8 in DCs. However, these signals only result in high levels of β8 expression in cells of the cDC1 lineage, CD8α(+), or CD103(+)CD11b(-) DCs, and this is associated with epigenetic changes in the Itgb8 locus. Together, these data provide a key illustrative example of how microenvironmental factors and cell lineage drive the generation of regulatory αvβ8-expressing DCs specialized for activation of TGF-β to facilitate Treg generation.

The integrin αvβ8 promotes activation of TGFβ by human peripheral monocyte and intestinal macrophage populations

Abstract Transforming growth factor beta (TGFβ) plays a key role in maintaining immune homeostasis, both preventing inflammation and promoting tissue repair. The cytokine is secreted as an inactive complex, with the function of TGFβ tightly regulated at the level of its activation. Our previous work in mice has demonstrated a crucial role for an integrin, αvβ8, in activation of TGFβ in the immune system. This pathway appears especially important in the intestine, with important functions in regulating T-cell response via integrin αvβ8 expression in dendritic cells and regulatory T-cells. However, how TGFβ is activated to regulate the human immune system is poorly understood. Here, we show that, in humans, integrin αvβ8 is highly expressed on blood monocytes, which promotes activation of TGFβ by these cells. When monocytes are differentiated to macrophages, high integrin β8 expression and TGFβ-activating function is observed on the more tolerogenic (M2-like) macrophages versus inflammatory (M1-like) macrophages. In both monocytes and macrophages, expression of β8 is upregulated by specific bacterial TLR ligands, suggesting that stimulation of the cells may promote their ability to activate TGFβ. In addition to peripheral immune cells, intestinal lamina propria mononuclear cells express high levels of integrin αvβ8, with increased levels seen in patients with inflammatory bowel disease. Highest levels of integrin αvβ8 are seen on a population of CD14+CD33+CD64+ cells, corresponding to intestinal macrophages. Thus, our data suggest that expression of integrin αvβ8 on monocytes may play an important role in the induction and function of anti-inflammatory macrophages in the intestine via TGFβ activation.

Integrin αvβ8-mediated TGFβ activation by effector regulatory T cells is essential for suppression of T cell-mediated inflammation (CAM1P.150)

Abstract Foxp3+ regulatory T-cells (Tregs) play a pivotal role in suppressing self-harmful T-cell responses to prevent inflammatory disease. An important cytokine in the development and function of Tregs is TGFβ, a latent cytokine that must be activated to function. Compelling evidence suggests that T-cells need to respond to TGFβ in order for Treg-mediated suppression to occur. Yet, how TGFβ is regulated to promote this suppression is poorly understood. We now show that both mouse and human Tregs have high expression of the TGFβ-activating integrin αvβ8, which enables these cells to activate high levels of latent TGFβ. However, deletion of integrin αvβ8 expression from Tregs resulted in no overt phenotype at rest, indicating that the integrin plays little role in controlling immunity during homeostasis. Strikingly, we find that integrin αvβ8 expression and function is highly upregulated on an activated/effector Treg subset marked by KLRG1, and that Tregs lacking expression of integrin αvβ8 were unable to function as suppressive cells during models of colitis and delayed type hypersensitivity in vivo. Thus, we have uncovered an essential mechanism by which effector Tregs suppress T-cells during inflammation, highlighting a key role for Treg-mediated activation of latent TGFβ in suppression of self-harmful T-cell responses. Our work therefore highlights a novel pathway that could be therapeutically targeted to treat inflammatory disease.

Expression and regulation of the TGF-β activating integrin αvβ8 on human mononuclear phagocytes (MUC8P.809)

Abstract Induction of Foxp3+ Tregs is important in suppressing immune responses to commensal bacteria and innocuous antigen in the gut. Previous work from our lab has shown that, in mice, expression of the integrin αvβ8 on intestinal dendritic cells (DC) is important for activation of the cytokine TGF-β and subsequent Treg induction, with lack of this pathway resulting in severe inflammatory bowel disease (IBD). Additionally, integrin αvβ8 is highly expressed on murine intestinal CD103+ DC compared to other intestinal mononuclear phagocytes, and is required for enhanced Treg induction by CD103+ intestinal DC and maintenance of immune homeostasis. However, pathways that control integrin αvβ8 expression are poorly understood and the role of integrin αvβ8 in human immunology is currently unknown. Here, we show that integrin αvβ8 is expressed preferentially on CD64+ macrophages and to a lesser extent on DC populations, in contrast to what is found in mouse models. Analysis of monocyte-derived macrophage populations indicated that M2-like macrophage populations preferentially expressed integrin αvβ8. Interestingly, treatment of monocyte-derived DCs with the LPS causes up-regulation of integrin αvβ8 expression, indicating that bacterial ligands may be an important cue in triggering integrin αvβ8 expression on DC. Thus, enhanced expression of integrin αvβ8 on certain human mononuclear phagocyte subsets may implicate these populations in the control of TGF-β dependent immune responses.

