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Page 343 Gonzalez Castillo et al. J Transl Genet Genom. 2025;9:338-51 https://dx.doi.org/10.20517/jtgg.2025.57

Table 1. Summary of different microdystrophin constructs*
Serotype Tissue tropism Promoter Company Development progress
AAV8 Skeletal, cardiac Spc5.12 Regenxbio Multicenter, phase I/II/III, open-label study. Entering pivotal phase
AAV8 Skeletal, cardiac Spc5.12 Genethon Completed Phase 1/2. Entering Pivotal phase
AAV9 Skeletal, cardiac, lesser extent CK8e Solid Switched to a new generation vector (myo-AAV)
CNS Biosciences
AAV9 Skeletal, cardiac, lesser extent CK7 Pfizer Development was stopped (missed primary point in phase III
CNS clinical trial)
AAVrh74 Skeletal, cardiac MHCK7 Sarepta/Roche FDA approved in 2024 (Elevydis). Long-term outcome studies
ongoing

[36]
*Adapted from Roberts et al. .

AAV-mediated gene therapy replacement challenges
Durability
DMD is a chronic neuromuscular disease and, as such, requires sustained dystrophin expression. Several
studies have shown that AAV vectors can persist in normal tissues, including muscle cells. However, there is
some uncertainty regarding the long-term persistence of the transgene in the dystrophic muscle and animal
model data might not be fully translatable to patients with DMD [41,42] . Decline in transgene expression can
presumably be related to immune response and vector dilution . As the vector genome is thought to
[43]
remain episomal and not integrate into the host genome, the cell turnover rate in growing muscle, as seen in
young patients, and repeated cycles of necrosis and regeneration in dystrophic cells can affect the
persistence of the transgene and potentially lead to a dilution effect. It should also be noted that
overactivation of the immune system in the microenvironment of dystrophic cells can limit AAV genome
persistence [41,44,45] .

AAV- immunogenicity
Systemic delivery of high doses of AAV can trigger immune system-mediated toxicity. The complement
system is a primary component of innate immunity and in vitro studies suggest that AAV capsid can
interact and activate complement components. This activation can also happen through the classic pathway
by immune complex formed from anti-AAV capsid antibodies [45-48] . The adaptive immune response to AAV
capsid has been reported in gene therapy trials for hemophilia, spinal muscular atrophy (SMA), and other
diseases.

[49]
To date, two fatal cases of liver failure have been reported following treatment with Elevidys . The
pathogenesis of liver injury is not yet fully understood. However, liver injury described in gene therapy
clinical trials using AAV vectors could potentially be a result of both innate (possible complement system
activation), and adaptive (T-cell mediated) immune response. Additionally, if the transgene is highly
immunogenic, it could also trigger immune toxicity [50,51] .

Other toxicities related to gene therapy include myocarditis, liver injury and thrombotic microangiopathy
(TMA), which can also be related to activation of both innate and adaptive responses against the AAV
[51]
vector capsid .
Some of the strategies under investigation to reduce AAV immunogenicity include inhibition of
complement receptor , AAV vector coating with a modified polymer to reduce interaction with
[52]
neutralizing antibodies (Nabs) , removal of CpG motifs from the AAV vector , and the use of less
[54]
[53]
immunogenic AAV serotypes .
[55]