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Journal of Virology, December 2005, p. 14473-14481, Vol. 79, No. 23
0022-538X/05/$08.00+0     doi:10.1128/JVI.79.23.14473-14481.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Human T-Cell Leukemia Virus Type 1 Expressing Nonoverlapping Tax and Rex Genes Replicates and Immortalizes Primary Human T Lymphocytes but Fails To Replicate and Persist In Vivo

Ihab Younis,^1,3,4 Brenda Yamamoto,^1,3,4 Andrew Phipps,^1,3,4 and Patrick L. Green^1,2,3,4*

Departments of Veterinary Biosciences,¹ Molecular Virology, Immunology, and Medical Genetics,² Center for Retrovirus Research,³ Comprehensive Cancer Center and Solove Research Institute, The Ohio State University, Columbus, Ohio 43210⁴

Received 5 May 2005/ Accepted 9 September 2005

Human T-cell leukemia virus type 1 (HTLV-1) is an oncogenic retrovirus associated primarily with adult T-cell leukemia and neurological disease. HTLV-1 encodes the positive trans-regulatory proteins Tax and Rex, both of which are essential for viral replication. Tax activates transcription initiation from the viral long terminal repeat and modulates the transcription or activity of a number of cellular genes. Rex regulates gene expression posttranscriptionally by facilitating the cytoplasmic expression of incompletely spliced viral mRNAs. Tax and Rex mutants have been identified that have defective activities or impaired biochemical properties associated with their function. To ultimately determine the contribution of specific protein activities on viral replication and cellular transformation of primary T cells, mutants need to be characterized in the context of an infectious molecular clone. Since the tax and rex genes are in partially overlapping reading frames, mutation in one gene frequently disrupts the other, confounding interpretation of mutational analyses in the context of the virus. Here we generated and characterized a unique proviral clone (H1IT) in which the tax and rex genes were separated by expressing Tax from an internal ribosome entry site. We showed that H1IT expresses both functional Tax and Rex. In short- and long-term coculture assays, H1IT was competent to infect and immortalize primary human T cells similar to wild-type HTLV-1. In contrast, H1IT failed to efficiently replicate and persist in inoculated rabbits, thus emphasizing the importance of temporal and quantitative regulation of specific mRNA for viral survival in vivo.

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* Corresponding author. Mailing address: The Ohio State University, 1925 Coffey Road, Columbus, OH 43210. Phone: (614) 688-4899. Fax: (614) 292-6473. E-mail: green.466{at}osu.edu.

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Journal of Virology, December 2005, p. 14473-14481, Vol. 79, No. 23
0022-538X/05/$08.00+0     doi:10.1128/JVI.79.23.14473-14481.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

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