Efficient Gene Delivery and Selective Transduction of Glial Cells in the Mammalian Brain by AAV Serotypes Isolated From Nonhuman Primates

Abstract

Adeno-associated viral (AAV) vectors have become the primary delivery agent for somatic gene transfer into the central nervous system (CNS). To date, AAV-mediated gene delivery to the CNS is based on serotypes 1-9, with efficient gene transfer to neurons only-selective and widespread transduction of glial cells have not been observed. Recently, additional endogenous AAVs have been isolated from nonhuman primate tissues. In this study, transduction obtained with AAV serotypes bb2, cy5, rh20, rh39, and rh43 was compared to that obtained with AAV8, another nonhuman primate isolate previously shown to perform well in mammalian brain. Titer-matched vectors encoding the enhanced green fluorescent protein (EGFP) reporter, driven by the constitutive CAG promoter, were injected into the hippocampus, striatum, or substantia nigra (SN) of adult rats. More widespread neuronal transduction was observed following infusion of cy5, rh20, and rh39 than observed with AAV8. Of interest, preferential transduction of astrocytes was observed with rh43. To optimize glial transduction, vector stocks driven by cell-specific promoters were generated-widespread and targeted transduction of astrocytes and oligodendrocytes was observed using rh43 and AAV8, driven by the glial fibrillary acidic protein (GFAP) and myelin basic protein (MBP) promoters, expanding the utility of AAV for modeling and treating diseases involving glial cell pathology.

Progress and prospects: Immunobiology of gene therapy for neurodegenerative disease: prospects and risks

“…In addition, there are now several different serotypes of AAV in use for the CNS, which have greater and more widespread transduction efficiencies than earlier serotypes. [86][87][88] Thus, for a re-administration protocol an immune response against AAV2 capsid proteins can be circumvented by re-administration with a different serotype. 77 As well as human serotypes, non-human primate AAV serotypes such as AAV Rh10 have also been explored for delivery to the CNS.…”

Gene Therapy for the Nervous System: Challenges and New Strategies

“…A large range of AAV capsids has been investigated for their CNS gene transfer properties by direct intracranial injection [99][100][101][102]. The majority of these studies have used strong ubiquitous promoters to provide a broad overview of transgene expression in different tissues and cell types throughout the body after intravascular infusions, or CNS cell types after intracranial delivery.…”

“…This could considerably influence the pre-clinical development process of therapeutic interventions for neurodegenerative diseases, which determines the AAV vectors that will be tested in human clinical trials. As discussed below in "New Strategies", the apparent discrepancy in CNS transduction profiles of AAV vectors with the same capsid but carrying different CNS cell specific promoters or the CBA promoter [102,[110][111][112] suggests that the latter promoter may not mediate detectable transgene expression in all cell types in the brain.…”

“…Apparently, AAV vectors carrying the original 2.2 kb Gfap promoter [150], or a smaller truncated version (gfaABC 1 D) [151], transduce astrocytes in the mouse brain effectively and with a great degree of specificity [102,111]. Similarly, AAV vectors carrying the myelin basic protein (MBP) promoter transduce oligodendrocytes at high efficiency and with excellent cellular specificity [102,110,112]. These findings are important because oligodendrocytes are a key therapeutic target for demyelinating CNS diseases, such as Canavan disease, and they challenge the widely held perception that no presently available AAV is capable of mediating efficient gene transfer to this cell population.…”

“…These findings with cell-type specific promoters raise the possibility that our current knowledge on the CNS tropism of systemically delivered AAVs is most likely incomplete as the studies carried out thus far have used scAAV vectors encoding GFP under different forms of the CBA promoter [21,36,49,97]. For new AAVs that display strong CNS tropism after systemic delivery using some version of the CAG/CBA promoter, it may be useful to extend studies to include scAAV vectors encoding a marker gene (GFP most likely) under different cell specific promoters for neurons [152], astrocytes [102,110,111], microglia [153], and oligodendrocytes [102,110,112] to develop a more complete understanding of its potential for global gene therapy interventions.…”