Immune profiling and RNA-seq uncover the cause of partial unexplained recurrent implantation failure

Detailed knowledge of the changes in endometrial immune cells during the window of implantation in unexplained recurrent implantation failure (RIF) patients, the functions performed by immune cells, and the interactions between them is largely lacking. This study aimed to classify RIF patients and explore the mechanism through endometrial immune profiling and RNA-seq analysis.This study enrolled a total of 172 patients, comprising 144 women with unexplained RIF and 28 fertile women. Endometrial samples were collected using endometrial scratching at the mid-luteal phase before in vitro fertilization treatment or pregnancy. Transcriptome sequencing and immunohistochemical staining of endometrial immune cells including natural killer (NK) cells, macrophages, T cells, and B cells were performed.Comparison of the percentage of endometrial immune cells and the RNA-seq information between RIF patients and fertile control patients.The proportions of uterine CD56+ uNK cells, CD57+ NKT cells, CD68+ macrophages, and CD19+ B cells were significantly elevated in RIF patients. In addition, the number of positive CD68 glandular lumens was significantly higher in RIF patients than in the fertile group. In addition, based on this result, we classified RIF patients into three categories.Hyperactivation of endometrial immune cells may be associated with reduced endometrial tolerance and recurrent implantation failure, affecting pregnancy outcomes in RIF patients.