DSP-3077 Phase I/IIa First Dosing: Novel Mechanism, No Efficacy Signal Yet, High Mechanistic Uncertainty

Sumitomo Pharma Doses First Patient in DSP-3077 Phase I/IIa Trial for Retinitis Pigmentosa

Sumitomo Pharma America has initiated its Phase I/IIa clinical trial for DSP-3077, a regenerative cell therapy, by treating the first patient with non-syndromic retinitis pigmentosa (RP). The open-label, single-arm, dose-escalation study aims to assess the tolerability and safety of two dose levels of DSP-3077, delivered via a single subretinal injection. The trial plans to enroll 12 patients across three cohorts. DSP-3077, which utilizes allogeneic retinal sheets derived from induced pluripotent stem (iPS) cells, received Orphan Drug Designation from the US Food and Drug Administration in March 2026 for the treatment of RP.

• DSP-3077 is an investigational regenerative cell therapy that leverages allogeneic retinal sheets derived from induced pluripotent stem (iPS) cells. This innovative approach utilizes a 3D retinal organoid, produced through the self-organizing cell culture technique known as the SFEBq method. The underlying technology was initially developed at RIKEN and further optimized through collaborations involving Sumitomo Chemical, Sumitomo Pharma, RACTHERA, and S-RACMO, aiming to generate multilayered retinal tissue with photoreceptor precursors.
• The Phase I/IIa clinical trial is designed as an open-label, single-arm, dose-escalation study to primarily evaluate the tolerability and safety of two distinct dose levels of DSP-3077. The therapy is administered via a single subretinal injection to adults with non-syndromic retinitis pigmentosa. Beyond safety, secondary objectives include assessing the engraftment of the retinal sheets, evaluating the therapeutic response, and monitoring the performance of the specialized device used for delivery.
• The study employs a structured cohort design, with each of the three cohorts enrolling four participants, leading to a total planned enrolment of 12 patients. Treatment groups within these cohorts are defined by visual acuity and dose. Furthermore, DSP-3077 was granted Orphan Drug Designation by the US Food and Drug Administration in March 2026, recognizing its potential to address retinitis pigmentosa, a rare, hereditary degenerative eye condition with limited existing therapeutic options.

Addressing the Significant Unmet Need in Retinitis Pigmentosa

Retinitis pigmentosa (RP) remains a condition with a profound unmet need: despite growing understanding of its underlying pathomechanisms, no causal therapy has yet been established. Current management relies primarily on supportive measures—visual aids, orientation training, and nutritional supplementation—none of which halt disease progression or address the root genetic etiology.

• Absence of disease-modifying therapy: All evaluated medical treatments, including hyperbaric oxygen delivery, topical brimonidine tartrate, vitamins, docosahexaenoic acid, gangliosides, lutein, oral nilvadipine, ciliary neurotrophic factor, and valproic acid, have demonstrated acceptable safety profiles across 19 randomized controlled trials but failed to show significant benefit on visual function. Long-term vitamin A supplementation showed a statistically slower decline in electroretinogram amplitude, though this represents only a modest therapeutic gain.

• Complication management without functional recovery: Cystoid macular edema and cystic macular changes can be addressed with systemic or topical carbonic anhydrase inhibitors—occasionally combined with steroids—yet reduction in retinal thickness does not consistently translate into improvement in visual acuity.

• Genotype-dependent treatment responses: The therapeutic benefit and risk profile of interventions such as vitamin A supplementation are influenced not only by disease phenotype but by the patient's specific genotype. This genetic heterogeneity substantially complicates treatment selection and the extrapolation of clinical outcomes across RP subtypes.

• Gene therapy delivery barriers: Although gene therapy holds considerable promise, challenges surrounding vector delivery efficiency, host immune responses, and the technical difficulty of targeting large or dominant-negative mutations continue to limit its scalability and broader clinical application.

• Pediatric evidence gap: No clinical data are currently available regarding the use of pharmacological interventions in the pediatric RP population, representing a critical and underaddressed gap in the evidence base.

• Research heterogeneity undermining guideline strength: The limited number of RCTs, combined with poor clinical outcomes and substantial inter-study heterogeneity, reduces the robustness of long-term management recommendations—making evidence-based clinical decision-making particularly challenging in this disease area.

