Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2017 Sep 15;8:184-197.
doi: 10.1016/j.omtn.2017.06.011. Epub 2017 Jun 21.

Rationally Engineered AAV Capsids Improve Transduction and Volumetric Spread in the CNS

Affiliations
Free PMC article

Rationally Engineered AAV Capsids Improve Transduction and Volumetric Spread in the CNS

Nicholas M Kanaan et al. Mol Ther Nucleic Acids. .
Free PMC article

Abstract

Adeno-associated virus (AAV) is the most common vector for clinical gene therapy of the CNS. This popularity originates from a high safety record and the longevity of transgene expression in neurons. Nevertheless, clinical efficacy for CNS indications is lacking, and one reason for this is the relatively limited spread and transduction efficacy in large regions of the human brain. Using rationally designed modifications of the capsid, novel AAV capsids have been generated that improve intracellular processing and result in increased transgene expression. Here, we sought to improve AAV-mediated neuronal transduction to minimize the existing limitations of CNS gene therapy. We investigated the efficacy of CNS transduction using a variety of tyrosine and threonine capsid mutants based on AAV2, AAV5, and AAV8 capsids, as well as AAV2 mutants incapable of binding heparan sulfate (HS). We found that mutating several tyrosine residues on the AAV2 capsid significantly enhanced neuronal transduction in the striatum and hippocampus, and the ablation of HS binding also increased the volumetric spread of the vector. Interestingly, the analogous tyrosine substitutions on AAV5 and AAV8 capsids did not improve the efficacy of these serotypes. Our results demonstrate that the efficacy of CNS gene transfer can be significantly improved with minor changes to the AAV capsid and that the effect is serotype specific.

Keywords: AAV; CNS; capsid; mutant.

