Abstract
BackgroundAssessment of T-cell diversity, besides giving insights about the molecular basis of tumor antigen recognition, has clinical implications since it provides criteria for evaluating antigen-specific T cells clinically relevant for spontaneous and vaccine-induced anti-tumor activity. Melan-A is one of the melanoma antigens most frequently recognized by peripheral and tumor-infiltrating lymphocytes in HLA-A2+ melanoma patients. Many clinical trials involving anti-tumor vaccination have been conducted using modified versions of this peptide.MethodsWe conducted an in-depth characterization of 210 T-cell receptor beta chain (TRB) clonotypes derived from T cells of HLA-A2+ melanoma patients displaying cytotoxic activity against natural and A27L-modified Melan-A peptides. One hundred and thirteen Melan-A-specific clonotypes from melanoma-free subjects, 199 clonotypes from T-cell clones from melanoma patients specific for melanoma antigens other than Melan-A, and 305 clonotypes derived from T cells of HLA-A2+ individuals showing unrelated specificities, were used as control. After sequence analysis, performed according to the IMGT definitions, TRBV and TRBJ usage, CDR3 length and amino acid composition were compared in the four groups of clonotypes.ResultsTRB sequences of Melan-A-specific clonotypes obtained from melanoma patients were highly heterogeneous, but displayed a preferential usage of few TRBV and TRBJ segments. Furthermore, they included a recurrent "public" amino acid motif (Glycine-Leucine-Glycine at positions 110-112-113 of the CDR3) rearranged with dominant TRBV and TRBJ segments and, in one case, associated with a full conservation of the entire TRB sequence.ConclusionContrary to what observed for public anti-Melan-A T-cell receptor alpha motifs, which had been identified in several clonotypes of both melanoma patients and healthy controls, the unexpectedly high contribution of a public TRB motif in the recognition of a dominant melanoma epitope in melanoma patients may provide important information about the biology of anti-tumor T-cell responses and improve monitoring strategies of anti-tumor vaccines.
Highlights
Assessment of T-cell diversity, besides giving insights about the molecular basis of tumor antigen recognition, has clinical implications since it provides criteria for evaluating antigenspecific T cells clinically relevant for spontaneous and vaccine-induced anti-tumor activity
Two hundred and ten Melan-A-specific clonotypes [[5,6,7,10,11,12,13,14,15,16,17,18] and manuscript in preparation], sequenced starting from T-cell lines or clones obtained from PBL and/or tumor-infiltrating lymphocytes (TIL) of melanoma patients ("Mel/M-A" group; Table 1), were compared with 113 Melan-A-specific clonotypes ("Ctrl/M-A" group) from healthy controls and from a subject with vitiligo [5,8,19], 199 clonotypes specific either for melanoma Ags other than Melan-A peptide or with undetermined specificity ("Mel/noM-A" group) obtained from T cells of melanoma patients [22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41], and 305 clonotypes prepared from HLA-A2+ melanoma-free patients ("Ctrl/HLA-A2+" group) selected because sequenced from T-cell lines and clones displaying CTL activity against unrelated Ags [42,43,44,45,46,47,48,49,50,51,52,53,54]
Preferential TRBV and TRBJ usage in HLA-A2/Melan-A restricted response in melanoma patients We first investigated whether clonotypes identified in HLA-A2+ melanoma patients with CTL specificity against Melan-A (Mel/M-A group) had a preferential usage of par
Summary
Assessment of T-cell diversity, besides giving insights about the molecular basis of tumor antigen recognition, has clinical implications since it provides criteria for evaluating antigenspecific T cells clinically relevant for spontaneous and vaccine-induced anti-tumor activity. Melan-A is one of the melanoma antigens most frequently recognized by peripheral and tumor-infiltrating lymphocytes in HLA-A2+ melanoma patients. The TRBV region, referred according to the ImMunoGeneTics (IMGT) database [1], is encoded by V, diversity (D), and joining (J) gene segments. The juxtaposition of these segments [2], the lack of precision during V(D)J gene rearrangement and the removal and/or addition of nontemplate encoded nucleotides at V(D)J junctions [3], create a region of hypervariability known as complementarity-determining region 3 (CDR3). Among the melanoma-associated Ags identified so far, Melan-A has received particular attention because of its immune dominance in HLA-A2+ patients. We identified several melanoma/HLA-A2-restricted TRB clonotypes (sequences showing different CDR3 in a given individual), and, after the definition of a common TR nomenclature, numbering and CDR3 designation, we studied in details their molecular features
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