Who first proposed the idea of nuclear transfer using differentiated cells?

The idea of generating clones through the transfer of nuclei from differentiated cells into enucleated egg cells was first proposed in 1938 by the German embryologist Hans Spemann.12

Although Spemann conceived the concept, he did not perform the experiment himself, as he believed the necessary microsurgical tools were unavailable at the time. While Ian Wilmut later became famous for successfully applying this technique to generate the first mammalian clone from an adult differentiated cell—the sheep Dolly—the theoretical foundation for using differentiated cells in nuclear transfer dates back to Spemann's work in the 1930s.132