Researchers have successfully generated immature human sperm from a person's blood cells by reprogramming them into stem cells and nurturing the resulting tissue inside a pouch grown on a mouse's kidney, marking a significant step towards producing functional human sperm entirely in the laboratory [1].
The procedure, described in the journal Cell Stem Cell, is the latest effort to replicate in humans what a handful of teams have already achieved in mice, including producing offspring from two male parent animals. No team has yet made mature human sperm, and the lab-grown cells in this study stopped developing at an immature stage.
Eoin Whelan, a reproductive biologist at the University of Pennsylvania and a member of the research team, said the technique is not ready for clinical use but could help scientists study the earliest stages of human sperm development and investigate the roughly 40 percent of male infertility cases that have no known cause. Kotaro Sasaki, a developmental biologist also at the University of Pennsylvania, noted that research in humans has lagged far behind work in mice because of differences in how the species develop and because human fetal development is difficult to study directly.
The approach involves converting blood cells into induced pluripotent stem cells, which behave like embryonic cells and can be chemically guided into becoming sperm precursors. Among the ethical concerns surrounding the technique is the possibility that lab-grown reproductive cells could be genetically edited to produce so-called designer babies.