Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder affecting 1 in 3,500 individuals worldwide due to inactivating mutations in the NF1 gene. Clinical features include benign and malignant tumor formation, cognitive and learning disabilities, peripheral neuropathy and musculoskeletal abnormalities. Cognitive symptoms in NF1 include impaired executive functioning, autism-associated features, speech and language delays, attention deficits, hyperactivity and impulsivity.

Disease manifestations are due to reduced expression of functional neurofibromin, the protein product of NF1 that inhibits Ras-dependent signaling by stimulating GTP hydrolysis via its GAP-related domain (GRD). Despite the high societal impact of NF1, there are few effective treatments for the management of cognitive symptoms, necessitating the development of new treatment modalities to fill gaps in clinical practice.

J. Elliott Robinson plans to address this need by developing novel gene therapies for NF1-associated cognitive deficits using new ‘systemic’ adeno-associated viral (AAV) vectors, such as AAV-PHP.eB, that freely cross the blood-brain barrier to provide efficient brain-wide transgene expression after intravenous administration. This was not possible with existing AAV serotypes, such as AAV9. Because the neurofibromin coding sequence is too large to be packaged in AAVs, he plans to create a library of GRD vector transgenes that utilize diverse promoter/enhancer elements to allow viral tropism and expression intensity to be tuned for maximum therapeutic efficacy.

This work will feature a new AAV capsid, AAV-CAPB10, that has improved brain targeting with limited tropism for the liver and peripheral organs. Because the GRD alone may not recapitulate all neurofibromin functions, Robinson also plans to develop viral vectors that use CRISPR-mediated activation (CRISPRa) to ameliorate haploinsufficiency by boosting expression of wildtype NF1 (or Nf1 in mice) at transcriptionally active sites.

Following vector validation and production, Robinson plans to perform randomized control trials in Nf1 knockout mice to determine the therapeutic efficacy of each systemic AAV gene therapy in vivo. These efforts will feature robust transcriptomic, proteomic, electrophysiological and behavioral analyses.

All viral vectors produced during this award will be actively disseminated throughout the NF1 research community in order to allow thorough, unbiased evaluation in different NF1 model systems and cell lines. If successful, these proposed experiments will provide a crucial first step in the development of central nervous system gene therapies for NF1 that may eventually be used to improve health outcomes of individuals with this condition.