Abstracts for the 25th Annual Scientific Meeting of the International ...

J Immunother Volume 33, Number 8, October 2010
Abstracts
the peptides incorporated in the vaccine as measured by ELISpot,
and by MHC/multimer reagents. Myeloid populations were identified
by flow cytometry, as a proportion of CD45+, lineage (CD3,
CD19, CD56)-negative cells. Mature myeloid suppressor cells (MSC)
were further defined as CD14 + HLA-DR, and myeloidderived
suppressor cells (MDSC) of two phenotypes were defined
as CD11b + CD33 + DRneg or CD33 + CD15 + . Regulatory T cell
populations also were defined as CD25bright FoxP3+ CD4+ by
multi-parameter flow cytometry. Twenty patients were evaluated,
half in each group, pre and after 4 vaccines. After four weeks of
weekly immunizations, the level of MSC did not change significantly
(median 1.7% after vaccine in both groups, Table 1 previous page).
In addition, other myeloid populations did not change significantly
after immunization+GMCSF (P = 0.7, 0.9, Table 1 previous page)
and were not different between groups (Table 1 previous page). Also,
there was no overall change in regulatory T cells in patients receiving
GM-CSF (P = 0.49, not shown). The suppressed immune responses
associated with GM-CSF in this trial do not appear to be
attributable to any of these defined regulatory cell population in
lymphoid or myeloid compartments of peripheral blood, but may
operate by other mechanisms that impact the immune response to
tumor-derived peptides.
Blockade of TGF-b Receptor Type I Signaling Reduces
the Ability Of FoxP3+ Cells to Inhibit Proliferation and
IFN-Gamma Production in Effectors Cells
Magdalena J. Polanczyk, Daniel Haley, Edwin Walker,
Emmanuel T. Akporiaye. Providence Medical Center, Earle A.
Chiles Institute, Portland, OR.
Transforming growth factor-beta (TGF-b) plays a crucial role in
tumor growth, metastasis and invasiveness. We already demonstrated
that the beneficial effect of systemic blockade of TGF-b
receptor type 1 by a small molecule inhibitor (SM16) in a murine
breast cancer model is T cell dependent. As TGF-b is capable
of redirecting peripheral CD4+ T cells toward a FoxP3+ Treg
phenotype, which contribute to immune suppression and tumor
evasion, the current studies were designed to evaluate how the
disruption of TGF-b signaling affects Treg function and contributes
to the antitumor effects of SM16. We demonstrate that
systemic blockade of TGF-b receptor type I by SM16 is insufficient
to prevent expansion of the Treg compartment. Instead, SM16
induced expansion of both Treg (CD4+CD25+FoxP3+ and
CD4+CD25-FoxP3+) and effector cell compartments in naı¨ ve
and tumor bearing mice (TBM). Strikingly, the SM16-induced
expansion of FoxP3+ cells was associated with reduced ability to
inhibit proliferation of effectors in in vitro suppression assays.
Finally, SM16 impaired the ability of FoxP3+ cells to suppress
IFN-g production by CD4+CD25-FoxP3- effector T cells. In
summary, our data suggest that SM16 may promote tumor
immunity by dampening the ability of FoxP3+ cells to inhibit
proliferation and IFN-g production in effectors cells.
Chronic Chemoimmunotherapy Maintains Long-Term Anti-
Tumor CD8+ T Effector Cell Activity and Results in the
Cure of Advanced Spontaneous Tumors
Rachael B. Rowswell-Turner, Lauren P. Virtuoso, Tao Gu,
Mehmet O. Kilinc, Nejat K. Egilmez. Microbiology and Immunology,
University at Buffalo, School of Medicine and Biomedical
Sciences, Buffalo, NY.
