Differential activation of innate immune responses by adenovirus and adeno-associated virus vectors.

Adenovirus vectors induce acute inflammation of infected tissues due to activation of the innate immune system and expression of numerous chemokines and cytokines in transduced target cells. In contrast, adeno-associated virus (AAV) vectors are not associated with significant inflammation experimentally or clinically. We tested the ability of AAV vectors to induce the expression of chemokines in vitro and to activate the innate immune system in vivo. In human HeLa cells and murine renal epithelium-derived cells (REC cells) the adenovirus vector AdlacZ induced the expression of multiple inflammatory chemokines including RANTES, interferon-inducible protein 10 (IP-10), interleukin-8 (IL-8), MIP-1beta, and MIP-2 in a dose-dependent manner. The use of AAVlacZ did not induce the expression of these chemokines above baseline levels despite 40-fold-greater titers than AdlacZ and greater amounts of intracellular AAVlacZ genomes according to Southern and slot blot analysis. This finding confirmed that the lack of AAVlacZ induction of chemokine was not due to reduced transduction. In DBA/2 mice, the intravenous administration of 2.5 x 10(11) particles of AAVlacZ resulted in the rapid induction of liver tumor necrosis factor alpha (TNF-alpha), RANTES, IP-10, MIP-1beta, MCP-1, and MIP-2 mRNAs. However, 6 h following injection, chemokine mRNA levels returned to baseline. As expected, administration of 10-fold less AdlacZ caused an induction of liver TNF-alpha and chemokine mRNAs that persisted for more than 24 h posttransduction. Whereas intravenous administration of 2.5 x 10(11) particles of AAVlacZ triggered a transient infiltration of neutrophils and CD11b(+) cells into liver, this response stood in contrast to widespread inflammation and toxicity induced by AdlacZ. Kupffer cell depletion abolished AAVlacZ but not AdlacZ-induced chemokine expression and neutrophil infiltration. In summary, these results show that AAV vectors activate the innate immune system to a lesser extent than do adenovirus vectors and offer a possible explanation for the reduced inflammatory properties of AAV compared to adenovirus vectors.

Adenovirus vector-induced inflammation: capsid-dependent induction of the C-C chemokine RANTES requires NF-kappa B.

Adenovirus vectors for gene therapy activate responses in the host that result in acute inflammation of transduced tissues. Our previous studies in vivo demonstrate that chemokines, including the C-C chemokine RANTES (regulated on activation, normal T cell expressed and secreted), contribute to the acute inflammation induced by adenovirus vectors. Various first-generation adenovirus vectors, including adCMV beta gal, were equally capable of inducing the expression of RANTES 3 hr after transduction in epithelial HeLa and REC cells. Deletional analysis of the human RANTES promoter revealed that induction by adCMV beta gal required the elements spanning base pairs -90 to -25 of the gene. Electrophoretic mobility shift assays demonstrated that nuclear extracts from adCMV beta gal-transduced HeLa cells bound to an NF-kappa B site at position -54. Overexpression of I-kappa B alpha suppressed adCMV beta gal induction of RANTES, confirming that this process was dependent on the nuclear translocation of NF-kappa B. The coxsackievirus-adenovirus receptor (CAR)-independent, serotype 3 adenovirus was equally capable of inducing the expression of RANTES in HeLa cells. This observation suggested that binding to CAR was not specifically required in adenovirus vector-induced RANTES expression. The use of RGD peptides to block adCMV beta gal interactions with alpha(v)-integrins reduced RANTES expression but also transduction efficiency. In CAR-deficient P815 cells, binding of adCMV beta gal to alpha(v)-integrins without efficient cell transduction did not result in increased RANTES expression. Expression of human CAR in P815 cells increased the binding and transduction efficiency of adCMV beta gal and resulted in RANTES expression in these cells. These results suggest that the induction of RANTES by adenovirus vectors is dependent on efficient interaction with its cell surface receptors and vector internalization. Understanding the biology of the host response to adenovirus vectors will impact the design of future generations of these agents aimed at reducing their immunogenicity and improving their safety.

Activation of p38 and ERK signaling during adenovirus vector cell entry lead to expression of the C-X-C chemokine IP-10.

The use of adenovirus vectors for human gene therapy is limited by potent inflammatory responses that result in significant morbidity. In kidney-derived epithelial cells (REC), activation of extracellular signal-regulated kinase 1/2 (ERK) and p38 kinase (p38) pathways occurred within 20 min of transduction with the serotype 5 adenovirus vector AdCMV beta gal. Inhibition of ERK and p38 with U0126 and SB203580, respectively, reduced the expression of IP-10 mRNA following transduction with AdCMV beta gal. To determine the role of the coxsackievirus-adenovirus receptor (CAR) or alpha(v) integrins in the activation of ERK and p38 and the expression of IP-10, REC cells were transduced with the fiber-modified and RGD-deleted adenovirus vectors AdL.F(RAEK-HA) and AdL.PB(HA), respectively. Compared with the wild-type capsid vector Ad5Luc, transduction with AdL.F(RAEK-HA) and AdL.PB(HA) resulted in reduced ERK-p38 activation and less IP-10 mRNA expression. The decreased IP-10 expression induced by the tropism-modified vectors was due to diminished transduction, since increasing multiplicity of infection resulted in increased IP-10 expression. Inhibition of adenovirus penetration with bafilomycin A1 or ammonium chloride attenuated the activation of ERK-p38 and IP-10 mRNA expression following infection, suggesting that endosomal escape was required to trigger these pathways. In vivo, direct inhibition of ERK and p38 signaling pathways inhibited adenovirus vector-induced IP-10 expression in mouse liver 1 h following transduction. These results demonstrate the importance of signaling via ERK and p38 in the early host response to adenovirus vectors and will permit the development of novel strategies to improve the safety and efficacy of these agents in human gene therapy.