Duchenne muscular dystrophy is an X-linked disorder caused by mutations in the DMD gene, the largest gene in the human genome, spanning 79 exons. These mutations abolish production of dystrophin, a structural protein that acts as a molecular shock absorber, linking the internal cytoskeleton of muscle fibers to the surrounding extracellular matrix. Without it, muscle cells degenerate under the mechanical stress of contraction, leading to progressive wasting, loss of ambulation, cardiomyopathy and premature death. The gene’s sheer size and its array of alternative promoters give rise to multiple dystrophin isoforms of different lengths: the full-length Dp427m isoform dominates in skeletal and cardiac muscle, while shorter versions such as Dp260 in the retina, Dp140 in the central nervous system and kidney, Dp116 in Schwann cells, and the ubiquitous Dp71 and Dp40 serve specialized roles in non-muscle tissues. Where a patient’s mutation falls on the gene determines which isoforms are lost, and thus which tissues bear the brunt of the disease.

Existing preclinical models fall short of capturing this complexity. The classic mdx mouse carries a nonsense mutation in the murine Dmd gene, but mouse and human DMD differ substantially in sequence, exon–intron organization and splicing regulation, and the mouse phenotype is comparatively mild. Humanized mice, in which specific murine exons have been replaced with human sequences, allow editing tools designed against human targets to be tested in vivo — but each line models only a single mutation. Because Duchenne lacks mutational hot spots and instead displays extreme heterogeneity across the gene, building a bespoke mouse for every clinically relevant variant is impractical, particularly for rare mutations. The Korean team, led by Hyuk-Jin Cha and Hyukjin Lee, reasoned that a renewable, patient-derived tissue that carries the patient’s own mutation might sidestep this limitation entirely.

Their solution exploits a structure usually regarded as a laboratory nuisance. When human pluripotent stem cells are injected into immunodeficient mice, they form teratomas containing disorganized derivatives of all three germ layers, including skeletal, cardiac and smooth muscle. Teratomas derived from Duchenne patient iPS cells recapitulate the absence of dystrophin, effectively recreating a patch of dystrophic human tissue inside a mouse. The researchers drew an analogy to patient-derived tumor xenografts, a mainstay of oncology drug development, and adapted the same framework to neuromuscular disease. From a bank of nine patient-derived iPS lines carrying missense, nonsense, duplication and deletion mutations, they focused on a line harboring a C-to-T transition in exon 6 that creates a premature stop codon — a mutation directly correctable by an adenine base editor, which chemically converts A·T base pairs to G·C without cutting the DNA double helix.

First, the team built an isogenic pair. Using electroporation, they delivered the adenine base editor into the mutant iPS cells and isolated edited clones that retained full pluripotency, confirmed by marker gene expression, alkaline phosphatase staining and teratoma formation. When differentiated in a dish over 16 days, the edited cells matured into spontaneously contracting cardiomyocyte-like cells, and immunoblotting revealed that the full-length Dp427m protein, absent in the mutant line, had been restored. A stepwise myogenic protocol — guiding cells through paraxial mesoderm, myogenic progenitor and myoblast stages over roughly 90 days — produced multinucleated, striated myotubes that likewise expressed robust Dp427m. These experiments established that correcting the single exon 6 mutation was sufficient to rescue the muscle-specific isoform in both cardiac and skeletal muscle lineages in vitro.

The ex vivo test followed. The researchers generated day-12 myogenic progenitors from the edited iPS cells, confirmed their expression of the progenitor markers PAX7 and MyoD by flow cytometry and immunofluorescence, and injected 100,000 of these cells into dystrophic teratomas grown from the uncorrected mutant cells. Four weeks later, immunoblotting showed that the engrafted progenitors had restored several shorter dystrophin isoforms — bands at approximately 117, 71 and 55 kilodaltons, presumably corresponding to Dp116, Dp71 and Dp40 — within the teratoma environment. Notably, however, neither the edited teratomas nor the progenitor-engrafted ones displayed the full-length Dp427m band seen in mature mouse muscle, suggesting that the teratoma’s developmental context did not yet support the maturation level required for the full-length protein.

