Date of Award

January 2011

Document Type

Open Access Thesis

Degree Name

Medical Doctor (MD)

Department

Medicine

First Advisor

Richard L. Edelson

Subject Area(s)

Medicine

Abstract

Background: Cutaneous T-cell lymphoma (CTCL) is a rare malignancy of the skin and fatal if untreated. The mid 1980s introduction of molecular tests for clonality revolutionized the capacity to diagnose the disease. Polymerase chase reaction (PCR) is now routinely performed on blood and involved skin to detect clonal T-cell receptor (TCR) gene rearrangements. It has been widely assumed that CTCL arises from a monoclonal T-cell population. Detection of one or two uniform γTCR gene rearrangement sequences is expected, depending on whether one or both alleles have undergone rearrangement in the original tumor progenitor cell. However, three or more clonal sequences are sometimes detected, and thus far no clear explanation for this finding has been offered. Clarification of the mechanism responsible for these multiple monoclonal populations is a prerequisite to the understanding of the pathogenesis of CTCL and for appropriate application of PCR determinations in the diagnosis and management of CTCL.

Objective: To elucidate the origin of γTCR gene rearrangements in CTCL tissues of single patients in which more than two clonal γTCR gene rearrangements have been detected by PCR and to determine if CTCL consists of a polyclonal T-cell population.

Methods: PCR of the γTCR genes was performed using DNA from a skin specimen showing high grade CTCL with three apparent clonal γTCR rearrangements. The amplified products were separated by gel electrophoresis, molecularly cloned in bacteria, and subjected to sequence analysis.

Results: Sequence analysis of the molecularly cloned PCR products revealed one clonal Vγ9,10 TCR gene rearrangement (184 base pair fragment) and two clonal Vγ1-8 TCR gene rearrangements (234 and 237 base pair fragments). The sequences of the two Vγ1-8 rearrangements were 86% similar. The Vγ9,10 sequence was 17% similar to the 234 base pair Vγ1-8 sequence and 19% similar to the 237 base pair Vγ1-8 sequence.

Conclusion: The dissimilarity in DNA sequences among the three rearranged clonal γTCR rearrangements suggests that either more than one T-cell clone is present in this patient's CTCL or that CTCL in this patient arose from a progenitor cell in which both γTCR alleles had not yet undergone rearrangement. This case is illustrative of the importance of understanding the complexities of tests for T-cell clonality, rather than expecting a simple positive or negative "malignancy" answer.

Comments

This is an Open Access Thesis.

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