PHILADELPHIA, May 14, 2026
GEMMA Biotherapeutics (GEMMABio) unveiled its new Duchenne muscular dystrophy (DMD) gene therapy program and presented promising preclinical findings for both its DMD candidate GB703 and investigational spinal muscular atrophy type 1 (SMA1) therapy GB221 during oral presentations at the American Society of Gene and Cell Therapy (ASGCT) 2026 Annual Meeting in Boston. The company stated that the data support continued advancement of both next-generation gene therapy programs aimed at addressing major limitations in current neuromuscular disease treatments.
GEMMABio highlighted that the DMD program represents a major expansion of its rare disease pipeline, with GB703 designed to potentially broaden mutation coverage and improve muscle delivery efficiency using an engineered adeno-associated virus (AAV) platform. The company also reported continued progress for GB221, a next-generation SMA1 gene therapy currently advancing through the CHARISMA Phase 1/2 clinical trial in pediatric patients.
GB703 Designed to Expand DMD Treatment Access
The investigational DMD therapy GB703 incorporates a novel hybrid micro-utro/dystrophin transgene engineered to potentially expand eligibility to patients with dystrophin mutations that may not respond effectively to existing microdystrophin therapies. Researchers explained that the therapy integrates a self-utrophin-derived exon region intended to broaden mutation coverage while reducing immunogenicity risks associated with conventional DMD gene therapies.
GEMMABio also developed a proprietary engineered AAV capsid known as GCap104, specifically designed to improve delivery to skeletal and cardiac muscle tissues at lower doses. Preclinical studies in mice and nonhuman primates demonstrated successful expression of the therapeutic transgene with favorable tolerability over a 60-day evaluation period.
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According to the company, the therapy showed measurable biological effects in mouse models of DMD, including restoration of key muscle-associated protein complexes and reductions in biomarkers associated with muscle damage. Researchers believe these findings may support future clinical development aimed at improving muscle function and slowing disease progression in patients with Duchenne muscular dystrophy.
Duchenne muscular dystrophy is one of the most severe inherited neuromuscular disorders worldwide, affecting approximately 1 in 5,000 live male births globally. The progressive disease causes ongoing muscle degeneration, cardiac complications, respiratory decline, and reduced life expectancy, with many patients losing ambulation during adolescence.
GB221 Advances Next-Generation SMA1 Gene Therapy
In addition to the DMD program, GEMMABio presented comprehensive preclinical data supporting the development of GB221, its investigational next-generation gene therapy for spinal muscular atrophy type 1. The therapy uses an AAVhu68 vector carrying a codon-optimized SMN1 gene designed to improve motor neuron function while reducing risks of sensory neuropathy and overexpression-related toxicity.
The company reported that GB221 incorporates specialized microRNA target site technology intended to silence transgene expression within dorsal root ganglia neurons, an approach designed to reduce peripheral sensory neurotoxicity observed with some earlier-generation SMA therapies.
Preclinical animal studies showed that GB221 significantly improved survival and neuromotor function in severe SMA mouse models. Treated animals demonstrated improved strength, trunk control, and survival beyond 120 days, compared with untreated mice that survived fewer than 15 days. Nonhuman primate studies also demonstrated broad motor neuron expression without evidence of liver toxicity, cardiac toxicity, or sensory neuropathy.
Rare Disease Gene Therapy Sector Accelerates
GEMMABio confirmed that the CHARISMA Phase 1/2 clinical trial evaluating GB221 in pediatric SMA1 patients under 12 months of age is progressing according to plan in Brazil. The study is designed to evaluate safety, tolerability, and early efficacy signals in infants with the severe neuromuscular disease.
The company stated that both GB703 and GB221 were engineered as next-generation therapies focused on improving safety, efficacy, and patient access through advanced vector design and optimized transgene engineering. As investment in rare disease biotechnology and genetic medicine continues to grow globally, GEMMABio’s latest findings reinforce the expanding role of innovative AAV gene therapies in treating severe inherited neuromuscular disorders.
Source: GEMMABio press release
