Allostimulatory Effects of Dendritic Cells with Characteristic Features of a Regulatory Phenotype

Tolerogenic dendritic cells (DCs) have the potential to prolong graft survival after transplantation. Tolerogenic DCs are in general characterized by a low expression of co-stimulatory molecule and a high IL-10:IL-12 production ratio. Based on promising results with earlier used alternatively activated DCs, we aimed to generate in culture potentially tolerogenic DC by simultaneously blocking GSK3 by lithium chloride (LiCl) and stimulating TLR2 by PAM3CysSerLys4.

Bone marrow-derived LiClPAM3 DCs were generated by the addition of LiCl 24 hours before harvesting, and one hour later PAM3CysSerLys4. The phenotype of the DCs was assessed by determining the expression of co-stimulatory molecules in flow cytometry and cytokine production in ELISA, whereas their functional properties were tested in a mixed lymphocyte reaction. A fully MHC mismatched heterotopic heart transplant preceded by infusion of donor-derived LiClPAM3 DC was performed to assess the tolerogenic potential of LiClPAM3 DCs in vivo.

LiClPAM3 DCs displayed a tolerogenic phenotype accompanied with a low expression of co-stimulatory molecules and a high IL-10:IL-12 production ratio. However, in mixed lymphocyte reaction, LiClPAM3 DCs appeared superior in T cell stimulation, and induced Th1 and Th17 differentiation. Moreover, mice pretreated with LiClPAM3 DC displayed a reduced graft survival. Analysis of LiClPAM3 DC culture supernatant revealed high levels of CXCL-1, which was also found in supernatants of co-cultures of LiClPAM3 DC and T cells. Nevertheless, we could not show a role for CXCL-1 in T cell proliferation or activation in vitro.

LiClPAM3 DCs display in vitro a tolerogenic phenotype with a high IL-10:IL-12 ratio, but appeared to be highly immunogenic, since allograft rejection was accelerated. As yet unidentified LiClPAM3 DC-derived factors, may explain the immunogenic character of LiClPAM3 DCs in vivo.