In Vivo Blockade of Individual Notch Ligands and Receptors Provides a New Targeted Therapeutic Approach In Graft-Versus-Host Disease

Abstract 819

Notch signaling is a cell-cell communication pathway with multiple functions in health and disease. Notch ligands of the Delta-like (Dll1, 3, 4) or Jagged (Jagged1, 2) family interact with one of four mammalian Notch receptors (Notch1-4), leading to proteolytic activation of the receptors by gamma-secretase. We have discovered a critical role for Notch signaling in the differentiation of pathogenic host-reactive T cells during graft-versus-host disease (GVHD) after allogeneic bone marrow transplantation (allo-BMT). Expression of the pan-Notch inhibitor DNMAML in donor T cells led to markedly reduced GVHD severity, without causing global immunosuppression (Blood 2011, 117(1): 299–308). These findings identify Notch signaling in alloreactive T cells as an attractive therapeutic target after allo-BMT. To explore preclinical strategies of Notch blockade in GVHD, we first assessed the effects of systemic pan-Notch inhibition with gamma-secretase inhibitors. In the B6 anti-BALB/c MHC-mismatched model of allo-BMT, administration of the gamma-secretase inhibitor dibenzazepine was as efficient as genetic strategies at blocking Notch target gene expression and production of inflammatory cytokines in donor T cells (IFN-γ, TNF-α, IL-2). However, dibenzazepine induced severe gastrointestinal toxicity after total body irradiation due to inhibition of both Notch1 and Notch2 in the gut epithelium. To avoid these side effects, we hypothesized that targeting individual Notch receptors or ligands could provide safe therapeutic Notch blockade after allo-BMT. Among the four mammalian Notch receptors (Notch1-4), donor alloreactive T cells expressed Notch1 and Notch2. Host dendritic cells expressed Notch ligands of the Jagged and Delta-like (Dll) families, with markedly increased Dll4 but not Jagged1/2 transcripts after total body irradiation. This suggested that blockade of Notch1 and/or Notch2 in T cells or Delta-like Notch ligands in dendritic cells could abrogate GVHD. To explore this possibility, we used specific monoclonal antibodies to neutralize Notch receptors and ligands in vivo after allo-BMT (Nature 2006, 444(7122):1083–7; Nature 2010, 464(7291): 1052–7). Combined blockade of Notch1 and Notch2 in vivo reduced the production of key inflammatory cytokines by alloreactive CD4+ and CD8+ T cells to a similar extent as DNMAML-mediated pan-Notch inhibition. Inhibition of Notch1 alone led to a large decrease in cytokine secretion, indicating that Notch1 is a dominant non-redundant Notch receptor in alloreactive T cells. Consistently, transplantation of Notch1-deficient but not Notch2-deficient B6 T cells allowed for decreased GVHD and improved survival in BALB/c recipients, similarly to global Notch inhibition by DNMAML. We then studied the consequences of inhibiting Dll1, Dll4 or both Dll1/Dll4 Notch ligands during acute GVHD. Combined Dll1/Dll4 blockade was as potent as DNMAML expression in decreasing cytokine production by alloreactive T cells, demonstrating that Delta-like and not Jagged ligands are the key Notch agonists at the alloimmune synapse. Dll4 inhibition was superior to Dll1 blockade in reducing cytokine production, abrogating GVHD, and prolonging recipient survival. Importantly, combined Dll1/Dll4 inhibition provided long-term protection against GVHD morbidity and mortality, while avoiding severe gastrointestinal side effects from Notch inhibition. Protection was observed even upon transient Dll1/Dll4 blockade during 1–2 weeks after transplantation. Altogether, our data suggest that Notch1 and Dll4 preferentially interact during alloreactive T cell priming and identify novel strategies to safely and efficiently target individual elements of the Notch pathway after allo-BMT. Humanized antibodies against Notch receptors and ligands were designed to block both mouse and human proteins, thus our preclinical work could lead to new strategies for GVHD control in human patients.