Loss of the TGFβ-Activating Integrin αvβ8 on Dendritic Cells Protects Mice from Chronic Intestinal Parasitic Infection via Control of Type 2 Immunity

Chronic intestinal parasite infection is a major global health problem, but mechanisms that promote chronicity are poorly understood. Here we describe a novel cellular and molecular pathway involved in the development of chronic intestinal parasite infection. We show that, early during development of chronic infection with the murine intestinal parasite Trichuris muris, TGFβ signalling in CD4+ T-cells is induced and that antibody-mediated inhibition of TGFβ function results in protection from infection. Mechanistically, we find that enhanced TGFβ signalling in CD4+ T-cells during infection involves expression of the TGFβ-activating integrin αvβ8 by dendritic cells (DCs), which we have previously shown is highly expressed by a subset of DCs in the intestine. Importantly, mice lacking integrin αvβ8 on DCs were completely resistant to chronic infection with T. muris, indicating an important functional role for integrin αvβ8-mediated TGFβ activation in promoting chronic infection. Protection from infection was dependent on CD4+ T-cells, but appeared independent of Foxp3+ Tregs. Instead, mice lacking integrin αvβ8 expression on DCs displayed an early increase in production of the protective type 2 cytokine IL-13 by CD4+ T-cells, and inhibition of this increase by crossing mice to IL-4 knockout mice restored parasite infection. Our results therefore provide novel insights into how type 2 immunity is controlled in the intestine, and may help contribute to development of new therapies aimed at promoting expulsion of gut helminths.

αv‐Integrin isoform expression in primary human tumors and brain metastases

To determine whether metastasis to brain is associated with altered expression patterns of integrins, we investigated the expression of αvβ3, αvβ5, αvβ6 and αvβ8 integrins in primary malignancies and metastases to brain of breast, lung and renal carcinomas and in malignant melanoma. Inhibitors of αv integrins are currently in clinical trials for glioblastoma. The role of integrins in the process of brain metastasis from other human tumors is unknown. Immunohistochemistry with novel integrin subtype specific rabbit monoclonal antibodies was performed on tissue microarrays of archival material of surgical biopsies taken from primary tumors and brain metastases. Integrin αvβ3 expression was increased in brain metastases compared to primary tumors of breast adenocarcinoma, non-small cell lung cancer, renal clear cell cancer and malignant cutaneous melanoma (all p < 0.01). Similarly, integrin αvβ8 expression was increased in brain metastases compared to primary tumors of breast cancer (p < 0.0001), lung cancer (p < 0.01) and renal cancer (p < 0.0001), with a similar trend in metastatic melanoma. Integrin αvβ5 was expressed in most primary tumors (98% breast cancer; 67% lung cancer; 90% renal cancer; 89% melanoma) and showed a stronger expression in brain metastases compared to primary tumors from lung cancer and melanoma (p < 0.05). Also integrin αvβ6 expression was increased in brain metastases compared to primary breast cancer (p < 0.001). The stronger αv-integrin expression in brain metastases, especially of αvβ3 and αvβ8 integrins, suggests that certain αv integrin are involved in the process of brain metastasis. αv Integrins may be therapeutic targets for patients with metastatic cancer in brain.

Matched rabbit monoclonal antibodies against αv-series integrins reveal a novel αvβ3-LIBS epitope, and permit routine staining of archival paraffin samples of human tumors

SummaryThe relationship between integrin expression and function in pathologies is often contentious as comparisons between human pathological expression and expression in cell lines is difficult. In addition, the expression of even integrins αvβ6 and αvβ8 in tumor cell lines is not comprehensively documented. Here, we describe rabbit monoclonal antibodies (RabMabs) against the extracellular domains of αv integrins that react with both native integrins and formalin fixed, paraffin embedded (FFPE) human tissues. These RabMabs, against αvβ3 (EM22703), αvβ5 (EM09902), αvβ6 (EM05201), αvβ8 (EM13309), and pan-αv (EM01309), recognize individual integrin chains in Western blots and in flow cytometry. EM22703 detected a ligand-induced binding site (LIBS), reporting an epitope enhanced by the binding of an RGD-peptide to αvβ3. αvβ8 was rarely expressed in human tumor specimens, and weakly expressed in non-small-cell lung carcinoma (NSCLC). However, ovarian carcinoma cell lines expressed αvβ8, as did some melanoma cells, whereas U87MG glioma lacked αvβ8 expression. We observed an unexpected strong expression of αvβ6 in tumor samples of invasive ductal breast adenoma, colorectal carcinoma (CRC), and NSCLC. αvβ3 was strongly expressed in some invasive NSCLC cohorts. Interestingly, PC3 prostate cell and human prostate tumors did not express αvβ3. The RabMabs stained plasma membranes in FFPE-immunohistochemistry (IHC) samples of tumor cell lines from lung, ovary, colon, prostate, squamous cell carcinoma of head and neck (SCCHN), breast, and pancreas carcinomas. The RabMabs are unique tools for probing αv integrin biology, and suggest that especially αvβ6 and αvβ8 biologies still have much to reveal.

