Proof-of-principle of NF1 gene therapy in plexiform neurofibroma xenograft mouse models

Neurofibromatosis type I is a rare neurocutaneous syndrome characterized by the development of disfiguring neurofibroma tumors with unmet clinical needs. As Neurofibromatosis Type I is a monogenic disease, the development of gene therapy is highly attractive, but it is currently unknown if rescuing the NF1 gene in established neurofibroma is sufficient for tumor regression. Here, we test this hypothesis by building two novel NF1 mouse models with reversible NF1 expression. In the first model, the human NF1 ^-/- Schwann cells named ipNF95.11b C/T are genetically modified with a doxycycline-inducible full-length mouse Nf1 gene. One month after cells implantation in the sciatic nerve, mice are split into two treatment groups and received either doxycycline or control water. Strikingly, most sciatic nerves from mice allowed to drink doxycycline water for one month do not display neurofibroma histologically (2 out of 16 sciatic nerves, 13%) whereas 75% (12 out of 16 sciatic nerves) develop or maintain a neurofibroma when drinking control water. In the second model, the human NF1 ^+/- Schwann cells named ipNF95.11 C are genetically modified with a doxycycline-inducible potent shRNA against the NF1 mRNA transcript. Strikingly, doxycycline withdrawal after neurofibroma establishment allowed limited neurofibroma maintenance (3 out of 14 sciatic nerves, 21%), whereas most sciatic nerves showed evidence of neurofibroma when kept on doxycycline (12 out of 14 sciatic nerves, 86%). Finally, intrathecal injection of the full-length Nf1 lentivirus in established 1-month ipNF95.11b C/T xenograft pNF significantly reduced tumor burden. All mice are female. Thus, we provide proof-of-principle of the efficacy of NF1 Gene Therapy in plexiform neurofibroma mice models, paving the way to the development of therapeutic gene therapy solutions for NF1 patients.