The hepatitis C virus (HCV) core protein-encoding sequence (HCcAg) is the most conserved gene in HCV genome and therefore may be useful to study broadly reacting T-cell epitopes. In this study BALB/c and C57BL/6 mice were immunized with a DNA based vaccine expressing the first 176 aa of HCcAg (pIDKCo). After i.m or i.p injection of pIDKCo in BALB/c mice, a detectable INF-gamma secreting response to the relevant class I-binding peptide DLMGYIPLVGA (PI) (aa 132-142) was detected suggesting the induction of HCcAg specific CD8+ T-cell effectors. CD8+ T-cell responses were also monitored in vivo by T-cell-mediated DTH reactions after subcutaneous injection of class I-binding viral peptide P 1. pIDKCo induced a strong P I -specific DTH response in both i.m and i.p immunized mice. To evaluate the T-cell response induced by pIDKCo in C57BL/6 mice, an HCcAg epitope was predicted based upon it containing the H-2K(b) binding motif XXXXF/YXXL (DLMGYIPL (P2)). pIDKCo induced a strong P2-specific DTH response with similar kinetics of swelling response to that observed in BALB/c mice. Previously, it had been demonstrated that only activated and protective CD8+ effector T cells could mediate a specific DTH in footpads of virally infected mice after local injection of viral class I-binding peptides. Hence, pIDKCo could prime a strong HCcAg-specific T-cell response in mice with the potential capacity to exert their specific effector functions in peripheral tissues. (C) 2003 Elsevier Inc. All rights reserved.