Vaccines, Blood & Biologics

Safety and Effectiveness of Gene Therapy

Principal Investigator: Andrew Byrnes, PhD
Office / Division / Lab: OCTGT / DCGT / GTIB

General Overview

Gene therapy holds great promise for treating cancer, inherited disorders, and other diseases. Gene therapy, also often referred to as 'gene transfer,' uses carriers called 'vectors' to deliver genes to tissues where they are needed. The genes in gene therapy vectors code for specific proteins that may treat disease. Gene therapy vectors can be engineered to produce a variety of therapeutic proteins, and researchers are investigating the safety and effectiveness of a variety of different types of vectors in hundreds of clinical trials in the US.

We are studying one type of commonly-used gene therapy vector that is made from a disabled cold virus -- the adenovirus vector. While adenovirus vectors are very efficient at delivering genes, adenovirus vectors can cause toxic effects that limit the amount of vector that doctors can give to patients. We are particularly interested in how to safely deliver large amounts of adenovirus vectors intravenously, with the goal of targeting tumors and other tissues. Another of our major goals is to develop animal models that reliably predict the safety and effectiveness of adenovirus vectors in humans.

Our lab and others have shown that when adenovirus vectors are injected intravenously, cells in the liver called Kupffer cells rapidly ingest and dispose of them. This not only prevents the vector from reaching its intended tissue but also kills the Kupffer cells themselves, damaging the liver. We are studying how Kupffer cells recognize adenovirus and how adenovirus kills these cells. In addition, we are trying to improve adenovirus gene therapy by preventing Kupffer cells from removing vector from the circulation. Our laboratory is also studying how both non-animal and animal models can be used to predict whether particular adenoviruses can be safely used in humans. New adenovirus gene therapy vectors are tested in animals before human clinical trials begin, and it is important for both researchers and the FDA to know how well these animal studies can predict safety.

Our studies will help us to understand the mechanisms for adenovirus vector removal by Kupffer cells, the resulting damage to liver, and the relevance of animal models to human outcomes. This new knowledge will enable researchers to design safer and more effective gene therapy vectors.

Scientific Overview

Adenovirus vectors have shown considerable promise in animal models and are currently being used in numerous clinical trials, especially for the therapy of cancer. We are interested in improving the safety and efficacy of adenovirus vectors, especially when administered through the vascular system. Certain properties of adenovirus vectors make them hazardous to administer intravenously in large doses, and our laboratory is trying to understand and fix this problem.

One of our major areas of interest is the innate immune response to adenovirus vectors. These rapid responses can cause serious toxicity and may severely limit the doses of adenovirus vectors that are safe to use. In addition, we are also studying how cells in the liver recognize adenovirus, since this is the major site of adenovirus removal from the circulation. A better understanding of these mechanisms will help us to develop strategies to improve vector efficacy and reduce toxicity. We will also gain a better understanding of the advantages and disadvantages of using different species of animals to predict the behavior of adenovirus vectors in humans, which is particularly relevant to the regulatory work of the FDA.

Our research on vector biodistribution is focused on how Kupffer cells and other liver cells recognize adenoviruses after they are injected intravenously. We are also interested in how adenovirus vectors interact with blood proteins, and how this in turn influences the clearance of vector by the liver. We recently showed that both scavenger receptors on Kupffer cells and natural antibodies in the blood contribute to the clearance of adenovirus vectors by Kupffer cells. We are currently studying how natural antibodies interact with adenovirus.

Our research on the innate immune response to adenovirus vectors includes not just studies on cytokine and chemokine responses, but also some less well-studied (but no less important) mediators. We have recently characterized the roles of complement and platelet activating factor and discovered how adenovirus vectors activate these two pathways. One particularly interesting finding is that the mechanisms of complement activation in animal models are completely different from the mechanisms that occur in in vitro studies. This unexpected observation has significant implications for how we should model adenovirus interactions with the complement system. Another interesting finding is that high doses of adenovirus vectors rapidly induce a burst of platelet activating factor in vivo that can lead to shock. As part of this work we showed that there are practical ways to block the effects of platelet activating factor and reduce toxicity due to this pathway.

