Researchers have hit a critical milestone in the production of human sperm cells in a laboratory. The team are thought to be the first in the world to have reached the halfway point in creating the cells, and have even replicated critical biological and chemical processes along the way.  

The breakthrough was announced at the Progress Educational Trust conference, by Azim Surani. Working with his team at the University of Cambridge, he created artificial testes in a dish, with all the different tissues grown in the lab, and is now trying to create human sperm.

The production of sperm within the body is, rather unsurprisingly, a complicated affair. Various teams around the world have professed to have achieved it, but these claims have been criticized, and no one has managed to fully replicate the process.

Last year one team in China, for example, announced they had made mouse sperm that could be used to make healthy offspring, but these were not fully formed sperm, instead, they were early stages of the cells known as spermatids. These immature sperm cells cannot swim, and so had to be injected into mouse eggs in order to fertilize them.

Even then, producing mouse sperm is one thing, but creating human sperm cells is another entirely. It takes about 13 days for a stem cell to develop into an immature sperm cell in the rodents, for humans this timescale is more like eight weeks. This much longer timescale has been a real stumbling block so far.

Now, the team think they have managed to hit the halfway point in sperm production, roughly four weeks, and even think that the cells in the lab are going through a critical stage known as “erasure”.

As people grow and age, the DNA in their cells accumulates molecular and chemical markers in relation to a whole host of external factors from smoking to stress. Known as epigenetic markers, these can be passed on to a person’s offspring, but the body also tries to wipe the slate clean when producing embryos. When a sperm fertilizes an egg, the DNA undergoes erasure, a process that cleans much of these markers away.

But even before all this, as the sperm is being produced in the testes, developing sperm also undergoes erasure. Incredibly, the sperm being developed in the lab shows signs that it too is being exposed to this process. “This process of erasure is much more comprehensive and global; you don’t see it anywhere else,” Surani told The Guardian. “We’re starting to see that erasure process.”

The group have submitted a paper detailing their results so far, and are now working to see if they can complete the second half of sperm production.