Lab-grown sperm could help—if the science holds

lab-grown sperm – A US start-up, Paterna Biosciences, says it can turn testis stem cells into sperm in the lab and help many men whose fertility treatments fail. But major experts warn that the claims still lack evidence, and that safety and genetics—especially what happens in

For many men, infertility is a silence that feels personal. It’s also common: around 1 in 10 couples have problems conceiving, and in half of cases the difficulty is wholly or partly down to sperm.

For some men, the usual fertility tools aren’t enough. Now a US start-up, Paterna Biosciences, is pitching a different path—one that starts not with sperm taken from the body, but with stem cells taken from the testes and coaxed into becoming sperm in the lab.

Paterna says the technique could enable almost all the men for whom fertility treatments currently fail to father children of their own. Its co-founder and head. Alex Pastuszak. also argues the approach can generate “high-single-digit to tens of thousands of sperm” from each piece of testicular tissue. The process, he says, takes around a month in the lab.

The boldest part of the promise is what happens next: Paterna has said it aims to implant embryos fertilised with lab-grown sperm into women as early as next year.

But the central question hanging over the project isn’t whether it sounds possible. It’s whether it’s proven.

Paterna’s claim still lacks evidence, and Pastuszak has offered a reason why: “I’m not going to publish something that will go into the public domain until we have protection around that.”

It’s not the first time a lab has staked out this territory. A French biotech company called Kallistem made a similar claim in 2015 and published a paper in 2016. Other researchers were not convinced, and nothing came of it.

Even some people willing to entertain the possibility of success are holding back until they see the data. Geert Hamer at the Amsterdam Reproduction & Development research institute in the Netherlands says that if Paterna has done what it claims. “it’s an enormous breakthrough.” Still. he describes the evidence gap as something that needs to be resolved with real proof. not hope.

The science problem sits underneath all of it: sperm are built through tightly choreographed cell division.

Men struggle to conceive for different reasons. Some have low sperm count, some have sperm that don’t swim well, and some have sperm that can’t enter an egg. In many of these situations, IVF paired with intracytoplasmic sperm injection (ICSI)—where a sperm is injected directly into an egg—can work.

But there are cases where semen contains no sperm at all. Around 1 in 100 men do not have any sperm in their semen. The number is described as “often-cited,” drawn from an old paper, and could be higher now due to an apparent decline in male fertility.

When the problem is obstruction—something blocking sperm from reaching the prostate—doctors can often remove it or take sperm directly from testes. When the problem is production, the story changes. If few or none are being produced in the testes, there’s nothing to harvest.

That is where Paterna wants to intervene.

To create sperm, the company starts with stem cells in the testes and drives them through development. The key moment is meiosis, a process during which chromosomes swap bits of DNA. Miles Wilkinson at the University of California. San Diego. who studies sperm stem cells. calls this “a very dangerous situation.” When DNA is broken. there’s a risk it isn’t put back together correctly. The concern is that imperfect lab conditions could raise the risk.

Wilkinson adds a possible safeguard: it is possible to remove cells from IVF embryos before implantation to test for mutations that might come from meiosis gone awry.

Imprinting adds another layer of risk. During sperm development in mammals, some genes are turned off by chemical tags known as imprinting. If that process goes wrong, it can cause serious developmental conditions.

Hamer says imprinting errors are common in mouse sperm derived from stem cells made from body cells. But he argues that because Paterna is using existing stem cells from the testes, the risk is likely lower.

Pastuszak says the lab-grown sperm appear normal. “We’ve shown that the sperm that we’re creating in vitro look molecularly exactly like the sperm that are made in the cysts [in the testes],” he says. “In some cases, actually better.”

Even if those molecular details hold up, there’s still the question of who would benefit.

Some men don’t produce sperm because they lack sperm stem cells altogether; Paterna’s approach wouldn’t help them. Others may have stem cells that exist but fail to turn into sperm, with mutations probably involved. Pastuszak says there’s long been a belief that a significant proportion of male infertility comes from genetic mutations.

But outside experts doubt the lab approach will solve infertility caused by mutations that block meiosis in the testes. Hamer says that if a mutation disrupts meiosis in the body. it’s also likely to disrupt meiosis in the lab. He thinks the main group that could benefit would be men who became infertile due to cancer treatments received as boys. with frozen testicular samples taken before therapy.

“If they’ve really achieved this, it would be great news for boys who become infertile due to chemotherapy,” Hamer says. He also stresses how small that group is among infertile men overall.

Wilkinson points to another limited niche: men who do produce a little sperm. For them. the current option is a many-hours-long procedure called microdissection testicular sperm extraction (mTESE). involving slicing a testis in half and searching for sperm formation. “If mTESE could be avoided, that would be great,” Wilkinson says. “So in vitro spermatogenesis has an exciting niche here.”.

If Paterna is right that the technique works even when no sperm exist in testes, then it would hinge on a different kind of defect.

Pastuszak says the company can derive sperm from men who do not produce any sperm in their testes. He argues that “most of these germ cells are maturation competent. ” and that the defect is in “the signalling from the support cells that provide the signals for those germ cells to mature [into sperm].”.

Again, there’s no evidence yet to verify the claim. The uncertainty matters because of what happens after the first generation.

If the lab-grown sperm carry a problematic mutation responsible for the infertility, male children conceived from that sperm could inherit it too and face infertility themselves—an outcome that would also be a worry in ICSI, though the most recent ICSI study did not find those worries to bear out.

Pastuszak’s answer is cautious. “I would say maybe,” he says. He also says there are tests at various stages that could screen out cells or embryos with harmful mutations.

The stakes of the debate are stark: if lab-grown sperm can’t be produced broadly, the promises won’t translate into real access for most families. If it can, the science may still need to show it can do so without passing along genetic problems.

The line between infertility treatment and genetic tinkering is also creeping closer.

If lab-grown sperm can’t be derived from most men with mutations causing lack of sperm. CRISPR gene editing is presented as a potential solution: correcting the mutation in the sperm stem cells so they can turn into sperm and lead to the birth of gene-edited children who would lack the harmful mutation.

Wilkinson calls out how difficult that would be. In most cases, there isn’t a clear idea of which mutation is responsible; associations are described as “tentative.” “There’s really very little proof,” he says.

Still, Pastuszak doesn’t rule CRISPR out. “I’m not going to take that off the table, because I think science and technology are going to continue to advance, and the goal here is to help a lot of people,” he says.

The idea rests on a requirement that’s far from trivial: using pre-implantation genetic testing to check for unintended changes, including potential safety issues tied to CRISPR.

That brings the conversation back to where it began—something men and couples often struggle to talk about, but cannot afford to ignore.

Paterna’s plan could, in theory, shift fertility medicine from harvesting what exists to manufacturing what’s missing. The problem is that fertility isn’t built on theory alone. It’s built on evidence, safety, and outcomes that withstand scrutiny.

And right now, as Pastuszak protects intellectual property by refusing to publish yet, the rest of the field is left with a choice: wait for the proof—or keep hoping without it.

lab-grown sperm Paterna Biosciences Alex Pastuszak stem cells male infertility IVF ICSI meiosis imprinting CRISPR gene editing mTESE fertility treatment genetic testing