Free Radicals - Michael Brooks [67]
To make his breakthrough, Nayernia had harvested stem cells from a mouse embryo, allowed them to develop a little, then removed the few that had transformed themselves into the progenitors of sperm cells. Once these had developed into fully fledged sperm cells, they were injected into mouse eggs.
Success depended on playing a numbers game. The researchers injected a total of 210 eggs with artificially grown sperm. Only sixty-five of those were properly fertilised and began dividing. Each one of these was implanted into the uterus of a mouse, but the process yielded only seven live births. Of those seven baby mice, six survived to adulthood.
Less than a year after the announcement of his creation of functioning sperm cells from embryonic stem cells, Nayernia announced the next step forward: sperm from adult human stem cells. Turning the embryonic stem cell breakthrough into a viable and useful technology would require making very large numbers of cloned embryos of infertile men – which for some people would raise an ethical dilemma. But use adult stem cells, such as those found in bone marrow, and you wouldn’t have to be cloned to get yourself some working sperm.
Adult stem cells are not as versatile as embryonic stem cells: they cannot develop into absolutely any kind of cell. But take them from the right place in the body and you can generally get what you want. Nayernia took bone marrow stem cells from adult men and nurtured them into spermatogonia – cells that will, given the right conditions, develop into sperm. These cells have to go through a series of developments before they can become sperm cells, including three bouts of division, known as meiosis. Nayernia has done this with mice, and has made preliminary – and contested – claims to have achieved it with human sperm. But regardless of whether he has achieved this, his work seems to show that there is no fundamental barrier to culturing sperm that work. It is only a matter of time and money. It doesn’t sound as though the creation of a new life is going to remain a miracle for long.
The sperm are only one side of the equation, of course. Whereas sperm can just be grown and injected into an egg, making the egg itself is a more complex proposition. Many months before a girl is born, primordial follicles have formed inside her. These are containers for the undeveloped version of the oocyte, the cell that can eventually mature into an egg. The primordial follicles are in a kind of suspended animation: their development is halted, but it will resume at any time between the onset of puberty and the beginning of the menopause. The steady stream of developing follicles is what gives a woman her fertility: each one of them has the potential to grow an egg to 200 times its original size in just a few months, and then burst open, releasing the egg into the Fallopian tube, beginning the process that can end with a new human life.
In 2003 a research team at the University of Pennsylvania announced that they had grown something resembling eggs in a Petri dish using embryonic stem cells harvested from mice. The eggs showed some signs of attempting cell division to prepare for maturity, but things went no further. Others have since achieved the same results, but that, really, is as far as this technique has gone. No one has yet managed to get a fertilisible egg to develop from stem cells. The problem may have to do with the environment in which the eggs develop. In natural conditions the medium in which they grow is a recipe honed by evolution, and both the ingredients and the texture seem to matter. Like industrial food scientists trying to recreate a competitor’s market-leading