Currently we are studying additional novel mediators and pathways that control innate immune responses, and how this contributes to toxicity caused by adenovirus vectors. Understanding these mediators and pathways is an essential step toward our goal of developing safer vectors and new ways to limit vector-induced toxicity.


Methods Mol Biol 2017;1643:187-96
Evaluating the impact of natural IgM on adenovirus Type 5 gene therapy vectors.
Xu Z, Tian J, Harmon AW, Byrnes AP

J Control Release 2016 Aug 10;235:379-92
Substitution of blood coagulation factor X-binding to Ad5 by position-specific PEGylation: Ppeventing vector clearance and preserving infectivity.
Krutzke L, Prill JM, Engler T, Schmidt CQ, Xu Z, Byrnes AP, Simmet T, Kreppel F

J Virol 2015 Mar 15;89(6):3412-6
Impact of natural IgM concentration on gene therapy with adenovirus type 5 vectors.
Qiu Q, Xu Z, Tian J, Moitra R, Gunti S, Notkins AL, Byrnes AP

Nat Med 2013 Apr;19(4):452-7
Coagulation factor X shields adenovirus type 5 from attack by natural antibodies and complement.
Xu Z, Qiu Q, Tian J, Smith JS, Conenello GM, Morita T, Byrnes AP

J Virol 2013 Apr;87(7):3678-86
Circulating antibodies and macrophages as modulators of adenovirus pharmacology.
Khare R, Hillestad ML, Xu Z, Byrnes AP, Barry MA

PDA J Pharm Sci Technol 2011 Nov 1;65(6):660-2
Breakout session C summary: current virus detection methods.
Byrnes AP, Willkommen H

PLoS One 2011;6(10):e26755
The role of endosomal escape and mitogen-activated protein kinases in adenoviral activation of the innate immune response.
Smith JS, Xu Z, Tian J, Palmer DJ, Ng P, Byrnes AP

Mol Ther 2010 Mar;18(3):609-16
Induction of shock after intravenous injection of adenovirus vectors: a critical role for platelet-activating factor.
Xu Z, Smith JS, Tian J, Byrnes AP

J Virol 2009 Jun;83(11):5648-58
Adenovirus activates complement by distinctly different mechanisms in vitro and in vivo: indirect complement activation by virions in vivo.
Tian J, Xu Z, Smith JS, Hofherr SE, Barry MA, Byrnes AP

Neuroreport 2008 Aug 6;19(12):1187-92
Th1 cytokines are upregulated by adenoviral vectors in the brains of primed mice
Lee MB, McMenamin MM, Byrnes AP, Charlton HM, Wood MJA

Hum Gene Ther 2008 May;19(5):547-54
Interaction of Systemically Delivered Adenovirus Vectors with Kupffer Cells in Mouse Liver.
Smith JS, Xu Z, Tian J, Stevenson SC, Byrnes AP

J Virol Methods 2008 Jan;147(1):54-60
A quantitative assay for measuring clearance of adenovirus vectors by Kupffer cells.
Smith JS, Xu Z, Byrnes AP

Genomics 2006 Apr;87(4):552-9
Quality prediction of cell substrate using gene expression profiling.
Han J, Farnsworth RL, Tiwari JL, Tian J, Lee H, Ikonomi P, Byrnes AP, Goodman JL, Puri RK

Virology 2006 Mar 30;347(1):183-90
Heparin-binding and patterns of virulence for two recombinant strains of Sindbis virus.
Bear JS, Byrnes AP, Griffin DE

IDrugs 2005 Dec;8(12):993-6
Challenges and future prospects in gene therapy.
Byrnes AP

Mol Ther 2006 Jan;13(1):108-17
Rapid Kupffer cell death after intravenous injection of adenovirus vectors.
Manickan E, Smith JS, Tian J, Eggerman TL, Lozier JN, Muller J, Byrnes AP


Contact FDA

(800) 835-4709
(240) 402-8010
Consumer Affairs Branch (CBER)

Division of Communication and Consumer Affairs

Office of Communication, Outreach and Development

Food and Drug Administration

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Building 71 Room 3103

Silver Spring, MD 20993-0002

Page Last Updated: 09/15/2017
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