Abstract
Adeno-associated viral (AAV) vectors are attractive tools for central nervous system (CNS) gene therapy because some vectors can cross the blood-brain barrier (BBB), allowing them to be used as minimally invasive treatments. A novel AAV vector recently evolved in vivo, AAV-PHP.eB, has been reported to cross the BBB more effectively than the existing gold standard AAV9, but not under all conditions. Here, we compared the efficacy of single-stranded AAV-PHP.eB and AAV9 in targeting mouse CNS and peripheral tissues after administration via various routes, in two different mouse strains (C57BL/6J and B6C3), and after packaging AAV-PHP.eB with a self-complementary genome. We found that AAV-PHP.eB produced higher CNS transduction than AAV9 after intravenous injection, but only in C57BL/6J and not in B6C3 mice. AAV-PHP.eB and AAV9 produced similar CNS transduction when the administration route did not require the vectors to cross the BBB. Packaging AAV-PHP.eB with a self-complementary genome increased overall CNS transduction, but at the expense of strong neuronal tropism. AAV-PHP.eB resulted in less transduction of liver tissue than AAV9 under all conditions. Taken together, these results suggest the potential for AAV-PHP.eB as a vector for CNS gene therapy applications, but consideration will be required for translation beyond mouse models.
Highlights
One of the biggest hurdles in the treatment of neurological diseases is finding effective methods to deliver therapeutics to the central nervous system (CNS)
We found that when the need for the vector to cross the blood-brain barrier (BBB) was eliminated by the administration method, AAV9 and AAVPHP.eB performed reaffirming that it is the ability of AAVPHP.eB to cross the BBB that increases its CNS transduction efficiency
Cell counts expressed as a percentage of DAPI-positive (DAPI+) cells revealed no significant differences in transduction efficiency between the two serotypes dependent on brain region or animal age, but both serotypes transduced significantly more DAPI+ cells in P1 than in adult animals in both the cortex (AAV-PHP.eB: P1, 21.2% ± 1.0% versus 3 months, 3.6% ± 2.9%, t(6) = 11.2, p < 0.0001; AAV9: P1, 18.9% ± 3.9% versus 3 months, 3.4% ± 2.4%, t(6) = 6.7, p = 0.0005) and the hippocampus (AAV-PHP.eB: P1, 16.0% ± 2.7% versus 3 months, 2.6% ± 2.1%, t(6) = 7.7, p = 0.0002; AAV9: P1, 16.9% ± 2.1% versus 3 months, 2.4% ± 2.3%, t(6) = 9.3, p < 0.0001)
Summary
One of the biggest hurdles in the treatment of neurological diseases is finding effective methods to deliver therapeutics to the central nervous system (CNS). Recombinant adeno-associated viral (rAAV) vectors have long been one of the most favored gene therapy vectors for CNS disease applications because of their ability to give stable, long-lasting transgene expression in non-dividing cells.[1] From a clinical standpoint, therapeutics that can be given by a noninvasive systemic route will be crucial for translation to humans on a large-scale basis. Naturally occurring AAV capsid serotypes have limited ability to cross the blood-brain barrier (BBB). This means they must either be given in very high doses intravenously (i.v.) or be administered by local injection into the CNS, making them inappropriate for use as a non-invasive treatment approach. The CREATE system produced the novel AAV-PHP.B capsid family (including AAV-PHP.B, and the second generation, AAV-PHP.eB), which differed from AAV9 by a heptamer amino acid insertion in the capsid sequence.[4,5] These capsids were generated by a Cre recombinase system that selected for capsids that were highly efficient at transducing the CNS in adult C57BL/6J mice after administration by i.v. injection, with AAVPHP.eB giving upward of a 50-fold increase in cell transduction in multiple brain regions.[4]
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