Successful pregnancy in placental mammals substantially depends on the establishment of maternal immune tolerance to the semi-allogenic fetus. Disorders in this process are tightly associated with adverse pregnancy outcomes including recurrent miscarriage (RM). However, an in-depth understanding of the systematic and decidual immune environment in RM remains largely lacking. In this study, we utilized single-cell RNA-sequencing (scRNA-seq) to comparably analyze the cellular and molecular signatures of decidual and peripheral leukocytes in normal and unexplained RM pregnancies at the early stage of gestation. Integrative analysis identifies 22 distinct cell clusters in total, and a dramatic difference in leukocyte subsets and molecular properties in RM cases is revealed. Specifically, the cytotoxic properties of CD8⁺ effector T cells, nature killer (NK), and mucosal-associated invariant T (MAIT) cells in peripheral blood indicates apparently enhanced pro-inflammatory status, and the population proportions and ligand–receptor interactions of the decidual leukocyte subsets demonstrate preferential immune activation in RM patients. The molecular features, spatial distribution, and the developmental trajectories of five decidual NK (dNK) subsets have been elaborately illustrated. In RM patients, a dNK subset that supports embryonic growth is diminished in proportion, while the ratio of another dNK subset with cytotoxic and immune-active signature is significantly increased. Notably, a unique pro-inflammatory CD56⁺CD16⁺ dNK subset substantially accumulates in RM decidua. These findings reveal a comprehensive cellular and molecular atlas of decidual and peripheral leukocytes in human early pregnancy and provide an in-depth insight into the immune pathogenesis for early pregnancy loss.

胎盘哺乳动物的成功妊娠很大程度上取决于母体对半同种异体胎儿的免疫耐受性的建立。这一过程中的疾病与不良妊娠结局密切相关，包括反复流产(RM)。然而，对 RM 的系统性和蜕膜免疫环境的深入了解仍然很大程度上缺乏。在这项研究中，我们利用单细胞 RNA 测序(scRNA-seq) 来比较分析蜕膜和外周白细胞的细胞和分子特征在妊娠早期的正常和不明原因的 RM 妊娠中。综合分析总共确定了 22 个不同的细胞簇，揭示了 RM 病例中白细胞亚群和分子特性的显着差异。具体来说，CD8 ^{+的细胞毒特性}外周血中的效应 T 细胞、自然杀伤 (NK) 和黏膜相关不变 T (MAIT) 细胞表明促炎状态明显增强，蜕膜白细胞亚群的群体比例和配体-受体相互作用显示优先免疫激活RM 患者。详细说明了五个蜕膜 NK (dNK) 亚群的分子特征、空间分布和发育轨迹。在 RM 患者中，支持胚胎生长的 dNK 亚群按比例减少，而另一个具有细胞毒性和免疫活性特征的 dNK 亚群的比例显着增加。值得注意的是，一种独特的促炎 CD56 ⁺ CD16 ⁺dNK 子集在 RM 蜕膜中大量积累。这些发现揭示了人类早期妊娠蜕膜和外周白细胞的全面细胞和分子图谱，并提供了对早期妊娠丢失的免疫发病机制的深入了解。