Christian F. Grimm

Immunotherapy of Murine Hepatocellular Carcinoma by α-Fetoprotein DNA Vaccination Combined with Adenovirus-Mediated Chemokine and Cytokine Expression

Most hepatocellular carcinomas (HCCs) express oncofetal alpha-fetoprotein (AFP). We and others have demonstrated efficient tumor control mediated by cellular immune responses in mice bearing subcutaneous tumors derived from the AFP-expressing murine HCC cell line Hepa 1-6 by DNA vaccination against AFP. In the present study, we examined AFP DNA vaccination in the AFP-expressing primary murine HCC model BW7756. In this model AFP DNA vaccination resulted in only minimal lymphocytic infiltration and failed to control tumor growth. To augment the AFP-specific cellular immune response, intratumoral expression of chemokine IP-10 (interferon-inducible protein-10) and the proinflammatory cytokine interleukin (IL)-12 by adenoviral vectors (AdmIL-12 and AdmIP-10) was analyzed. Intratumoral injection of AdmIL-12 and AdmIP-10 resulted in transient tumor regressions, without prolongation of animal survival. By contrast, AFP DNA vaccination followed by intratumoral injection of AdmIL-12 and AdmIP-10 resulted in tumor regression in all animals and in prolongation of animal survival; in 25% of animals the tumors became undetectable. This study demonstrates for the first time that activation of effector cells against a tumor antigen induced by the combination of DNA vaccination and intratumoral chemokine and cytokine expression is superior to the respective treatment strategies alone. This effect may be mediated by attraction of activated effector cells to the tumor tissue.

Induction of cytotoxic T lymphocyte responses against hepatitis delta virus antigens which protect against tumor formation in mice

The cellular immune response is a crucial defense mechanism against hepatotropic viruses and in chronic viral hepatitis prevention. Moreover, hepatitis delta virus (HDV) immunogenicity may be an important component in the development of prophylactic and therapeutic vaccines. Therefore, we evaluated the immunogenicity of the small (HDAg) or large delta antigen (LHDAg) to be used as a DNA-based vaccine. We immunized different mouse haplotypes, determined cellular immune responses, and tested protection of animals against tumor formation using syngeneic tumor cells stably expressing the delta antigens. Both LHDAg and HDAg primed CD4+ and CD8+ T cell immunity against both forms of delta antigens. CD8+ T cell frequencies were about 1% and antigen-specific CD8+ T cells remained detectable directly ex vivo for at least 35 days post-injection. No anti-delta antibody responses could be detected despite multiple detection systems and varied immunization approaches. We observed protection against syngeneic tumor formation and growth in mice immunized with DNA plasmids encoding secreted or intracellular forms of HDAg and LHDAg but not with recombinant HDAg establishing the generation of significant cellular immunity in vivo. Both CD4+ and CD8+ T cells were required for antitumoral activity as determined by in vivo T cell depletion experiments. The results indicate that DNA-based immunization with genes encoding LHDAg and HDAg induces strong T cell responses and, therefore, is an attractive approach for the construction of therapeutic and prophylactic T cell vaccines against HDV.

Immunotherapy directed against alpha-fetoprotein results in autoimmune liver disease during liver regeneration

BACKGROUND & AIMS Priming immune responses against alpha-fetoprotein (AFP) highly expressed in the majority of hepatocellular carcinomas results in significant antitumoral T-cell responses. Liver regeneration in humans and mice, however, is also associated with increased AFP expression. Therefore, we evaluated the risk of AFP-directed immunotherapeutic approaches to induce autoimmunity against the regenerating liver. METHODS Mice were immunized with DNA encoding mouse AFP. For induction of liver regeneration, partial hepatectomy was performed and mice were monitored by serial histopathologic examinations and measurements of serum ALT activities (U/L), and by determination of the kinetics of AFP-specific T-cell responses. RESULTS Livers of AFP immune mice without partial hepatectomy were characterized by minor lymphocytic infiltrations without transaminase elevations. By contrast, a significant hepatocyte damage was observed in regenerating liver that correlated well with the number of AFP-specific CD8(+) T cells, the activity of liver regeneration, and the level of AFP synthesis. Autoimmune liver damage was mediated by CD4(+) T cell-dependent CD8(+) cytotoxic T lymphocytes. CONCLUSIONS These results show that priming of T-cell responses against shared tumor-specific self antigens may be accompanied by induction of autoimmunity dependent on the level of expression of the self antigen and have important implications for the development of antitumoral vaccines targeted against antigens that are not strictly tumor-specific.