AAV.SPR capsid delivers RS1 to foveal photoreceptors from a safe, peripheral injection site, overcoming problems experienced with conventional AAV capsids
Atsena’s lead AAV.SPR program, ATSN-201, is now advancing into a pivotal clinical trial in patients with X-linked retinoschisis
DURHAM, NC, March 27, 2026 – Atsena Therapeutics, a clinical-stage gene therapy company focused on reversing or preventing blindness from inherited retinal diseases, today announced the publication of a peer-reviewed study in Molecular Therapy that establishes the scientific rationale for AAV.SPR, its proprietary laterally spreading capsid, as a critical enabling technology for retinal gene therapy. The study provides rigorous preclinical evidence that lateral spread is not simply a performance advantage; it is necessary for delivering certain gene therapies to the central retina safely and effectively.
Building on this foundational research, ATSN-201, Atsena’s investigational gene therapy delivering a functional RS1 gene via the AAV.SPR capsid, is currently being evaluated in the Phase 1/2/3 LIGHTHOUSE Trial. XLRS is a monogenic X-linked disease caused by mutations in RS1, which encodes retinoschisin, a protein secreted primarily by photoreceptors that plays a critical role in maintaining retinal cell organization and synaptic function. The disease is characterized by the formation of schisis cavities — abnormal splitting of the retinal layers — that cause impaired visual acuity beginning in early childhood and ultimately lead to blindness. XLRS affects approximately 30,000 males in the United States and European Union, and there are currently no approved treatments.
“AAV.SPR represents a technological breakthrough in ocular gene therapy. For decades, the field has grappled with a fundamental tradeoff: either place the vector directly under the fragile fovea and risk iatrogenic damage or inject it intravitreally and fail to achieve therapeutic levels of gene expression while also contending with inflammation,” said Shannon E. Boye, Ph.D., Co-Founder and Chief Scientific Officer of Atsena Therapeutics. “This publication demonstrates that AAV.SPR can transduce virtually all foveal cones from a safe, peripheral injection site. It also reveals why conventional capsids can never achieve the same result, even in theory: RS1 stays where the vector goes, and a non-spreading capsid simply cannot get to the fovea from the periphery. These data provide a rigorous scientific foundation for the exciting results we are now seeing in our clinical trial.”
The Problem AAV.SPR Addresses: Subretinal Injection of Conventional AAV Capsids and Intravitreal Delivery Fall Short for XLRS and Many Other Retinal Diseases
The fovea, the small, densely packed region of the central retina responsible for sharp, detailed vision, is the primary therapeutic target in many inherited retinal diseases (IRDs). Yet reaching it safely has been a formidable hurdle in the retinal gene therapy field.
The treatment of photoreceptor-mediated diseases relies on efficient gene delivery to these cells, with therapeutically meaningful transduction levels attained only when adeno-associated virus (AAV) vectors are delivered subretinally. Conventional AAV capsids remain confined to the margins of the subretinal bleb formed at the point of injection. Delivering genes to foveal photoreceptors has therefore historically required placing the injection directly underneath the fovea, surgically detaching this irreplaceable structure in the process. In diseases such as XLRS, where characteristic schisis cavities make the central retina fragile and prone to damage, foveal detachment is strongly contraindicated. This created an apparent impasse: the cells that most needed treatment could not be safely reached.
Two earlier clinical trials conducted by the National Eye Institute and by AGTC, Inc. attempted to work around this constraint by delivering vector intravitreally, injecting it into the gel-filled cavity in front of the retina rather than beneath it. Neither trial demonstrated efficacy, and intravitreally delivered AAV led to significant, chronic inflammation in some patients. As the new publication explains, no AAV capsid has demonstrated efficient photoreceptor transduction following intravitreal administration in nonhuman primates at levels sufficient for therapeutic efficacy.
