Intravital imaging of donor allogeneic effector and regulatory T cells with host dendritic cells during GVHD

Graft-versus-host disease (GVHD) is a systemic inflammatory response due to the recognition of major histocompatibility complex disparity between donor and recipient after hematopoietic stem cell transplantation (HSCT). T-cell activation is critical to the induction of GVHD, and data from our group and others have shown that regulatory T cells (T_regs) prevent GVHD when given at the time of HSCT. Using multiphoton laser scanning microscopy, we examined the single cell dynamics of donor T cells and dendritic cells (DCs) with or without T_regs postallogeneic transplantation. We found that donor conventional Tcells (T_cons) spent very little time screening host DCs. T_cons formed stable contacts with DCs very early after transplantation andonly increased velocity in the lymph node at 20 hours after transplant. We also observed that T_regs reduced the interaction time between T_cons and DCs, which was dependent on the generation of interleukin 10 by T_regs. Imaging using inducible T_regs showed similar disruption of T_con-DC contact. Additionally, we found that donor T_regs induce host DC death and down-regulate surface proteins required for donor T-cell activation. These data indicate that T _regs use multiple mechanisms that affect host DC numbers and function to mitigate acute GVHD.