In the field of tissue engineering, this is the era of organoids. Researchers are limited in the size of tissue they can produce because of the lack of a robust method of generating the blood vessel networks needed to support large tissue sections, but are otherwise making significant progress in the generation of functional organ tissue. Initially this is producing the greatest benefit for further research and development, allowing tests to be conducted in living tissue at a much faster pace and lower cost. For many tissue types, however, organoids also offer the possibility of benefits realized through transplantation, as in many cases they are capable of integrating with existing organ tissue to improve its function.
Scientists report using human pluripotent stem cells to grow human intestinal tissues that have functioning nerves in a laboratory. The paper puts medical science a step closer to using human pluripotent stem cells (which can become any cell type in the body) for regenerative medicine and growing patient-specific human intestine for transplant. "One day this technology will allow us to grow a section of healthy intestine for transplant into a patient, but the ability to use it now to test and ask countless new questions will help human health to the greatest extent." This ability starts with being able to model and study intestinal disorders in functioning, three-dimensional human organ tissue with genetically-specific patient cells. The technology will also allow researchers to test new therapeutics in functioning lab-engineered human intestine before clinical trials in patients.
Researchers started out by subjecting human pluripotent stem cells to a biochemical bath that triggers their formation into human intestinal tissue in a petri dish. The process was essentially the same as that used in a 2010 study, which reported the first-ever generation of three-dimensional human intestinal organoids in a laboratory. Intestinal tissues from the initial study lacked an enteric nervous system, which is critical to the movement of waste through the digestive tract and the absorption of nutrients. The gastrointestinal tract contains the second largest number of nerves in the human body. When these nerves fail to work properly it hinders the contraction of intestinal muscles. To engineer a nervous system for the intestinal organoids already growing in one petri dish, researchers generated embryonic-stage nerve cells called neural crest cells in a separate dish. The neural crest cells were manipulated to form precursor cells for enteric nerves. The challenge at this stage was identifying how and when to incorporate the neural crest cells into the developing intestine. "We tried a few different approaches largely based on the hypothesis that, if you put the right cells together at the right time in the petri dish, they'll know what do to. It was a long shot, but it worked." The appropriate mix caused enteric nerve precursor cells and intestines to grow together in a manner resembling developing fetal intestine.
A key test for the engineered intestines and nerves was transplanting them into a living organism - in this case laboratory mice with suppressed immune systems. This allowed researchers to see how well the tissues grow and function. Study data show the tissues work and are structured in a manner remarkably similar to natural human intestine. They grow robustly, process nutrients and demonstrate peristalsis - series of wave-like muscle contractions that in the body move food through the digestive tract.