Why is it difficult to clone primates using somatic cell nuclear transfer?

Cloning primates using somatic cell nuclear transfer (SCNT) is exceptionally difficult due to significant technical and biological challenges. While SCNT has been used to clone various mammals, the process in primates is fraught with low success rates and high rates of developmental failure.12

Key factors contributing to these difficulties include:

• Low Embryo Viability: Cloned primate embryos often fail to develop beyond the early stages. For instance, early attempts to clone macaques resulted in embryos that could not progress past the blastocyst stage or failed to establish viable pregnancies after implantation.12
• Technical Complexity: The process requires precise manipulation to remove the nucleus from an egg without damaging it. While refinements like using polarized light to visualize the nucleus have improved outcomes, the procedure remains highly sensitive.2
• Reprogramming Challenges: The mechanism by which the egg’s cytoplasm reprograms the DNA of a differentiated somatic cell is not fully understood. Inefficient reprogramming often leads to birth defects or the failure of the fetus to survive gestation.32
• Resource Constraints: SCNT is resource-intensive, often requiring a large number of egg cells to produce a single viable result, which presents both practical and ethical hurdles.243