Fine Characterization and Determination of Cross-Reactivity of HCV-specific CD4+ T Cell Epitopes

Introduction: An important component of a successful immune response is a strong and durable CD4+ T cell response directed against multiple epitopes covering the whole HCV polyprotein. However, few HCV CD4+ epitopes have been characterized in detail so far. Here, we study a set of HCV CD4+ T cell specificities concerning their optimal length, HLA restriction and cross-genotype reactivity.

Methods: HCV-specific CD4+ T cells from PBMC from 40 HCV patients with different disease outcome (15 spontaneous resolvers) and healthy controls were in vitro expanded with a set of 24 frequently targeted HCV genotype (GT) 1a 20mer peptides. Additionally online available HCV-sequences (www.hcvdb.org) were aligned and genotype specific-variants were made for a subset of the epitopes. CD4+ T cell responses were analyzed after 10 days of culture by ELISPOT and confirmed with intracellular cytokine staining for INF-γ after restimulation with GT-specific peptides. Additionally all patients with spontaneously resolved infection were serotyped for past exposure of HCV genotype 1–6. The IL28 haplotype as well as MHC class II molecules were determined in all patients.

Results: As expected, the spontaneous resolvers show significantly more CD4+ responses (5 on average) against HCV-specific peptides than other patient groups including patients who show a sustained virological response after therapy (SVR). Testing with genotype specific peptide variants revealed varying response patterns which depend on the genotype the individual patient was exposed to.

Conclusions: Cross-genotype reactivity can be observed for some CD4+ epitopes, but varying degrees of cross reactivity in individual patients might (among other variables) depend on the exact sequence of the priming hepatitis C virus(es).

Literatur: Schulze zur Wiesch et al. Blood 2007 110:1559-1569