Maybe We Can't Grow a Heart, But Can We Heal One?
In the near future, we'll be more likely to see stem-cell-based therapies rather than outright organ replacement.
"We're shooting at the moon in trying to make a heart or make a liver, and you discover so many things along the way that sometimes you don't want to go to the moon after all," Wagner says.
For instance, instead of wholesale organ replacement, doctors are finding that simply injecting an organ with certain stem cells can produce a healing effect. A large number of ongoing investigations expect cell therapy to eventually change the treatment of any given chronic condition, Wagner says. Maybe in a decade, he says, they will yield therapies for conditions such as as heart disease and stroke. And perhaps, later on, for Alzheimer's and Parkinson's. In 2013, a published clinical trial that involved injecting cells into diseased heart tissue showed that "every patient in the stem-cell-treatment group improved."
"Are they going to be cures? Probably not in a 10-year time frame," Wagner says. "But they are going to show enough benefit that they would be adopted, opposed to what's currently done clinically."
And then there are practical concerns to growing entire organs. It may not prove to be a viable business model to tailor-make organs for individual patients. "Private industry is going to have to raise millions and millions of dollars not around the science, but around the practicality," Wagner says. "Specifically, what patients are you going to treat, how many per year, what's your reimbursement rate going to be, how long it's going to take to get through the FDA. All these practical regulatory business concerns — and often that's what is putting a barrier between an interesting report that you read about a study in rodents or even in pigs and if it ever gets translated to humans."
But the Baby Steps Still Matter
If, today, we built a human body using only lab-grown parts, the anatomy would be sparse. The body would have a bladder, a trachea, some blood vessels, some muscle fiber, skin, tear ducts, and a urethra — maybe a sphincter.
These are the simpler organs of the body. There are four levels of organ complexity, the first being flat surfaces like skin, the second hollow tubes like trachea, the third hollow structures, like the bladder and stomach, and the fourth solid structures, such as the liver and lungs. "Up to this point, we've been able to implant the first three types in patients," Atala says, "but we have not yet implanted solid structures in patients. That's still years away."
One of the barriers to that next step is feeding those organs. A kidney requires a lot of vessels to keep functioning. And not just big arteries, but tiny capillaries to feed all the cells. Over the summer, Johns Hopkins researchers found a way to grow networks of tiny human blood vessels in mice, the type that could someday feed a lab-grown kidney or other complicated organ, or to simply repair capillaries damaged by diabetes. "This is why we are very excited about it — because the vasculature is relevant for almost any tissue type," Sharon Gerecht, a researchers on the study, says. Still, the field remains in infancy.
"You have to remember, the field started with mouse cells in 2006, so it is pretty young," she says. "We still don't know exactly how pluripotent they are. Do they remember that they were diseased and old before? We still don't know this, and it will take time for research to find out."