Genetic Immunization of Chimpanzees Chronically Infected with the Hepatitis B Virus, Using a Recombinant Retroviral Vector Encoding the Hepatitis B Virus Core Antigen

Abstract

Cytotoxic T lymphocyte (CTL) activity and CD4+ helper T cell responses to the hepatitis B virus (HBV) core antigen (HBcAg) have been implicated in clearance of acute and chronic HBV infections. We showed that intramuscular injections of a novel recombinant retroviral vector expressing an HBcAg-neomycin phosphotransferase II (HBc-NEO) fusion protein induces HBc/eAg-specific antibodies and CD4+ and CD8+ T cell responses in mice and rhesus monkeys. We have now immunized three chronically infected chimpanzees, each with 10(10) CFU of nonreplicating retroviral vector particles expressing the HBc-NEO fusion protein. Of two immunized chimpanzees examined for CTL responses, one developed HBcAg-specific CTLs and showed marginal, transient elevations of alanine aminotransferase (ALT) levels following injection. However, both chimpanzees remained positive for serum HBeAg, negative for anti-HBe antibody by conventional assays, and displayed no change in HBV viral load throughout the study. In contrast, the third chimpanzee exhibited a traditional seroconversion evidenced by a loss of serum HBeAg and the subsequent emergence of anti-HBe antibodies within 24 weeks after the first injection. Simultaneously, two transient ALT flares and a significant decrease in the serum HBV DNA levels were noted. Despite its limitations, the present study demonstrates (1) the safety of treatment with high titers of retroviral vector in chimpanzees, (2) the capability of a retroviral vector expressing HBcAg to stimulate immune responses in HBV chronic carrier chimpanzees, and (3) that retroviral vector immunization may be therapeutically beneficial in the treatment of chronic HBV infection.

Cellular and humoral immune responses induced by intradermal or intramuscular vaccination with the major hepatitis B surface antigen

“…16,26 In different animal models the HBV-specific T-and B-cell responses could be enhanced by DNA-based genetic immunization and thereby the immune responses could be modified by cytokine coimmunizations and different vaccination routes. 13,14,27,28 However, in an uncontrolled trial the therapeutic vaccination with soluble middle HBsAg (HBsϩpreS2) resulted in viral clearance in about 25% of patients with chronic hepatitis B. 15 In addition, intradermal application of soluble HBsAg induced specific CTL activation in mice indicating that the proteinbased immunizations could also be very effective in the treatment of chronic hepatitis B.…”

“…12 Therefore, DNA-based genetic immunization procedures are currently under development. 13,14 Moreover, pilot studies showed that the therapeutic vaccination with soluble HBV surface antigens led to viral clearance in a significant part of the patients with chronic hepatitis B. Thus, although the involved mechanisms remain to be investigated it can be suggested that protein-based immunizations could also be effective in the treatment of chronic hepatitis B.…”

Latest Developments in Gene Transfer Technology: Achievements, Perspectives, and Controversies over Therapeutic Applications

“…Studies are currently in progress to generate more viral vectors to be used in the AIDS vaccine programs [34], and develop therapeutic vaccines for patients with AIDS [35]. Several research programs are addressing the possibility of developing either preventive or therapeutic DNA-based vaccines against malaria [29,30,32,36,37], tuberculosis [26,32], hepatitis A, B and C viruses [38][39][40][41][42][43][44][45], influenza virus [27,28], Ebola virus [31], and La Crosse virus [46]. Interestingly, the same principle of genetic immunization may be used to treat allergies [18] and autoimmune diseases [47,48], or to prevent the rejection of transplanted allograft tissues [49,50].…”

Humoral and cellular immunogenecity of DNA vaccine based on hepatitis B core gene in rhesus monkeys

“…Sallberg et al reported that DNA immunization of HBV core gene using retrovirus as vector could markedly decrease the HBV DNA level in the sera of experimental chimpanzees, and even induce the seroconversion of HBeAg to anti-HBe [49] . Our results showed that using plasmid as vector the DNA vaccine could also stimulate the immune responses in nonhuman primate rhesus monkeys, which was obviously helpful and beneficial for the host to inhibit and eventually eradicate chronically infected virus, including hepatitis B virus.…”