DNA-mediated immunization in a transgenic mouse model of the hepatitis B surface antigen chronic carrier state.

Abstract

Transgenic mice expressing the sequences coding for the envelope proteins of the hepatitis B virus (HBV) in the liver have been used as a model of the HBV chronic carrier state. We evaluated the possibility of inducing a specific immune response to the viral envelope antigens and thus potentially controlling chronic HBV infection. Using HBV-specific DNA-mediated immunization in this transgenic model, we show that the immune response induced after a single intramuscular injection of DNA resulted in the complete clearance of circulating hepatitis B surface antigen and in the long-term control of transgene expression in hepatocytes. This response does not involve a detectable cytopathic effect in the liver. Adoptive transfer of fractionated primed spleen cells from DNA-immunized mice shows that T cells are responsible for the down-regulation of HBV mRNA in the liver of transgenic mice. To our knowledge, this is the first demonstration of a potential immunotherapeutic application of DNA-mediated immunization against an infectious disease and raises the possibility of designing more effective ways of treating HBV chronic carriers.Hepatitis B virus (HBV) is the most common etiologic agent for infectious liver disease. Following initial infection, some individuals fail to resolve their infection and thereby become chronic carriers. The proportion of HBV-infected persons proceeding to the chronic carrier state is 5-20% of those infected as adults and as high as 95% with perinatal transmission such as occurs in areas where HBV is endemic. There are estimated to be more than 250 million chronic HBV carriers in the world today and there is a significant association between persistent infection and liver cirrhosis or hepatocellular carcinoma (1). The control of HBV infection is thought to be mediated by both humoral and cellular immune responses involving neutralizing antibodies as well as class I and class II major histocompatibility complex (MHC)-restricted T cells (2-4). Patients who successfully clear the virus following acute infection mount a multispecific polyclonal immune response to several HBV antigens, whereas those who remain persistently infected develop only a weak and more restricted antiviral response (5-9). In infected newborns, a diminished antiviral immune response that may be due to neonatal tolerance mechanisms (see ref. 10) probably plays an important role in viral persistence. In chronically infected patients empty viral particles carrying the HBV surface antigen (HBsAg) are produced and secreted in large amounts by the hepatocytes, whether or not the virus replicates in the liver. These particles persist in the serum and the corresponding HBsAg-specific neutralizing antibodies (anti-HBs) are either not induced or remain undetectable by conventional techniques due to the formation of immune complexes (11).We have used transgenic (Tg) mice that constitutively express the HBsAg (12) as a model of chronic HBV carriers to study the possibility of inducing an immune response to HBsAg and thus contr...

Multiepitopic HLA-A*0201-Restricted Immune Response Against Hepatitis B Surface Antigen After DNA-Based Immunization

“…To date, several constructs have been tested in different animal models (mice and nonhuman primates) in which Abs (15,16), CD4 ϩ T cell proliferative responses (17), and CD8 ϩ CTL were induced (18 -20). Results obtained in HBsAg-transgenic mice, an animal model for HBV chronic carriers, suggested that DNA-based immunization against HBsAg could induce or increase the immune response in chronically infected patients (6,17). These results have been further confirmed in duck and woodchuck as animal models for hepadnavirus infection (21,22).…”

“…Several observations suggest that cytotoxic T cells are required for the viral clearance, although lysis of infected hepatocytes is unlikely to be the only mechanism through which CD8 ϩ T cells exert their anti-viral effect. Indeed, in transgenic mouse models for HBV gene expression and/or replication, CTL mediate not only the down-regulation of viral gene expression (5,6) but also the control of viral replication (7). This phenomenon is probably due to the anti-viral effects of Th1 cytokines (i.e., IFN-␥, IFN-␣, IFN-␤, and TNF-␣) secreted by CD8 ϩ T cells after antigenic stimulation or following a concomitant viral infection (8).…”

Update of Liver Disease Related to Chronic Hepatitis B Virus Infection.

“…DNAvaccination is probably a more potent method to induce antigen-specific immunity than protein or peptide vaccine. It is reported that immunization with plasmids that contain HBsgene can profoundly reduce the production of HBsAgin transgenic mice that produce HBsAgin their livers (14). This may be a promising approach to cure patients with chronic HBVinfection, and more detailed study should be done to increase the efficacy and to elucidate the mechanismof viral clearance.…”

Immune therapy of hepatitis B virus chronic infection

“…Younossi et al 1 suggest that ascertainment bias due to an interest in iron storage disorders explains the high prevalence of HFE mutations in the series from Brisbane 2 and Boston. 4 In these later two studies, most but not all iron overload in nonalcoholic steatohepatitis (NASH) was associated with mutations of the HFE gene. We would argue that the high prevalence of HFE mutations and mild iron overload in these studies reflect the ethnic background of patients referred to these centers and the interactions of these HFE mutations and the factors that result in NASH.…”

“…The theoretical basis for immune therapy in chronic HBV infection comes from animal models suggesting the possibility of using hepatitis B surface and core epitopes 2,3 or DNA immunizations 4,5 to stimulate immune responses. Moreover, pilot studies of vaccine-specific therapy in humans with chronic hepatitis B showed encouraging results.…”