Rapamycin-conditioned dendritic cells activated with monophosphoryl lipid-A promote allograft acceptance in vivo

Aim: To date, there is no human dendritic cell (DC) based therapy to prevent allograft rejection in transplanted patients. Here, we evaluate a potential protocol using a murine in vivo transplant model. Materials & methods: We generated murine bone marrow-derived DCs (BM-DCs), modulated with rapamycin (Rapa) and activated with monophosphoryl lipid A (Rapamycin-treated and monophosphoryl lipid A-matured DCs [Rapa-mDCs]). DCs phenotype was evaluated by flow cytometry, cytokine production by ELISA and their T-cell stimulatory ability was tested in co-cultures with CD4⁺ T cells. Using an in vivo skin graft model, we evaluated DCs tolerogenicity. Results: In vitro, Rapa-mDCs exhibit a semi-mature phenotype given by intermediate levels of co-stimulatory molecules and cytokines, and inhibit CD4⁺ T-cell proliferation. In vivo, skin-grafted mice treated with Rapa-mDCs show high allograft survival, accumulation of Foxp3⁺ Tregs and cytokine pattern modification. Conclusion: Rapa-mDCs re-educate the inflammatory microenvironment, promoting skin-allograft survival.