title: Stimulating PD-1-negative signals concurrent with blocking CD154 co-stimulation induces long-term islet allograft survival.
abstract: BACKGROUND
  A balanced network of positive and negative T-cell co-stimulatory signals is important in regulating T-cell activation. Blocking CD28, CD154 (CD40L), or both co-stimulatory molecules has been efficacious in preventing acute allograft rejection in certain but not all transplantation models. In the present study, the authors tested the hypothesis that stimulating programmed death 1 (PD-1)-triggered negative signals concurrent with blocking CD154 co-stimulatory signals would facilitate islet allograft tolerance.
  
  
  METHODS
  The authors used a dimeric PD-L1 immunoglobulin (Ig) fusion protein to stimulate the inhibitory receptor PD-1, and a monoclonal antibody to block CD154. The effects of PD-1 engagement and CD154 blockade on lymphocyte activation were determined by cell proliferation, flow cytometry, and a model of islet transplantation.
  
  
  RESULTS
  PD-L1Ig inhibited the proliferation of both CD4+ and CD8+ T cells stimulated by anti-CD3. The inhibitory effect of PD-L1Ig was enhanced by concurrent blockade of CD154 co-stimulatory signals, as demonstrated by T-cell proliferation and expression of cell surface activation markers. PD-L1Ig and anti-CD154 also synergistically blocked the activation and maturation of antigen-presenting cells. In an islet transplantation model, treatment of recipient C57BL/6 (H-2b) mice with PD-L1Ig and anti-CD154 induced long-term survival of DBA/2 (H-2d) islet allografts, whereas treatment with each reagent alone failed to prevent islet allograft rejection.
  
  
  CONCLUSIONS
  These results suggest that engaging the negative receptor PD-1 exhibits critical immunoregulatory effects in the allograft response, and blocking positive co-stimulatory molecules with active delivery of inhibitory signals may represent a novel therapeutic strategy in transplantation.
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000276:immunology; D000954:Antigens, Surface; D051017:Apoptosis Regulatory Proteins; D001483:Base Sequence; D023201:CD40 Ligand / Q000276:immunology*; D017931:DNA Primers; D006085:Graft Survival / Q000276:immunology*; D016381:Islets of Langerhans Transplantation / Q000276:immunology*; D008213:Lymphocyte Activation / Q000276:immunology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D016133:Polymerase Chain Reaction; D061026:Programmed Cell Death 1 Receptor; D011506:Proteins / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000276:immunology; D015398:Signal Transduction / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology; D014184:Transplantation, Homologous / Q000276:immunology
chemical_list: D015703:Antigens, CD; D000954:Antigens, Surface; D051017:Apoptosis Regulatory Proteins; D017931:DNA Primers; C491383:Pdcd1 protein, mouse; D061026:Programmed Cell Death 1 Receptor; D011506:Proteins; D011993:Recombinant Fusion Proteins; D023201:CD40 Ligand