Cloning and Stem Cells

Therapeutic cloning by somatic cell nuclear transfer offers potential for treatment of a wide range of degenerative disease. Nuclear transplantation with neo ^r-marked somatic nuclei from 10–13-year-old cows was used to generate cloned bovine fetuses. Clone fetal liver (FL) hematopoietic stem cells (HSC) were transplanted into two busulfan-treated and one untreated nuclear donor cows. Hematopoiesis was monitored over 13–16 months by in vitro progenitor and HSC assays. Chimerism was demonstrated by PCR in blood, marrow, lymph nodes, and endothelium, peaking at levels of 9–17% in blood granulocytes but at lower levels in lymphocyte subsets (0.1–0.01%). Circulating progenitors showed high levels of chimerism (up to 60% neo ^r+) with persisting fetal features. At sacrifice, the animal that had no pre-transplant myelosupression showed persisting donor cells in blood and lymph nodes, and in marrow 0.25% of progenitor cells and a detectable fraction of stem cells were neo ^r+. The fetal HSC showed a 10-fold competition advantage over adult HSC. Cloning generated histocompatible HSC capable of long-term multilineage engraftment in a large animal model.