Mouse alpha-fetoprotein-specific DNA-based immunotherapy of hepatocellular carcinoma leads to tumor regression in mice

Analysis of CD4+ T-Cell responses to a novel alpha-fetoprotein-derived epitope in hepatocellular carcinoma patients

PURPOSE

Alpha-fetoprotein (AFP) is a tumor-associated antigen in hepatocellular carcinoma and is a target for the development of cancer vaccine. Four immunodominant AFP-derived HLA-A*0201-restricted peptides have been identified and the administration of these peptides with an adjuvant has stimulated AFP-specific CTL responses in hepatocellular carcinoma patients. However, no AFP-derived CD4 T-cell epitope has yet been reported and the status of AFP-specific CD4(+) T-cell responses in hepatocellular carcinoma patients is not fully understood. The aim of this study was to analyze naturally occurring CD4(+) T-cell responses to AFP.

EXPERIMENTAL DESIGN

We analyzed the ability of CD4(+) T cells to recognize an HLA-DR-restricted AFP-derived epitope in 41 hepatocellular carcinoma patients and 24 non-hepatocellular carcinoma control patients using intracellular cytokine assays for IFN-gamma.

RESULTS

Here, for the first time, we report the identification of an AFP-derived CD4(+) T-cell epitope that is recognized by circulating lymphocytes from hepatocellular carcinoma patients in association with HLA-DR. The absence of detectable responses in healthy donors and patients with chronic liver disease suggests that AFP-specific CD4(+) T cells in the responder patients had been previously expanded in vivo in response to the tumor. The anti-AFP CD4(+) T-cell response was only detected in hepatocellular carcinoma patients with normal or mildly elevated serum AFP levels who were in the early stage of disease.

CONCLUSION

Our data will be instrumental in the development of cancer vaccine using AFP-derived immunogens.

Activation of dendritic cells by local ablation of hepatocellular carcinoma

BACKGROUND/AIMS

Local ablation methods are an effective treatment for hepatocellular carcinoma (HCC). The rate of recurrence or development of intra-hepatic metastases may be lowered by antitumoral immune responses. Since HCCs are in general only weakly immunogenic, cell injury induced by local tumor ablation (PEI/RFTA) may increase HCC immunogenicity and may release endogenous adjuvants that activate dendritic cells (DC). The aim of the study, therefore, was the analysis whether PEI or RFTA induced injury results in an adjuvant effect for immune responses to HCCs.

METHODS

Eight HCC patients were treated with PEI or RFTA and serially analyzed for 4 weeks. Plasmocytoid (PDC) and myeloid dendritic cells (MDC) were analyzed directly ex vivo and in vitro using FACS and proliferation assays.

RESULTS

HCC ablation induced a functional transient activation of MDC but not of PDC associated with increased serum levels of TNF-alpha and IL-1beta.

CONCLUSIONS

These findings suggest that the combination of PEI or RFTA and active antigen specific immunotherapeutic approaches using DCs is a promising approach for the induction of sustained antitumoral immune responses aiming at the reduction of tumor recurrence and metastases in HCC patients.

Molekulare Therapie in der Gastroenterologie und Hepatologie

During recent years, molecular techniques have significantly impacted our understanding and therapeutic concepts in gastrointestinal and liver disease. In a number of diseases, diagnostic work-up includes molecular data that supplements the phenotypical evaluation. This includes monogenic diseases as well as the identification of genetic risk factors (e. g. NOD2/CARD15 mutation in Crohn's disease) and viral disease. Attempts to replace liver transplantation in hereditary liver disease by targeted molecular interventions (e. g. via viral vectors) are still experimental, but the associated techniques have improved considerably. The molecular identification of therapeutic targets was followed by the development of specifically tailored therapeutics. These agents are mainly used in the treatment of chronic inflammatory bowel disease and gastrointestinal tumors.

Gene therapy of liver diseases

Many liver diseases lack satisfactory treatment and alternative therapeutic options are urgently needed. Gene therapy is a new mode of treatment for both inherited and acquired diseases, based on the transfer of genetic material to the tissues. Genes are incorporated into appropriate vectors in order to facilitate their entrance and function inside the target cells. Gene therapy vectors can be constructed on the basis of viral or non-viral molecular structures. Viral vectors are frequently used, due to their higher transduction efficiency. Both the type of vector and the expression cassette determine the duration, specificity and inducibility of gene expression. A considerable number of preclinical studies indicate that a great variety of liver diseases, including inherited metabolic defects, chronic viral hepatitis, liver cirrhosis and primary and metastatic liver cancer, are amenable to gene therapy. Gene transfer to the liver can also be used to convert this organ into a factory of secreted proteins needed to treat conditions that do not affect the liver itself. Clinical trials of gene therapy for the treatment of inherited diseases and liver cancer have been initiated but human gene therapy is still in its infancy. Recent progress in vector technology and imaging techniques, allowing in vivo assessment of gene expression, will facilitate the development of clinical applications of gene therapy.

