Whitehead biologist Rudolf Jaenisch spoke at Thomas Jefferson University in Philadelphia this Friday sharing with an audience of about 300 his thoughts on nuclear reprogramming (http://www.the-scientist.com/2005/4/25/13/1), and the promise of therapeutic cloning. Consistent with his former arguments and testimony before congress in 2001, he argued that human reproductive cloning is dangerous to the extent that it could be considered impossible. From this, he reasoned that critics worried about the destruction of viable human embryos during traditional routes to embryonic stem cells should have less to argue about with regards to stem cell lines created by somatic cell nuclear transfer. A fertilized embryo does have the potential to develop into a normal human baby whereas a cloned embryo does not. Nevertheless, Jaensich said he is hopeful that researchers can limit the use of egg cells in creating clonal totipotent stem cell lines. If only they can recapitulate the nuclear reprogramming that occurs during somatic cell nuclear transfer, the need for egg cells can be obviated, presumably skirting any reasonable bioethical arguments. But that may be a big presumption, and groups such as Jaenisch?s will never be able understand the complex reprogramming steps without doing the SCNT experiments in mammalian (including human) egg cells.