Human-Pig chimera is a step towards replacement organs


Human cells (green) differentiated into endoderm progenitors (red)

Every day, 22 people in America die while waiting for an organ transplant. But when scientists can grow replacement livers or kidneys or pancreases inside of animal hosts, medicine’s organ shortage may end. That’s the hope anyway—and this week there’s more reason to hope than ever that it might become reality.

❝ The key to producing human organs in other animals is the chimera, a mixture of cells from more than one species growing together as a single animal. For decades, researchers have struggled to coax Petri dishes of stem cells into functional, three-dimensional tissues and organs, hampered by technical challenges and political stonewalling. Now, two milestone papers have taken two big steps toward solving the chimeric riddle. Will you be ordering up a homo-porcine gallbladder on Amazon this time next year? No. No, definitely not. But researchers have done two things they’ve never done before: 1. Combine two large, distantly-related species into one embryo. And 2. Use organs from one species grown in another to actually treat disease…

❝ With other advances, scientists are hoping to do away with artificial insulin altogether. About 30 million Americans have diabetes; more than 3 million of them rely on artificial insulin to stay alive. Chimeras could potentially help those patients make their own insulin—and Hiromitsu Nakauchi, a stem-cell biologist at the University of Tokyo and Stanford, showed you can do just that in a paper published yesterday in Nature. At least, you can in rats. His team used genetic tweaks to prevent rats from making their own pancreases. Then they injected mouse stem cells (complete with all the necessary pancreas-making genes) into the developing pancreas-less rat embryos. The rats grew normally. The only thing different was their pancreases were made almost entirely of mouse cells.

Then they went a step further. From those rat-mouse chimeras, Nakauchi’s team took out tiny clusters of pancreatic cells that make insulin (called islets) and transplanted them into diabetic mice. The islets settled in and made enough insulin to keep the host mice’s blood glucose levels in a normal range for more than a year. In layman’s terms? The mice were cured. It’s the first time a chimera-created organ has ever treated a medical condition.

❝ …Scientists will have to improve human stem cells’ colonization of their animal hosts. The Salk team’s next hurdle is trying to embed one human cell in 1,000, or even 100 pig cells. “That’s when we can start thinking about practical applications,” says Wu. But that’s also when ethical questions start to become more urgent.

More urgent, that is, for people who consider religious ideology more important than keeping someone alive. Folks more concerned with the creation of new species or sub-species and the uses thereof – instead of reducing numbers in the thousands and more of individuals who have to die – are socially, criminally out of touch with human needs.

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