Bioengineering the Human Heart
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It's the stuff of science fiction. And, perhaps, Gothic horror. Researchers at Massachusetts General Hospital (MGH) have just announced that they have taken the first steps toward bio-engineering a human heart.
The new heart is being fabricated from components culled from other donated hearts which have been stripped of the components that would generate an immune response, and the new heart recipient's own cardiac muscle cells generated from induced pluripotent stem cells.
“Generating functional cardiac tissue involves meeting several challenges,” says Jacques Guyette, PhD, of the MGH Center for Regenerative Medicine (CRM), who is the lead author of the report. “These include providing a structural scaffold that is able to support cardiac function, a supply of specialized cardiac cells, and a supportive environment in which cells can repopulate the scaffold to form mature tissue capable of handling complex cardiac functions.”
The study included 73 human hearts that had been donated through the New England Organ Bank, determined to be unsuitable for transplantation and recovered under research consent. The team decellularized hearts from both brain-dead donors and from those who had undergone cardiac death. There was little difference between the reactions of organs from the two donor groups to the complex decellularization process.
“Regenerating a whole heart is most certainly a long-term goal that is several years away, so we are currently working on engineering a functional myocardial patch that could replace cardiac tissue damaged due a heart attack or heart failure,” says Guyette. “Among the next steps that we are pursuing are improving methods to generate even more cardiac cells – recellularizing a whole heart would take tens of billions – optimizing bioreactor-based culture techniques to improve the maturation and function of engineered cardiac tissue, and electronically integrating regenerated tissue to function within the recipient’s heart.”
Instead of using genetic manipulation to generate iPSCs from adult cells, the team used a newer method to reprogram skin cells with messenger RNA factors, which should be both more efficient and less likely to run into regulatory hurdles. They then induced the pluripotent cells to differentiate into cardiac muscle cells or cardiomyocytes, documenting patterns of gene expression that reflected developmental milestones and generating cells in sufficient quantity for possible clinical application. Cardiomyocytes were then reseeded into three-dimensional matrix tissue, first into thin matrix slices and then into 15 mm fibers, which developed into spontaneously contracting tissue after several days in culture.
The last step reflected the first regeneration of human heart muscle from pluripotent stem cells within a cell-free, human whole-heart matrix. The team delivered about 500 million iPSC-derived cardiomyocytes into the left ventricular wall of decellularized hearts. The organs were mounted for 14 days in an automated bioreactor system developed by the MGH team that both perfused the organ with nutrient solution and applied environmental stressors such as ventricular pressure to reproduce conditions within a living heart. Analysis of the regenerated tissue found dense regions of iPSC-derived cells that had the appearance of immature cardiac muscle tissue and demonstrated functional contraction in response to electrical stimulation.
Team leader Harald Ott, MD, of the MGH CRM and the Department of Surgery, an assistant professor of Surgery at Harvard Medical School, adds, “Generating personalized functional myocardium from patient-derived cells is an important step towards novel device-engineering strategies and will potentially enable patient-specific disease modeling and therapeutic discovery. Our team is excited to further develop both of these strategies in future projects.”