Current strategies in cancer gene therapy

Cancer gene therapy is the most studied application of gene therapy. Many genetic alterations are involved in the transformation of a normal cell into a neoplastic one. The two main gene groups involved in cancer development are oncogenes and tumor suppressor genes. While the latter eliminates cancerous cells via apoptosis, the former enhances cell proliferation. Therefore, apoptotic genes and anti-oncogenes are widely used in cancer gene therapy. In addition to oncogenes and tumor suppressor genes, chemotherapy and gene therapy can be combined through suicide gene strategy. A suicide gene encodes for a non-mammalian enzyme; this enzyme is used to convert a non-toxic prodrug into its active cytotoxic metabolite within the cancerous cells. Tumor suppressor genes, anti-oncogenes and suicide genes target cancer cells on the molecular level. On the other hand, cancer is immunogenic in nature; therefore, it can also be targeted on the immunological level. Boosting the immune response against cancerous cells is usually achieved via genes encoding for cytokines. Interleukin-12 gene, for example, is one of the most studied cytokine genes for cancer gene therapy applications. DNA vaccines are also used after conventional treatments to eliminate remnant malignant cells. All these therapeutic strategies and other strategies namely anti-angiogenesis and drug resistant genes are briefly reviewed and highlighted in this article.

Spontaneous tumor-specific humoral and cellular immune responses to NY-ESO-1 in hepatocellular carcinoma

PURPOSE

Hepatocellular carcinoma (HCC) is the fifth most common cancer around the world. Although several therapeutic approaches for treatment of HCC are available, survival rates for HCC patients are still very poor because of inefficient treatment options. For HCC, as well as other tumors, antigen-specific immunotherapy remains a viable approach that is dependent on the definition of tumor-associated antigens. NY-ESO-1, a member of the cancer testis antigen family, is one possible candidate for a tumor-specific antigen in HCC. The aim of this study was to show the relevance of NY-ESO-1 in hepatocellular carcinoma.

EXPERIMENTAL DESIGN

Sera samples from 189 HCC patients were analyzed for NY-ESO-1-specific antibodies. Forty-nine HCC patients were screened for NY-ESO-1 mRNA expression in HCC tissue. Selected patients were followed for up to 3 years to correlate their immune response with their clinical course of events. NY-ESO-1-specific CD4+ and CD8+ T-cell responses from NY-ESO-1 seropositive patients were analyzed and a NY-ESO-1+ specific cytotoxic T-cell line was generated.

RESULTS

Twelve of 49 analyzed tumor samples expressed NY-ESO-1 mRNA and 23 of 189 patients showed NY-ESO-1-specific antibody responses. These humoral immune responses were accompanied by NY-ESO-1-specific functional CD4+ and CD8+ T-cell responses. Finally, NY-ESO-1 humoral responses were dependent on the presence of NY-ESO-1-expressing tumors.

CONCLUSIONS

This is the first report of a spontaneous immune response in HCC patients to a known tumor-specific antigen, NY-ESO-1 protein. Our data favor the possibility of immunotherapeutic strategies for the treatment of HCC.

Immunoregulation of dendritic and T cells by alpha-fetoprotein in patients with hepatocellular carcinoma

BACKGROUND/AIMS

Novel immunotherapeutic and other strategies are being explored for the treatment of hepatocellular carcinoma (HCC). Alpha-fetoprotein (AFP) may be a target antigen for immunotherapy. Little is known, however, about the immunobiology of AFP. Therefore, the impact of AFP on dendritic cells (DC), CD4+ and CD8+ T cells was studied in detail.

METHODS

Immune cells from peripheral blood of 27 HCC patients were studied using FACS, ELISPOT, and proliferation assays.

RESULTS

The in vitro generation, maturation, and T cell stimulatory capacity of DCs were not altered by AFP up to concentrations of 20 microg/ml. Higher AFP concentrations (> 20 microg/ml) resulted in phenotypic changes on DCs without impairing their capacity to stimulate CD4+ T cells. Frequencies and function of DCs and AFP specific T cells were not reduced in HCC patients independent on serum AFP levels. Finally, T lymphocytic infiltrations in the liver were not dependent on AFP serum levels.

