David Hackam is a pediatric surgeon at the Johns Hopkins Children’s Center. Unfortunately, Dr. Hackam spends a good deal of his time removing dead sections of intestine from sick babies, but he would deeply love to be able to do more than just take out intestines but actually replace the dead or dying intestinal tissue. It is that desire that has driven Hackam and his colleagues to grow intestines in the laboratory.
They begin with stem cells taken from the small intestines of human infants and mice and apply them to intestine-shaped scaffolds. The stem cells dig in, grow and form mini-intestines that just might be able to treat disorders like necrotizing enterocolitis and Crohn’s disease someday. Transplantation experiments in laboratory animals have shown that this laboratory-grown tissue and scaffolding are not rejected, but integrate into the tissues of the animals. Experiments in dogs have shown that the scaffold allowed dogs to heal from damage to the colon lining, essentially restoring healthy bowel function.
The study is a “great breakthrough,” says Hans Clevers, a stem cell biologist at the Hubrecht Institute in Utrecht, the Netherlands, who was not involved in the new research. Clevers and his colleagues were the first to identify stem cells in the intestine, and his lab developed the technique Hackam’s team used to grow intestinal tissue.
Making replacement organs by growing cells on scaffolds molded into the shape of the organ is not a new idea, since other researchers have used exactly this technique to make bladders and blood vessels. However, the laboratory-grown intestines made by Hackam and his group come closer to the shape and structure of a natural intestine than anything created in the laboratory before. In previous experiments carried out in other laboratories, the gut lining has been grown on flat scaffolds or in culture flasks. Under these conditions, the tissue tends to roll up into little balls that have the absorptive surface on the inside. Hackam and his coworkers, however, overcame this problem by using a scaffold fabricated from materials similar to surgical sutures. This material can be molded into any desired intestinal size and shape, and in Hackam’s hands, the scaffolds formed a true tube-shaped (like a real gut), with tiny projections on the inner surface that can help the tissue form functional small intestinal villi (the small fingers of tissue that increase the surface area of the intestine to increase nutrient absorption. “They can now make sheets of cells that can be clinically managed,” Clevers says. “Surgeons can handle these things and just stick them in.”
To grow the gut lining in the lab, the researchers painted the scaffold with a sticky collagen-rich substance and then dripped onto it a solution of stem cells from the small intestine. This concoction was grown in a culture system for a week. Interestingly, Hackam and his team found that if they added connective tissue cells, immune cells, and probiotics (bacteria that help maintain a healthy gut), all of these things helped the stem cells mature and differentiate.
Hackam’s group also sutured intestines grown from mouse stem cells into the tissue surrounding the abdominal organs of the mouse. The lab-grown intestines developed their own blood supply and normal gut structures despite the fact that they were not connected to the animals’ digestive tract. “Using the mouse’s own stem cells, we can actually create something that looks just like the native intestine,” Hackam says. The next step, he says, is “to hook it up.”
Before “hooking it up,” Hackam needed to be sure that the scaffold could be tolerated in living animals. Therefore he tested the new scaffold in dogs. He removed sections of large intestinal lining and replaced it with pieces of scaffolding. The dogs made a complete recovery: their gut lining regrew onto the scaffold and functioned normally to absorb water from the colon. After a few weeks, the scaffolding had completely dissolved and was replaced with normal connective tissue. “The scaffold was well tolerated and promoted healing by recruiting stem cells,” Hackam says. “[The dogs] had a perfectly normal lining after 8 weeks.”
This technique could help more than just dogs and mice, but could aid human patients. According to Hackam, scaffolds could be custom-designed for individual human patients to replace a portion of an intestine or the entire organ. This could be a revolutionary treatment for patients with necrotizing enterocolitis, a condition that destroys intestinal tissue in about 12% of premature babies in the United States. It could also potentially repair the intestines of patients with Crohn’s disease, an inflammatory bowel disorder that can have life-threatening complications and that affects more than 500,000 people in the United States. However, these lab-grown intestines must pass several other tests before they are ready for human clinical trials, Hackam cautions.
The first test that these laboratory-grown intestines must pass is the absorption test. Laboratory-grown small intestines must be transplanted into live animals and they must properly absorb food. Also, the technology that is used will also require some adjustments. For example, Mari Sogayar, a molecular biologist at the University of São Paulo in Brazil, points out that the collagen product that helps the stem cells stick to the scaffold is not meant for use in people. In the next experiments, Hackam says, the researchers plan to use a surgical-grade alternative.
“I take care of children who have intestinal deficiencies, eating deficiencies, and they are very much at wits’ end,” Hackam says. “I think what we can offer in the scientific community is a path toward something that one day will help a child.”