DCs sensitized with mPD-L1-Ig fusion protein improve the effect of heart transplantation in mice by promoting the generation of T-reg cells

• PD-L1-IgG1 fusion protein could inhibit the activation of immature dendritic cells.
• Treatment of PD-L1-IgG1 could improve the survival time of cardiac allografts.
• Treatment of PD-L1-IgG1 could induce the generation of T-reg cells in vivo.

PurposeTo detect the effects of DCs sensitized by mPD-L1-Ig fusion protein in heart transplantation in mice as well as its mechanisms.MethodThe mPD-L1-IgG1 construct was used to build a yeast expression system, and the fusion protein was expressed by secretion after the transfection of the GS115 yeast strain, purified by affinity chromatography and ion exchange chromatography, and assayed by SDS–PAGE and Western blot. The ability of the fusion protein to bind to the acceptor PD-1 was tested by ELISA, and the ability of the fusion protein to inhibit the function of T cells was tested by mixed lymphocyte reaction (MLR).ResultsWe used the new PD-L1-IgG1 fusion protein to sensitize imDCs and maintained the immature state of DCs, so as to induce stable and effective immune tolerance to heart transplantation. After the treatment of DCs by mPD-L1-Ig in vitro, the levels of CD80, CD40 and I-Ab expression on DCs are relatively weaker, the ability of DCs to stimulates the proliferation of allogeneic spleen T cells was significantly decreased (P < 0.01), and the levels of Th1 (IL-2, IFN-γ) and Th2 (IL-4, IL-10) secreted by induced allogeneic T cells were significantly decreased (P < 0.01). An in vivo experiment also revealed that DCs sensitized by mPD-L1-IgG1 could prolong the survival time of a transplanted heart to 17.8 ± 1.12 days, and alleviate the pathological change of the cardiac allografts compared with other three groups.ConclusionDCs sensitized by the yeast-expressed mPD-L1-Ig fusion protein are shown to alleviate the cardiac allograft rejection in mice.