The behaviour of the endometrium during its receptive phase is highly dependent on the endometrial cell type composition. Each cell type has its role in the endometrial preparation for the invading embryo. Alteration in the immune cells dialogue could be the main reason for unsuccessful implantation in certain patients. Immune cell homeostasis is often improved by intrauterine administration of autologous PBMC. There have been numerous reports on the positive effects of the intrauterine administration of autologous PBMC on the IVF outcomes (embryo implantation and ongoing pregnancy success). However, there is little data on the direct effect of the PBMC administration on the cell composition of the endometrium. This study will focus on the changes in the endometrial cell populations by PBMC treatment that could lead to IVF outcome improvement. The aim of this project is to analyze the effect of intrauterine administration of autologous PBMC on the endometrial cell populations and on the IVF outcome parameters (implantation and ongoing pregnancy success as IVF outcome variables).