Figures

Figure 1
Figure 1
Rationally Designed AAV2 Capsid Mutants Significantly Enhance Striatal Transduction Adult Sprague-Dawley rats received intrastriatal injections of an AAV2 vector (2 μL of 1.2 × 1012 vg/μL for all viruses) as defined in Table 1. One month later, the animals were sacrificed and processed for transgene (GFP) immunoreactivity. (A–H) Representative images of GFP immunoreactivity in the striatum following the injection of (A) T2 WT (n = 8), (B) T2 1Y (n = 7), (C) T2 2Y#1 (n = 6), (D) T2 2Y#2 (n = 8), (E) T2 3Y (n = 7), (F) T2 6Y (n = 8), (G) T2 3Y +T +dH (n = 12), and (H) T2 3Y +dH. Insets are higher magnification images taken at the periphery of the transduction area. (I) Stereological quantification of striatal GFP+ neurons revealed that T2 3Y, T2 3Y +T +dH, and T2 3Y +dH transduced significantly more striatal neurons than any other capsid (*p < 0.001) followed by T2 1Y (#p < 0.004 versus remaining groups except T2 3Y +T). Several capsid serotypes did not exhibit an improvement over WT (T2 2Y#2, T2 6Y, T2 4Y +T, T2 3Y +T), and T2 2Y#1 exhibited significant impairment in transduction as compared with the T2 WT control (##p < 0.03). The T2 3Y +T capsid showed higher transduction versus T2 2Y#1, T2 2Y#2, and T2 6Y (**p < 0.01). (I) Error bars represent mean + SD. (H) Scale bar, 1 mm (inset scale bar, 50 μm); scale bar applies to all micrographs.
Figure 2
Figure 2
Removal of the Canonical HSPG Binding Site Significantly Improves Viral Vector Spread The volume of transduction from animals shown in Figure 1 and Figure S1 was estimated using the Cavalieri method. (A) Volumetric measurements of striatal transduction revealed that the vector spread was significantly enhanced with the T2 3Y +dH and T2 3Y +T +dH capsids as compared with any other capsid (*p < 0.0001). Moreover, all T-V mutants exhibited significantly enhanced transduction volume (#p < 0.0001 versus T2 WT, T2 1Y, T2 2Y#1, T2 2Y#2, T2 3Y, T2 6Y) compared with other capsids, with the exception of T2 4Y +T, which was not different from T2 3Y. **p < 0.005 versus T2 WT, T2 2Y#1, and T2 2Y#2, T2 6Y; ##p < 0.05 versus T2 2Y#1, T2 2Y#2, and T2 6Y; ***p < 0.01 versus T2 2Y#1. Error bars represent the mean + SD. (B) Plot of GFP+ cells versus transduction volume. A clear pattern emerged for several of the capsid mutants tested. For instance, both T2 3Y and T2 1Y infected an increased number of neurons within a limited volume. In contrast, T2 3Y +dH and T2 3Y +T +dH (which transduced a similar number of neurons as T2 3Y) transduced neurons over a much greater volume.
Figure 3
Figure 3
Increase in Transduction Efficacy Is Reflected by Increased GDNF Transgene Levels An AAV genome containing an expression cassette encoding human glial cell line-derived neurotrophic factor (GDNF) was packaged into T2 WT or T2 1Y, and the same capsid mutants with a GFP expression cassette were utilized as controls. Adult Sprague-Dawley rats received unilateral intrastriatal injections of either vector (2 μL of 1.2 × 1012 vector genomes/μL for all viruses); 1 month later, the striatum was collected for ELISA protein measurements and histology. (A and B) Representative images of striatal GDNF immunoreactivity from animals injected with T2 1Y-GDNF (A) or T2 WT-GDNF (B). (C) ELISA protein measurements of the human GDNF transgene levels in the AAV-injected striatal samples from animals injected with either T2 WT-GDNF (n = 8), T2 WT-GFP (n = 4), T2 1Y-GDNF (n = 7), or T2 1Y-GFP (n = 4). Transduction with T2 1Y-GDNF resulted in significantly higher striatal GDNF levels than that produced by T2 WT-GDNF (#p = 0.01). No GDNF was detected in either GFP control-treated subject. *p = 0.01 versus T2 WT-GDNF and p = 0.001 versus T2 1Y-GDNF. Error bars represent the mean + SD.
Figure 4
Figure 4
AAV2 Capsid Mutations Significantly Improve Transduction of the Hippocampus Adult Sprague-Dawley rats received unilateral intrahippocampal injections of either T2 WT, T2 1Y, or T2 3Y virus (2 μL of 1.2 × 1012 vg/μL). One month later, the animals were sacrificed and processed for transgene (GFP) immunoreactivity. (A–C) Representative micrographs of T2 WT transduction in the hippocampus; white boxes in (A) are regions shown in (B) and (C). (D–F) Representative micrographs of T2 1Y mutant AAV transduction throughout the hippocampus; white boxes in (D) are regions shown in (E) and (F). (G–I) Representative micrographs of T2 3Y transduction throughout the entire hippocampus; white boxes in (G) indicate regions shown in (H) and (I). Note that all viruses transduce dentate granule cells (A, D, and G). (J) Unbiased stereological quantitation of GFP+ neurons showed that the T2 1Y virus (n = 9) transduced significantly more cells than the T2 WT virus (n = 8), and the T2 3Y virus (n = 7) transduced significantly more than T2 WT and T2 1Y in the hippocampus (*p < 0.05 versus T2 WT and #p < 0.05 versus T2 1Y, one-way ANOVA, Tukey’s post hoc). (K) Unbiased stereological quantitation of the transduction volume showed a trend toward a difference among the T2 WT (n = 8), T2 1Y (n = 9), and T2 3Y (n = 7) viruses (p = 0.065, one-way ANOVA) in the hippocampus. Scale bars, 500 μm (G, also applies to A and D); 100 μm (H, also applies to B and E); 50 μm (I, also applies to C and F).
Figure 5
Figure 5
Incorporation of Tyrosine Mutants into AAV5 and AAV8 Capsids Does Not Improve Transduction Properties following Intrastriatal Injections Adult Sprague-Dawley rats received intrastriatal injections of either AAV5 or AAV8 vectors (2 μL of 1.2 × 1012 vg/μL) as defined in Table 1. One month later, the animals were sacrificed and processed for transgene (GFP) immunoreactivity. (A–D) Representative micrographs of striatal GFP immunoreactivity following injection with AAV5 capsid mutants: (A) T5 WT (n = 9), (B) T5 2Y (n = 8), (C) T5 5Y (n = 8), and (D) T5 1Y (n = 8). (E and F) Stereological cell counts of transduced neurons (E) or transduction volume (F) suggests that incorporation of these mutations does not improve transduction compared with WT AAV5. In contrast, the incorporation of five mutations (T2 5Y) resulted in a dramatic reduction in transduction (*p < 0.0001). (G–J) Representative micrographs of striatal GFP immunoreactivity following transduction with AAV8-based capsids: (G) T8 WT (n = 8), (H) T8 2Y +T (n = 7), (I) T8 1Y (n = 8), and (J) T8 2Y (n = 7). (K and L) As indicated by the stereological quantification (K) and volumetric analysis (L), there were no significant differences between the various mutants except a modest reduction in the number of transduced cells with the T8 2Y virus as compared with T8 2Y +T (**p = 0.02). (E, F, K, and L) Error bars represent the mean + SD.
Figure 6
Figure 6
AAV2 Capsid Tyrosine Mutations Do Not Alter the Tropism of the Viral Vector, while Deletion of Heparan Sulfate Binding Eliminates Glial Tropism Adult Sprague-Dawley rats received intrastriatal injections of AAV2 vectors (2 μL of 1.2 × 1012 vg/μL) as defined in Table 1. One month later, the animals were sacrificed and processed for dual-label viral genome in situ hybridization (brown punctate staining) and glial cell IHC (blue-gray staining). (A–D) Representative sections from animals injected with T2 WT (A) and T2 3Y (B) indicate that both viruses display tropism for astrocytes, as indicated by GFAP+ cells containing brown in situ hybridization puncta (arrows), whereas T2 3Y +dH (C) and T2 3Y +T +dH (D) do not appear to contain viral genomes, indicating a loss of astrocyte tropism (arrowheads). (E–H) Representative sections from animals injected with T2 WT (E) and T2 3Y (F) indicate that both viruses display tropism for oligodendrocytes, as indicated by Oligo2+ cells containing brown in situ hybridization puncta (arrows), whereas T2 3Y +dH (G) and T2 3Y +T +dH (H) do not appear to contain viral genomes, indicating a loss of oligodendrocyte tropism (arrowheads). (I–L) Representative sections from animals injected with T2 WT (I), T2 3Y (J), T2 3Y +dH (K), and T2 3Y +T +dH (L) show that Iba1+ cells do not appear to contain viral genomes, indicating a lack of microglial tropism (arrowheads). Additional in situ hybridization-IHC results with other AAV mutant capsids are in Figures S3–S6. Scale bars, 25 μm (D, H, and L, and apply to all images in each row).

