Nov. 9, 2021 -- Monkey embryonic stem cells have been coaxed for the first time into becoming sperm that can fuse with an egg in vitro, according to preliminary findings published in Fertility and Sterility Science.

Scientists have already successfully made sperm from mouse stem cells, but the rhesus macaque monkeys used in this new work are much more like humans. The findings take researchers a step closer to creating lab-made sperm to treat male infertility, but achieving that aim remains a distant target.

In this latest study, investigators used embryonic stem cells from rhesus macaque monkeys to make immature sperm cells known as spermatids. These early sperm cells lack a head and the tail needed to propel them toward an egg.

Investigators successfully got the spermatids to fuse with eggs in the lab and produce early embryos. In 12% of the cases, the embryos grew to a stage that would be able to implant into a uterus and contribute to forming a placenta.

No baby monkeys resulted from this work done in lab dishes, but researchers plan to implant these embryos into a surrogate monkey to see if development progresses to birth. Their far-future plan includes inducing macaque skin cells instead of embryonic stem cells to become spermatids.

Although promising advances using monkeys often don’t make it to human applications, the work can still add information about why the process of sperm production can sometimes fail, the authors write.

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F&S Science: “Blastocyst development after fertilization with in vitro spermatids derived from nonhuman primate embryonic stem cells.”

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