Grafted stem cells team up with natives

By Roibeard O’hEineachain

Barcelona — Limbal stem cell transplants can dramatically improve the outcome of corneal grafts in patients who otherwise would have been considered hopeless, according to an ophthalmologist based in Sweeden.
Speaking at the 6th Winter Refractive Surgery Meeting of the ESCRS, Ulf Stenevi observed that the stem cells continue to contribute to the epithelium for several years and their presence may have a regularising effect in the prevention of conjunctivalisation and vascularisation.

Since 1997, Dr Stenevi, of the Department of Ophthalmology, Sahlgren's University Hospital, Mölndal, Sweden, has used stem cell-assisted grafts in about a dozen patients, most with severe chemical burns.
Their corneas largely maintained a fairly normal appearance without opacities, conjunctivalisation or vascular in-growth, Dr Stenevi noted.

Furthermore, he reported that his analysis of epithelial cells from one patient’s eye showed that epithelial cells from the transplanted stem cells continue to live on in the patient’s epithelium where they appear to somehow enable their own epithelial cells to act more normally.

FISH Analysis
In his study, Dr Stenevi carried out FISH (Fluorescent In Situ Hybridisation) analysis on a tissue sample from the epithelium of a man who received a stem cell-assisted corneal transplant three years previously.
The patient had severe chemical burns in both eyes and had undergone six previous transplants unsuccessfully.

The patient’s cornea looked quite normal at the time of the study and was clear and free of conjunctivalisation. The donor eye was from a woman so the donor-derived epithelial cells could be easily distinguished from those of the recipient by the FISH technique.

“The beauty of this technique is that when the donor and recipient are of different gender, you can actually tell which cell comes from whom and it is not as cumbersome as DNA-fingerprinting,” Dr Stenevi told EuroTimes.
His analysis showed that epithelial cells from the donor made up only a minority (about 30%) of the epithelial cell population. Nonetheless, the “sick” cells from the recipient appeared to behave normally without the problems of recurrent erosion, fibrosis and vascular in-growth that occurred in his six previous transplants.

“So, in essence, that means that 30% of healthy cells and 70% of sick cells still makes up a healthy looking cornea. What this suggests is that healthy transplant cells will somehow talk to their neighbours and make them behave like healthy cells.

“We know that there is a cascade of signals going on within the epithelium and within the cornea all the time. We don’t yet understand the language. Nonetheless, the fact that most of the epithelial cells were host-derived in an eye that had epithelial problems in every previous transplant strongly suggests that some sort of communication between the host and recipient cells had a role in the graft’s success,” Dr Stenevi explained.

Limbal crescent
Dr Stenevi noted that he performs allogenic stem cell transplants using the method described by Dr Sundmacher in Germany. The technique performs a de-centred trephination on the donor eye which includes a 90o crescent of limbal tissue.

A central trephination is carried out on the patient and single sutures keep the donor tissue in place. He concludes the procedure by placing a bandage contact lens on the eye. Patients remain on a regimen of topical steroids for the life of the graft.

“I keep patients on steroids on a permanent basis. The majority of surgeons would use systemic immunosupression if you transplant between individuals. There is no evidence to show whether or not you need systemic immunosuppression with the technique I use, and there are patients in my practise who cannot tolerate immunosuppression for the rest of their lives, and whose grafts have survived with a regimen of dexamethasone,” Dr Stenevi observed.

When performing autologous grafts, Dr Stenevi dissects a piece of tissue from the healthy eye that is about 5 mm along the juncture of the clear cornea and limbus and about 3 mm to 4 mm into the conjunctiva.

He then places the excised tissue into a similar dissection in the unhealthy eye and waits for a few weeks to see if the eye re-epithelialises efficiently. If it does, a normal corneal transplant is performed. In these cases, patients only require a normal tapering topical steroid regimen.

Long-term outcome still undetermined
Dr Stenevi pointed out that, in cases that would previously have been considered unsuitable for keratoplasty, stem cell transplants seem to work most of the time.
However, since the main indication for the procedure — severe chemical burning — is rare and the experience with the technique has been short, what remains unclear is how long this type of graft will survive in the eye.

“I would be surprised if results are as good with this technique as with other indications such as keratoconus where the eye is otherwise healthy with good epithelium, tear film and without blood vessels.

“On the other hand, if you do not include stem cells, PKP is meaningless because we know that the graft will always fail and the alternative would be a keratoprosthesis or some other kind of more severe surgery,” he explained.

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