Abstract Book 2010 - CIMT Annual Meeting

022 Pfirschke | Immune monitoring
The repertoire of melanoma antigens recognized by T cell responses
in malignant melanoma patients
Christina Pfirschke 1 , Christoffer Gebhardt 2 , Alexander Enk 2 , Philipp Beckhove 1
1 Translational Immunology Unit, German Cancer Research Center (DKFZ), Heidelberg, Germany
2 Department of Dermatology, University of Heidelberg, Heidelberg, Germany
Malignant melanoma, the leading cause of skin cancer
related death, is worldwide constantly increasing.
During the recent years the development of novel, improved
immunotherapeutic strategies have therefore
become highly important. Pre-existing memory CD4
and CD8 T cell responses are present in patients with
many tumor entities and provide a repertoire of functional
and potentially productive immune cells. Boosting
patients tailored of such T cells with selected
long peptides resembles a new strategy in melanoma
immunotherapy.
We here evaluated the presence and specificity of
the repertoire of preexisting tumor-antigen specific
T cells in 38 melanoma patients analyzed 1-4 month
after primary tumor rejection. We have determined by
an ex vivo short-term IFNγ ELISPOT assay the reactivity
of spontaneously induced T cells in the blood of
malignant melanoma patients against a broad variety
of melanoma tumor-associated antigens (TAAs). To
this end, long peptides (50aa) that cover several MHC
class I- and II-restricted epitopes were used as test antigens
while human IgG was investigated as negative
control antigen. As antigen presenting cells, we used
dendritic cells generated in vitro from monocytes
and pulsed with different synthetic 50aa peptides
derived from immunodominant regions of described
melanoma TAAs like MelanA/MART-1, tyrosinase,
gp100/pmel17, NY-Eso-1, p53, MDM2, NA17-A, TRP2,
MAGEA1, MAGE-C2, GAGE-1, MIF and RAB38/NY-
Mel-1. In order to analyze the role of regulatory T cells
(Tregs) in suppressing TAA-specific T cell responses,
Tregs were depleted from a part of the purified CD3+
T cell fractions using αCD25-magnetic beads.
More than 80% of the analyzed T cell samples of melanoma
patients reacted against at least one tested
peptide. T cells of HLA-A2 positive and HLA-A2 negative
patients recognized the polypeptides to a similar
extent. Additionally, more than 70% of the responding
T cell samples reacted in a polyvalent manner
to 4 or more tested peptides at the same time. Some
peptides, such as MelanA/MART-1 (56%), tyrosinase
(55%) and NA17-A (50%), as well as MAGE-A1
(44%), MDM2 (42%), GAGE-1 (41%), RAB38/NY-Mel
(40%), TRP2 (35%) and p53 (35%) were preferentially
recognized whereas other melanoma TAAs, such
as MIF (30%), MAGE-C2 (29%), gp100/pmel17 (24%)
and NY-Eso-1 (18%) elicited lower spontaneous T cell
responses. Interestingly, the depletion of Tregs from
the investigated T cell fractions did not result in an
increase of T cell response compared with the non
Treg depleted T cell samples.
Summarized, our data demonstrate that in a majority
of malignant melanoma patients in the peripheral
blood a polyvalent repertoire of tumor-reactive
memory T cells exists. In contrast to other kinds of
tumors investigated, including colon cancer, for malignant
melanoma we did not detect a major role of
Tregs for control of tumor reactive memory T cells.
Moreover, some analyzed antigens appear to be dominant
targets of spontaneous effector T cell responses
providing a potential new criterion for selection of
vaccine antigens for melanoma immunotherapy.
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