Abstracts (complete list) - Wissenschaft Online

Marcin Wlodarski, Zachary Nearman, Alan Lichtin, Hans-Dieter Volk, Jaroslaw
Maciejewski
IMMUNODOMINANT CYTOTOXIC T LYMPHOCYTE EXPANSIONS
IN PATIENTS WITH UNEXPLAINED NEUTROPENIA.
Some cases of idiopathic neutropenia (IN) may result from a T cell-mediated immune
attack directed against myeloid progenitors. Unlike in large granular lymphocyte
leukemia (LGL) that is characterized by highly skewed chronic lymphoproliferation,
cytotoxic T-cell (CTL) expansions in IN may not be discovered using traditional
laboratory tools. We hypothesized that a precise T-cell receptor (TCR) repertoire
analysis may uncover CTL expansions in IN that are pathophysiologicaly analogous to
those seen in large granular lymphocyte leukemia (LGL) and thus can serve as markers
for CTL mediated process.
We previously established algorithms for TCR analysis and in-vivo tracking of CTL
responses that include TCR variable beta (VB) phenotyping followed by subcloning of
TCR-VB families and clonotypic sequencing, or multiplex VB-PCR and sequencing of the
entire VB repertoire. For quantitative clonotype tracking we introduced a novel
clonotypic Taqman-PCR that allows for a very precise detection of patient-specific TCR
VB chains. Using this approach we studied patients with neutropenia: 12/20 displayed
CTL expansions that were less dominant than those detectable in LGL but clearly
distinguishable from subclinical CTL expansions in healthy controls. As a surrogate of
cytotoxic activity, we found markedly increased production of interferon-G in most
patients irrespective of the presence of immunodominant CTL clones.
These results suggest that while CTL clonalities are detectable only in a proportion of
patients, cytotoxic pathophysiology may be a general mechanism in idiopathic
neutropenia and immunodominant expansions indicate an autoimmune process.
Conversely, highly polarized responses in a subset of neutropenic LGL patients may
represent the “extreme” end of the clonal continuum.