Scientists make human mini-liver from induced pluripotent stem cells

Last Updated: 2020-06-09

By Will Boggs MD

NEW YORK (Reuters Health) - Scientists have bioengineered human mini-livers from induced pluripotent stem cells (iPSCs) and successfully transplanted them into immunodeficient rats, according to a new report.

"After the transplantation of the mini human iPSC-livers, it really looked like a small human liver, and most impressive was when we extracted the human mini-livers out of rats, we saw that the livers looked in color and structure like livers and when we looked at the blood of the rats transplanted, we found human proteins circulating," Dr. Alejandro Soto-Gutierrez of the University of Pittsburgh, Pennsylvania, told Reuters Health by email.

Autologous bioengineered livers could provide transplantable grafts for the many patients with end-stage liver disease who languish on wait lists, Dr. Soto-Gutierrez and colleagues note in Cell Reports.

The team recently reported the generation of liver grafts using genetically engineered human iPSCs differentiated into liver cells. But bioengineering of an entire liver graft using human iPSCs-derived cells for transplantation has not been described, they say.

The main limitation of bioengineered liver constructs so far has been the insufficient endothelial-cell repopulation of the vasculature, making them highly susceptible to thrombosis, as well as the lack of other critical cell types found in the liver, such as bile duct epithelial cells.

In the current work, Dr. Soto-Gutierrez and colleagues developed protocols for hepatocyte, cholangiocyte, and endothelial cell differentiation of human iPSCs and seeded decellularized liver scaffolds with the resulting cells, along with liver-derived fibroblast and mesenchymal stem cells to mimic the liver microstructure.

The resulting mini-livers expressed cell-cell and cell-extracellular-matrix molecules and functioned at levels found in human adult and fetal livers, engineered liver grafts assembled with primary liver cells, or in three-dimensional cultures containing freshly isolated primary human fetal and adult hepatocytes.

The researchers then performed auxiliary liver transplantation of these grafts into immune-compromised rats, which they killed four days later.

Harvested grafts resembled normal liver tissue, and histological staining showed that the hepatocytes retained their morphology and their parenchymal positions. Immunohistochemical staining confirmed that hepatic function was retained in the transplanted grafts.

"The next steps are to genetically engineer those iPSCs to create human livers that will be universal donors (they will not be rejected by anybody), extend the survival of the transplanted rats to not days but weeks or months, and, finally, we are already scaling up the systems for human-size scale with pig bioengineered liver grafts," Dr. Soto-Gutierrez said. "Hopefully, the pig work will be published in the coming months."

"The long-term plans are to combine the human iPSC technology and the human-scale manufacturing of the pig work to generate human liver grafts for transplantation from skin cells or fibroblasts," he said. "We also need to corroborate safety!"

"In the shorter term, it will be possible to make human liver grafts that can help patients with acute liver failure where only temporary liver function is required," Dr. Soto-Gutierrez said. "The long-term dream is to be able to biofabricate universal entire livers for transplantation for patients with chronic liver disease (e.g., cirrhosis) where the only solution is replacement of the whole liver."

Dr. David Hay of the MRC Center for Regenerative Medicine at the University of Edinburgh, whose team has also generated 3-D human liver tissue from pluripotent stem cells, told Reuters Health by email, "The study is interesting, and it further supports the notion that structure and function (are important) in organ physiology and regeneration."

"It is a long way from the clinic, though, and it is an extremely complex procedure," he said. "So the cost to mass manufacture and deploy in the clinic will be prohibitive, until the process can be simplified."

"There are also serious potential issues with poor blood flow and clotting, (and) the short transplantation times are a concern and are probably driven by the issues with blood flow," said Dr. Hay, who was not involved in the new work.

"This will be a useful in vitro tool, albeit complex to make, for the field," he concluded. "However, from a clinical translational standpoint, the technology is unlikely to reach the clinic (as a transplantable piece of tissue) in the next 5-10 years."

The study did not have commercial funding, but the Dr. Soto-Gutierrez and some of his coauthors have patents related to the work and have founded a company focusing on biofabrication of autologous human hepatocytes using stem-cell technology.

SOURCE: https://bit.ly/2Uerll2 Cell Reports, online June 2, 2020.