Prenatal ultrasound scans can detect congenital heart defects (CHDs) before birth. Some 1% of all children born per year have some kind of CHD. Most of these children will require some kind of rather invasive, albeit life-saving surgery but an estimated 25% of these children will die before their first birthday. This underscores the need for netter therapies of children with CHDs.
To that end, Shaun Kunisaka from C.S. Mott Children’s Hospital in Ann Arbor, Michigan and his colleagues have used induced pluripotent stem cell (iPSC) technology to make patient-specific heart muscle cells in culture from the baby’s amniotic fluid cells. Because these cells can be generated in less than 16 weeks, and because the amniotic fluid can be harvested at about 20-weeks gestation, this procedure can potentially provide large quantities of heart muscle cells before the baby is born.
In this paper, which was published in Stem Cells Translational Medicine, Kunisaki and others collected 8-10 milliliter samples of amniotic fluid at 20 weeks gestation from two pregnant women who provided written consent for their amniocentesis procedures. The amniotic fluid cells from these small samples were expanded in culture, and between passages 3 and 5, cells were selected for mesenchymal stem cell properties. These amniotic fluid mesenchymal stem cells were then infected with genetically engineered non-integrating Sendai viruses that caused transient expression of the Oct4, Sox2, Klf4, and c-Myc genes in these cells. The transient expression of these four genes drove the cells to dedifferentiate into iPSCs that were then grown and then differentiated into heart muscle cells, using well-worked out protocols that have become rather standard in the field.
Not only were the amniotic fluid mesenchymal stem cells very well reprogrammed into iPSCs, but these iPSCs also could be reliably differentiated into cardiomyocytes (heart muscle cells, that is) that had no detectable signs of the transgenes that were used to reprogram them, and, also, had normal karyotypes. Karyotypes are spreads of a cell’s chromosomes, and the chromosome spreads of these reprogrammed cells were normal.
As to what kinds of heart muscle cells were made, these cells showed the usual types of calcium cycling common to heart muscle cells. These cells also beat faster when they were stimulated with epinephrine-like molecules (isoproterenol in this case). Interestingly, the heart muscle cells were a mixed population of ventricular cells that form the large, lower chambers of the heart, atrial cells, that form the small, upper chambers of the heart, and pacemaker cells that spontaneously form their own signals to beat.
This paper demonstrated that second-trimester human amniotic fluid cells can be reliably reprogrammed into iPSCs that can be reliably differentiated into heart muscle cells that are free of reprogramming factors. This approach does have the potential to produce patient-specific, therapeutic-grade heart muscle cells for treatment before the child is even born.
Some caveats do exist. The use of the Sendai virus means that cells have to be passaged several times to rid them of the viral DNA sequences. Also, to make these clinical-grade cells, all animal produces in their production must be removed. Tremendous advances have been made in this regard to date, but those advancements would have to be applied to this procedure in order to make cells under Good Manufacturing Practices (GMP) standards that are required for clinical-grade materials. Finally, neither of these mothers had children who were diagnosed with a CHD. Deriving heart muscle cells from children diagnosed with a CHD and showing that such cells had the ability to improve the function of the heart of such children is the true test of whether or not this procedure might work in the clinic.