AAV PHP.eB-CMV-GFP

Rare genetic diseases affect approximately 300 million people worldwide, 74% of which are childhood-onset and have neurological manifestations. The use of viral vectors to correct or replace dysfunctional genes has shown significant preclinical and clinical benefits in inherited pediatric diseases, particularly those in which non-cell-autonomous mechanisms such as cross-correction are efficacious (i.e., X-linked adrenoleukodystrophy malformation or Batten's disease). However, the field still faces significant challenges, particularly for diseases caused by genes encoding non-secreted proteins whose dysfunction affects large areas of the brain that cannot be reached by intracerebral delivery. Methods to engineer viral capsids, such as peptide insertion, chemical modifications, shuffled genomic libraries, directed evolution, or rationally targeted mutagenesis, have resulted in the generation of a tenth of artificial variants among which some have been designed to cross more efficiently the blood-brain barrier (BBB) when delivered into the bloodstream. By inserting random sequences into the cap gene containing lox sites and performing multiple rounds of selection in Cre transgenic mice, Deverman and colleagues created a series of brain-penetrating adeno-associated virus (AAV) vector variants. One of these vectors, AAV-PHP.B, induced transgene expression in the central nervous system at least 40-fold greater than the parental AAV9 capsid after intravenous injection and retained cell tropism toward peripheral organs. In follow-up studies, the same research team further evolved PHP.B variants to achieve better neuronal transduction. By applying the same Cre recombinase-based AAV target evolution strategy to the PHP.B capsid, they isolated the AAV-PHP.eB variant that showed enhanced CNS infectivity, enabling the reduction of the viral load delivered intravenously.