Abstract
Fibroblastic reticular cells (FRCs) maintain the architecture of secondary lymphoid organs, which optimize interactions between antigen-presenting dendritic cells and reactive naive T cells. In this issue of the JCI, Zhao, Jung, and colleagues investigated CD4+FoxP3+ regulatory T cell development and long-term heart allograft survival in recipients treated with peritransplant costimulatory blockade to inhibit CD40/CD40 ligand (CD40L) signaling. Treatment with an anti-CD40L monoclonal antibody (mAb) increased the lymph node (LN) population of Madcam1+ FRCs and altered their transcription profile to express immunoregulatory mediators. Administration of nanoparticles, containing the anti-CD40L mAb and a targeting antibody against high endothelial venules, delivered the treatment into LNs of allograft recipients. Direct LN delivery of the costimulatory blockade allowed decreased dosing and increased the efficacy in extending graft survival. The results provide insights into mechanisms by which FRCs can promote donor-reactive tolerance, and establish a strategy for administering costimulation-blocking reagents that circumvent systemic effects and improve allograft outcomes.