We have recently demonstrated that immunization with hepatitis C virus-like particles (HCV-LPs) generated in insect cells can elicit both humoral and cellular immune responses in BALB͞c mice. Here, we evaluate the immunogenicity of HCV-LPs in HLA2.1 transgenic (AAD) mice in comparison to DNA immunization. HCV-LP immunization elicited a significantly stronger humoral immune response than DNA immunization. HCV-LP-immunized mice also developed stronger HCV-specific cellular immune responses than DNA-immunized mice as determined by using quantitative enzyme-linked immunospot (ELISpot) assay and intracellular cytokine staining. In BALB͞c mice, immunization with HCV-LPs resulted in a >5 log10 reduction in vaccinia titer when challenged with a recombinant vaccinia expressing the HCV structural proteins (vvHCV.S), as compared to 1 log 10 decrease in DNA immunization. In HLA2.1 transgenic mice, a 1-2 log10 reduction resulted from HCV-LP immunization, whereas no reduction was seen from DNA immunization. Adoptive transfer of lymphocytes from HCV-LP-immunized mice to naive mice provided protection against vvHCV.S challenge, and this transferred immunity can be abrogated by either CD4 or CD8 depletion. Our results suggest that HCV-LPs can induce humoral and cellular immune responses that are protective in a surrogate HCV challenge model and that a strong cellular immunity provided by both CD4 and CD8 effector lymphocytes may be important for protection from HCV infection.

Recombinant hepatitis C virus (HCV)-like particles (HCV-LPs) containing HCV structural proteins (core, E1, and E2) produced in insect cells resemble the putative HCV virions and are capable of inducing strong and broad humoral and cellular immune responses in mice and baboons. Here, we present evidence on the immunogenicity and induction of protective immunity by HCV-LPs in chimpanzees. Chimpanzees (two in each group), were immunized with HCV-LPs or HCV-LPs plus AS01B adjuvant. After immunizations, all animals developed an HCV-specific immune response including IFN-␥ ؉ , IL-2 ؉ , CD4 ؉ , and CD8 ؉ T cell and proliferative lymphocyte responses against core, E1, and E2. Upon challenge with an infectious HCV inoculum, one chimpanzee developed transient viremia with low HCV RNA titers (10 3 to 10 4 copies per ml) in the third and fourth weeks after the challenge. The three other chimpanzees became infected with higher levels of viremia (10 4 to 10 5 copies per ml), but their viral levels became unquantifiable (<10 3 copies per ml) 10 weeks after the challenge. After the HCV challenge, all four chimpanzees demonstrated a significant increase in peripheral and intrahepatic T cell and proliferative responses against the HCV structural proteins. These T cell responses coincided with the fall in HCV RNA levels. Four naïve chimpanzees were infected with the same HCV inoculum, and three developed persistent infection with higher viremia in the range of 10 5 to 10 6 copies per ml. Our study suggests that HCV-LP immunization induces HCV-specific cellular immune responses that can control HCV challenge in the chimpanzee model. envelope proteins ͉ prevention ͉ protective immunity ͉ vaccine ͉ viral clearance H epatitis C virus (HCV) is a major public health problem.Approximately 170 million people are infected by the virus worldwide (1, 2). HCV causes a high rate of chronic infection, which can lead to complications of chronic liver disease such as liver cirrhosis and hepatocellular carcinoma. The efficacy of therapy for chronically infected patients is less than satisfactory. Development of an effective vaccine may hold the key to controlling HCV infection. HCV displays high genetic and antigenic diversities, with at least six different genotypes and diverse quasispecies within infected individuals (1, 2). In addition to this inherent problem, the lack of convenient and robust tissue culture systems and small animal models further hampers the effort to develop an effective HCV vaccine (3). The use of recombinant HCV envelope proteins as a vaccine candidate has been met with variable success. High titers of anti-E1/E2 antibodies could be induced and possibly resulted in lower propensity to chronicity upon HCV challenge (3-5). Recently, a combined modality of plasmid DNA and adenoviral vector to deliver HCV structural and nonstructural antigens induced a strong HCV-specific cell-mediated immunity in chimpanzees and resulted in attenuated HCV infection after challenge (6). However, in this study, no obvious difference was observe...

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