We called the ambitious program, ‘Egg Farming,’ over 30 years ago when I worked at Edinburgh University. That goal drew a step closer today as my graduate student from so many years ago published results of growing human eggs in vitro, to a blaze of publicity.
We started by growing mouse and rat eggs in Petri dishes. They were tiny cells nested in follicles that nurse their development, and some reached full size in a week and even ovulated a fertile egg into the culture medium. Our sole competitor in this new science was in the USA where John Eppig developed a more efficient method, and he called the first pup conceived from an egg grown in vitro, ‘Egbert.’ He was a strange and obese animal, and we worried if egg farming was too risky to apply in veterinary or human medicine, but many healthy mice were born later.
It seemed a huge leap from mouse to clinic. Human eggs grow more slowly in the ovary, and we expected the cultures would take weeks or even months and be risky. Progress was agonizingly slow because human ovarian tissue is rarely available for research, especially at the premenopausal ages required. Instead of relying on rodents, we needed intermediate species to forge better methods, and turned to sheep and cow ovaries. Visits to the local slaughterhouse for discarded tissue from butchered carcasses were some of the most unpleasant experiences ever, and almost turned me vegetarian from hearing the crack of the bolt-gun followed by a heavy slump. But they helped us to gain new knowledge when human tissue was unavailable.
Professor Telfer’s team in Edinburgh has succeeded with human eggs through careful work with clinical colleagues who asked consent from women to donate tiny slivers of ovarian tissue during C-section. The biopsy doesn’t harm them.
They watched eggs growing in dishes from the earliest stages to full size when a nuclear division occurred and signaled they were ready for fertilization. It is puzzling why the growth is much faster in vitro than in the body, though it is welcome if the eggs are no less competent for making babies. They look normal, but we know from experience how deceptive appearances can be. The only sure test is to fertilize eggs to see if they create healthy embryos, and that will require a special license under UK law.
Why is farming eggs worth the trouble and long struggle?
Progress will continue at a dawdling pace because a mature egg is the rarest cell in the body. For every egg ovulated each month, a man makes 3 billion sperm cells which offer researchers enough material for galloping discoveries in testes. Animals that fertilize eggs outside the body, like frogs and most other species, release as many eggs as they can make because the cost to them is small while superovulation maximizes the chance of making babies. But ovulation in mammals with internal fertilization and pregnancy is restrained by the limited accommodation of the uterus. Nature has arranged a bottle-neck in the egg production line to ensure that few eggs, or only one or at most two in humans, ripen at a time. The rest are consigned to the trash, which egg farming aims to rescue.
If more eggs can be ripened in vitro there will be benefits for animal breeding technology and young patients will have a better chance of preserving their fertility after freezing ovarian tissue during sterilizing treatment for cancer and other diseases. Egg farming will work better for child patients with their larger stores of eggs than in adults. Nearly a quarter-century ago, our first patient at an infant age had ovarian tissue stored while she was treated for Wilm’s tumor. The news from Edinburgh today was welcome for her and others with investments in the frozen ovary bank.
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