Spot Biosystems has emerged from stealth with $40 million in financing and early clinical data supporting the use of engineered extracellular vesicles (EVs) to deliver full-length dystrophin in patients with Duchenne muscular dystrophy (DMD).

The company also reported preclinical findings published in the journal Nature Biomedical Engineering, which it said demonstrated successful non-viral delivery of full-length dystrophin to skeletal muscle in mouse and non-human primate models.

DMD is caused by mutations in the dystrophin gene and leads to progressive muscle degeneration. Current gene therapy approaches largely rely on adeno-associated viral (AAV) vectors, which face limitations including restricted genetic cargo capacity, immune responses and challenges associated with repeat dosing.

Spot Biosystems is developing an EV-based platform designed to overcome these constraints by delivering larger genetic payloads without using viral vectors.

According to the company, the preclinical study showed that EV-delivered dystrophin messenger RNA generated sustained protein expression in DMD mouse models and improved measures of muscle strength, endurance and motor function. Repeated intravenous dosing in non-human primates was reported to produce dystrophin expression without evidence of liver, kidney or cardiac toxicity.

The company has translated the approach into an investigator-initiated clinical trial at Shanghai Children’s Medical Center. Early results from the first two paediatric patients treated in the study showed successful delivery of full-length dystrophin to skeletal muscle tissue.

Spot Biosystems reported that the patients experienced more than 1000% and 2000% increases in dystrophin levels after one month of dosing, alongside improvements in muscle function that persisted for up to six months after treatment cessation. The findings remain preliminary and are based on a two-patient cohort.

Andrew Lee, co-founder of Spot Biosystems, said: “By using the body’s own delivery machinery to carry medicines that viral vectors cannot, we are able to successfully deliver the complete dystrophin gene to skeletal muscle and generate a positive response in animals, primates, and now in early trials with human patients.”

The company said the technology is capable of carrying full-length dystrophin, which is significantly larger than the genetic payload typically accommodated by viral gene therapy vectors. It also believes the platform could support repeat dosing, a potential advantage for chronic genetic disorders requiring long-term treatment.

Paul Heidenreich, professor and vice-chair for quality in the department of medicine at Stanford University School of Medicine, said: “While additional research on longer treatment regimens is needed, early sustained and improved muscle function without liver, kidney, or cardiac toxicity is a promising outcome for the future of EV-based gene therapy.”

Spot Biosystems said it plans to continue enrolling patients and generating data through the ongoing trial while exploring a future regulatory pathway in the USA.

The company believes the platform may have applications beyond DMD, potentially enabling delivery of larger genetic therapies across a range of rare diseases.