FINAL PROGRAM - Society for Immunotherapy of Cancer

Oral Presentation Abstracts
antigen-specific manner. Currently, vaccine platforms that express
the full-length human Brachyury protein are under development
and a Phase I clinical trial of a heat-killed yeast-Brachyury vector is
in preparation. We hypothesize that the eradication of Brachyuryexpressing
tumor cells via Brachyury-based immunotherapeutic
approaches could be efficient at eliminating tumor cells with
invasive/metastatic potential as well as tumor resistance to
conventional therapies.
Key Words: Cancer vaccine, Tumor associated antigen.
IMMUNOLOGICALTARGETING OF EPITHELIALTO
MESENCHYMALTRANSITION AS A STRATEGYTO
PREVENT BREAST CANCER METASTASES
Noriko Kawashima 1 , Baomei Wang 1 , Fabio Santori 1 , Karsten
Pilones 1 , Frank Pajonk 2 , Sandra Demaria 1
1
New York University Scool of Medicine, New York, NY
2
David Geffen School of Medicine at UCLA, Los Angeles, CA
The identification of a subset of breast cancer (BC) cells with
properties of cancer stem cells (CSCs), that are responsible for
tumorigenesis, metastasis and recurrence, and are intrinsically
more resistant to chemotherapy and radiation, provides an
unprecedented opportunity to develop new treatment strategies.
The transcription factor Twist plays a key role in induction of
epithelial to mesenchymal transition (EMT) and acquisition of
CSCs properties by BC cells. Twist is also a key regulator of
metastasis in the 4T1 mouse model of breast cancer, and has been
implicated in resistance to chemotherapy and radiation, and in
early disease relapse after adjuvant treatment in patients. Therefore,
strategies to target Twist could be effective for the prevention of
metastatic BC.
Using the SYFPEITHI Epitope Prediction computer-based algorithm
we have identified a Twist-derived peptide (pTw9) that forms
stable complexes with H2-Kd with DC50 of >6 hr, and was able
to sensitize P815 cells to lysis by 4T1 tumor-specific CTL isolated
from mice that rejected 4T1 tumor. A pTw9-specific CTL line
established by repeated in vitro re-stimulation specifically killed
4T1 cells, confirming that pTw9 is an endogenously produced CTL
epitope. Immunization experiments with pTw9 confirmed that
this peptide is immunogenic in naïve mice. To determine whether
CTL targeting pTw9 can prevent the generation of CSCs in vivo
and inhibit metastases, we have prepared 4T1 cells expressing
ZsGreen-cODC fusion protein, which contains the degron of
ornithine decarboxylase leading to rapid proteasome-mediated
degradation of the reporter protein. Tumor cells that accumulate
ZsGreen-cODC to detectable levels have the characteristics
of CSCs and can be imaged in vivo (Vlashi et al., J Natl Cancer
Inst. 2009, 101:350-9). 4T1-ZsGreen-cODC cells injected s.c.
into RAG2-deficient mice were allowed to spontaneously
metastasize to the lungs. Lungs were harvested 30 days later,
digested, and analyzed by flow cytometry for the presence of
EpCAM+ZsGreen+ tumor cells. ZsGreen+ cells represented on
average 4.4 ± 4.9% of EpCAM+ tumor cells in the lung (range
0.6 to 15.0%). Since the injected population did not contain
detectable ZsGreen+ cells, results suggest that 4T1 cells with
CSC characteristics are generated in vivo and enriched in the
spontaneous lung metastases.
Use of 4T1-ZsGreen-cODC cells will allow the tracking of tumor
cells with CSCs properties in vivo. This system provides a unique
tool to test the hypothesis that immunological targeting of Twist
can inhibit EMT and the generation of tumor cells with breast
CSCs properties.
Key Words: Breast cancer, CD8+ T cells, Tumor associated antigen.
POTENTIAL FOR IMMUNOTHERAPEUTIC
CONTROL OF CSC-LIKE CELLS THROUGH THEIR
EXPRESSION OF FAS AND DR5 DEATH RECEPTORS
Fransisca Go, Deborah A. Knight, Mark J. Smyth, Trina J. Stewart
Cancer Immunology Research Program, Peter MacCallum Cancer
Centre, Melbourne, VIC, Australia
There is accumulating evidence for a role for cancer stem cells
(CSC) in the recurrence of cancer and in the development of
metastatic disease. Therefore, although CSC comprise only a small
proportion of cells within a tumor, they should be considered
an important population for therapeutic targeting. Since CSC
are resistant to standard radiotherapy and chemotherapeutic
treatments, identification of alternative treatment strategies, such
as immunotherapeutic modalities, is required. Given the growing
number of immunotherapies being used to treat cancer and
the fact that some chemotherapies may actually prime immune
responses, it is important that a better understanding of the
susceptibility of CSC to various immunotherapeutic modalities is
investigated. Therefore, the immunological characterization of CSC
becomes essential for the identification of immune-associated
molecules expressed by CSC, which can be potentially exploited
as an immunotherapy. The majority of studies on CSC have utilized
cells from patient samples or human cell lines. However, these
xenograft models are conducted in immunocompromised mice,
which limits our ability to investigate immune interactions and
immunotherapeutic responses. Therefore, a CD44+CD24-/low
subpopulation of cells within the murine AT-3 mammary carcinoma
cell line was identified that had CSC-like characteristics, including
an ability to differentiate and repopulate the line, and a resistance
to chemo- and radiotherapy. These cells can then be used as a
model system to study interactions between breast CSC and a
competent immune system and to investigate their susceptibility
to immunotherapeutic strategies. This AT-3 CSC-like subpopulation
was immunologically characterized through their surface molecule
expression profile and their susceptibility to a range of cell death
pathways. Similar levels of the surface molecules Rae-1, CD155,
CD54 (NK cell-killing); and higher levels of Fas (Fas-killing) and
DR5 (TRAIL-killing) were expressed on AT-3.CSC compared to
other non-CSC tumor cells. This expression profile correlated with
an in vitro sensitivity to cell death by NK cells; and through the
recognition of the death receptors, Fas or DR5, by either FasL- or
TRAIL-expressing cells; or anti-Fas and anti-DR5 mAbs. Indeed,
the AT-3.CSC were actually shown to be more sensitive to both
ABSTRACTS AND
POSTER LISTINGS
FINAL PROGRAM • SITC 26 TH ANNUAL MEETING
November 4-6, 2011 • North Bethesda, MD • www.sitcancer.org
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