Scientists have converted cells from human testes into stem cells that grew into muscle, nerve cells and other kinds of tissue, according to a study published Wednesday in the online edition of Nature.
The stem cells offer another potential alternative to embryonic stem cells for researchers who aim to treat diseases such as diabetes and Parkinson's by replacing damaged or malfunctioning cells with custom-grown replacements.
Scientists have also derived flexible adult stem cells from skin, amniotic fluid and menstrual blood.
The new cells were created from sperm-making cells obtained from testicular biopsies of 22 men.
They are theoretically superior to traditional embryonic stem cells because they can be obtained directly from male patients and used to grow replacement tissue that their bodies won't reject, Sabine Conrad of the University of Tuebingen in Germany and her colleagues wrote.
The cells also have an ethical advantage in that they do not require the destruction of human embryos.
Experiments in mice suggested that reproductive cells -- also known as germ cells -- were good candidates for making stem cells because they naturally express low levels of the "pluripotency" genes that make embryonic stem cells so versatile, said Renee A. Reijo Pera, director of the Center for Human Embryonic Stem Cell Research and Education at Stanford University, who was not involved in the study.