The goal of this 2 step-up, exploratory study is to test safey, tolerability and PK/PD profiles in healthy volunteers and safety, tolerability and efficacy in sudden sensorineural hearing loss patients as an early salvage therapy.

The main questions it aims to answer are:

1. whether is it safe and tolerable when healthy volunteers and sudden sensorineural hearing loss patients take multiple doses of NS101 against FAM19A5
2. whether is it effective in reversing hearing capability in sudden sensorineural hearing loss patients who fails to show sufficient recovery despite of oral standard steroid therapy.

Patients and heathly volunteers will be given NS101 15mg/kg or 30mg/kg systemically less than 3 months per protocol.

This is placebo controlled, double blinded study, which means there will be a group who receives placebo (i.e. fake drug) for study purpose.

Part A: healthy volunteers

Part B:

Inclusion Criteria:

• unilateral ideopathic SSNHL greater than 45dB at the average of 4 frequencies in PTA (contralateral hearing is less than 30dB)
• Subject who has completed investigator-recognized standard treatment within 30 days of symptom onset and is able to undergo randomization visit within 35 days.
• Subjects who, in the opinion of the investigator, have received sufficient systemic steroid therapy for approximately 2 weeks recovery
• A combination regimen consisting of approximately 2 weeks of systemic steroid therapy and intratympanic steroid administration

Exclusion Criteria:

• other otologic or systemic diseases
• retrocochlear lesion

Currently there is no plan to share IPD at this stage