Transplantation of hESC-derived otic progenitors into models of neuropathic deafness:long term analysis and safety

Deafness is a major public health issue, with more than 3 million people in the UK suffering a moderate to profound hearing loss. The numbers rise to more than 10 million if we include sufferers of mild impairments. Most forms of deafness are, in fact, progressive, neurodegenerative disorders which involve loss of sensory hair cells (cells that converts sounds into an electrical signal) and their associated neurons (responsible to take the signal to the brain). Both these cells are only produced in the womb, therefore if they become damaged are not replaced and hearing loss is irreversible. The only treatment available is the cochlear implant, but it needs the preservation of the sensory neurons to function. When the damage occurs primarily at the neurons, in a condition known as auditory neuropathy, the therapeutic options are very limited and implant performance is poor. A stem cell-based therapy could, in theory, repopulate the deaf ear with the cell types that have been lost and offer new opportunities for functional recovery.

We have recently established that transplantation of human otic progenitors, generated in the laboratory from human embryonic stem cells, can replace lost auditory neurons in the gerbil and elicit a level of functional restoration. The aim of this project is to assess the long-term behaviour and biosafety of transplanted human stem cell in animals with a damaged auditory nerve, resembling the condition observed in human auditory neuropathies.
The cells to be applied have been extensively studied in culture, and we have evidence that they can differentiate into functional cells when treated with the appropriated conditions. We are performing more experiments in vitro, trying to understand their molecular and functional properties. But in order to evaluate the interaction with a host and the responses they may trigger, as well as if their beneficial effects are sustained long-term, they would have to be tested in an animal model.
Questions we would like to address involve the number of cells needed to achieve maximum recovery, if the functional recovery is permanent and whether the cells delivered into the cochlea can spread into other tissues. Moreover, it will be important to find out if they can originate tumours, or have other unwanted effects.
An important issue to highlight with our work is that these experiments will be performed with human cells, the actual putative therapeutic tools. The information obtain from these studies should advance their future application in human clinical trials and the development of a therapy for deafness.

We have recently developed a method to generate otic progenitors from hESCs. Moreover, when these otic neuroprogenitors are transplanted into a deaf gerbil, they engraft, differentiate into auditory, spiral ganglion neurons and elicit a functional recovery measured by auditory brainstem evoked responses (ABRs). These advances open new possible therapeutic opportunities. In this project, we are planning to obtain necessary data to facilitate the development towards the clinical application. The general aim of the project is to study the long term impact and biosafety of hESC-derived otic neuroprogenitors. We will transplant them into a gerbil model of auditory neuropathy and will monitor the functional performance and general wellbeing of the host for a period of up to two years. Specific elements to determine are: actual need for immunosupression, since there is some indication that the inner ear could be an immuneprivileged site; dose-effect, to determine if applying different numbers of cells could have an impact on the histological structure and/or functional recovery; long term efficacy, to evaluate if the recovery obtained is sustainable in the long run and safety and biodistribution, to evaluate the long term implications on general welfare of delivering stem cells into the ear. Also to determine if they will remain localized to the ear or if they will spread to other tissues. Functional analysis will be done using ABRs and general histological studies will be facilitated by using fluorescently-tagged cells. We will determine if the transplanted cells are still proliferative by staining for markers like pH3 and PCNA. Sample tissue from key organs (brain, lung, liver, etc) will be taken for histological analysis and qPCR of reporter/marker genes, to detect if cells have colonized organs beyond the cochlea. Furthermore, the wider applicability of this treatment will be tested in models of auditory neuropathy on other species such as the mouse and rat.

Academic beneficiaries: Obvious, immediate beneficiaries will be academic colleagues from the hearing and regenerative medicine fields. Data obtained with this work should stimulate new strategies for deafness research and should also facilitate broader translational research using hESCs. The postdoc working in this project will develop skills in data analysis and management that could be employed outside the academic remit.
Clinical scientists and health providers: This research is already having an impact nationally and internationally, stimulating young surgeons to acquire scientific training by studying for a PhD. I am currently hosting a visiting ENT surgeon from Brazil, doing an intercalated year as part of her PhD program, and in October I will receive a UK ENT specialty registrar starting his PhD thesis. I have lectured to clinical audiences (surgeons and audiologists), highlighting the potential application of this research. I will continue to engage with health professionals at conferences and workshops.
Potential patient groups: This research has the potential to improve the hearing of patients with nerve damage and also those using cochlear implants. I have presented the work to patient groups, explaining the potential benefits to be obtained from this regenerative strategy. I have been invited to present work at events organized by charities and I have written articles in newsletters for cochlear implant users and the deaf community in general. I am a Trustee to the Ear Foundation, a charity dedicated to promote research and education in medical and social aspects of deafness and hearing, and to facilitate the bridging between clinical services, families of implanted patients and schools. Through the EF, I have coordinated a seminar series entitled 'Scientific Advances in Hearing Loss: made accessible for all', inviting leading hearing scientists to talk about their work to a non-specialist audience. I am routinely contacted by email by patients looking for information and advice.
Wider, general public. This research has already had an important impact increasing scientific awareness of the wider public. Past publications have attracted substantial media interest; our 2009 Stem Cells paper and our recent Nature paper had worldwide coverage by the radio, TV and printed press. I have engaged with the press, emphasizing the importance of medical research and the need for the humane use of animals. An example of the positive impact this communication achieved can be seeing at http://speakingofresearch.com/2012/09/14/human-embryonic-stem-cells-restore-hearing-in-deaf-gerbils/#comments. Research in my lab has been featured in a Horizon-style documentary by Russian TV about future therapies for deafness and also in three different episodes of the BBC2 TV magazine program 'See Hear' (September 2010, October 2011 and November 2012). Our lab participated at the University of Sheffield Researcher's Night 2012, an event that welcomed over five hundred members of the public offering them the opportunity to learn about stem cells and deafness. The event was part of the Europe-wide Researchers' Night 2012.
Public and charity sector. This research will help to raise the profile of deafness and the need to support charities that work with this disability. I have been a speaker at several fundraising events for deafness charities (i.e. Action on Hearing Loss) and I am a Trustee for the Ear Foundation.
Industrial impact. I have ongoing collaborations with Neusentis-Pfizer Regenerative Medicine (through a MRC-CASE studentship), with Cochlear Ltd (with a previous MRC Translational grant) and with Acousia (a new biotech company backed by Boehringer Ingelheim, through a Consultancy Agreement). The research in this project is likely to raise further interest from other potential industrial partners. I will actively explore any industrial interaction that would facilitate the translational development of this therapy.