Like other forms of cancer immunotherapy, intra-tumoral delivery
of microsphere encapsulated IL-12 and GM-CSF leads to only
short-lived tumor regression in the Her-2/neu spontaneous
mammary tumor model. IL-12/GM-CSF treatment promotes an
initial loss of T regulatory cells from tumors which corresponds
with tumor regression. However, T regulatory cells inevitably reinfiltrate
the tumor and tumor growth resumes as CD8+ T effector
cells are rendered nonfunctional. With multiple intratumoral IL-
12/GM-CSF treatments, the T-regulatory cell rebound is progressively
exacerbated and tumor specific CD8+ T cells are lost. To
circumvent this counter-regulatory response we have specifically
targeted the T-regulatory cell re-infiltration of the tumor and
draining lymph nodes. Low-dose chemotherapy has been associated
with depletion of T-regulatory cells and has been shown to
enhance tumor immunotherapy. In our studies repeated administration
of cyclophosphamide and IL-12/GM-CSF microspheres
over a period of nine weeks led to complete and durable regression
of spontaneous tumors, while either treatment alone was ineffective
in achieving long-term cure. Importantly, whereas contribution of
CD8+ T-cells to tumor regression in the immunotherapy alone
group was minimal, tumor kill was strictly dependent on CD8+
T-cells in the chemoimmunotherapy group. Further analysis
revealed that chemoimmunotherapy enhanced both the proliferation
(2-fold) and the cytotoxic activity of CD8+ T cells (up to 4.7
fold) over that of immune therapy alone as assessed by BrdU
uptake and granzyme B, perforin, and IFN-g expression. Ultimately,
persistent suppression of the post-therapy T regulatory
cell rebound led to an elevated activity index (Proliferating CD8+
T cells: T regulatory cells) in the tumor, which correlated with
tumor regression. These studies demonstrate that homeostatic
counter-regulation, a major challenge of immune-based cancer
therapies, can be overcome by chronic chemoimmunotherapy.
CD4+Foxp3+ Regulatory T Cells are Dependent on PI3K
Pathway Allowing for Their Selective Inhibition
Raed N. Samara, Yujun Dong, Maher Abdalla, Mikayel
Mkrtichyan, Laurent Ozbun, Yufei Jiang, Jiahua Qian,
Samir Khleif. Vaccine Branch, NCI, Bethesda, MD.
Naturally-occurring Regulatory T cells (Tregs) mediate tumor
immune-evasion. Their depletion or inactivation increases antitumor
responses and decreases tumor burden. In this study, we
identified the differences in the role of PI3K/Akt pathway in T cell
receptor signal transduction in Tregs and conventional T cells
(Tconv), and exploited such differences to selectively deplete Tregs
in vivo, while keeping other T cell subsets unaffected. We found
that unlike Tconv, Tregs are mainly dependent on the PI3K-Akt
pathway for polyclonal signaling downstream of the T cells
receptor (TCR) in vitro. Inhibiting the PI3K-Akt pathway by
small molecule inhibitors in Tregs decreased S6 phosphorylation,
and completely abrogated their proliferation in response to TCR/
CD28/IL-2 stimulation. In contrast, these inhibitors had minimal
effects on S6 phosphorylation and proliferation in Tconv cells. In
vivo, administering PI3K or Akt inhibitors preferentially reduced
the number of Tregs and Foxp3 mRNA, increased specific CD8
T cell immune responses to vaccination, and resulted in decreased
Treg-dependant tumor growth, which was reversed after reinfusing
Tregs, indicating that inhibitors of PI3K and Akt directly
target Tregs in vivo. Accordingly, we conclude that TCR/CD28/IL-
2 signaling is mainly dependent on PI3K pathway in Tregs, but not
in Tconv cells, and inhibiting PI3K and Akt directly target Tregs
both in vitro and in vivo. This forms the basis for a clinicallyrelevant
selective Treg cell inhibition strategy in vivo using small
molecule inhibitors.
Assessing and Countering Negative Immune Regulation in
Renal Cell Cancer Patients-Results of a Randomized Phase
II Trial with IMA901
Steffen Walter*, Norbert Hilf*, Regina Mendrzyk*,
Dominik Maurer*, Toni Weinschenk*, Alexandra Kirner*,
Vincenzo Brontew, Susanna Mandruzzatow, Graham Pawelecz,
Evelyna Derhovanessianz, Arnulf Stenzlz, Carsten Reinhardt*,
Harpreet Singh*. *Immatics Biotechnologies; zUniversity of Tuebingen,
Tuebingen, Germany; w University of Padova, Padova, Italy.
Background: IMA901 is a therapeutic cancer vaccine for the
treatment of renal cell cancer patients based on the selection of
naturally presented tumor-associated peptides (9 HLA-class I- and
1 HLA class II-binding peptides). A previous phase I study
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