Problem: A significant rate of spontaneous abortion is observed in cattle pregnancies produced by somatic cell nuclear transfer (SCNT). Major histocompatibility complex class I (MHC-I) proteins are abnormally expressed on the surface of trophoblast cells from SCNT conceptuses. Method of study: MHC-I homozygous compatible (n = 9), homozygous incompatible (n = 8), and heterozygous incompatible (n = 5) pregnancies were established by SCNT. Eight control pregnancies were established by artificial insemination. Uterine and trophoblast samples were collected on day 35 ±1 of pregnancy, the expression of immunerelated genes was examined by qPCR, and the expression of trophoblast microRNAs was assessed by sequencing.Results: Compared to the control group, trophoblast from MHC-I heterozygous incompatible pregnancies expressed increased levels of CD28,