Graduation Date

Summer 8-13-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Programs

Pathology & Microbiology

First Advisor

Javeed Iqbal

Abstract

Peripheral T-cell Lymphoma (PTCL) consists of numerous distinct disease entities. With the current diagnostic criteria over a third of the cases cannot be further classified and are called "not otherwise specified" (PTCL-NOS). Using gene expression profiling (GEP) of tumors, we identified two novels PTCL-NOS molecular subgroups either characterized by high expression of GATA3 (33%), which is associated with Th2 cell differentiation, or high expression of TBX21 (49%) which regulates Th1 cell maturation. Therefore, stratifying patients for diagnosis and identifying the underlying genetic basis to improve clinical therapy becomes critical to prognosis.

First, we performed DNA copy number analysis by using the OncoScan® platform, which revealed recurrent chromosomal imbalances are highly discordant between PTCL-GATA3 and PTCL-TBX21. Triple-deletion of TP53;PTEN;CDKN2A has been detected in 23% verse 0% in PTCL-GATA3 and PTCL-TBX21, contributing inferior overall survival (OS) in this group. Most interestingly, a distinct molecular subtype characterized by heterozygous loss of TP53 and PTEN accounts for 35% in PTCL-GATA3, with hot-spot TP53R175H mutation identified to contributes to the dysfunction of TP53 signaling.

Second, to evaluate the role of TP53 and PTEN in T-cell lymphomagenesis, we disrupted p53 and/or Pten with the Cre-loxP system, which induced p53R172H mutation and Pten deletion specifically in CD4+ T cells. Impaired T-cell development was observed due to p53;Pten deficiency. Acute loss of p53;Pten results in SP CD4+ T cell and DN T cell lymphoma between 8-24.6 weeks after birth. In contrast, long-term p53; Pten deficiency characterized by markedly pleomorphic morphology at a latency of 27.7-89.1 weeks after birth. Strikingly, the predominant subset of heterozygous loss of p53;Pten tumor-bearing mice committed to a CD8+ immunophenotype.

To characterize the T-cell biology of p53;Pten deficiency, functional characterization of 4-week old age CD4+ splenocytes were isolated from 6 genotypes of mice for all the in vitro studies. As expected, p53R172Hswitches CD4+ T cells from arrest into proliferation in the context of Pten-deficiency in an antigen-dependent and independent manner. Strikingly, we found the dose of Pten dictates cell growth by regulation of apoptotic cell death. We also demonstrated that IL-2 is not required for initial expansion, but is required for the long-term survival of primed T cells in vitro. Besides, heterozygous loss of p53 and Pten has more capacity to skew naïve CD4+ T cells into Th2 phenotypes. Lastly, we also observed that cell-intrinsic programming by genetic alterations imparts affects the differential engraftment fitness after adoptive transfer.

Available for download on Friday, June 16, 2023

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