For the first time, scientists have created early-stage embryos using cloned cells from adults.

A study from Advanced Cell Technology published Thursday in the journal Cell Stem Cell highlights how researchers were able to create embryos from the skin cells of two men, ages 35 and 75. Tissue from the embryos featured exact DNA matches with the donors.

Last year, scientists at Oregon Health and Science University made a major breakthrough with the first early-stage human clones derived from infant and fetal cells. However, the experiment drew criticism because early-stage human embryos are destroyed when cells are extracted from them.

This more recent experiment involving adult cells, funded by the South Korean government and performed in California, has large implications for advances in medical treatment. However, the success ratio was low: Scientists attempted 39 times to create stem cells but succeeded only once with each donor.