Post-transplant cyclophosphamide and bortezomib inhibit dendritic cell maturation and function and alter their IκB and NFκB.

Impairing dendritic cell (DC) function to prevent graft versus host disease (GvHD) is an appealing concept. DC antigen presentation is NF-κB pathway-dependent and bortezomib might therefore play a role in preventing alloreactivity. We obtained DC from the blood of patients enrolled in a phase I study using post-transplant cyclophosphamide and bortezomib for prevention of GvHD. Control samples were obtained from patients receiving standard GvHD prevention regimen. Pre-treatment samples were also collected from enrolled patients. DC isolated on days +1, +4, and +7 showed progressive decrease in the expression of maturation markers in comparison to control. In a DC-CD4+ mixed lymphocyte reaction (MLR) where DC isolated from the recipient blood before graft infusion were the stimulator cells, T cell proliferation measured by bromodeoxyuridine (BrdU) integration was decreased in samples obtained on days +14 and +21 in comparison to control group. Finally, measured by real-time PCR, the expression of IκB progressively increased while the expression of NF-κB decreased in DC on days +1, +4, and +7, in comparison to pre-treatment paired controls. We conclude that our data further justify exploring the role of bortezomib in GvHD prevention and propose a novel mechanism of action of bortezomib in DC.