Administration of helper-dependent adenoviral vectors and sequential delivery of different vector serotype for long-term liver-directed gene transfer in baboons

Abstract

The efficiency of first-generation adenoviral vectors as gene delivery tools is often limited by the short duration of transgene expression, which can be related to immune responses and to toxic effects of viral proteins. In addition, readministration is usually ineffective unless the animals are immunocompromised or a different adenovirus serotype is used. Recently, adenoviral vectors devoid of all viral coding sequences (helper-dependent or gutless vectors) have been developed to avoid expression of viral proteins. In mice, liver-directed gene transfer with AdSTK109, a helper-dependent adenoviral (Ad) vector containing the human alpha(1)-antitrypsin (hAAT) gene, resulted in sustained expression for longer than 10 months with negligible toxicity to the liver. In the present report, we have examined the duration of expression of AdSTK109 in the liver of baboons and compared it to first-generation vectors expressing hAAT. Transgene expression was limited to approximately 3-5 months with the first-generation vectors. In contrast, administration of AdSTK109 resulted in transgene expression for longer than a year in two of three baboons. We have also investigated the feasibility of circumventing the humoral response to the virus by sequential administration of vectors of different serotypes. We found that the ineffectiveness of readministration due to the humoral response to an Ad5 first-generation vector was overcome by use of an Ad2-based vector expressing hAAT. These data suggest that long-term expression of transgenes should be possible by combining the reduced immunogenicity and toxicity of helper-dependent vectors with sequential delivery of vectors of different serotypes.

Figure 1

Expression of hAAT in baboons after administration of Ad5hAATΔE1 and Ad2hAATΔE1. Baboons 12402, 12486, 12490, and 12497 received Ad5hAATΔE1 followed by Ad2hAATΔE1 at the doses indicated in Table 1. Two naive animals of similar age and weight (13110 and 13121) were used as controls for Ad2hAATΔE1 administration. Arrows indicate the time of vector injection.

Figure 2

Cellular immune responses to adenoviral antigens in baboons 12490 and 12497. Baboons were treated as indicated in Fig. 1 and Table 1. Both animals were sacrificed 4.5 months after Ad2hAATΔE1 infusion. Splenocytes were restimulated in vitro as described in Materials and Methods section to perform proliferation (A) and CTL (B) assays. Target cells were fibroblasts from skin biopsies of each animal infected with Ad2hAATΔE1 or uninfected. E/T ratio, effector:target ratio.

Figure 3

Expression of hAAT in baboons after administration of Ad5hAATΔE1 or AdSTK109. Treatment of the four animals that received Ad5hAATΔE1 (12402, 12486, 12490, and 12497) is described in Fig. 1. Baboons 13250, 13277, and 13729 received 3.3 × 10¹¹, 3.9 × 10¹¹, and 3.6 × 10¹¹ particles per kg, respectively, of AdSTK109 vector.