1. ^*Experimental Immunology Laboratory, IRCCS Maugeri Foundation, Pavia, Italy
2. ^†Department of Human and Hereditary Pathology, Institute of Dermatology, University of Pavia, Pavia, Italy
3. ^‡Immunohematology and Transfusion Center, IRCCS Policlinico S. Matteo, Pavia, Italy
4. ^§Biotechnology Research Laboratory, IRCCS Policlinico S. Matteo, Pavia, Italy
5. ^¶Unit of Human Cancer Immunotherapy, National Tumor Institute, Milan, Italy
6. ^#Department of Clinical and Biological Sciences, University of Turin, Turin, Italy

Correspondence: Claudia Giachino, Department of Clinical and Biological Sciences, University of Turin, Regione Gonzole 10, 10043 Orbassano, Italy; Email: claudia.giachino@unito.it

Received 6 February 2003; Revised 21 March 2003; Accepted 30 March 2003; Published online 23 July 2003.

Abstract

Vitiligo patients possess high frequencies of circulating CD8⁺ T lymphocytes specific for the melanocyte differentiation antigen Melan-A/MART-1. These self-specific T cells exhibit intact functional properties and their T cell receptors are selected for a narrow range of high affinities of antigen recognition, suggesting their important role in the pathogenesis of vitiligo. In order to understand the molecular base for this unexpected, optimal T cell receptor recognition of a self-antigen, a tetramer-guided ex vivo analysis of the T cell receptor repertoire specific for the Melan-A antigen in a patient affected by vitiligo is reported. All T cell receptors sequenced corresponded to different clonotypes, excluding extensive clonal expansions and revealing a large repertoire of circulating Melan-A-specific T lymphocytes. A certain degree of T cell receptor structural conservation was noticed, however, as a single AV segment contributed to the chain rearrangement in 100% of clones and a conserved amino acid sequence was found in the chain complementarity determining region 3 of various high affinity cells. We suggest that the conserved chain confers self-antigen recognition, necessary for intrathymic selection and peripheral homeostasis, to many synonymous T cell receptors, whereas the chain fine tunes the T cell receptor affinity of the specific cells. In addition, we demonstrate that many high avidity T cell clones from this patient were capable of specifically lysing normal, HLA-matched melanocytes. These autoreactive clones persisted for more than 3 y in the patient's peripheral blood. These data, together with the skin-homing potential of the clones, directly point to the in vivo pathogenic role of melanocyte-specific cytotoxic T lymphocytes in vitiligo.