Molecular and functional bases of self-antigen recognition in long-term persistent melanocyte-specific CD8+ T cells in one vitiligo patient

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 alpha chain rearrangement in 100% of clones and a conserved amino acid sequence was found in the beta chain complementarity determining region 3 of various high affinity cells. We suggest that the conserved alpha chain confers self-antigen recognition, necessary for intrathymic selection and peripheral homeostasis, to many synonymous T cell receptors, whereas the beta 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

T-cell dynamics after high-dose chemotherapy in adults: elucidation of the elusive CD8(+) subset reveals multiple homeostatic T-cell compartments with distinct implications for immune competence

Recovery of total T cell numbers after in vivo T-cell depletion in humans is accompanied by complex perturbation within the CD8(+) subset. We aimed to elucidate the reconstitution of CD8(+) T cells by separate analysis of putative naïve CD95(−) CD28(+), memory CD95(+) CD28(+) and CD28(−) T cell compartments after acute maximal depletion by high-dose chemotherapy (HD-ChT) in women with high-risk breast cancer. We found that recovery of putative naïve CD8(+) CD95(−) CD28(+) and CD4(+) CD95(−) CD28(+) T cells, was compatible with a thymus-dependent regenerative pathway since their recovery was slow and time-dependent, their values were tightly related to each other, and their reconstitution patterns were inversely related to age. By analysing non-naïve T cells, a striking diversion between putative memory T cells and CD28(−) T cells was found. These latter increased early well beyond normal values, thus playing a pivotal role in total T-cell homeostasis, and contributed to reduce the CD4 : CD8 ratio. In contrast, putative memory T cells returned to values not significantly different from those seen in patients at diagnosis, indicating that this compartment may recover after HD-ChT. At 3–5 years after treatment, naïve T cells persisted at low levels, with expansion of CD28(−) T cells, suggesting that such alterations may extend further. These findings indicate that CD28(−) T cells were responsible for ‘blind’ T-cell homeostasis, but support the notion that memory and naïve T cells are regulated separately. Given their distinct dynamics, quantitative evaluation of T-cell pools in patients undergoing chemotherapy should take into account separate analysis of naïve, memory and CD28(−) T cells