Evaluation of DB-OTO Safety and Efficacy in Pediatric Patients with Biallelic Otoferlin Gene Mutations Inducing Congenital Hearing Loss

The primary objective of this clinical trial is to evaluate the **safety** and **tolerability** of DB-OTO in children and infants diagnosed with biallelic otoferlin gene (hOTOF) mutations. This is clinically relevant as it addresses the potential risks and adverse effects associated with the administration of DB-OTO, a gene therapy product, in a vulnerable pediatric population. Ensuring the safety and tolerability of the treatment is crucial before considering its broader application in managing congenital hearing loss secondary to biallelic mutations of the otoferlin gene (OTOF).

The secondary objective is to evaluate the preliminary efficacy of DB-OTO in children and infants diagnosed with biallelic hOTOF mutations. This involves assessing the initial therapeutic benefits of the treatment, which is essential for determining its potential effectiveness in improving hearing outcomes in this patient group.

The clinical trial involves a total of **14 participants** diagnosed with **Congenital Hearing Loss Secondary to Biallelic Mutations of the Otoferlin Gene (OTOF)**. The study population includes both male and female subjects under the age of 18, with specific age cohorts for infants and children. Participants were selected based on the presence of pathogenic mutations in both alleles of the OTOF gene and specific audiological criteria, such as the absence of an auditory brainstem response (ABR) neural signal and the presence of otoacoustic emissions (OAE) or cochlear microphonic. The trial population is considered vulnerable due to the inclusion of minors. Participants are required to adhere to country-specific pediatric immunization schedules and maintain effective contraception if of childbearing potential. The general health status of participants is monitored to ensure no clinically significant laboratory findings at screening, and there is no evidence that hearing loss is temperature-dependent. Lifestyle considerations such as diet and physical activity are not specified in the available data.

The clinical trial is designed as a **Phase 1/2**, open-label, multicenter study to evaluate the safety, tolerability, and efficacy of **DB-OTO** in children and infants with **congenital hearing loss** due to biallelic mutations of the **Otoferlin gene (OTOF)**. The trial involves a single ascending dose cohort with unilateral intracochlear injection, followed by a bilateral injection expansion cohort. The trial is not categorized as low intervention and is expected to conclude by April 19, 2031, with recruitment having started on May 12, 2023.

Participants will undergo a series of study visits, beginning with an inclusion (screening) visit to confirm eligibility based on specific criteria, such as the presence of pathogenic mutations in both alleles of the OTOF gene and audiological criteria. The trial will include follow-up visits to monitor the incidence and severity of treatment-emergent adverse events, as well as changes in auditory brainstem response and behavioral audiometry. The end-of-study visit will assess the overall outcomes and safety of the treatment.

The expected length of participant involvement is approximately 18 months, covering the short-term follow-up period. Conditions that may lead to early termination from the study include the emergence of clinically significant laboratory findings or adverse events that compromise participant safety. Participants must adhere to contraception requirements if applicable, and any deviation from protocol-defined criteria may also result in early withdrawal from the trial.

The clinical trial involves the administration of **DB-OTO**, an investigational gene therapy product designed for the treatment of children and infants with biallelic otoferlin gene (**hOTOF**) mutations. **DB-OTO** is formulated as an **injection** and is delivered via an **intracochlear** route. The therapy consists of two adeno-associated viral serotype 1 (AAV1) vectors: **DB-OTO-5** and **DB-OTO-3**. **DB-OTO-5** encodes the 5' component of the human Otoferlin gene isoform 5 (hOtofv5) with a hair cell-specific promoter, myosin 15 (Myo15), while **DB-OTO-3** encodes the 3' component of hOtofv5. The administration involves a single ascending dose cohort with unilateral intracochlear injection, followed by a bilateral injection expansion cohort.

There are no non-experimental treatments, such as standard-of-care therapy, placebo, or comparator treatment, included in this study. The trial is designed to evaluate the safety, tolerability, and efficacy of **DB-OTO**. Participant compliance with the dosing schedule is monitored throughout the study to ensure accurate assessment of the investigational product's effects. The trial does not specify a maximum daily dose, total dose, or treatment period, as the focus is on the initial safety and tolerability of the gene therapy.

Efficacy in this clinical trial will be assessed through secondary endpoints focusing on auditory function improvements in children and infants with biallelic otoferlin gene (hOTOF) mutations. The primary efficacy parameters include changes in auditory brainstem response (ABR) intensity thresholds, measured in decibels Hearing Level (dB nHL) across frequency domains. Additionally, behavioral audiometry will be utilized to evaluate changes in pure-tone audiometry intensity thresholds in the treated ear, as well as changes in speech awareness threshold (SAT) and speech reception threshold (SRT) in the treated ear.

The assessment of these efficacy parameters will be conducted using validated audiological tests. The auditory brainstem response (ABR) will be measured to determine changes in intensity thresholds, while behavioral audiometry will assess pure-tone audiometry and speech thresholds. These measurements will be collected at specified timepoints throughout the trial to monitor changes in auditory function following treatment with DB-OTO. The data collected will be analyzed to determine the efficacy of the treatment in improving auditory outcomes in the study population.