Monoclonal antibodies against GARP/TGF-β1 complexes inhibit the immunosuppressive activity of human regulatory T cells in vivo

Abstract

Regulatory T cells (Tregs) are essential to prevent autoimmunity, but excessive Treg function contributes to cancer progression by inhibiting antitumor immune responses. Tregs exert contact-dependent inhibition of immune cells through the production of active transforming growth factor-β1 (TGF-β1). On the Treg cell surface, TGF-β1 is in an inactive form bound to membrane protein GARP and then activated by an unknown mechanism. We demonstrate that GARP is involved in this activation mechanism. Two anti-GARP monoclonal antibodies were generated that block the production of active TGF-β1 by human Tregs. These antibodies recognize a conformational epitope that requires amino acids GARP137-139 within GARP/TGF-β1 complexes. A variety of antibodies recognizing other GARP epitopes did not block active TGF-β1 production by Tregs. In a model of xenogeneic graft-versus-host disease in NSG mice, the blocking antibodies inhibited the immunosuppressive activity of human Tregs. These antibodies may serve as therapeutic tools to boost immune responses to infection or cancer via a mechanism of action distinct from that of currently available immunomodulatory antibodies. Used alone or in combination with tumor vaccines or antibodies targeting the CTLA4 or PD1/PD-L1 pathways, blocking anti-GARP antibodies may improve the efficiency of cancer immunotherapy.

Targeting TGF-β Signaling for Therapeutic Gain

“…Another example is GARP, which is required for activation of latent TGF-b on Tregs and platelets (Stockis et al 2009;Tran et al 2009). Blocking the interaction of GARP with latent TGF-b at the surface of Treg cells using antibodies that bind a specific conformational motif of GARP could block TGF-b activation, and, consequently, also the immunosuppressive activity of Tregs (Cuende et al 2015). This antibody may therefore impose a more specific TGF-b blockade immunotherapy for cancer, probably with fewer side effects than blocking TGF-b receptors or ligands, because of the restricted pattern of GARP expression.…”

Cutting Edge: Active TGF-β1 Released from GARP/TGF-β1 Complexes on the Surface of Stimulated Human B Lymphocytes Increases Class-Switch Recombination and Production of IgA

“…This results in the display of GARP/latent TGF-b1 complexes on TCRstimulated Tregs. We also showed that the activation of latent TGF-b1 by stimulated Tregs is GARP dependent, and that this active TGF-b1 exerts paracrine immunosuppressive actions at a short distance, when Treg to T effector cell contacts are allowed (13,14). We derived mAbs against GARP/latent TGF-b1 complexes that block active TGF-b1 production by human Tregs.…”

Novel approaches for preventing acute graft-versus-host disease after allogeneic hematopoietic stem cell transplantation

“…[34,35] Tregs are also featured by a dependency on IL-2 for their homeostasis. [35,36] Importantly, several studies have demonstrated that Treg cotransplantation at a Treg/CD4 + Tconv ratio of 1/1 or 1/2 prevented aGVHD in mouse to mouse [37,38] as well as in humanized mice [39,40] [50] In mice, the B-cell protective activity appears to be mediated by their secretion of IL-10. Recently, impairment in IL-10-producing B cells (regulatory B cells, Breg) was also described in patients with cGVHD.…”

“…This is partly due to differences between human and murine immune systems, and more importantly, to the large genetic diversity within the human species in contrast to what is present in inbred mice. Recent developments in humanized models of GVHD may provide additional tool for testing new immunoregulatory approaches on human immune cells in vivo and offers the possibility to assess various donors with different genetic background, [39,40,49] while the canine model of unrelated dog-leukocyte antigen-mismatched transplantation has remained the only animal model that allows direct translation to the clinic. [55] The holy grail of GVHD prophylaxis is to efficiently prevent grade >1 aGVHD without compromising post-transplant immune recovery and graft-versus-tumor effects.…”