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Correspondence to: Pedro Romero, Division of Clinical Onco-Immunology, Ludwig Institute for Cancer Research, Centre Hospitalier Universitaire Vaudois BH 19-602, 1011 Lausanne, Switzerland. Tel:41-21-314-01-78 Fax:41-21-314-74-77 E-mail:pedro.romero{at}isrec.unil.ch.
Using fluorescent HLA-A*0201 tetramers containing the immunodominant Melan-A/MART-1 (Melan-A) tumor-associated antigen (Ag), we previously observed that metastatic lymph nodes of melanoma patients contain high numbers of Ag-experienced Melan-Aspecific cytolytic T lymphocytes (CTLs). In this paper, we enumerated and characterized ex vivo Melan-Aspecific cells in peripheral blood samples from both melanoma patients and healthy individuals. High frequencies (
1 in 2,500 CD8+ T cells) of Melan-Aspecific cells were found in 10 out of 13 patients, and, surprisingly, in 6 out of 10 healthy individuals. Virtually all Melan-Aspecific cells from 6 out of 6 healthy individuals and from 7 out of 10 patients displayed a naive CD45RAhi/RO- phenotype, whereas variable proportions of Ag-experienced CD45RAlo/RO+ Melan-Aspecific cells were observed in the remaining 3 patients. In contrast, ex vivo influenza matrixspecific CTLs from all individuals exhibited a CD45RAlo/RO+ memory phenotype as expected. Ag specificity of tetramer-sorted A2/Melan-A+ cells from healthy individuals was confirmed after mitogen-driven expansion. Likewise, functional limiting dilution analysis and interferon
ELISPOT assays independently confirmed that most of the Melan-Aspecific cells were not Ag experienced. Thus, it appears that high frequencies of naive Melan-Aspecific CD8+ T cells can be found in a large proportion of HLA-A*0201+ individuals. Furthermore, as demonstrated for one patient followed over time, dramatic phenotype changes of circulating Melan-Aspecific cells can occur in vivo.
Key Words: melanoma, tetramer, influenza matrix, immunotherapy, tumor immunity
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