Stem Cell and Genetic Therapies for Hair Cell-Related Hearing Loss

Hair Cell Transplantation

As for transplantation as a method to regenerate lost hair cells, Dr. Ryan described the work by his team at UCSD.

Transplantation is the reverse side of the regeneration story in that there is considerable interest now in the role of hair cell replacement through stem cells, he said. It has been found that many types of stem cells tolerate transplantation into the inner ear, and sometimes will integrate into target tissues. However, inner ear tissue appears to have limited ability to induce stem cells to adopt an appropriate phenotype for the site without extra help.

His team found that in the case of sensory cells, transplanted immature hair cells can integrate into a damaged sensory epithelium if the appropriate access is provided, which they did in vitro. He said that there also appears to be a ‘critical period’ for transplantation; cells that are too immature or too mature cannot integrate to repair a damaged epithelium.

That suggests to us that if there is going to be a transplantational strategy for replacement of cells in the inner ear, we will have to be very careful about the developmental stage at which these cells are transplanted, he said.

In contrast to these in vitro results, Dr. Ryan’s team had much less success with in vivo delivery in rats. And yet, we think that cellular therapy has a lot of potential applications in the inner ear, with most transplanted stem cells surviving, and even integrating into some tissues. Access to some tissue sites-especially the organ of Corti and spiral ganglion-is a critical factor. And, achieving the appropriate cellular phenotype is the most significant challenge to transplantation, he said.

Legal Issues

In the final presentation, Dr. Liang lauded the advent of genomic medicine, but warned the audience about legal issues and conflict of interest in this new era.

It is estimated that in five years, by 2012, half of all drugs and devices will be bioproducts, he said, adding that basic science and clinical use need commercial development to enhance and further the application of discoveries.

The law has recognized that cutting-edge basic science and clinical research create issues of conflict of interest, he said, noting that physicians have a fiduciary duty to their patients to disclose all conflicts of interest-even if the financial or other benefit to the physician is concurrent with effective patient treatment.