As far-fetched as it may sound, performing prenatal surgery on a fetus still growing inside its mother’s womb is actually possible. This specialized procedure is done to repair birth defects like spina bifida, in which a baby’s back bones don’t form properly around the spinal cord. This opening in the spine that leads to excess spinal fluid and leaves spinal cord nerve cells unprotected from the surrounding tissue.  These abnormalities can lead to brain damage, paralysis and loss of bladder control.

Although prenatal surgery to close up the defect can reduce future neurological problems in the child’s life, there is an increased danger of significant complications including preterm birth, separation of the placenta from the uterus and premature breaking on the amniotic membrane (ie breaking the mother’s water).

Microscopy image of iSkin, three-dimensional cultured skin derived from human iPSCs. Credit: Kazuhiro Kajiwara.

A research team at Japan’s National Research Institute for Child Health and Development is trying to overcome these problems by developing a less invasive prenatal therapy for spina bifida using stem cells. And this week, they published a Stem Cell Reports study that shows encouraging preclinical results in rodents.

The most severe and common form of spina bifida called myelomeningocele usually leads to the formation of a fluid-filled bulge protruding from a newborn’s back. The team’s therapeutic approach is to graft 3D layers of stem cell-derived skin early in the pregnancy to prevent the bulge from forming in the first place. This minimally invasive procedure would hopefully be less risky than the surgical approach.

To demonstrate a proof of concept for this approach, skin graft experiments were performed on fetal rats that had myelomeningocele-like symptoms induced by the hormone retinoic acid. Human amniotic fluid cells collected from two pregnancies with severe fetal defects were used to derived human iPSCs which were then specialized into skin cells. Over a 14-week period – a timeline short enough to allow the eventual human procedure to be performed within the 28^th to 29th week of pregnancy – the cells were grown into 3D layers they call, “iSkin”.

The iSkin grafts were transplanted in 20 fetal rats through a small cut into the wall of the uterus. At birth, the myelomeningocele defect in four rats was completely covered and partially covered in another eight rats. It’s encouraging to note that no tumors formed from the skin transplants, a concern when dealing with iPSC-derived cell therapies. In press release, team lead Dr. Akihiro Umezawa spoke about the promise of this approach but also the work that still lies ahead:

“We are encouraged by our results and believe that our fetal stem cell therapy has great potential to become a novel treatment for myelomeningocele. However, additional studies in larger animals are needed to demonstrate that our fetal stem cell therapy safely promotes long-term skin regeneration and neurological improvement.”