Harari A, Enders FB, Cellerai C, Bart PA, Pantaleo G.

Cytotoxic CD8 T-cells exert their antiviral and anti-tumor activity primarily through the secretion of cytotoxic granules. Degranulation activity and cytotoxic granules (perforin plus granzymes) generally define CD8 T-cells with cytotoxic function. In this study we have investigated the expression of granzyme K (GrmK) compared to GrmA, GrmB and perforin. The expression of the cytotoxic granules has been assessed in virus-specific CD8 T-cells specific to Influenza (Flu), EBV, CMV and HIV-1. We observed a dichotomy between GrmK and perforin expression in virus-specific CD8 T-cells. The profile in Flu-specific CD8 T-cells was: perforin(-)GrmB(-)GrmA(+/-)GrmK(+); in CMV: perforin(+)GrmB(+)GrmA(+)GrmK(-/+); and in EBV and HIV-1: perforin(-/+)GrmB(+)GrmA(+)GrmK(+). On the basis of the delineation of memory and effector CD8 T-cells with CD45RA and CD127, GrmK(+) profile was associated with early stage memory CD8 T-cells differentiation, perforin(+)GrmB(+)GrmA(+) profile with advanced stage differentiation and GrmB(+)GrmA(+)Grmk(+) profile with intermediate stage differentiation. Furthermore, perforin and GrmB but not GrmA and GrmK correlated with cytotoxic activity. Finally, changes in antigen exposure in vitro and in vivo during primary HIV-1 infection and vaccination modulated cytotoxic granule profiles. These results advance our understanding of the relationship between distinct profiles of cytotoxic granules in memory CD8 T-cells and function, differentiation stage and antigen exposure.