We studied immunoregulatory properties of cultured human stem cells of mesenchymal and ectodermal origins after their administration to mice. Xenotransplantation of mesenchymal stem cells from human placenta reduced the number of CD11c(+)dendritic cells in mouse spleens, but did not affect activation of dendritic cells from mouse spleen in culture. It was also shown that splenocytes isolated from animals 10 days after transplantation of mesenchymal stem cells more actively proliferated in response to the polyclonal stimulation. At the same time, transplantation of neither mesenchymal nor neural stem cells affected the ratio of CD4(+)/CD8(+)T cells and their total content in the peripheral blood in comparison with the corresponding parameters in the control groups.