MOUSE CHIMAERAS OBTAINED BY INJECTION OF CELLS INTO BLASTOCYST

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 cells1,2 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 vitro5,6. © 1968 Nature Publishing Group.