Blocking immunosuppression by human Tregs in vivo with antibodies targeting integrin αVβ8

Abstract

Human regulatory T cells (Tregs) suppress other T cells by converting the latent, inactive form of TGF-β1 into active TGF-β1. In Tregs, TGF-β1 activation requires GARP, a transmembrane protein that binds and presents latent TGF-β1 on the surface of Tregs stimulated through their T cell receptor. However, GARP is not sufficient because transduction of GARP in non-Treg T cells does not induce active TGF-β1 production. RGD-binding integrins were shown to activate TGF-β1 in several non-T cell types. Here we show that αVβ8 dimers are present on stimulated human Tregs but not in other T cells, and that antibodies against αV or β8 subunits block TGF-β1 activation in vitro. We also show that αV and β8 interact with GARP/latent TGF-β1 complexes in human Tregs. Finally, a blocking antibody against β8 inhibited immunosuppression by human Tregs in a model of xenogeneic graft-vs.-host disease induced by the transfer of human T cells in immunodeficient mice. These results show that TGF-β1 activation on the surface of human Tregs implies an interaction between the integrin αVβ8 and GARP/latent TGF-β1 complexes. Immunosuppression by human Tregs can be inhibited by antibodies against GARP or against the integrin β8 subunit. Such antibodies may prove beneficial against cancer or chronic infections.

Intracellular and extracellular TGF-β signaling in cancer: some recent topics

“…TGF-β2 has been reported to be increased in some cancers [237,238]; however, the mechanisms of activation for the latent TGF-β2 complex have been poorly investigated. In addition, although the functions of GARP in Tregs have recently been elucidated [212], its function in platelets and other cells need clarification. It is thus intriguing to characterize the latent TGF-β complexes and determine how these complexes are activated under physiological and pathological conditions.…”

“…Interestingly, the failure to develop the secondary palate and reduction of Smad2 phosphorylation without other defects in Garp-deficient mice are similar to the phenotype of Tgfb3-null mice. Although GARP forms a complex with the SLC containing TGF-β1 in human Tregs [212], GARP is co-localized with TGF-β3 in the medial edge epithelial cells in mouse embryos, and it directly interacts with latent TGF-β3, suggesting that GARP plays a crucial role in regulation of TGF-β3 signaling during mouse development.…”

“…Similar to LTBPs, GARP directly binds to the SLC of TGF-β by disulfide linkages through Cys192 and Cys331 of GARP and Cys33 of pro-TGF-β1 as well as by noncovalent association, which prevents the secretion of TGF-β1 [217]. Integrin αvβ8 dimers are present on stimulated Tregs, recognize the RGD motif in β1-LAP, and release active TGF-β1 from the latent TGF-β1-GARP complex [212]. GARP overexpression in T cells induces expression of Foxp3 and enhances their immunosuppressive functions, while silencing of GARP in Tregs attenuates their suppressive activity [218,219].…”

“…GARP overexpression promotes Treg activity and cancer progression in breast cancer-bearing mice, whereas administration of GARPspecific monoclonal antibodies attenuates the progression of cancer metastasis. Most recently, antibodies against the integrin β8 subunit as well as antibodies against GARP have been shown to inhibit the immunosuppression induced by human Tregs in a model of xenogeneic graftversus-host disease [212]. Administration of these antibodies alone or in combination with immune checkpoint inhibitors may improve the efficiency of cancer immunotherapy.…”

Integrin αvβ8 serves as a Novel Marker of Poor Prognosis in Colon Carcinoma and Regulates Cell Invasiveness through the Activation of TGF-β1

“…αvβ8 expression in human cancer cells is involved in the progression of epithelial malignancies; increased αvβ8 expression is also associated with decreased survival in non-small cell lung carcinoma, triplenegative basal-type breast cancer, and advanced ovarian cancer [19][20][21]. Additionally, αvβ8-mediated TGF-β activation regulates tumor immune tolerance, which results in the decreased infiltration of cytotoxic T cells and proinflammatory tumor-associated macrophages to the tumor center [19,22,23].…”