Preferential Expression of Integrin αvβ8 Promotes Generation of Regulatory T Cells by Mouse CD103+ Dendritic Cells

Immune responses in the intestine are controlled by regulatory T cells (Tregs), which prevent inflammation in response to commensal bacteria. A specific population of intestinal dendritic cells (DCs), marked by expression of CD103, generate Tregs more efficiently than other DC populations through mechanisms that involve retinoic acid and transforming growth factor (TGF)-β. However, it is not clear how CD103(+) DCs are specialized for this function. We investigated the ability of CD103(+) DCs to promote Treg generation through activation of TGF-β and the role of integrins with the αv subunit in this process. Naïve T cells were cultured with purified DCs from mesenteric lymph nodes (MLNs) or intestines of wild-type and αv conditional knockout mice to assess generation of Tregs. Antigens were administered orally to mice, and antigen-specific generation of Tregs was measured in intestinal tissues. Expression of the integrin αv subunit was measured in purified subpopulations of DCs by quantitative polymerase chain reaction and immunoblot analyses. In vitro, CD103(+) DCs generated more Tregs in the presence of latent TGF-β than other MLN DCs. Efficient generation of Tregs required expression of the integrin αv subunit by DCs; mice that lacked αv in immune cells did not convert naïve T cells to intestinal Tregs in response to oral antigen. CD103(+) DCs derived from the MLNs selectively expressed high levels of integrin αvβ8 compared with other populations of DCs. Expression of αvβ8 is required for CD103(+) DCs to become specialized and activate latent TGF-β and generate Tregs during the induction of tolerance to intestinal antigens in mice.

Mesangial Cell Integrin αvβ8 Provides Glomerular Endothelial Cell Cytoprotection by Sequestering TGF-β and Regulating PECAM-1

Integrins are heterodimeric receptors that regulate cell adhesion, migration, and apoptosis. Integrin αvβ8 is most abundantly expressed in kidney and brain, and its major ligand is latent transforming growth factor-β (TGF-β). Kidney αvβ8 localizes to mesangial cells, which appose glomerular endothelial cells and maintain glomerular capillary structure by mechanical and poorly understood paracrine mechanisms. To establish kidney αvβ8 function, mice with homozygous Itgb8 deletion (Itgb8(-/-)) were generated on outbred and C57BL/6 congenic backgrounds. Most Itgb8(-/-) mice died in utero, and surviving Itgb8(-/-) mice failed to gain weight, and rarely survived beyond 6 weeks. A renal glomerular phenotype included azotemia and albuminuria, as well as increased platelet endothelial cell adhesion molecule-1 (PECAM-1) expression, which was surprisingly not associated with conventional functions, such as endothelial cell hyperplasia, hypertrophy, or perivascular inflammation. Itgb8(-/-) mesangial cells demonstrated reduced latent TGF-β binding, resulting in bioactive TGF-β release, which stimulated glomerular endothelial cell apoptosis. Using PECAM-1 gain and loss of function strategies, we show that PECAM-1 provides endothelial cytoprotection against mesangial cell TGF-β. These results clarify a singular mechanism of mesangial-to-endothelial cell cross-talk, whereby mesangial cell αvβ8 homeostatically arbitrates glomerular microvascular integrity by sequestering TGF-β in its latent conformation. Under pathological conditions associated with decreased mesangial cell αvβ8 expression and TGF-β secretion, compensatory PECAM-1 modulation facilitates glomerular endothelial cell survival.

Expression of αvβ8 integrin on dendritic cells regulates Th17 cell development and experimental autoimmune encephalomyelitis in mice

Th17 cells promote a variety of autoimmune diseases, including psoriasis, multiple sclerosis, rheumatoid arthritis, and inflammatory bowel disease. TGF-β is required for conversion of naive T cells to Th17 cells, but the mechanisms regulating this process are unknown. Integrin αvβ8 on DCs can activate TGF-β, and this process contributes to the development of induced Tregs. Here, we have now shown that integrin αvβ8 expression on DCs plays a critical role in the differentiation of Th17 cells. Th17 cells were nearly absent in the colons of mice lacking αvβ8 expression on DCs. In addition, these mice and the DCs harvested from them had an impaired ability to convert naive T cells into Th17 cells in vivo and in vitro, respectively. Importantly, mice lacking αvβ8 on DCs showed near-complete protection from experimental autoimmune encephalomyelitis. Our results therefore suggest that the integrin αvβ8 pathway is biologically important and that αvβ8 expression on DCs could be a therapeutic target for the treatment of Th17-driven autoimmune disease.