Identification of a highly cross-reactive CD8+ T cell repertoire that recognizes an HEV peptide and an apoptotic epitope

Introduction: Hepatitis E virus (HEV) infection is associated with extrahepatic manifestations, including autoimmune disorders. Several mechanisms have been suggested by which infections can initiate autoimmunity. One mechanism is cross-reactivity, where a foreign antigen shares sequence or structural similarity with self-antigens. Another mechanism could be that T cells are responsive to caspase-cleaved (apoptotic) antigens derived from effector T cells undergoing apoptosis, thereby contributing to immunopathology of autoimmune diseases. Here we hypothesize that CD8+ T cells can be cross-reactive to HEV antigens as well as to apoptotic antigens.

Objectives: To elucidate cross-reactivity of CD8+ T cells to HEV and apoptotic epitopes.

Patients and Methods: CD8+ T cells isolated from HEV seronegative, healthy individuals were expanded in-vitro using HEV genotype 3 overlapping peptides spanning all 3 open reading frame-encoded proteins. T cell response was examined by intracellular cytokine staining (ICS) while cross-reactivity was determined by the frequency of apoptotic epitope-specific CD8+ T cells as measured by dextramer staining. Cross-reactive CD8+ T cells were sorted and the T cell receptor (TCR) repertoire was analysed.

Results: Notable HEV-specific CD8+ T cell were detected in 3 out of 4 unexposed individuals tested by ICS. In one donor, we detected strong cross-reactivity between an HEV 9mer peptide and apoptotic epitope MYH9 – 478. After 14 days in-vitro stimulation with the HEV peptide, up to 25% of CD8+ T cells were MYH9 – 478 dextramer positive, which produced cytokine upon HEV peptide restimulation. Interestingly, sequence analysis of TCR showed a highly oligoclonal repertoire, with a maximum of two T cell clonotypes. All clones showed an unusual CDR3 motif in the TCR β chain with multiple glycines, which may help to explain the flexibility of the TCR to interact with two very different epitopes (2 out of 9 a.a homology).

Conclusion: Our study provides evidence for cross-reactive HEV-specific CD8+ T cells in HEV seronegative individuals. The cross-reactivity with apoptotic epitopes gives these T cells autoinflammatory potential. The unusual glycine-rich region in TCR may be a feature of highly cross-reactive T cells and of diagnostic characteristic.