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| Research
Group |
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| Research
Interests |
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For
many years, melanoma has been used as a model for the study of T cell
mediated immune responses to tumors in humans. Melanoma is a malignant
tumor that originates from melanocytes, cells specialized in the synthesis
of melanin and responsible for the pigmentation of the skin and the eye.
A large number of defined melanoma antigens that mediate tumor recognition
by T cells have been identified. These can be mostly grouped in two categories,
one derived from genes uniquely expressed by cancer but not normal cells,
and the other comprising melanocyte-specific differentiation antigens.
The latter include proteins that are expressed by both melanoma cells
and normal melanocytes. Receptors on T cells specifically recognize short
peptides derived from these antigens exposed on the surface of melanoma
cells in association with specific MHC molecules. Our interest is directed
to molecular aspects that underlie the expression of tumor antigens and
are involved in the recognition of tumor cells by the immune system. Current
research efforts are focused on the detailed characterization of some
of these antigens and their derived T cell epitopes from the biochemical
and structural point.
| Current Projects |
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Characterization
of the Melan-A/MART-1 protein. Spontaneous T-cell mediated immune
responses in HLA-A2 melanoma patients are frequently observed against
an epitope derived from the melanocytic differentiation antigen named
Melan-A. Melan-A is a small transmembrane protein of unknown function.
It bears no homology to the other known melanocytic antigens, which typically
reside in melanosomes (organelles where pigment is synthesized and stored)
and are directly involved in pigment formation. We have started characterizing
Melan-A in normal and transformed melanocytic cells using biochemical
and microscopical methods. In addition, to understand its role in melanocytic
cells, we are originating in vitro Melan-A knock-down cells using
the siRNA technology.
Modeling
to TCR-peptide-MHC interactions. Due to development of reagents such
as peptide-MHC tetramers that allow to isolate from the blood or from
a lymph node all lymphocytes whose TCR are specific for a given p-MHC,
a lot of TCR sequence data have been generated, which require structural
informations to be interpreted. For example, more than 70 TCR sequences
have been identified in CD8+ T cells directed against HLA A2-Melan A peptide.
Even with the recent proteomics projects, systematic crystal structure
determinations of these TCR bound to their ligand would not be feasible
and alternative methods are needed to interpret the biological data.
To
this end, we are developing the tools to construct reliable 3D models
of any TCR-p-MHC complex, combining homology modeling and ab
initio predictions. These methods have been applied to a specific
murine system and are now used to construct 3D models for entire TCR repertoires
specific for a given epitope, such as Melan-A/HLA A2. Comparison of these
structures allows to find conserved 3D motifs that are not identifiable
at the sequence level.
To
complement these structural data, functional approaches are also developed,
based on free energy simulation methods. These methods have been used
to reproduce the experimental TCR affinity difference for a wild type
and a mutant peptide and are also developed further to understand how
peptide modifications would alter p-MHC binding as well as TCR-p-MHC binding.
| Selected
publications |
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Michielin,
O. and Karplus, M. 2002. Binding free energy differences in a TCR-peptide-MHC
complex induced by a peptide mutation: A simulation analysis. J. Mol.
Biol. 324:547-569.
De
Mazière, A.M., Muehlethaler, K., van Donselaar, E., Salvi, S.,
Davoust, J., Cerottini, J.-C., Lévy, F., Slot, J.W. and Rimoldi,
D. 2002. The melanocytic protein Melan-A/MART-1 has a subcellular localization
distinct from typical melanosomal proteins. Traffic 3:678-693.
Rimoldi,
D., Muehlethaler, K., Salvi, S., Valmori, D., Romero, P., Cerottini, J.-C.
and Lévy, F. 2001. Subcellular localization of the melanoma-associated
protein Melan-AMART-1 influences the processing of its HLA-A2-restricted
epitope. J. Biol. Chem. 276:43189-43196.
Sliz,
P., Michielin, O., Cerottini, J.-C., Luescher, I., Romero, P., Karplus,
M. and Wiley, D.C. 2001. Crystal structures of two closely related but
antigenically distinct HLA-A2/melanocyte-melanoma tumor-antigen peptide
complexes. J. Immunol. 167:3276-3284.
Valmori,
D., Dutoit, V., Rubio-Godoy, V., Chambaz, C., Liénard, D., Guillaume,
P., Romero, P., Cerottini, J.-C. and Rimoldi, D. 2001. Frequent cytolytic
T-cell responses to peptide MAGE-A10254-262 in melanoma. Cancer Res. 61:509-512.
Rimoldi,
D., Rubio-Godoy, V., Dutoit, V., Liénard, D., Salvi, S., Guillaume,
P., Speiser, D., Stockert, E., Spagnoli, G., Servis, K., Cerottini, J.-C.,
Lejeune, F., Romero, P. and Valmori, D. 2000. Efficient simultaneous presentation
of NY-ESO-1/LAGE-1 primary and non-primary open reading frame derived
CTL epitopes in melanoma. J. Immunol. 165:7253-7261.
Rimoldi,
D., Salvi, S., Schultz-Thater, E., Spagnoli, G.C. and Cerottini, J.-C.
2000. Anti-MAGE-3 antibody 57B and anti-MAGE-1 antibody 6C1 can be used
to study different proteins of the MAGE-A family. Int. J. Cancer 86:749-751.
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