Hepatitis C virus–like particles induce virus-specific humoral and cellular immune responses in mice

Abstract

We have recently described the production of hepatitis C virus-like particles (HCV-LPs) in insect cells that resemble the putative virions. Here we evaluate the humoral and cellular immunogenicity of the virus-like particles with or without viral p7 protein, a small viral polypeptide that resides between the structural and nonstructural regions of the HCV polyprotein and whose function has not been defined. Immunized BALB/c mice developed high titers of anti-E2 antibodies and virus-specific cellular immune responses including cytotoxic T lymphocytes and T helper responses with gamma interferon production. The virus-like particles without p7 generated a higher cellular immune response with a more T H 1 profile than the particles with p7. Immunization of heat-denatured particles resulted in substantially lower humoral and cellular responses, suggesting that the immunogenicity is strongly dependent on particle Hepatitis C virus (HCV) is a positive-stranded RNA virus that belongs to the Flaviviridae family. The HCV genome contains a single open reading frame coding for a polyprotein that is cleaved into structural and nonstructural proteins by hostand virus-specific proteases. The structural proteins consist of core and 2 envelope glycoproteins E1 and E2. Given the global health burden of HCV infection, there is a paramount need to develop a vaccine against HCV. 1 However, a robust infectious tissue culture system for passaging and expanding the virus and for testing neutralizing antibodies is still lacking. Therefore, newer approaches have to be adopted for HCV vaccine development.Because HCV is an enveloped virus, neutralizing determinants likely reside on the surface of the envelope. The envelope protein E2 of HCV contains highly variable sequences within the N-terminal region (HVR1), which are thought to contain neutralizing B-cell epitopes. 2 Immunization of chimpanzees with recombinant E1/E2 proteins can induce hightiter anti-envelope antibodies but only protects animals from a low-dose viral challenge with the homologous strain. 3 Studies in humans and chimpanzees have indicated that failure to generate multispecific cellular immune responses against HCV in the acute phase of infection is associated with chronicity. 4-7 Therefore, an ideal HCV vaccine should be able to induce strong humoral immune responses against the envelope proteins and to prime broad, HCV-specific T-helper and cytotoxic T-cell responses (for review, see Houghton 8 and Lechmann and Liang 9 ).Virus-like particles are attractive as a recombinant protein vaccine, because they mimic closely the properties of native virions. Papillomavirus-and rotavirus-like particles synthesized in insect cells have been shown to generate protective immunity. [10][11][12] These studies showed that virus-like particles can induce not only high-titer neutralizing antibodies but also strong cytotoxic T lymphocyte (CTL) responses in immunized animals. [13][14][15] Our laboratory has recently reported the synthesis of hepatitis C virus-like particles in insect cel...

Immunization with hepatitis C virus-like particles results in control of hepatitis C virus infection in chimpanzees

“…This observation is in contrast to the significant effect of this adjuvant in the mouse study (8)(9)(10). Although a minor enhancing effect of this adjuvant was observed in our previous baboon study (11), we believe this adjuvant in formulation with HCV-LPs is probably not useful in higher primates, including humans.…”

“…We have previously reported the synthesis of HCV-like particles (HCV-LPs) by using a recombinant baculovirus containing the cDNA of HCV structural proteins, core, E1, and E2 (7). The HCV-LPs induced virus-specific humoral and cellular immune responses in BALB/c mice (8) and HLA-A 2.1 transgenic (AAD) mice (9,10). These HCV-LP-induced immune responses protected mice from challenge with recombinant HCV-vaccinia expressing HCV structural proteins (vvHCV.S) in a surrogate HCV-vaccinia challenge model (9).…”

“…Standard T cell proliferation assays were performed on PBMCs collected at various time points, as described in the SI. Enzyme-linked immunoassay (EIA) for anti-core or E1/E2 has been described previously (8). Anti-HCV seroconversion after the challenge was monitored by the commercially available assay EIA 2.0 (Abbott Laboratories, Abbott Park, IL).…”

Virus‑like particles as a vaccine delivery system: Myths and facts

“…1) have been tested in mice and baboons and shown to be effective at stimulating both cellular and humoral immune responses. 7,53,59 In one experiment, -8 week-old female BALB/c mice were immunized intramuscularly three times, at three week intervals with 20 µg insect cell derived HCV VLP, produced by co-expressing HCV coreE1-E2. Because of the lack of a suitable animal model for HCV infections a recombinant vaccinia virus expressing HCV structural proteins (vvHCV.S) was used as a model system.…”

Hepatitis C virus ultrastructure and morphogenesis

“…Although putative HCV-LPs were observed by EM in large ER cisternae in the insect cells infected with these recombinant baculoviruses, they were not secreted and could only be purified by cell lysis and detergent treatment. As for the VLPs of papillomaviruses and retroviruses, which are currently being evaluated for vaccine strategies (Stanley et al, 2002;Young et al, 2003), the HCV-LPs produced by insect cells induce humoral and cellular immune responses and are therefore promising as candidate vaccines against HCV (Baumert et al, 1999;Lechman et al, 2001;Murata et al, 2003). The HCV-LPs obtained with the baculovirus expression system have also been used to investigate binding to host-cell plasma membranes and for studies of HCV receptors (Wellnitz et al, 2002;Triyatni et al, 2002;Saunier et al, 2003).…”