Atsena Therapeutics Reports New Preclinical Data Demonstrating Robust MYO7A Expression and Favorable Safety for ATSN-301, a Laterally Spreading Dual AAV Vector-based Gene Therapy for Usher Syndrome Type 1B

• Dual vector and AAV.SPR technologies combine to drive supraphysiological levels of full-length MYO7A in non-human primate retina, reaching the macula without foveal detachment
• Six-month GLP toxicology study establishes NOAEL at the highest dose tested, with no systemic toxicity and biodistribution confined largely to the retina
• Atsena plans to submit an IND for ATSN-301 in 2027
• Data presented at the ESGCT 33rd Annual Congress and detailed in a manuscript posted to bioRxiv

DURHAM, N.C., Oct. 30, 2026 (GLOBE NEWSWIRE) -- Atsena Therapeutics, a clinical-stage gene therapy company focused on reversing or preventing blindness from inherited retinal disease, today announced new preclinical data for ATSN-301, a gene therapy for the treatment of Usher Syndrome Type 1B (USH1B). ATSN-301 combines Atsena’s proprietary dual AAV vector (DNA recombination) technology with its laterally spreading AAV.SPR capsid to reconstitute full-length MYO7A and deliver it to the macula without the need for foveal detachment. The data demonstrated robust, full-length MYO7A expression, a favorable safety margin and no observed adverse effect level (NOAEL) at the highest dose tested in a six-month GLP toxicology study. These results are detailed in a manuscript posted to bioRxiv and in a presentation at the European Society for Gene and Cell Therapy (ESGCT) 33^rd Annual Congress, taking place October 27-30, 2026, in Hamburg, Germany.

“These preclinical data show our dual vectors doing exactly what they were engineered to do: reconstituting full-length MYO7A at supraphysiological levels and reaching the macula from an extrafoveal injection, without the surgical risk of foveal detachment. We are the first to show MYO7A expression in the nonhuman primate retina by immunohistochemistry of retinal cross sections, confirming that the protein is expressed in the right cells and layers of the retina, not just present in a tissue sample,” said Shannon E. Boye, Ph.D., Co-Founder and Chief Scientific Officer of Atsena Therapeutics. “Additionally, the six-month GLP toxicology study demonstrated a clean safety margin at the highest dose tested. These data support our plan to submit an IND in 2027.”

ATSN-301 for Usher Syndrome Type 1B

MYO7A, the gene mutated in USH1B, encodes a protein essential for hearing and vision. Patients are born profoundly deaf with vestibular dysfunction and typically develop progressive retinitis pigmentosa in the first decade of life. There are no currently approved treatments for vision loss associated with USH1B. The MYO7A coding sequence (~6.7 kb) exceeds the ~4.8 kb packaging capacity of a single AAV vector, requiring a dual vector approach to deliver the full-length gene. ATSN-301 reconstitutes full-length MYO7A by co-delivering two AAV vectors that recombine at the DNA level, an approach that avoids intentional production of multiple truncated proteins (split inteins) or transcripts (mRNA trans-splicing or RNA End Joining) that have the potential to generate truncated proteins that carry a possible toxic gain-of-function risk. In addition, ATSN-301 splits the MYO7A gene upstream of the tail domain, so the front-half vector encodes none of it. Because the tail domain binds other cellular proteins, this design avoids any potential gain-of-function effects from a truncated product. Other dual-vector approaches split further downstream, meaning their front-half vector encodes part of the tail domain.

In preclinical testing, Atsena’s optimized dual vectors, packaged in the AAV.SPR capsid, produced supraphysiological levels of full-length MYO7A in cynomolgus macaques. Following extrafoveal subretinal injection, AAV.SPR’s lateral spread delivered MYO7A to the macula and distal retina without surgical detachment of the fovea, an important consideration for USH1B patients who often retain central vision well into adulthood.

A six-month GLP toxicology study in non-human primates established a NOAEL for ATSN-301 at the highest dose evaluated. Truncated protein was minimal and had no impact on retinal safety, with no electroretinogram (ERG) changes and clean retinal histopathology. There was also no treatment-related systemic toxicity, no meaningful immunogenicity, and biodistribution was confined almost entirely to the injected retina. Atsena plans to submit an Investigational New Drug (IND) application to the U.S. Food and Drug Administration (FDA) for ATSN-301 in 2027.

About AAV.SPR

AAV.SPR, one of Atsena’s novel capsids, spreads laterally beyond the subretinal injection site to enable safe and efficient transduction of the central retina when injected into areas outside the macula. Preclinical studies in non-human primates have demonstrated that AAV.SPR promotes transgene expression well beyond subretinal injection bleb margins, in contrast to benchmark AAV vectors, which remain confined to the original bleb margins. At clinically relevant doses, AAV.SPR efficiently transduces foveal cones without the need for surgical detachment and has a favorable safety profile relative to benchmark capsids. AAV.SPR is the capsid platform underlying ATSN-201 (XLRS), ATSN-301 (USH1B), and ATSN-401 (Stargardt disease). For more information, visit atsenatx.com/our-approach/laterally-spreading-aav/.

About Dual Vector Technology

Some of the most prevalent inherited retinal diseases are caused by mutations in genes too large to fit inside a single adeno-associated virus (AAV) vector, placing them out of reach for conventional gene therapy approaches. The field has pursued several strategies to reconstitute a full-length protein from two AAV vectors, including DNA recombination, protein trans-splicing (split-intein), mRNA trans-splicing, and RNA end-joining, each reconstituting the gene at a different stage — DNA, protein, or RNA — and with different design trade-offs.

Atsena’s dual-vector platform is built on DNA recombination using a dual hybrid design in which two vectors co-transduce the same cell and their transgene halves are joined through the cell’s natural recombination and joining processes. Splice donor and acceptor sites then remove any intervening sequence from the transcript, yielding full-length mRNA before translation. Because this mechanism relies only on the cell’s own DNA recombination and splicing machinery, it does not require the deliberate expression of an additional protein or RNA species, which is a potential safety advantage. Atsena delivers this dual vector technology with the AAV.SPR capsid, which enables efficient transduction of foveal cones without the need for surgical detachment.

Atsena is applying this dual vector platform across its pipeline, including ATSN-301 for USH1B and ATSN-401 for Stargardt disease. For more information, visit atsenatx.com/our-approach/dual-vector-technology/.

About Atsena Therapeutics

Atsena is a clinical-stage gene therapy company developing best-in-class treatments for the reversal or prevention of blindness from inherited retinal diseases. The company’s lead program is evaluating ATSN-201 in a pivotal Phase 3 clinical trial for X-linked retinoschisis (XLRS), a genetic condition typically diagnosed in childhood that often leads to blindness later in life. Atsena is also developing ATSN-101, an investigational gene therapy for Leber congenital amaurosis type 1 (LCA1), as part of its exclusive strategic collaboration with Nippon Shinyaku Co., Ltd.; ATSN-101 has completed a Phase 1/2 trial and Atsena expects to initiate a global pivotal Phase 3 clinical trial evaluating ATSN-101 in the coming months. Atsena is advancing ATSN-301 toward an IND in 2027, and is also developing ATSN-401, a gene therapy for Stargardt disease. Atsena’s pipeline is powered by a proprietary adeno-associated virus (AAV) technology platform, featuring its novel laterally spreading AAV.SPR capsid and proprietary dual vector technology, designed to overcome the challenges presented by inherited retinal disease. For more information, visit atsenatx.com.

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