Human Stem Cells Made From Eggs

Stem Cells Production Is in Pursue (Image credited to docwirenews.com)

It was 1996 when biologists first used a mammalian skin cell with an egg cell, cloning Dolly the sheep. That was the start of the race to make a human embryo the same way. The method, called somatic cell nuclear transfer (SCNT), replaces the DNA in an egg cell’s nucleus with the genetic material from the nucleus of a skin cell, then tricks the egg cell to start dividing as if it had been fertilized with sperm. The result is an embryo that is an almost perfect genetic copy of the skin cell donor. In humans, the goal of SCNT is “nonreproductive cloning” – making embryos, then removing stem cells from the embryo and cultivating them to grow into tissues that could cure diseases, replace organs and heal injuries.

But getting eggs to act like embryos turned out to be far more difficult in humans than in sheep. It was not until 2013 that Shoukhrat Mitalipov of the Oregon Health and Science University finally made SCNT work in humans, through careful tweaking and fine-tuning based on experiments with more than 1,000 rhesus monkey eggs. His final protocol requires a few dozen steps. Among Mitalipov’s secrets, stimulating reprogramming activity by priming the eggs with caffeine and by precisely dosing them with chemicals that coil and uncoil DNA’s twisted strands, and applying a gentle electric jolt to get the egg to begin dividing. In this case, an embryo created will not develop into a fetus.

There are now other methods to make stem cells, but those made via SCNT have unique value because they are genetic copies of the living person who donated the skin cells (other methods either use foreign cells or involve genetic reprogramming). Thus, replacement tissues made from them shouldn’t trigger the immune system rejection that dooms many transplants. Making purpose-built tissues may be far in the future because figuring out the exact recipes to turn cells into functioning bone, heart or spinal cord will take time. But Mitalipov’s triumph has big near-term benefits in giving researchers a new tool to understand all the details of how stem cells grow, divide and differentiate.