As a fetus develops, its body is bathed in amniotic fluid: a warm, salty soup of nutrients, hormones, and antibodies produced by its mother. And into that fluid, a fetus is constantly sloughing off or peeing out cells, which provide genetic material that doctors can pull out with a needle and examine for signs of disease in a process called amniocentesis. Now, researchers working in the U.K. have discovered that some of those cells are still alive, and they can be grown up into three-dimensional organoids — mini lung, kidney, and small intestines — providing a possible new tool to study and even diagnose congenital fetal diseases.
It’s “a huge shock that there are viable epithelial cells in the amniotic fluid — totally unexpected!” said stem cell researcher Emma Rawlins via email. Senior group leader at the Gurdon Institute at Cambridge University, Rawlins was familiar with the research conducted at University College London and published Monday in Nature Medicine, but was not involved in it. The cells “are a great way of growing fetal organoids from externally exposed organs,” such as the lung, kidney and intestine, she added.
For years, researchers have studied fetal development and congenital diseases using postmortem fetal tissue to create organoid models, but that’s not without controversy.
Now, said Mattia Gerli, stem cell biologist at UCL and the first author of the paper, during a press briefing: “For the first time, we can actually access the fetus without touching the fetus, which is quite exciting on my end.”
Organoids are created from human stem cells to study adult diseases as well as fetal development and disease. Researchers use adult stem cells by accessing bone marrow, urine, and even menstrual effluent. But studying the fetus has often been limited to studying certain tissues because researchers need access to fetal tissue from terminated pregnancies.
As a first step, the UCL researchers isolated epithelial cells, which line the inside of organs, from human amniotic fluid collected during amniocentesis or other procedures used for prenatal diagnostics from 12 pregnancies between the 16th week and 34th week of gestation. Gerli added that the cells that they were able to isolate were technically not stem cells, but progenitor cells whose tissue identity is programmed. After making a map of what they found in the amniotic fluid, they identified the epithelial progenitors of three different cell types from the lung, the small intestine, and the kidney. The researchers then seeded the cells in a three-dimensional culture using a gel matrix to support them and grow them into organoids.
“This is very low-tech, it’s very easy to apply,” Gerli said.
In hindsight, Delilah Hendriks, a stem cell biologist at Princess Máxima Center for Pediatric Oncology and the Hubrecht Institute in the Netherlands, said that she agreed. She was not involved in the study. “I think that is sometimes the trick to a good paper,” Hendriks said. “It sounds quite easy, or logical.” She added that it’s a very good first step in the direction of coming up with a “non-destructive way” to further investigate medical conditions.
Why hadn’t this been done before? “It’s something that we wonder ourselves,” said Paolo De Coppi, the senior author of the paper, adding that this topic has been discussed in the lab for a long time. The main difficulties that researchers encountered was isolating live amniotic fluid cells since about 98% of cells floating in amniotic fluid are dead.
Gerli added that what clicked for him was being able to look into the fluid using single cell sequencing techniques, which helped confirm and identify the origin of the progenitor cells. “So, I think it was a bit of luck, an update of additional information that we generated that were missing in the literature.”
The cells that the researchers were able to identify are sometimes affected by congenital malformation, which is De Coppi’s main interest as a pediatric and fetal surgeon at UCL and Great Ormond Street Hospital. In the paper, the researchers focused on three birth defects. One is called congenital diaphragmatic hernia (CDH), where part of the diaphragm is missing, and as a result, part of the abdominal organs move up into the chest and compress the lung. In utero, the lungs are filled with liquid, but when babies are born they need to breathe. If the lung is being compressed, the lung will not develop normally. Only 70% of fetuses with this condition will survive.
The second step of the research was to answer the question, could these amniotic fluid organoids be used to improve prenatal diagnosis?
Currently for CDH there’s an experimental therapy using a balloon in the fetus at about 25 weeks of gestation. The fetal surgeon places a balloon inside the windpipe of the fetus keeping all the fluid produced by the lung in place and allowing the lung to maintain its pressure and expand against the abdominal organs. Even though it’s effective, the researchers were not sure how to monitor the treatment. By using the organoid, the researchers wanted to see if there was an improvement in the organoid before and after the placement of the balloon.
They were able to compare normal lung organoids to organoids derived from CDH amniotic fluid and noticed the latter were impaired. After the fetal procedure they observed that the CDH organoids looked similar to the normal cells based on their gene expression.
“This is basically an indication that our platform could be utilized to monitor disease [but] obviously this will need validation … from the clinic,” said Gerli.
De Coppi agreed that the platform needs to be validated, but made clear that these models are not ready for clinical use. He and his colleagues are also not suggesting any new treatment of the conditions that are discussed in the paper. He added that these cells derived from amniotic fluid will be an alternative to other sources of lung, kidney, and small intestine epithelial cells, but not other cells that require access to fetal tissue.
There are over 30,000 amniocenteses a year done in the U.K., and as many as 200,000 in the U.S. It’s not as common as it once was 20-30 years ago, but this procedure has no ethical ramifications compared to the controversy that comes up when using postmortem fetal tissue. Fetal tissue is available up to 20-22 weeks after conception. Amniocenteses are generally done between the 15th and 20th week of pregnancy, but can be done later.
Will this be an alternative to fetal tissue research? “No way!” said Lawrence Goldstein, an advocate for fetal tissue research and professor emeritus in the department of cell and molecular medicine in the department of neurosciences at the University of California, San Diego, who was also not involved in the study. Hendriks and Goldstein, who both study organoids focusing on other tissues like the brain and liver, explain that since the researchers only identified three cell types in the amniotic fluid, there’s not an immediate applicability to other tissues being studied. Hendriks added that she’ll stick with fetal tissue since there are fewer steps to isolating a needed tissue type.
In the future, De Coppi envisions that organoids can be used to test medication in vitro before delivering it to the patient. Another example involving CDH would be to study why those lungs don’t develop normally.
“We’re pretty excited about the possibility of implementing personalized medicine starting from these organoids,” said Gerli.
Erin Perrone, a fetal surgeon at the University of Michigan who specializes in CDH, noted that fetal therapies for CDH are experimental and traditionally offered only to those suffering the most severe consequences. She added that, “I would expect that newer techniques that can get down to the genetic and molecular level of the disease will only improve our diagnostic capabilities. That could help us delineate better what could happen to that patient and if that patient would respond to fetal interventions or not. But I think it’s going to take a while before we get there.”
Megan Molteni contributed reporting.