The programmed cell death ligand 1 (PD-L1) and its receptor programmed cell death 1 (PD-1) deliver inhibitory signals to regulate immunological tolerance during immune-mediated diseases. However, the role of PD-1 signaling and its blockade effect on human dental pulp stem cells (hDPSCs) differentiation into the osteo-/odontogenic lineage remain unknown. We show here that PD-L1 expression, but not PD-1, is downregulated during osteo-/odontogenic differentiation of hDPSCs. Importantly, PD-L1/PD-1 signaling has been shown to negatively regulate the osteo-/odontogenic differentiation of hDPSCs. Mechanistically, depletion of either PD-L1 or PD-1 expression increased ERK and AKT phosphorylation levels through the upregulation of Ras enzyme activity, which plays a pivotal role during hDPSCs osteo-/odontogenic differentiation. Treatment with nivolumab (a human anti-PD-1 monoclonal antibody), which targets PD-1 to prevent PD-L1 binding, successfully enhanced osteo-/odontogenic differentiation of hDPSCs through enhanced Ras activity-mediated phosphorylation of ERK and AKT. Our findings underscore that downregulation of PD-L1 expression accompanies during osteo-/odontogenic differentiation, and hDPSCs-intrinsic PD-1 signaling inhibits osteo-/odontogenic differentiation. These findings provide a significant basis that PD-1 blockade could be effective immunotherapeutic strategies in hDPSCs-mediated dental pulp regeneration.

程序性细胞死亡配体 1 (PD-L1) 及其受体程序性细胞死亡 1 (PD-1) 在免疫介导的疾病中传递抑制信号以调节免疫耐受。然而，PD-1 信号传导的作用及其对人牙髓干细胞 (hDPSCs) 分化成骨/牙源性谱系的阻断作用仍然未知。我们在这里展示了 PD-L1 表达，而不是 PD-1，在 hDPSCs 的成骨/牙源性分化过程中被下调。重要的是，已显示 PD-L1/PD-1 信号传导对 hDPSCs 的骨/牙源性分化负调节。从机制上讲，PD-L1 或 PD-1 表达的消耗通过上调 Ras 酶活性增加了 ERK 和 AKT 磷酸化水平，这在 hDPSCs 成骨/牙源性分化过程中起关键作用。使用靶向 PD-1 以防止 PD-L1 结合的 nivolumab（一种人类抗 PD-1 单克隆抗体）治疗，通过增强 Ras 活性介导的 ERK 和 AKT 磷酸化成功地增强了 hDPSCs 的骨/牙源性分化。我们的研究结果强调，在骨/牙源性分化过程中伴随着 PD-L1 表达的下调，并且 hDPSCs 内在的 PD-1 信号传导抑制了骨/牙源性分化。这些发现为 PD-1 阻断可能是 hDPSCs 介导的牙髓再生中的有效免疫治疗策略提供了重要基础。我们的研究结果强调，在骨/牙源性分化过程中伴随着 PD-L1 表达的下调，并且 hDPSCs 内在的 PD-1 信号传导抑制了骨/牙源性分化。这些发现为 PD-1 阻断可能是 hDPSCs 介导的牙髓再生中的有效免疫治疗策略提供了重要基础。我们的研究结果强调，在骨/牙源性分化过程中伴随着 PD-L1 表达的下调，并且 hDPSCs 内在的 PD-1 信号传导抑制了骨/牙源性分化。这些发现为 PD-1 阻断可能是 hDPSCs 介导的牙髓再生中的有效免疫治疗策略提供了重要基础。