Differential induction of donor-reactive Foxp3+ Treg via blockade of CD154 vs. CD40

Recently published studies in both murine models and a meta-analysis of NHP renal transplant studies showed that anti-CD154 reagents conferred a significant survival advantage over CD40 blockers in both animal models and across multiple organs. Here we sought to compare the induction of donor-reactive Foxp3+ iTreg in mice treated with anti-CD154 vs. anti-CD40 mAb. Results indicated that while treatment with anti-CD154 resulted in a significant increase in the frequency of donor-reactive CD4+ Foxp3+ iTreg following transplantation, treatment with anti-CD40 or Cd40 deficiency failed to recapitulate this result. Because we recently identified CD11b as an alternate receptor for CD154 during alloimmunity, we interrogated the role of CD154:CD11b interactions in the generation of Foxp3+ iTreg, and found that blockade of CD11b in Cd40-/- recipients resulted in increased donor-reactive Foxp3+ iTreg as compared to CD40 deficiency alone. Mechanistically, CD154:CD11b inhibition decreased IL-1β from CD11b+ CD11c+ dendritic cells, and blockade of IL-1β synergized with CD40 deficiency to promote Foxp3+ iTreg induction and prolong allograft survival. Taken together, these data provide a mechanistic basis for the observed inferiority of anti-CD40 blockers as compared to anti-CD154, and illuminate an IL-1β-dependent mechanism by which CD154:CD11b interactions prevent the generation of donor-reactive Foxp3+ iTreg during transplantation.