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U.S. Department of Health and Human Services

Vaccines, Blood & Biologics

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Viral Safety Studies in Xenotransplantation and Gene Therapy Products

Principal Investigator: Carolyn A. Wilson, PhD
Office / Division / Lab: OCTGT / DCGT / GTIB

General Overview

Gammaretroviruses are simple animal viruses that are related to HIV, the cause of AIDS.

These viruses might pose risks in several regulated biologics products, both as contaminants and in their use for gene therapy, in which they act as carriers, or "vectors" to deliver genes that treat a disease by producing a therapeutic molecule. For example, a derivative of a mouse gammaretrovirus was used for gene therapy given to children in two clinical trials in Europe for X-linked Severe Combined Immunodeficiency Disease (X-SCID, more commonly known as the "Bubble Boy Disease"). Although this therapy appeared to provide clinical benefit to most of the children, some patients developed the blood cancer leukemia. This demonstrated that these animal viruses can cause disease in humans, although except for the X-SCID clinical trials, gammaretroviruses used for gene therapy have not caused cancer.

In addition, pig gammaretroviruses are potential contaminants in some other products, such as proteins derived from pig plasma. These viruses are of particular concern in xenotransplantation products, that is, the use of living cells, tissues, or organs for treatment of human disease.

We study the gammaretrovirus porcine endogenous retrovirus (PERV), which occurs in all pigs. Using molecular biology, tissue culture, and animal models, we study the conditions that affect virus infection and transmission, especially those factors that influence the ability of PERV to infect human cells. The goal of this work is to develop methods for preventing transmission of PERV, as well as to generate data that guides regulatory policies for effectively screening animals, xenotransplantation products obtained from those animals, and recipients of those products, for risk of PERV transmission.

Through a collaborative program with the National Toxicology Program, our laboratory is also in the process of assessing preclinical models that may prove useful for assessing the tumorigenic potential of retroviral vectors.

In addition to our studies on gammaretroviruses, our laboratory uses retroviral vector technology to study a CDC Category A potential agent of bioterrorism, Ebola virus (an agent of viral hemorrhagic fever). Category A agents are high-priority agents considered to pose a major threat to national security. We are trying to identify regions of the Ebola virus envelope that are highly conserved (do not readily mutate from generation to generation) and critical for infection. Based on that information we will try to develop antiviral or vaccine strategies that can protect against a broad range of varieties of the Ebola virus.

Scientific Overview

Our laboratory is primarily interested in studying the host and cellular determinants of viral entry for porcine endogenous retroviruses (PERV). PERV is a gammaretrovirus found in the genome of pigs and at least two types of PERV (PERV-A and PERV-B) can infect human cells, while PERV-C is pig-tropic. We use retroviral vectors carrying chimeric or mutated PERV envelopes to study the sequences on the PERV envelope required for viral entry. In addition, we are studying the PERV-A receptor on both permissive and non-permissive host cells to improve our understanding of the cellular factors that influence the human tropism of PERV.

In addition, we are involved in a study sponsored by the National Toxicology Program aimed at identifying the best preclinical model to assess tumorigenic potential of retroviral vectors. The study is designed to use large group sizes in order to gain statistical confidence in the sensitivity of the model for detecting tumorigenic events. The study will be performed in several phases in order to allow for in vivo assessment of various types of retroviral vectors (gammaretrovirus, lentivirus, and spumavirus), each with an assortment of backbone configurations that will allow determination of the tumorigenic impact of various vector modifications, such as presence or absence of the retroviral U3, internal enhancer elements, etc.

Finally, our laboratory has recently become interested in studying the category A agent, Ebolavirus. We are trying to identify highly conserved regions that are critical for entry in order to determine if these regions would make good antiviral or vaccine targets.


