Abstracts

Rationale: Vanishing White Matter Disease (VWM) is a progressive childhood leukodystrophy that presents with ataxia, spasticity, neurological decline, and seizures which lead to premature death. There are no treatments. Caused by autosomal recessive, loss of function mutations in the subunits of eukaryotic initiation factor 2B (eIF2B), VWM most commonly originates from pathologic variants in subunit 5 (EIF2B5). Due to VWM’s monogenic nature, it is a promising candidate for adeno-associated virus (AAV)-mediated gene replacement therapy.


Methods: Prior studies of VWM revealed that astrocytes are a critical target for therapy, as their differentiation, morphology, and function are impaired, thus mediating disease progression. We first characterized the newly identified and severe VWM Eif2b5^I98M murine model through clinically relevant, in life assessments including mobility, gait, and myelin loss by magnetic resonance imaging (MRI). Molecular characterization through the identification of biomarkers was also investigated. To provide targeted disease correction, we designed four gene replacement constructs to drive therapeutic EIF2B5 expression in astrocytes—a critical cell type for VWM pathology. We are currently evaluating our AAV vectors (AAV-EIF2B5) in two murine VWM models, Eif2b5^R191H, a patient orthologous VWM murine model, and Eif2b5^I98M, and are monitoring disease progression using traditional and clinically relevant readouts.


Results: The I98M mice display significant mobility loss, ataxic gait, and demyelination all within a strikingly short life span (5.5 months). Important for assessing therapeutic impact, these mice are the only VWM model that also experience epileptic seizures starting around 4-5 months of age. Molecular characterization indicates that the integrated stress response (ISR) is dysregulated, confirming a hallmark of VWM disease pathogenesis. Recent preliminary data suggests that I98M and R191H mice have increased infiltration of neuroinflammatory microglia. Due to the novelty of these findings, further investigation is needed to better understand the role of microglia in disease development. Ongoing gene therapy efficacy studies in both models indicate that our AAV-EIF2B5 vectors delay disease progression, and partially rescue motor function. After treatment, I98M survival is significantly extended (~2-fold); however, these animals are still experiencing severe and life-limiting seizures. Thus, further uncovering of uncorrected disease mechanisms, such as the role of other cell types and pathways, is critical for our continuing efforts to generate a comprehensive, targeted, and durable therapy.


Conclusions:
Overall, we expect the development of a lead gene therapy candidate in which the data is strengthened through the evaluation of clinically relevant measures in two murine models of varying VWM manifestations, allowing for translation to the clinic.




Funding: T32TR004543
TL1TR002735