Abstract Book 2010 - CIMT Annual Meeting

003 Altvater | Therapeutic vaccination
Presentation of tumor-associated epitopes by activated human
γδ T cells induces expansion of specific CD8+ T cells from
naïve precursors
Bianca Altvater 1 , Silke Landmeier 1 , Sibylle Pscherer 1 , Anna Hansmeier 1 , Barbara Savoldo 2 ,
H. Juergens 1 , Claudia Rossig 1
1 University Children´s Hospital Münster, Department of Pediatric Hematology and Oncology,
Albert-Schweitzer-Str. 33, 48149 Münster
2 Center for Cell and Gene Therapy, Baylor College of Medicine, Houston, TX, U.S.A
Efficient antigen presentation is an important
prerequisite for the induction of therapeutic T-cell
immunity against viral and tumor antigens. In an
Epstein Barr virus (EBV) model, we previously demonstrated
that bisphosphonate-activated γδ T cells
are potent stimulators of functional EBV-specific T
cell responses in both normal donors and Hodgkin
lymphoma patients. Here, we extended these observations
by investigating the capacity of activated γδ
T cells to induce primary T-cell responses against
the tumor-associated, poorly immunogeneic antigens
PRAME and STEAP-1 from the naive T-cell
repertoire.
Peripheral blood-derived γδ T cells were expanded
from three individual HLA-A2 positive healthy
donors by stimulation with the aminobisphosphonate
zoledronic acid (1 µg/ml) in the presence of
rhIL-2 (100 U/ml) and rhIL-15 (10 ng/ml). To investigate
the ability of activated γδ T cells to stimulate
expansion of PRAME- and STEAP-1 specific
cytotoxic T cells (CTL) in vitro, purified autologous
CD8+ T cells were cocultured with either dendritic
cells (DCs) or activated γδ T cells pulsed with
pools of HLA-A2 restricted peptides derived from
either STEAP-1 or PRAME, followed by two stimulations
with peptide-pulsed K-562 cells, genemodified
to express human HLA-A2, CD80, CD40L,
and OX40L (K-562-APCs). ELISPOT analysis demonstrated
efficient and equivalent induction of
specific CD8+ T-cell responses by both DCs and
γδ T-APCs. Both types of CTLs had a predominant
effector memory phenotype (CCR7-CD45R0+).
Even though antigen-experienced precursor CTLs
against the tumor-associated antigens are absent in
the majority of healthy donors, these experiments
do not formally prove that the expanded T cells are
a consequence of T-cell priming. To demonstrate
the origin of CTLs from antigen-naïve T cells, we
performed additional coculture experiments using
CD45RA+ T cells, purified from the CD8+ T-cell
population by magnetic cell selection, as responder
cells. Again, ELISPOT analysis after primary stimulation
with PRAME peptide-pulsed autologous
DCs or γδ T-APCs demonstrated specific and potent
CTL reactivity against both pooled and individual
PRAME peptides. Importantly, γδ T-APC induced
CTLs were not inferior to those generated using the
DC gold standard.
Thus, γδ T cells represent a promising source of
highly efficient professional APC for antigen-specific
immunotherapy of cancer. In current experiments,
we are establishing the capacity of γδ T
cells endogenously expressing STEAP-1 or PRAME
full-length antigen in inducing functional primary
CTL responses.
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