A Critical Biological Insight: RS1 Goes Where the Capsid Goes — and No Further
A key finding in the new publication addresses a question central to the biology of XLRS gene therapy: Because it is a secreted protein, could RS1 expressed by photoreceptors at a peripheral injection site simply diffuse across the retina and reach the fovea on its own, even without foveal transduction?
The answer, the study shows, is no. By subretinally delivering a mixture of AAV containing a tagged RS1 construct and AAV-GFP in non-human primates (NHPs), the researchers demonstrated that RS1 protein is localized strictly to the area where photoreceptors are transduced by the AAV vector. Wherever GFP expression ended, RS1 expression ended too. RS1 does not migrate meaningfully beyond the transduced cells. To achieve RS1 expression at the fovea following peripheral subretinal injection, a spreading capsid is required.
This finding has direct implications not only for XLRS, but for all retinal gene therapies where central photoreceptor transduction is the goal and submacular injection or intravitreal injection carries unacceptable risk.
The Solution: AAV.SPR Uniquely Enables Safe Delivery to the Central Retina
AAV.SPR, Atsena’s proprietary laterally spreading capsid, was engineered to solve this problem. When administered via peripheral subretinal injection, safely away from the fovea. AAV.SPR spreads laterally well beyond the margins of the injection bleb, transducing photoreceptors across a substantially larger area of retina than conventional capsids. Key preclinical findings from the publication include:
- Foveal cone transduction without detachment. In NHP studies, two small peripheral subretinal injections of AAV.SPR transduced up to 99% of foveal cones without any surgical detachment of the fovea. Conventional AAV5, delivered identically, transduced zero foveal cones.
- Exceptional lateral spread. Transgene expression from AAV.SPR was detected more than 7 mm beyond the subretinal bleb margins in NHP retina. This spread lends itself to success in clinical outcome measures such as microperimetry which require improvements in pre-specified retinal loci.
- Higher potency at the injection site. AAV.SPR transduced a higher percentage of photoreceptors within the bleb itself relative to conventional capsids, providing greater therapeutic gene expression at equivalent doses.
- Correct RS1 localization. AAV.SPR-mediated RS1 expression in NHP retina localized correctly to photoreceptor inner segments and photoreceptor-bipolar cell synapses, precisely mimicking the natural pattern of RS1 expression.
The study also demonstrates that the same lateral spreading properties that make AAV.SPR suited for XLRS are broadly applicable to other IRDs in which safe delivery to the central retina is the goal, including Usher syndrome and conditions where foveal cones are the last remaining functional photoreceptors.
From Bench to Clinic: ATSN-201 Advances into Pivotal Trial
The clinical data accumulated to date in the LIGHTHOUSE Trial validate the potential of the AAV.SPR approach in patients. ATSN-201 has demonstrated a favorable safety profile and has been well-tolerated thus far, with no related serious adverse events. The majority of treated patients have shown improvements in retinal structure, including foveal schisis closure, as well as meaningful functional improvements assessed by microperimetry and visual acuity. This is the first time any gene therapy has been shown to reverse this structural hallmark of XLRS and provide functional improvements. Having completed enrollment in the Phase 1/2 portions of the study, Atsena is preparing to advance ATSN-201 into the pivotal Phase 3 portion of the study.
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 clinical trial for X-linked retinoschisis (XLRS), a genetic condition that is typically diagnosed in childhood and leads to blindness later in life. The company’s proprietary pipeline also includes gene therapies in development for Usher Syndrome Type 1B and for Stargardt Disease. Atsena is also developing ATSN-101, a first-in-class, 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 with positive results (https://doi.org/10.1016/s0140-6736(24)01447-8), and Atsena expects to initiate a global pivotal Phase 3 clinical trial evaluating ATSN-101 in the second half of 2026.
Founded by pioneers in ocular gene therapy, Atsena is led by an experienced team dedicated to addressing the needs of patients with vision loss. For more information, please visit https://atsenatx.com/.
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