Strong Hepatitis C Virus (HCV)–specific Cell-mediated Immune Responses in the Absence of Viremia or Antibodies Among Uninfected Siblings of HCV Chronically Infected Children

Background. Cell-mediated immune (CMI) responses to hepatitis C virus (HCV) antigens in adults without seroconversion or viremia are biomarkers for prior transient infection. We investigated HCV-specific CMI responses in seronegative children living with HCV-infected siblings. Methods. Children 3–18 years of age living with HCV-infected siblings were screened for HCV antibodies and HCV RNA. Peripheral blood mononuclear cells (PBMCs) were evaluated for HCV-specific CMI responses by interferon c (IFN-c) enzyme-linked immunospot assay using 3 recombinant HCV protein antigens. Flow cytometry phenotypically characterized IFN-c-secreting cells. Results. Forty-five seronegative children and 5 seropositive viremic siblings had functionally viable PBMCs. Among the 45 seronegative siblings, 15 (33.3%) had positive HCV-specific IFN-c responses, and subsequent RNA testing revealed that 3 were viremic. Compared with the 5 seropositive viremic children, the median number of HCV-specific spot-forming units was significantly higher in the 12 seronegative aviremic children (P5.002) and in the 3 seronegative viremic children (P5.025). Flow cytometric analysis revealed that IFN-c was synthesized mainly by CD41 T cells. Conclusion. Strong HCV-specific CD41 T cell responses were detectable in higher frequency amon