Researchers in Cambridge have reportedly made primitive forms of artificial sperm and eggs, according to The Guardian.

Scientists reported made the early-stage sex cells by culturing human embryonic stem cells under carefully-controlled conditions for a week, according to the news outlet.

The cells are reportedly believed to have the potential to grow into mature sperm and eggs, although this has never been done in the lab before. The next step for the researchers is reportedly to inject the cells into mouse ovaries or testicles to see if they fully develop in the animals.

The study, which was published in the Journal Cell, will reportedly give insight into fertility problems and early stages of embryonic development and hopefully enable the development of new kinds of reproductive technology, according to the Xinhuanet.

“Researchers have been attempting to create human primordial germ cells in the petri dish for years,” stated Jacob Hanna of Weizmann Institute of Science in Israel, who led the study.

He added, “PCGs arise within the early weeks of embryonic growth, as the embryonic stem cells in the fertilized egg begin to differentiate into the very basic cell types. Once these primordial cells become ‘specified,’ they continued developing toward precursor sperm cells or ova ‘pretty much on autopilot.’”

The idea reportedly started with the 2006 invention of inducted pluripotent stem cells, which are adult cells that are “reprogrammed” to look and act like embryonic stem cells, which will then be able to differentiate into any cell type. Although researchers in Japan were reportedly successful with getting mouse iPS cells to differentiate into PGCs, efforts to replicate the achievement in human cells have failed.

For the recent study, Hanna’s team reportedly created a new type of iPS cells that they have called “naive cells.” The “naive cells” reportedly rejuvenate iPS cells one step further.

“This work tells us that the extrapolation can be unreliable. I’m not saying that all work in mice doesn’t apply in humans, but there are fundamental differences we need to be wary of,” stated Azim Surani, who led the work at the Gurdon Institute in Cambridge.

He added, “It’s not impossible that we could take these cells on towards making gametes, but whether we could ever use them is another question for another time.”