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Date of Award
Doctor of Philosophy (PhD)
Human T-cell leukemia virus type 1 (HTLV-1) is the etiologic agent of the malignancy adult Tcell leukemia (ATL), a malignancy for which there is no effective therapy. Drugs targeting the viral enzyme integrase have been in use for several years as part of the treatment regimen for patients with human immunodeficiency virus type 1 (HIV-1), and similar classes of compounds have been shown to inhibit human T-cell leukemia virus type 1 (HTLV-1) integration in vitro. The purpose of the studies described in this thesis was to investigate the changes in HTLV-1 genomic integration sites during ATL progression in vivo and the role of inhibitors of the viral integrase on HTLV-1 infectivity in vitro. We also wanted to deepen our understanding of the role of interferon on HTLV-1 production in vitro by determining the effect of the interferonstimulated gene product ISG15 on HTLV-1 production in vitro.
As part of our analysis of integration sites, we used 454 high throughput sequencing to analyze DNA from a total of 9 ATL patients of which 3 displayed no change in viral RNA, 5 patients showed increasing viral RNA and 1 patient received no therapy and showed prolonged stable disease but subsequent progression. Our study compared integration site preferences across time points from patients in each category. For each patient sample, we were able to ix identify integration sites at baseline and compare them with those present at the time of disease progression. The data showed significant differences between integration sites at baseline and at the time of disease progression. Seven out of nine patients demonstrated an increase in the number of integration sites at progression time points, compared to baseline samples. In one patient, at the start of treatment, only two integration sites were detected, but 6 weeks into the chemotherapy regimen, 40 completely new integration sites were identified.
Our work on integrase inhibitors demonstrated that the anti-HIV-1 drug, raltegravir, which is clinically approved for patients with this virus, as well as the more recent diketo acid derivative, MK-2048, are active inhibitors of HTLV-1 infection in vitro. These agents were effective in inhibiting cell-free and cell-to-cell transmission of HTLV-1 in lymphoid and nonlymphoid cells. The drugs also inhibited HTLV-1 immortalization of human peripheral blood mononuclear cells. We utilized a novel adaptation of the Alu assay for viral integration to show that the drugs inhibit viral integration without affecting reverse transcription. These data support the administration of raltegravir and other integrase inhibitors as treatments for patients with HTLV-1-associated diseases.
We also demonstrated that the interferon-stimulated protein, ISG15, is a host restriction factor that inhibits late stages of the HTLV-1 viral life cycle. ISG15 was able to mediate this antiviral effect in its free form, in contrast to its action in HIV-1-infected cells, which requires coordinate action of ISG15 and an ubiquitin-like conjugation system of proteins. The data presented in this thesis provide novel insights into the mechanisms by which HTLV-1 may be acting to cause disease progression in infected individuals. Taken together, x these data will lead to a better understanding of the molecular mechanisms underlying HTLV-1 infection and will advance therapeutic options for patients with HTLV-1 associated diseases.
Chair and Committee
Timothy Graubert, Deborah Lenschow, Jason Weber, Katherine Weilbaecher, Zhongsheng You
Seegulam, Muhammad Esa, "Mechanism of Action of Anti-Human T-Cell Leukemia Virus Therapy Directed at Integration and Virus Assembly" (2013). Arts & Sciences Electronic Theses and Dissertations. 1040.
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