FX-322 in Adults With Severe Sensorineural Hearing Loss

Inclusion Criteria: 1. Subject has read and voluntarily signed the Informed Consent Form (ICF) after all questions have been answered and prior to any study-mandated procedure. 2. Adult aged 18-65 years inclusive. 3. Documented medical history consistent with acquired (non-genetic) severe sensorineural hearing loss (documented audiogram at least 6 months prior to screening required). 4. A pure tone average of 71-90 dB at 500Hz, 1000Hz, 2000Hz, and 4000Hz at Screening in the ear to be injected. 5. Ability to communicate well with the Investigator and is willing to comply with and complete all the study procedures. Exclusion Criteria: 1. Subject has previously participated in a FX-322 clinical trial. 2. Perforation of tympanic membrane or other tympanic membrane disorders that would interfere with the delivery and safety assessment of an intratympanic medication or reasonably be suspected to affect tympanic membrane healing after injection in study ear. This includes a current tympanostomy tube. 3. Any conductive hearing loss of greater than 15 dB at a single frequency or greater than 10 dB at two or more contiguous octave frequencies in the study ear at the Screening visit or on the prior audiogram (if the Investigator feels there is not a true conductive hearing loss, the Medical Monitor should be consulted). 4. Active chronic middle ear disease or a history of major middle ear surgery, as an adult, in the ear to be injected. 5. Subject has had an intratympanic injection in either ear within 3 months of the screening visit. 6. History of clinically significant vestibular symptoms at the discretion of the investigator. For example, BPPV may be considered acceptable whereas Meniere's would not. 7. History of clinically significant systemic autoimmune disease (e.g. rheumatoid arthritis, Sjogren's syndrome, multiple sclerosis, psoriasis). 8. Exposure to another investigational drug within 28 days prior to injection of study drug. 9. Evidence of any active or chronic disease or condition that could interfere with, or for which the treatment of might interfere with, the conduct of the study, or that would pose an unacceptable risk to the subject in the opinion of the investigator following a detailed medical history, physical examination, and vital signs (systolic and diastolic blood pressure, pulse rate, body temperature). 10. Females of childbearing potential (those who are not surgically sterilized or post- menopausal) may not participate in the study if any of the following conditions exist: * Pregnant or intend to become pregnant * Nursing (lactating) * Does not agree to use adequate birth control methods for the duration of the study (adequate birth control methods are: hormonal- oral, implantable, transdermal or injectable contraceptives; mechanical- spermicide in conjunction with a barrier such as a condom or diaphragm, IUD, or surgical sterilization of a partner. NOTE: all female subjects of childbearing potential must consent to a urine pregnancy test as described in the Schedule of Assessments. Male subjects should use condoms with spermicide during the study or remain abstinent. Subjects should not donate sperm or ova during the study period. 11. Any known factor, condition, or disease that, in the view of the Investigator, might interfere with treatment compliance, study conduct or interpretation of the results.