Mouse Chimaeras obtained by the Injection of Cells into the Blastocyst

Abstract

CHIMAERAS occur naturally in a variety of species of mammals, including man. For example, cells are exchanged through vascular connexions between the bovine free-martin and its male twin, leading both to the mixing of blood cells^1,2 and to female germ cells in the testes of the male foetus². Limited chimaerism was produced experimentally by injecting tissue into mouse foetuses shortly before term³ or by injecting spleen cells into adult mice which were rendered immunologically tolerant by X-irradiation⁴. Mosaicism, extending to most tissues of the body in mice, was achieved by fusing pre-implantation embryos together in vitro^5,6.