Cloning animals from nuclei that are genetically marked by terminal differentiation remains inefficient, with most clones dying during gestation. In February 10 online Nature, Konrad Hochedlinger and Rudolf Jaenisch from Massachusetts Institute of Technology, Cambridge, USA, show that monoclonal mice can be generated by nuclear transfer from mature B and T donor cells.

Hochedlinger & Jaenisch transferred nuclei from peripheral lymph node cells of mice into enucleate oocytes. From the resulting cloned blastocysts they removed embryonic stem cells (ESC), and injected these ESCs into another tetraploid host blastocyst. Using this two-step cloning procedure they created animals cloned from B-cell nuclei that were viable and carried fully rearranged immunoglobulin alleles in all tissues. Similarly, mice cloned from a T-cell nucleus carried rearranged T-cell-receptor genes in all tissues (Nature 2002, DOI 10.1038/nature718).

"This is an unequivocal demonstration that a terminally differentiated cell can be reprogrammed to produce an adult...