Early Post-Transplant Notch Signaling Activity Is Critical for the Differentiation of Pathogenic Alloantigen-Specific T Cells Mediating Acute Graft-Versus-Host Disease

Blocking Notch signaling after allogeneic bone marrow transplantation prevents acute graft-versus-host disease (GVHD) in mice, with key roles for Notch1/2 receptors and Delta-like-1/4 ligands (Dll1/4) (Zhang, Blood 2011; Tran, JCI 2013). To investigate the consequences of Notch inhibition in alloantigen-specific T cells, we identified a short 2-day window of Notch activity early after transplantation during which Notch blockade is critical for maximal prevention of acute GVHD. We describe new mechanistic models to study alloantigen-specific T-cells within this window, and provide insights into early events associated with Notch blockade. In a MHC-mismatched model, transgenic C57Bl/6 CD4⁺ 4C T-cells directly recognizing host I-A^d alloantigens induced lethal GVHD in BALB/c recipients. 4C CD4⁺ T-cells were sensitive to Notch blockade, which resulted in the downregulation of Notch target genes in and impaired production of inflammatory cytokines, concordant with findings in polyclonal responses (Zhang, Blood 2011; Tran, JCI 2013). Nonetheless, serial analysis revealed preserved 4C CD4⁺ T-cell activation, proliferation and expansion upon Dll1/4 blockade. In the B10.D2→BALB/c MHC-matched model of sclerodermatous GVHD, donor-derived CD4⁺Vb3⁺ T-cells, responding to a Mtv6-encoded BALB/c superantigen, demonstrated massive expansion and dominant Th1 polarization of Vb3⁺ T-cells in lymphoid tissues and the liver. Despite this, Notch blockade in Vb3⁺ T-cells inhibited cytokine production, but preserved activation and proliferation. These findings document dissociated effects of Notch inhibition on proliferation and cytokine production in alloantigen-specific T-cells, allowing further focused evaluation of Notch signaling functions in alloimmunity.