Robust systemic transduction with AAV9 vectors in mice: efficient global cardiac gene transfer superior to that of AAV8

Abstract

It has been recently shown that recombinant adeno-associated virus serotype 8 (rAAV8) is a robust alternative serotype vector that overcomes many of the limitations of rAAV2 and transduces various tissues efficiently and globally through systemic vector administration. AAV9 is a serotype newly isolated from human tissues, but our knowledge of the biology of rAAV9 in vivo is currently limited. Here, we demonstrate by a series of comprehensive side-by-side experiments with rAAV8 and 9 vectors delivered via different routes or at various doses in mice that rAAV9 vectors share the robustness of rAAV8, i.e., (1) very high liver transduction efficiency irrespective of whether vectors are administered intravascularly or extravascularly and (2) substantial transduction in the heart, skeletal muscle, and pancreas by peripheral vein injection. Importantly, rAAV9 transduced myocardium 5- to 10-fold higher than rAAV8, resulting in over 80% cardiomyocyte transduction following tail vein injection of as low as 1.0 x 10(11) particles per mouse. Thus rAAV9, as well as rAAV8, is a robust vector for gene therapy applications and rAAV9 is superior to rAAV8 specifically for cardiac gene delivery by systemic vector administration.

FIG. 1

Plasma hF.IX levels in mice following injection of hF.IX-expressing rAAV8 or 9 vector via four different routes. Adult male (M) or female (F) C57BL/6 mice were injected with 8.0 × 10¹⁰ vg/ mouse of AAV8- or 9-hF.IX16 via portal vein (PV), tail vein (TV), intraperitoneal (IP), or subcutaneous (SC) injection. Combinations of serotype–vector administration route–animal sex are indicated. Plasma hF.IX levels were determined 1 day, 4 days, and 1, 2, 4, 6, 8, and 12 weeks postinjection and are shown as a bar graph with means ± standard deviations (n = 3–5 each).

FIG. 2

rAAV8 and 9 vector genome forms in the liver transduced via the SC or PV route. Total liver DNA extracted from AAV8- or 9-hF.IX16-transduced liver samples was subjected to Southern blot analysis with a noncutter restriction enzyme that does not cut the ds vector genomes (SacI) or a single-cutter restriction enzyme that cuts the ds vector genomes asymmetrically near the 5′ end (BamHI). Concatemers were not detected in the samples transduced with rAAV8 via the SC route. Conc, ds concatemers; CM, supercoiled ds circular monomer genomes; H-T, head-to-tail molecules; T-T, tail-to-tail molecules; M, 30 ds-vg/dge standard.

FIG. 3

Representative photomicrographs of sections of the liver, heart, skeletal muscle, and pancreas 10 days after tail vein injection of AAV8- or 9-CMV-lacZ at various doses ranging from 1.0 × 10¹⁰ to 1.8 × 10¹² vg/mouse. Each section was stained with X-Gal and nuclear fast red. Scale bars represent 100 μm.

FIG. 4

Comparison of tissue tropism between rAAV8 and rAAV9. Double-stranded vector genome copy numbers per diploid genomic equivalent (ds-vg/dge) in each tissue were used to assess the vectors’ tissue tropism. Adult male mice were injected with either AAV8-CMV-lacZ or AAV9-CMV-lacZ at a dose of 3.0 × 10¹¹ (‘‘lo’’ or low) or 1.8 × 10¹² (‘‘hi’’ or high) vg/mouse via the tail vein, and ds vector genome copy numbers in 10 major tissues (i.e., Lv, liver; B, brain; Lu, lung; H, heart; S, spleen; K, kidney; I, intestine; T, testis; P, pancreas; M, skeletal muscle) were determined 10 days postinjection by Southern blot analysis. Each bar represents a ratio of ds rAAV9 genomes to ds rAAV8 genomes (rAAV9/8 ratio) in each tissue at each vector dose (lo and hi). The ratio serves as a factor by which rAAV9 vector infects a tissue better than rAAV8. The raw ratio was determined only by rAAV8 and 9 vector copy numbers in a tissue, while the normalized ratio represents the ratio in a tissue corrected for liver transduction efficiency with each serotype vector.

FIG. 5

Transduction efficiency in the heart relative to that in the liver (i.e., heart/liver transduction efficiency ratios) as a function of injected vector dose. (A) Heart/liver transduction (Tx) efficiency ratios were determined based on the amount of ds vector genome copy numbers in the heart and liver. (B) Heart/liver transduction efficiency ratios were determined based on the transduction efficiencies determined by X-Gal staining. A discrepancy in the values (ratios) between white and black bars at the same vector dose represents a distinct transduction efficiency in the heart between rAAV8 and rAAV9 vectors at a given vector dose.