Stem Cell Gene Therapy Replaces Boy's Entire Epidermis

Ricki Lewis, PhD

November 08, 2017

A boy who had lost most of his epidermis is back to school and playing soccer 2 years after receiving "life-saving regeneration of virtually the entire epidermis" with genetically modified autologous epidermal stem cells, according to a report published online today in Nature. 

The boy presented at the burn unit of Children's Hospital at Ruhr University in Bochum, Germany, in June 2015, with blistered skin characteristic of junctional epidermolysis bullosa (JEB) and associated bacterial skin infections. Within days, about 60% of his epidermis had vanished.

"The first few days we just tried to keep him alive. Then we tried to promote spontaneous healing by changing the dressings, treating him with antibiotics, and using nutritional interventions, but nothing helped," recalled first author, Tobias Hirsch, MD, from the burn center, at a news conference. "We treated him with alloplastic tissue replacement, and transplanting skin from his father, but it was rejected. After 2 months we thought he would die and we could do nothing more, so we changed to palliative care."

But the boy's parents wouldn't give up and asked Dr Hirsch to search the medical literature again. That lead to Michele De Luca, MD, from the Center for Regenerative Medicine at the University of Modena and Reggio Emilia in Italy and his colleagues. In 2006 they had published a case report in Nature Medicine about a man whom they had treated with several small grafts derived from his own epidermal stem cells genetically modified to have functional copies of the gene that was mutant, LAMB3 . It was the same gene that was mutant in the boy.

LAMB3 is one of three genes that encode a laminin protein that links the epidermis to the dermis. Mutations in other genes cause JEB too. In the United States, prevalence for all types of JEB is 1 or 2 per million live births. About 40% of patients survive to reach adolescence. Half a million people worldwide have some form of epidermolysis bullosa (EB).

In September 2015, the researchers cultured primary keratinocytes from a 4-cm2 biopsy specimen from an unblistered area in the boy's left inguinal region. Then they used retroviral vectors to introduce LAMB3 genes. The grafts grew, thanks to included epidermal stem cells. "It's very similar to what we've been using for full-thickness burns: Take a biopsy and isolate cells. The difference is the genetic modification of those cells, when we introduce extra copies of the LAMB3 gene needed to restore the epidermal machinery," Dr De Luca said. (Full-thickness burns cause much more extensive damage than does JEB.)

Three types of cultures grew into grafts from the boy's cells: holoclones, which  are all stem cells; paraclones, which are specialized cells; and meroclones, which are partly differentiated cells. The transgenic grafts harbor all three types of clones, but only the holoclones persist.

Procedures in October 2015 covered the boy's limbs and in November, his back. A smaller intervention in January 2016 was done to fill in smaller areas of the thorax, thighs, right hand, and shoulders. The patches were up to several inches in diameter and were applied on a properly prepared wound bed. A fibrin substrate prevented shrinkage of larger grafts.

"It takes days for engraftment, and a few weeks to stabilize, and the skin becomes robust. Once this happens, then the epidermis looks basically normal, and that's also true at the molecular level in terms of the adhesion machinery that has been replaced," explained Dr De Luca. "Within 5 weeks, the cells had covered about 80% of the boy's body," he added.

Even hairs grew. "Normally in a burn patient's skin graft the surface is sealed by the skin, so there's no chance for skin appendages to redevelop. These patients have to apply ointments once or twice daily, which becomes a major issue for their quality of life. In this child we saw that his hair regrew and he had no further need for ointment," Dr Hirsch said.

While the patient was regrowing his epidermis, which knit smoothly to the dermis, the cell cultures continued, in case he needs a future graft. Those cultures revealed that the epidermis regenerates completely each month, from a small population of founder stem cells, and not from waves of transit-amplifying progenitor cells as had been thought.

The patient left the hospital in February 2016. At the 2-year mark, some 20 epidermal cell divisions later, "all biological and clinical measures were fine, stable, robust, and the functionality quite good," Dr De Luca said. He added that the man treated in 2006 is doing well, too. "All of the data in terms of stability of the transgenic epidermis is telling us that this is going to be a stable situation."

The boy has not had an immune response to the grafts because the cells are autologous, nor have transgenes inserted into oncogenes.

Today he attends school and has smooth skin. He's athletic, but when he gets bumps and bruises, they heal normally, within 2 weeks, said Tobias Rothoeft , MD, also from University Children's Hospital in Bochum. "In fact we're discussing whether to do another transplant because he behaves like his healthy siblings. But blisters are restricted to the 2% to 3% of his body in the areas where we didn't transplant."

The researchers conclude, "transgenic epidermal stem cells can regenerate a fully functional epidermis virtually indistinguishable from a normal epidermis, in the absence of related adverse events so far."

Their findings, they write, provide a blueprint for development of combinations of ex vivo cell and gene therapies to treat other forms of EB.

In an accompanying News and Views article, Mariaceleste Aragona, PhD, and Cédric Blanpain, MD, PhD, from the Laboratory of Stem Cells and Cancer at the Free University of Brussels, Belgium, write that the study "demonstrates the feasibility and safety of replacing the entire epidermis using combined stem cell and gene therapy. In addition, the work provides insights into the cellular hierarchy that governs epidermal maintenance in humans."

They call for continued monitoring of the boy to detect development of skin cancer (for which people with EB are at elevated risk) and appearance of blistered zones. "Nonetheless, the authors' work marks a major step forward in the quest to use stem-cell therapies to treat disease," they conclude.

Dr De Luca and another author are cofounders and members of the board of directors of Holostem Terapie Avanzate in Modena, Italy. The other authors and the commentators have disclosed no relevant financial relationships.

Nature. Published online November 8, 2017. Study abstract, News and Views extract

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