Virology 2014 Nov 27;475:110-9
Mutations altering the gammaretrovirus endoproteolytic motif affect glycosylation of the envelope glycoprotein and early events of the virus life cycle.
Argaw T, Wilson CA

PDA J Pharm Sci Technol 2014 Nov-Dec;68(6):626-30
FDA's Activities Supporting Regulatory Application of "Next Gen" Sequencing Technologies.
Wilson CA, Simonyan V

J Virol 2012 Sep;86(17):9096-104
Detailed mapping of determinants within the porcine endogenous retrovirus envelope surface unit identifies critical residues for human cell infection within the proline-rich region.
Argaw T, Wilson CA

Virology 2012 Jun 5;427(2):118-26
Comparison of the convergent receptor utilization of a retargeted feline leukemia virus envelope with a naturally-occurring porcine endogenous retrovirus A.
Mazari PM, Argaw T, Valdivieso L, Zhang X, Marcucci KT, Salomon DR, Wilson CA, Roth MJ

Virol J 2012 Jan 25;9:32
Induction of ebolavirus cross-species immunity using retrovirus-like particles bearing the Ebola virus glycoprotein lacking the mucin-like domain.
Ou W, Delisle J, Jacques J, Shih J, Price G, Kuhn JH, Wang V, Verthelyi D, Kaplan G, Wilson CA

J Virol Methods 2011 Jun;174(1-2):99-109
Development and characterization of rabbit and mouse antibodies against ebolavirus envelope glycoproteins.
Ou W, Delisle J, Konduru K, Bradfute S, Radoshitzky SR, Retterer C, Kota K, Bavari S, Kuhn JH, Jahrling PB, Kaplan G, Wilson CA

Virology 2010 Jan 5;396(1):135-42
Phenylalanines at positions 88 and 159 of Ebolavirus envelope glycoprotein differentially impact envelope function.
Ou W, King H, Delisle J, Shi D, Wilson CA

Retrovirology 2009 Jan 14;6:3
Identification of two distinct structural regions in a human porcine endogenous retrovirus receptor, HuPAR2, contributing to function for viral entry.
Marcucci KT, Argaw T, Wilson CA, Salomon DR

Methods Mol Biol 2009;506:477-88
The US and EU regulatory perspectives on the clinical use of hematopoietic stem/progenitor cells genetically modified ex vivo by retroviral vectors.
Wilson CA, Cichutek K

Cell Mol Life Sci 2008 Nov;65(21):3399-412
Porcine endogenous retroviruses and xenotransplantation.
Wilson CA

J Virol 2008 Aug;82(15):7483-91
Identification of residues outside of the receptor binding domain that influence infectivity and tropism of porcine endogenous retrovirus.
Argaw T, Figueroa M, Salomon DR, Wilson CA

Virology 2008 Jun 5;375(2):637-45
Functional hierarchy of two L domains in porcine endogenous retrovirus (PERV) that influence release and infectivity.
Marcucci KT, Martina Y, Harrison F, Wilson CA, Salomon DR

Xenotransplantation 2007 Jul;14(4):309-15
No evidence of PERV infection in healthcare workers exposed to transgenic porcine liver extracorporeal support.
Levy MF, Argaw T, Wilson CA, Brooks J, Sandstrom P, Merks H, Logan J, Klintmalm G

Virus Res 2006 Nov;121(2):205-14
Identification of two amino acid residues on Ebola virus glycoprotein 1 critical for cell entry.
Mpanju OM, Towner JS, Dover JE, Nichol ST, Wilson CA

J Virol 2006 Apr;80(7):3135-46
Mice transgenic for a human porcine endogenous retrovirus receptor are susceptible to productive viral infection.
Martina Y, Marcucci KT, Cherqui S, Szabo A, Drysdale T, Srinivisan U, Wilson CA, Patience C, Salomon DR

Virology 2006 Mar 5;346(1):108-17
The infectivity and host range of the ecotropic porcine endogenous retrovirus, PERV-C, is modulated by residues in the C-terminal region of its surface envelope protein.
Gemeniano M, Mpanju O, Salomon DR, Eiden MV, Wilson CA

Am J Transplant 2005 Aug;5(8):1837-47
Pseudotyping of porcine endogenous retrovirus by xenotropic murine leukemia virus in a pig islet xenotransplantation model.
Martina Y, Kurian S, Cherqui S, Evanoff G, Wilson C, Salomon DR

Mol Ther 2004 Dec;10(6):976-80
Workshop on long-term follow-up of participants in human gene transfer research.
Nyberg K, Carter BJ, Chen T, Dunbar C, Flotte TR, Rose S, Rosenblum D, Simek SL, Wilson C

J Gen Virol 2004 Jan;85(Pt 1):15-9
Limited infection without evidence of replication by porcine endogenous retrovirus in guinea pigs.
Argaw T, Colon-Moran W, Wilson CA


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