In what was clearly a scientific breakthrough, Weizmann Institute of Science researchers were able to cause human stem cell tissue to grow into kidneys that are genetically human and functioned fully in mice. This breakthrough is an important step in working towards a solution of the problem of the global shortage of kidney donors. This story was placed on both the AP and Reuters wires, ultimately appearing in many media outlets.

Here is the story that Reuters Health ran on December 23, 2002.

STEM CELLS BECOME WORKING HUMAN KIDNEYS IN MICE

NEW YORK (Reuters Health) – Human stem cells transplanted into mice eventually developed into working, mouse-sized human kidneys, researchers report in a new study.

The results offer hope that investigators may one day be able to grow human-sized kidneys in humans, potentially saving the lives of the more than 50,000 people in the US alone who need a new kidney but must await a donor.

The human stem cells were between 7 and 8 weeks of gestational age, meaning they had been extracted from aborted fetuses. These cells are similar to embryonic stem cells, which are extracted from embryos created at in vitro fertilization clinics that are not going to be used.
Fetal cells are easier to obtain than embryonic stem cells, however: the latter are currently mired in controversy, for embryos are inevitably destroyed when stem cells are extracted.
The researchers also succeeded in growing a mouse-sized pig kidney in the mice using stem cells extracted from pig embryos. The pig-derived organs also appeared to be accepted by human immune system cells injected into the mice.
Donating organs from one species to another, a field known as xenotransplantation, has long been stymied by several glitches-most notably, the fact that the human immune system often identifies the implanted pig organ as a foreign invader and destroys it, a process known as rejection.
So the fact that pig kidneys escaped detection by human cells suggests that one day, doctors may be able to offer humans an organ grown from pig cells, boosting the supply of kidneys even further.
The researchers, led by Dr. Yair Reisner of the Weizmann Institute of Science in Rehovot, Israel, published their findings in the advance online edition of Nature Medicine.

Reisner and colleagues performed their experiments in mice whose immune systems had been entirely knocked out. The researchers transplanted stem cells from human and pig fetuses of different gestational ages, and found that those which produced the healthiest kidneys came from human fetuses between 7 and 8 weeks gestational age and pig fetuses with a gestational age of 4 weeks.

These pig and human-derived kidneys were functional, the authors report, meaning that they produced urine for their new host.
Importantly, Reisner and colleagues discovered that stem cell-derived kidneys were nourished by blood flowing from the mice’s own blood vessels, and not from blood vessels derived from the donor animal. This could significantly reduce the risk that the host’s body would reject the organ, thinking it is foreign, the authors note.

“Our results show that when human and pig kidney precursors are obtained from 7-to 8-week human or 3.5-to 4-week pig gestation and transplanted into immunodeficient mice, they survive, grow and undergo complete nephrogenesis, forming a functional organ able to produce urine,” Reisner and colleagues write.