Molecular Mimicry of Human Cytochrome P450 by Hepatitis C Virus at the Level of Cytotoxic T Cell Recognition

Kammer, Andreas R.; van der Burg, Sjoerd H.; Grabscheid, Benno; Hunziker, Isabelle P.; Kwappenberg, Kitty M.C.; Reichen, Jürg; Melief, Cornelis J.M.; Cerny, Andreas

Peptide Recognition by Cross-reactive CTL Lines. HCV core 178-induced CTL lines derived from donor 2 were used to test the biologic function of the peptides in cytotoxicity assays. Despite different MHC binding affinities and abilities HCV core ϩ CYP2A7 ϩ CYP2A6 2 (17%) 2 (20%) ‡ HCV core ϩ CYP2A7 3 (25%) 2 (20%) HCV core 4 (33%) 4 (40%) None 3 (25%) 2 (20%) *Number (percentage) of individuals recognizing the indicated peptides after primary induction with HCV core 178. CTL responses of Ͼ15% specific lysis at an E/T ratio of 40:1 in primary induction cultures were considered positive. ‡ One of these patients was not positive for CYP2A6 according to the criteria mentioned above, but CYP2A6-recognizing cell lines could be established by limiting dilution. to stabilize MHC complexes, all three peptides were recognized by CTLs with the same efficiency (Fig. 3 A) . The higher off-rate of the CYP peptides had no effect on CTL recognition when the peptide-pulsed target cells were further incubated without peptide for up to 24 h before exposure to CTLs (Fig. 3 B ). An explanation for this phenomenon could be the CD8 dependency of target recognition. Although lysis of target cells presenting HCV core 178 is markedly reduced by the anti-CD8 antibody OKT8, recognition of CYP2A7 is less affected and there is no effect on recognition of CYP2A6 (Fig. 3 C) . These findings were unexpected but similar findings had been observed by al-Ramadi et al., demonstrating that the pattern of functional activities of variant peptides does not always correlate with MHC binding (31) . In fact, other mechanisms involved in the interaction between the CTL and the target cell may be important, such as the TCR affinity for the MHC-peptide-complex, and CD8 binding to MHC class I, as well as other costimulatory and cell adhesion molecules (32) . To assess the role of CD8 binding on CTL-target cell interaction, we used a panel of three different anti-CD8 antibodies and tested their effect on target cell lysis. A representative experiment is shown in Fig. 3 C using the OKT8 antibody. Although recognition of HCV core 178 depends in part on CD8 availability, self-peptide recognition of CYP2A6 does not. Further studies will be required to define the mechanism responsible for the discrepancy observed between peptide-MHC binding and CTL-mediated cytotoxicity.