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Genes 2017, 8(2), 79; doi:10.3390/genes8020079

Transgene Expression and Host Cell Responses to Replication-Defective, Single-Cycle, and Replication-Competent Adenovirus Vectors

Virology and Gene Therapy Graduate Program, Mayo Graduate School, Rochester, MN 55905, USA
La Jolla Institute for Allergy and Immunology, La Jolla, CA 92037, USA
Department of Medicine, Division of Infectious Diseases, Mayo Clinic, Rochester, MN 55905, USA
Department of Immunology, Mayo Clinic, Rochester, MN 55905, USA
Department of Molecular Medicine, Mayo Clinic, Rochester, MN 55905, USA
Author to whom correspondence should be addressed.
Academic Editor: Selvarangan Ponnazhagan
Received: 8 December 2016 / Revised: 3 February 2017 / Accepted: 7 February 2017 / Published: 18 February 2017
(This article belongs to the Special Issue Gene Therapy)
View Full-Text   |   Download PDF [3384 KB, uploaded 18 February 2017]   |  


Most adenovirus (Ad) vectors are E1 gene deleted replication defective (RD-Ad) vectors that deliver one transgene to the cell and all expression is based on that one gene. In contrast, E1-intact replication-competent Ad (RC-Ad) vectors replicate their DNA and their transgenes up to 10,000-fold, amplifying transgene expression markedly higher than RD-Ad vectors. While RC-Ad are more potent, they run the real risk of causing adenovirus infections in vector recipients and those that administer them. To gain the benefits of transgene amplification, but avoid the risk of Ad infections, we developed “single cycle” Ad (SC-Ad) vectors. SC-Ads amplify transgene expression and generated markedly stronger and more persistent immune responses than RD-Ad as expected. However, they also unexpectedly generated stronger immune responses than RC-Ad vectors. To explore the basis of this potency here, we compared gene expression and the cellular responses to infection to these vectors in vitro and in vivo. In vitro, in primary human lung epithelial cells, SC- and RC-Ad amplified their genomes more than 400-fold relative to RD-Ad with higher replication by SC-Ad. This replication translated into higher green fluorescent protein (GFP) expression for 48 h by SC- and RC-Ad than by RD-Ad. In vitro, in the absence of an immune system, RD-Ad expression became higher by 72 h coincident with cell death mediated by SC- and RC-Ad and release of transgene product from the dying cells. When the vectors were compared in human THP-1 Lucia- interferon-stimulated gene (ISG) cells, which are a human monocyte cell line that have been modified to quantify ISG activity, RC-Ad6 provoked significantly stronger ISG responses than RD- or SC-Ad. In mice, intravenous or intranasal injection produced up to 100-fold genome replication. Under these in vivo conditions in the presence of the immune system, luciferase expression by RC and SC-Ad was markedly higher than that by RD-Ad. In immunodeficient mice, SC-Ad drove stronger luciferase expression than RC- or RD-Ad. These data demonstrate better transgene expression by SC- and RC-Ad in vitro and in vivo than RD-Ad. This higher expression by the replicating vectors results in a peak of expression within 1 to 2 days followed by cell death of infected cells and release of transgene products. While SC- and RC-Ad expression were similar in mice and in Syrian hamsters, RC-Ad provoked much stronger ISG induction which may explain in part SC-Ad′s ability to generate stronger and more persistent immune responses than RC-Ad in Ad permissive hamsters. View Full-Text
Keywords: adenovirus; replication-competent; replication-defective; vaccines; cancer therapy; genome replication; animal models adenovirus; replication-competent; replication-defective; vaccines; cancer therapy; genome replication; animal models

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Crosby, C.M.; Barry, M.A. Transgene Expression and Host Cell Responses to Replication-Defective, Single-Cycle, and Replication-Competent Adenovirus Vectors. Genes 2017, 8, 79.

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