Hepatitis C virus (HCV)‐specific T‐cell responses among recombinant immunoblot assay‐3–indeterminate blood donors: a confirmatory evidence of HCV exposure

BACKGROUND: Blood donors are routinely screened for hepatitis C virus (HCV) infection. Some show weak anti-HCV responses, often restricted to a single antigen on confirmatory immunoblot (recombinant immunoblot assay [RIBA]) testing. The aim of this study was to investigate the extent to which such RIBA-indeterminate donors had previously been exposed to HCV. STUDY DESIGN AND METHODS: T-cell responses to HCV recombinant proteins (core, NS3, and NS3 helicase) were analyzed using an interferon-gamma (IFN-gamma) enzyme-linked immunospot (ELISpot) assay and quantification of cytokines in culture supernatants in 27 RIBA-indeterminate donors, 60 RIBA-confirmed donors (48 with and 12 without HCV RNA), and 30 RIBA-negative donors. RESULTS: HCV-specific T-cell responses were identified in 13 (48%) RIBA-indeterminate donors, 33 (55%) RIBA-confirmed donors, and 4 (13%) RIBA-negative controls (p = 0.008 and p < 0.001, respectively). The magnitude of the T-cell response among indeterminate donors was similar to that of RIBA-confirmed donors for all HCV antigens and the specificity of the ELISpot results was confirmed by antigen-specific cytokine production (interleukin-2 and IFN-gamma) in short-term culture supernatants. CONCLUSIONS: These findings confirm that approximately half of RIBA-indeterminate donors have resolved a previous HCV infection and suggest that ELISpot might be a useful tool to clarify the status of such donors and help in their counseling and management.