Tumor Antigen-specific T-cells are Present in the CD8[alpha][alpha]+ 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-ionomycin 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 CD8[beta] chain. CD8[alpha][alpha]+ and tetramer-specific T-cells may represent a valuable marker to gauge long-term antigen-specific T-cell memory.