Abstract
Certain gene therapy protocols may require multiple administrations of vectors to achieve therapeutic benefit to the patient. This may be especially relevant for vectors such as adenoviral vectors that do not integrate into the host chromosome. Because immunocompetent animal models used for gene transfer studies develop neutralizing antibodies to adenoviral vectors after a single administration, little is known about how repeat administrations of vectors might affect transgene expression and vector toxicity. We used mice deficient in the membrane spanning region of immunoglobulin (IgM), which do not develop antibodies, to evaluate the effect of repeated intravenous administration of first-generation and helper-dependent adenoviral vectors expressing human alpha 1-antitrypsin (hAAT). The duration and levels of transgene expression were evaluated after repeated administration of vectors. Toxicity was assessed by measuring the level of liver enzymes in the serum and the degrees of hepatocyte hypertrophy and proliferation. We found that previous administration of first-generation adenoviral vectors can alter the response to subsequent doses. These alterations included an increase in transgene expression early (within 1 and 3 days), followed by a rapid drop in expression by day 7. In addition, previous administrations of first-generation vectors led to an increase in toxicity of subsequent doses, as indicated by a rise in liver enzymes and an increase in hepatocyte proliferation. In contrast to first-generation vectors, use of the helper-dependent adenovirus vector, Ad-STK109, which contained no viral coding regions, did not lead to increased toxicity after multiple administrations. We conclude that the response of the host to adenoviral vectors can be altered after repeated administration, compared with the response after the initial vector dose. In addition, these experiments provide further evidence for the relative safety of helper-dependent adenoviral vectors for gene therapy, compared with first-generation vectors.
Highlights
Adenoviral vectors are being evaluated for use in somatic gene therapy for the treatment of a variety of human diseases
We further demonstrated that multiple doses of a helper-dependent vector, AdSTK109, did not lead to increased toxicity with subsequent administration, in contrast to the results with first-generation vectors, suggesting a further advantage of this type of vector for gene therapy
The reason for increased transgene expression in immunodeficient mice, compared with immunocompetent mice in some experiments, is not clear. This difwhen the ͱ-gal vector was given first (2 ϫ 109 pfu/mouse), followed by AdhAAT⌬E1 (2 ϫ 109 pfu/mouse); human ␣1-antitrypsin (hAAT) was expressed in naive and Adͱgal⌬E1-pretreated ȐMT mice, but not in C57BL/6J mice previously treated with Adͱgal⌬E1. These results indicated that the absence of B-cell–mediated immunity in ȐMT mice allowed for transgene expression from adenoviral vectors in mice previously exposed to vectors, presumably due to lack of neutralizing antibodies
Summary
Adenoviral vectors are being evaluated for use in somatic gene therapy for the treatment of a variety of human diseases. Certain gene therapy protocols may require multiple administrations of vectors to achieve therapeutic benefit to the patient. This may be especially relevant for vectors such as adenoviral vectors that do not integrate into the host chromosome. Because immunocompetent animal models used for gene transfer studies develop neutralizing antibodies to adenoviral vectors after a single administration, little is known about how repeat administrations of vectors might affect transgene expression and vector toxicity. Materials and Methods: We used mice deficient in the membrane spanning region of immunoglobulin (IgM), which do not develop antibodies, to evaluate the effect of repeated intravenous administration of first-generation and helper-dependent adenoviral vectors expressing human ␣1-antitrypsin (hAAT). Toxicity was assessed by measuring the level of liver enzymes in the serum and the degrees of hepatocyte hypertrophy and proliferation
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