Tumor Antigen-specific T-cells are Present in the CD8αα+ T-cell Effector-memory Pool

CD8(+) T-cell memory formation has recently been demonstrated to be associated with CD8 alpha alpha homodimer expression by T-cells in mice. Up to now, the knowledge about the clinical significance of CD8 alpha alpha(+) T-cells in humans is limited. We assessed in longitudinally collected blood samples from patients with melanoma, who underwent a peptide-based vaccination, the role of CD8 alpha alpha(+) T-cells in tumor-specific cellular immune responses. Phenotypic analysis showed that the expression of CD8 alpha alpha(+) by T-cells was stable over time and associated with a CD45RA(+/-)CCR7(-) effector-memory profile. Melan-A/ MART-1-specific T-cells were identified in the CD8 alpha alpha(+) T-cell compartment by tetramer technology. Detection of intracellular cytokine production (interleukin-2, interferon-gamma, and tumor necrosis factor-alpha) upon phorbol 12-myristate 13-acetate-iono-mycin stimulation in CD8 alpha alpha(+) and CD8 alpha beta(+) T-cells revealed that CD8 alpha alpha(+) T-cells show a unique cytokine production pattern (tumor necrosis factor-alpha and interferon-gamma production) as compared with CD8 alpha beta(+) T-cells. T-cell receptor-CDR3 length analysis revealed that Melan-A/MART-1-specific CD8 alpha alpha(+) T-cells showed a similar T-cell receptor-repertoire as compared with Melan-A/MART-1-specific CD8 alpha beta(+) T-cells. Our results show that CD8 alpha alpha(+) T-cells represent a compartment of CD45RA(+/-) effector-memory cells in the peripheral circulation of patients with melanoma and suggest that CD8 alpha alpha(+) T-cells may originate from CD8(+) T-cells that have down-regulated the expression of the CD8P chain. CD8 alpha alpha(+) and tetramer-specific T-cells may represent a valuable marker to gauge long-term antigen- specific T-cell memory.