Lessons from a solid tumor
Institut für Zellbiologie, Abteilung
Immunologie, Universität Tübingen, Auf der Morgenstelle 15, D-72076 Tübingen,
Germany
A number of different
strategies are currently available for the screening of tumor cells for tumor-associated
antigens (TAA). Expression cloning followed by assaying T-cell or antibody
reactions, gene expression profiling, and proteome analysis have been used
to characterize antigens that may serve as targets for tumor diagnostics or
specific immunotherapy. While the search for T cell epitopes from TAA has
been comparatively successful for melanoma antigens, there is still a discrepancy
between large numbers of TAA and small numbers of known T cell epitopes for
most other tumors. In order to approach this problem, we established a strategy
which combines complementary methods for the identification of such targets
for the immune system in an individual setting.
Most of the recent
studies have been carried out in in vitro systems. Nevertheless,
there could be quite dramatic differences between the antigens or epitopes
presented by a tumor in its natural host and the conditions of cell culture.
To characterize the antigenic state of tumors in vivo, we
have been studying solid tumors (RCC, CCA) ex vivo for their gene expression
compared to regular tissues, and for their HLA peptide presentation.
Comparative gene
expression profiling was carried out by high density oligonucleotide microarrays.
To obtain homogenous tumor cell samples, either surgical procedures or laser
capture microdissection were employed.
Identification
of HLA-presented peptides was achieved either by the predict, calibrate, and
detect approach with the help of synthetic peptides, or by MHC peptide repertoire
(ligandome) analysis involving the characterization of as many peptides as
possible. The HLA ligands were classified by the rate of overexpression and
by the cancer-relatedness of their source proteins. Our studies allowed the
preparation of individually tailored peptide vaccine cocktails for renal cell
carcinoma patients.