Open AccessPostmortem Analysis in a Clinical Trial of AAV2-NGF Gene Therapy for Alzheimer's Disease Identifies a Need for Improved Vector Delivery
Author(s) -
Michael J. Castle,
Fernando C. Baltanás,
Imre Kovács,
Alan H. Nagahara,
David Barba,
Mark H. Tuszynski
Publication year - 2020
Publication title -
human gene therapy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.633
H-Index - 149
eISSN - 1557-7422
pISSN - 1043-0342
DOI - 10.1089/hum.2019.367
Subject(s) - basal forebrain , nerve growth factor , cholinergic neuron , nucleus basalis , cholinergic , genetic enhancement , neuroscience , medicine , gene delivery , ciliary neurotrophic factor , neurotrophic factors , biology , receptor , gene , genetics
Nerve growth factor (NGF) gene therapy rescues and stimulates cholinergic neurons, which degenerate in Alzheimer's disease (AD). In a recent clinical trial for AD, intraparenchymal adeno-associated virus serotype 2 (AAV2)-NGF delivery was safe but did not improve cognition. Before concluding that NGF gene therapy is ineffective, it must be shown that AAV2-NGF successfully engaged the target cholinergic neurons of the basal forebrain. In this study, patients with clinically diagnosed early- to middle-stage AD received a total dose of 2 × 10 11 vector genomes of AAV2-NGF by stereotactic injection of the nucleus basalis of Meynert. After a mean survival of 4.0 years, AAV2-NGF targeting, spread, and expression were assessed by immunolabeling of NGF and the low-affinity NGF receptor p75 at 15 delivery sites in 3 autopsied patients. NGF gene expression persisted for at least 7 years at sites of AAV2-NGF injection. However, the mean distance of AAV2-NGF spread was only 0.96 ± 0.34 mm. NGF did not directly reach cholinergic neurons at any of the 15 injection sites due to limited spread and inaccurate stereotactic targeting. Because AAV2-NGF did not directly engage the target cholinergic neurons, we cannot conclude that growth factor gene therapy is ineffective for AD. Upcoming clinical trials for AD will utilize real-time magnetic resonance imaging guidance and convection-enhanced delivery to improve the targeting and spread of growth factor gene delivery.