Similar articles

See all similar articles

Cited by 15 articles

See all "Cited by" articles

References

    1. Kantor B., Bailey R.M., Wimberly K., Kalburgi S.N., Gray S.J. Methods for gene transfer to the central nervous system. Adv. Genet. 2014;87:125–197. - PMC - PubMed
    1. Manfredsson F.P., Mandel R.J. Development of gene therapy for neurological disorders. Discov. Med. 2010;9:204–211. - PubMed
    1. Marks W.J., Jr., Baumann T.L., Bartus R.T. Long-term safety of patients with Parkinson’s disease receiving rAAV2-neurturin (CERE-120) gene transfer. Hum. Gene Ther. 2016;27:522–527. - PubMed
    1. Bartus R.T., Herzog C.D., Chu Y., Wilson A., Brown L., Siffert J., Johnson E.M., Jr., Olanow C.W., Mufson E.J., Kordower J.H. Bioactivity of AAV2-neurturin gene therapy (CERE-120): differences between Parkinson’s disease and nonhuman primate brains. Mov. Disord. 2011;26:27–36. - PMC - PubMed
    1. Polinski N.K., Gombash S.E., Manfredsson F.P., Lipton J.W., Kemp C.J., Cole-Strauss A., Kanaan N.M., Steece-Collier K., Kuhn N.C., Wohlgenant S.L., Sortwell C.E. Recombinant adenoassociated virus 2/5-mediated gene transfer is reduced in the aged rat midbrain. Neurobiol. Aging. 2015;36:1110–1120. - PMC - PubMed

LinkOut - more resources

Feedback