Trials soon to test treatment for blindness due to chemical burns

Published in The Hindu on December 19, 2012

SLET - L.V. Prasad Eye Institute

The SLET procedure has been performed on nearly 50 patients so far. – Photo: L.V. Prasad Eye Institute

“It is a disruptive technology for treating blindness caused by chemical burns,’ said Dr. Virender S. Sangwan, Associate Director, Clinical Research at the L.V. Prasad Eye Institute, Hyderabad. “We anticipate starting the human clinical trials to test the safety and efficacy of the technology by mid 2013.”

He was referring to the Simple Limbal Epithelial Transplantation (SLET), where the limbal stem cells harvested from the healthy eye are allowed to grow in the damaged eye thereby restoring corneal transparency. The technique was developed jointly by Dr. Sangwan and his team at Hyderabad and Dr. Sheila MacNeil and others at the University of Sheffield, U.K.

Chemical burns permanently damage the limbal stem cells found in the eye and this in turn causes loss in corneal transparency. Hence the need for harvesting limbal stem cells from the healthy eye.

The Institute had successfully pilot tested the method in six patients and the results were published early this year (The Hindu, March 1, 2012). Dr. Sangwan and his team are now more confident of the method. “The membrane supports the limbal stem cell growth and allows the transfer of cells from the membrane to the affected cornea,” he explained.

The Sheffield team published a paper a few days ago in the Acta Biomaterialia journal describing the technique of producing a new and better 3D membrane structure. The L.V. Prasad Eye Institute has started using this membrane to grow the limbal stem cells.

“We started using the older version of the membrane since late 2010,” he said. “We are now trying to use the newer 3D membrane in the lab to grow limbal stem cells. We don’t foresee any difficulty in growing them. We think it is an interesting membrane and has the potential for clinical translation,” he said.

The University of Sheffield and L.V. Prasad Eye Institute had signed a Memorandum of Understanding with the Wellcome Trust Foundation in 2010. According to the MOU, Sheffield is tasked with developing the membrane, and the Hyderabad institute is responsible for using the membrane to grow limbal stem cells harvested from discarded eye bank corneas.

Biggest difference

The biggest difference between SLET and the cultivated limbal epithelial transplantation (CLET) is the cost difference and a significant reduction in contamination risk.

In the CLET procedure, an amniotic membrane is used as a scaffold for growing and expanding the limbal stem cells. This takes place in a lab, and the expanded cells are then transferred to the damaged eye. According to him, growing the limbal stem cells in the lab alone costs around 14,000 pounds in the U.K. In the case of SLET, this cost is directly saved as there is no need to grow the cells.

But the bigger gain comes from the cost of the membrane per se. “A piece of amniotic membrane used for one surgery costs $700 in the U.S. Ours will cost less than $10,” he stressed.

It is not the cost saving alone that makes SLET attractive. “We can make the technique widely available to doctors in small hospitals and clinics. The synthetic membrane can be mass produced like contact lenses,” he noted.

On the other hand, the availability of amniotic membrane is limited or highly regulated in many countries. In the case of India, hospitals performing CLET process the membrane themselves for internal use.

Since the growth of stem cells and their migration takes place in the damaged eye, the risk of contamination is less. Also, the need to visit the hospital twice — first to remove the limbal stem cells from the healthy eye and subsequently for transferring the expanded cells to the damaged eye — is eliminated.

The Institute has performed the SLET procedure on nearly 50 patients so far, and 30 of them have already completed one year. “We estimate [that] the success rate is about 76 per cent. We have not yet analysed all the results,” he said. The success rate of CLET is 71 per cent. This is based on about 200 cases and who have completed a maximum follow-up of seven years. “Looks like it [SLET] is better [than CLET],” he said.

The results based on 28 cases done till March this year were presented last month at the annual meeting of the American Academy of Ophthalmology in Chicago.

“The success rate was 76 per cent in these 28 cases,” he said. It is based on this data that he estimates that the success rate for the 50-odd cases will be 76 per cent. According to him, CLET will be performed in the failed cases.