The in vivo arm of the study tackled a delivery problem that has dogged the base-editing field. Adenine base editors such as ABE8e span roughly 5.4 kilobases, exceeding the approximately 4.7-kilobase packaging limit of adeno-associated virus vectors — and AAV immunogenicity has already produced severe, sometimes fatal adverse events in Duchenne gene therapy trials. Messenger RNA encapsulated in lipid nanoparticles, the platform proven by COVID-19 vaccines, accommodates large transcripts readily and avoids viral immunogenicity. The team first attempted a split-editor strategy, encoding the editor in two fragments joined by intein sequences that self-splice after translation, but found that the split mRNAs produced essentially no protein, likely because their engineered 5′ untranslated regions impaired ribosomal scanning. Full-length constructs with naturally functional leader sequences, by contrast, expressed robustly. Formulated by microfluidic mixing into uniform spherical nanoparticles of roughly 60 to 76 nanometers with low polydispersity, the SpRY mRNA–LNP conjugates outperformed even plasmid delivery when tested in patient iPS cells.

Injected directly into teratomas in mice, the editor showed a clear dose response: a single 10-microgram dose yielded about 1 percent editing, while escalating to 80 micrograms achieved up to roughly 15 percent in primary teratomas. Because teratomas vary unpredictably in size, composition and maturation, the researchers then devised a secondary transplantation scheme — sectioning one primary teratoma into four pieces and regrowing them in additional mice — to produce more uniform tissue. In these sequentially matured teratomas, editing efficiencies approached 100 percent at the highest dose, and, strikingly, two of four high-dose samples showed robust restoration of full-length Dp427m by long-exposure immunoblotting. Targeted sequencing of six predicted off-target exonic sites revealed no detectable A-to-G conversion above background, even at the highest dose, underscoring the specificity of the approach in human tissue.

Why did only some fully edited teratomas produce the full-length protein? Single-cell RNA sequencing of a Dp427m-positive and a Dp427m-negative teratoma provided the answer. Both contained broadly distributed DMD transcripts reflecting baseline activity of shorter isoforms, but only the positive sample harbored an enriched myogenic cluster — one of twenty identified cell populations — marked by elevated expression of skeletal muscle genes such as RYR3, LDB3, FBXO32 and MYOM1, along with cardiac maturation markers including TNNT2 and RYR2. Myogenic maturation, the data showed, is a critical determinant of whether corrected DNA translates into the clinically relevant full-length isoform. The authors caution that teratoma growth is inherently difficult to control and that animal welfare limits restrict teratoma size, so reproducible modeling of Dp427m recovery will require further optimization — potentially through inducible myogenic programming to bias teratomas toward muscle. Still, the platform establishes a proof of concept: a scalable, mutation-inclusive, patient-specific human tissue in which cell therapy and in vivo base editing can be tested side by side, bringing the field a step closer to evaluating personalized gene correction before it is ever infused into a patient.

Subject of Research: A patient-derived teratoma platform for evaluating ex vivo cell therapy and in vivo base editing to restore dystrophin in Duchenne muscular dystrophy

Article Title: Patient-derived teratomas as a humanized platform for dystrophin restoration by ex vivo cell therapy and in vivo base editing

Article References: Park, M. J., Kim, H.-B., Hwang, Y., Kim, Y.-J., Park, J.-C., Lim, H.-K., Park, Y.-G., Moon, S., Lee, H., & Cha, H.-J. (2026). Patient-derived teratomas as a humanized platform for dystrophin restoration by ex vivo cell therapy and in vivo base editing. Experimental & Molecular Medicine. https://doi.org/10.1038/s12276-026-01854-5

Image Credits: AI Generated

DOI: 10.1038/s12276-026-01854-5

Keywords: Duchenne muscular dystrophy, dystrophin, base editing, induced pluripotent stem cells, teratoma, lipid nanoparticles, gene therapy, myogenic progenitors, Dp427m, xenograft model, mRNA delivery, single-cell RNA sequencing