Background: The relationship between degranulation activity (measured by CD107a mobilization), the content of cytotoxic granules, direct cytotoxic capacity and the differentiation stage of virus-specific CD8 T-cells has not been extensively investigated.

Methods: Seventy subjects with HIV-1-, CMV-, EBV- and Fluspecific CD8 T-cell responses were analyzed either for CD107a mobilization or for the expression of perforin (P), granzyme A (A), granzyme B (B) and granzyme K (K), CD127 (IL-7Ra), CCR7 and CD45RA by polychromatic flow cytometry. CFSE dilution and Cr51 release assays were also performed. No significant differences were observed in the degranulation activity in Flu-, EBV-, CMVand HIV-1-specific CD8 T-cells (ranging from 40 –60%, P > 0.05).

 

Results: Analysis of A, B, K and P on CD8 T-cells identified 16 populations. Expression of cytotoxic granules varied within virus-specific CD8 T-cells. >35% of CMV-specific T-cells were PþAþBþKþ/_, >40% of HIV-1- and EBV-specific T-cells were P-Aþ/_Bþ/_Kþ and >60% of Flu-specific T-cells were P-A-B-Kþ (differences between viruses: all P<0.001). Differentiated cells mostly contained P and B, but not A or K while these latter were mainly found in CD8 T-cells at early stage of differentiation (CCR7þCD127þCD45RA-). In vitro cytotoxic activity was strongly related to the cytotoxic granules expression profile. Only P and B and not A or K were positively correlated with cytotoxicity (both P<0.05). Of note, virus-specific proliferating CD8 T-cells were contained within the CD127þP-B- T-cell population.

 

Conclusion: Distinct patterns of granules content are found for different virus-specific CD8 T-cells and they were correlated with the differentiation stage. Cytotoxic activity strongly correlated with perforin expression but not with degranulation activity. Cytotoxic activity is predominant in virus-specific CD8 T-cells at advanced stage of differentiation while proliferation capacity at early stage of differentiation.