Evaluating DSP-3077: Key Endpoints in the Phase I/IIa Trial

Clinical trials in Retinitis Pigmentosa (RP) rely on a combination of structural and functional endpoints to characterize disease progression and evaluate therapeutic efficacy. Among structural measures, ellipsoid zone (EZ) line width — assessed by spectral-domain optical coherence tomography (SD-OCT) — is a central endpoint, with reported progression rates ranging from 91 μm/year in PDE6-associated RP to 140 μm/year in broader cohorts. Complementary to this, fundus autofluorescence (FAF)-derived hyperautofluorescent ring measurements track the contraction of the preserved photoreceptor zone, with horizontal diameter decreasing at 103–149 μm/year, vertical diameter at 92–120 μm/year, and ring area declining by 0.3–0.9 mm²/year depending on the study population. These structural endpoints exhibit high inter-eye symmetry and strong correlation with one another (r = 0.78 between EZ width and hyperautofluorescent ring area), supporting their use as reliable surrogate markers of photoreceptor loss.

Functional endpoints span electrophysiological, psychophysical, and perimetric assessments. Electroretinography (ERG) — including full-field ERG (with light-adapted 30 Hz flicker amplitude used as a primary outcome in at least one interventional trial) and multifocal ERG (mfERG) measuring response amplitude density and implicit time across 0–20 degrees of eccentricity — captures retinal function with high objectivity, with outer ring responses declining approximately 6–10% per year. Visual field testing encompasses Goldmann perimetry, Humphrey Field Analyzer (HFA) 10-2 mean deviation, and static automated perimetry (Central 30-2), with visual field loss progressing at approximately 14.5% per year for target III4e. The Full-Field Stimulus Threshold (FST) test — measuring perception thresholds to white, blue, and red stimuli in decibels — is particularly valuable in advanced disease states where ERG amplitudes are near-extinguished and visual acuity and field are severely compromised. Best-corrected visual acuity (BCVA) via ETDRS charts and microperimetry-based retinal sensitivity mapping round out the functional assessment toolkit.

Patient-reported outcomes and quality-of-life instruments constitute an important third domain of endpoints. The National Eye Institute Visual Function Questionnaire-25 (NEI-VFQ-25) is the most widely employed measure, with RP patients scoring a mean of 47.8 ± 15.8 compared to 94.8 ± 4.3 in healthy controls — underscoring the substantial functional burden of the disease. Reading speed, assessed using the Minnesota Low-Vision Reading Acuity Chart (MNREAD), has also been incorporated, with a threshold of 80 words per minute identified as clinically meaningful and associated with improved NEI-VFQ-25 scores. Additional endpoints reported across trials include contrast sensitivity, color vision, central macular thickness by OCT, and multifocal visual evoked potentials (mfVEP), reflecting the multidimensional nature of outcome assessment in this disease.

Sumitomo Forges Ahead in Ocular Regenerative Medicine

Retinitis pigmentosa (RP) represents a significant challenge in ophthalmology, being a leading cause of blindness with no established treatment. The progressive loss of photoreceptors in RP patients leads to irreversible vision impairment, creating a profound unmet medical need. The initiation of Sumitomo Pharma America's Phase I/IIa clinical trial for DSP-3077, an allogeneic retinal sheet derived from induced pluripotent stem (iPS) cells, marks a pivotal moment in the quest for effective therapies. This regenerative cell therapy aims to replace the degenerated photoreceptors, a strategy supported by research demonstrating the survival and maturation of iPS-derived retinas and their ability to form photoreceptor synapses after subretinal transplantation in preclinical models. This approach also elegantly bypasses the ethical concerns previously associated with fetal tissue transplantation, offering a more sustainable and acceptable therapeutic avenue.

This move positions Sumitomo Pharma America as an early leader in the burgeoning field of ocular regenerative medicine. The Orphan Drug Designation granted to DSP-3077 underscores the severity and rarity of RP, offering regulatory advantages that could streamline its path to market and enhance commercial viability. Furthermore, successful development of DSP-3077 would not only address a critical patient need but also validate the broader potential of allogeneic iPS cell platforms for treating other degenerative conditions, potentially expanding the company's pipeline into new therapeutic areas.

However, the journey ahead is not without its complexities. As an early-stage trial, the primary focus remains on establishing the tolerability and safety of this novel cell therapy and its subretinal delivery method. Translating preclinical success into meaningful functional recovery in human RP patients, given the disease's intricate pathology, presents a substantial hurdle. Additionally, the inherent challenges of manufacturing consistency for iPS cell-derived products and the specialized nature of subretinal injection require careful consideration. The coming phases will be critical in determining if DSP-3077 can indeed offer a new horizon of hope for individuals living with retinitis pigmentosa, potentially reshaping the treatment landscape for inherited retinal degenerations.