Safety, Tolerability and Efficacy for CGF166 in Patients With Unilateral or Bilateral Severe-to-profound Hearing Loss

The study will evaluate the safety, tolerability, and potential efficacy of CGF166 and the
associated delivery procedures in patients with severe-to-profound unilateral or bilateral
hearing loss. Eligible patients are required to have documented, non-fluctuating hearing
loss. Part A and Part B enrollment is complete. Part C enrollment is open.

For all Parts A, B and C of the study,

Inclusion criteria:

1. Written informed consent must be obtained before any assessment is performed.

2. For all Parts A, B and C of the study, male or female patients, 18 to 75 years old,
inclusive, with severe-to-profound bilateral hearing loss or unilateral hearing loss
with intact vestibular function in the nonoperative ear. Non-fluctuating
severe-to-profound hearing loss is required for the study ear and is defined as:

- PTA within 10 dB of the PTA obtained at least 11 months previously.

- Word recognition within 20% of previous test at least 11 months previously

3. Candidate ear ("study ear"): Minimal residual hearing based on the pure tone average
of 0.5, 1, 2, and 4 kHz thresholds of ≤110 dB HL

4. Candidate ear ("study ear"): Pure tone audiometric thresholds of ≥50 dB HL for each
testable octave frequency of 0.125 and 0.250 kHz, ≥70 dB HL for each testable octave
frequency from 0.5 through 8 kHz and sentence recognition scores ≤50% at screening.

6. Patients with intact vestibular function in at least one ear (non-study ear) as measured
by vestibular evoked myogenic potential (VEMP) 7. Able to communicate well with the
investigator, to understand and comply with the requirements of the study 8. MRI scan
within 6 months or at screening to confirm suitability for inner ear surgery 9. Patients
must weigh at least 40 kg to participate in the study, and must have a body mass index
(BMI) <45 kg/m2. BMI = Body weight (kg) / [Height (m)]2

Exclusion Criteria:

1. Patients with hearing loss caused by genetic/developmental disorders, e.g., cochlea
aplasia

2. Patients with existing conductive hearing loss or mixed hearing loss as judged by the
Principal Investigator following a thorough review of all of the trial hearing
assessments;

3. Patients with a history of cochlear implant in the study ear

4. Hearing loss due to any other cause that would not be expected to respond to hair cell
regeneration, for example mechanical trauma or central auditory lesions or lack of an
auditory nerve

5. Patients who will require ototoxic drugs as routine therapy over the course of the
study, for example cystic fibrosis patients

6. Any contraindication to the planned surgery or anesthesia as determined by the surgeon
or anesthesiologist

7. Previous surgery in the study ear

8. Any otological history, such as chronic otitis, cholesteatoma, tympanic membrane
perforation, that suggests poor candidacy for cochlear implant or inner ear surgery or
suggests potential interference with study auditory or vestibular function tests

9. Pregnant women

10. Abnormal vital signs and/or ECG that suggest potential contraindication for planned
study anesthesia

11. Past serious adverse reaction to anesthesia

12. Meniere's Disease

13. History of radiation therapy to the head and neck

14. Participation in a clinical trial within the last 30 days

15. Immunocompromised patients, as judged by the investigators based on patient history,
physical exam and CBC