Introduction: Hepatitis C virus (HCV)-specific T lymphocyte responses have been demonstrated in peripheral blood from injection drug users (IDUs) persistently HCV antibody and RNA negative despite high-risk behavior. We have termed these apparently HCV resistant cases "Exposed Uninfecteds" (EUs), and have studied the evolution of T-cell responses to determine if they are protective in nature.
Methods: Twenty-one EU cases were studied using a questionnaire to ascertain injecting behavior details. Peripheral blood mononuclear cells were isolated from whole blood and an interferon-gamma (IFN-γ) enzyme-linked immunosorbent spot (ELISPOT) assay used to detect T-cell responses to a panel of HCV proteins. EU cases were subdivided by injecting drug patterns into (1) cases in rehabilitation who stopped injecting, (2) prisoners (infrequent/noninjectors), and (3) cases who continued to inject.
Results: EUs continuing to inject had significantly stronger (P < .01) and more frequent (P < .05) HCV-specific IFN-γ ELISPOT responses than controls or noninjecting EUs. EUs in rehabilitation lost their T-cell responses during follow-up, while those continuing to inject maintained them.
Conclusions: HCV-specific T-cell responses in EU cases wane within months of cessation of injection drug use. Maintenance of these T-cell responses appears to be dependent on continuing HCV exposure through injection drug use.