What happened in the 2007 macaque cloning experiments?

In 2007, researchers conducted two distinct types of experiments involving the cloning of macaque embryos using somatic cell nuclear transfer (SCNT):

• Reproductive Cloning Attempts: Scientists attempted to produce viable macaque clones by implanting 100 cloned embryos into 50 female macaques. These efforts were unsuccessful, as none of the embryos resulted in a viable pregnancy. In these experiments, the cloned embryos generally only survived to the blastocyst stage of development.12
• Therapeutic Cloning Research: Researchers also utilized SCNT to derive stem cells from cloned macaque embryos. This process was exceptionally difficult; starting with 304 egg cells, the team successfully derived only two lines of stem cells. One of these lines contained an abnormal Y chromosome. However, the successfully derived stem cells were able to differentiate into mature brain neurons and heart cells.3

These experiments highlighted the significant technical challenges associated with primate cloning, which were not overcome until over a decade later when scientists announced the first live births of SCNT-cloned macaques.2