Download Autoreactive Memory Stem T Cells in Type 1

2014 Research Grant Program Winning Abstract
Autoreactive Memory Stem T Cells in Type 1 Diabetes
By Paolo Monti
Type 1 diabetes (T1D) results from a chronic autoimmune destruction of insulinproducing pancreatic beta cells. It is now widely accepted that autoreactive T cells play
an important role in the pathogenesis of the disease. Consequently, T cells are also
major targets of immunomodulatory strategies that aim to prevent or delay the immune
mediated loss of islet beta cell function. These strategies have had modest success,
prompting efforts into better defining the mechanisms that drive differentiation of
quiescent naive autoreactive clones into pathogenic effector and memory T cells.
Autoreactive T cells in patients with T1D display characteristics of cells that have already
encountered their cognate antigen, including proliferation to lower antigen concentration
or in the absence of costimulatory signals, reduced telomere length, and the presence of
specific late activation and memory markers. Memory stem T cells (Tscm) represent a
novel subset of long-lived memory T cells with the ability of self-renewal and the
plasticity to differentiate into potent effectors. The Tscm subset initially described in mice
and subsequently in man, was shown to play an important role is sustaining long-term
chronic T cell responses to infections and cancer. Tscm can be distinguished from other
T cell subset through a core set of surface markers including CD62L, CCR7, IL-2Rbeta,
CD95 and CD45RA.
The objective of this proposal is to determine whether autoreactive T cells with a Tscm
phenotype are present in patients with T1D.
To address this point, we designed a 12 parameter flow cytometry panel to be used on a
4 laser equipped BD LSRFortessa™. The panel will allow to identify CD8+ GAD65
specific clones by staining with HLA-A*0201-GAD65114-122 pentamers (Proimmune)
and to determine their relative frequency within the CD3+CD8+ naïve (Tn, CD45RA,
+CCR7+), Tcm (CD45RA-, CCR7+), Tem (CD45RA-, CCR7-), Temra (CD45RA+,
CCR7-) and Tscm (CD45RA+ CCR7+, CD122+, CD95+) subsets. The following BD
antibodies will be used (marker-fluorochrome): CCR-7-BUV395, CD95-FITC, CD122-PE,
CXCR4-Pe-Cy5.5, CD45RA-PE-Cy7, CD3-APC-Cy7, CD8-BV500, CD4 Pacific Blue. In
addition to surface markers, the live/dead UV kit (Invitrogen) and APC labelled HLAA*0201GAD65114-122 pentamers will be used for staining.
As samples we will use we will use 68 subjects already stored in our repository. These
include 35 patients with recent onset (<6 months) type 1 diabetes (median age, 14 years;
range, 8-29 years; 18 males) 13 autoantibody positive at risk subjects (median age, 18
years; range 2-42 years; 5 males), and 20 healthy control subjects (median age, 15.6
years; range 7-40 years; 9 males). We require at least 20 million PBMC per sample. The
direct identification of GAD65 specific T cells with fluorescent pentamers can be
performed on patients expressing the HLA-A*0201 allele. Our study samples were
selected for the expression of the HLA-A*0201 allele.
We do acknowledge that there may be limitations related to precursor frequency of
autoreactive T cells. In direct staining with fluorescent pentamers the precursor
frequency of antigen specific T cells is expected to be between 10-100 per million CD8 T
cells. Considering that the relative proportion of Tscm in CD4+ and CD8+ T cells is
around 1.5% this can represent a limitation for detection of antigen specific T cells.
However, in our previous experience in immuno-monitoring of patients with type 1
diabetes post islet transplantation, the frequency of GAD65 specific T cells was around
1000-2000 per million. Assuming this frequency of GAD65 specific T cells data
generated from >2 million CD8+ T cells per sample should be representative and
informative of the donor.