CONCLUSIONS

These studies clearly demonstrate that (i) DC-based immunotherapeutic approaches are a promising approach for HCC treatment and (ii) AFP-reactive T cell clones have not been deleted from the human T cell repertoire establishing AFP as a potential target for T cell based immunotherapy of HCC.

Antitumor immunity induced by DNA vaccine encoding alpha-fetoprotein/heat shock protein 70

AIM: To construct a DNA vaccine encoding human alpha-fetoprotein (hAFP)/heat shock protein 70 (HSP70), and to study its ability to induce specific CTL response and its protective effect against AFP-expressing tumor.

METHODS: A DNA vaccine was constructed by combining hAFP gene with HSP70 gene. SP2/0 cells were stably transfected with pBBS212-hAFP and pBBS212-hAFP/HSP70 eukaryotic expression vectors. Mice were primed and boosted with DNA vaccine hAFP/HSP70 by intramuscular injection, whereas plasmid with hAFP or HSP70 was used as controls. ELISPOT and ELISA were used to detect IFN-γ - producing splenocytes and the level of serum anti-AFP antibody from immunized mice respectively. In vivo tumor challenge was measured to assess the immune effect of the DNA vaccine.

RESULTS: By DNA vaccine immunization, the results of ELISPOT and ELISA showed that the number of IFN-γ - producing splenocytes and the level of serum anti-AFP antibody were significantly higher in rhAFP/HSP70 group than in hAFP and empty plasmid groups (95.50 ± 10.90 IFN-γ spots/10⁶ cells vs 23.60 ± 11.80 IFN-γ spots/10⁶ cells, 7.17 ± 4.24 IFN-γ spots/10⁶ cells, P < 0.01; 126.50 ± 8.22 μg/mL vs 51.72 ± 3.40 μg/mL, 5.83 ± 3.79 μg/mL, P < 0.01). The tumor volume in rhAFP/HSP70 group was significantly smaller than that in pBBS212-hAFP and empty plasmid groups (37.41 ± 7.34 mm³vs 381.13 ± 15.48 mm³, 817.51 ± 16.25 mm³, P < 0.01).

CONCLUSION: Sequential immunization with a recombinant DNA vaccine encoding AFP and heat shock protein70 could generate effective AFP-specific T cell responses and induce definite antitumor effects on AFP-producing tumors, which may be suitable for some clinical testing as a vaccine for HCC.

Immunotherapeutic strategies for hepatocellular carcinoma

There is a continuing need for innovative, alternative therapies for hepatocellular carcinoma (HCC). Immunotherapy for cancer is attractive because of the exquisite specificity of the immune response. Activation of an HCC-specific response can be accomplished by strategies targeting tumor-associated self-antigens (for example, alpha-fetoprotein [AFP]). Gene array studies have added to the list of HCC-specific gene products that can be targeted. Alternatively, the immune response can be targeted against viral antigens in those patients infected with hepatitis B or C virus. Uncharacterized and mutated antigens can also be targeted with whole tumor cell or tumor lysate-based immunization strategies or with vectors coding for genes that make the tumor immunogenic, allowing the immune system to naturally evolve specificity against immunogenic target antigens. Strategies being investigated in animal models include increasing tumor immunogenicity by targeting cytokines or costimulatory molecules to tumor; immunization with tumor cells fused with antigen-presenting cells; adoptive transfer of viral antigen-specific T cells; and targeting AFP-expressing HCC cells by DNA, adenovirus, peptide, and dendritic cell (DC) strategies. Strategies that have been tested in human clinical trials include adoptive transfer of lymphocytes and autologous tumor-pulsed DC as well as 2 AFP-based strategies: AFP-derived peptides in Montanide and AFP peptides pulsed onto autologous DC. These trials, testing novel immune-based interventions in HCC subjects, have resulted in immunologic responses and have impacted recurrence and survival in HCC subjects.

Biologic therapy of liver tumors

Nonresectable primary and metastatic liver tumors are common malignancies that lack therapies allowing substantial prolongation of survival. Recent progress in molecular and cell biology has opened the way to novel therapies based on biological modifiers, gene transfer, and autologous stem cells. It is now possible to transfer therapeutic genes to the tumor or pericancerous tissue, and to control their expression for long periods of time. It is also feasible to generate autologous endothelial progenitor cells that can be recruited by tumoral vessels acting as vehicles to convey therapeutic genes to the interior of the tumor mass. Combination of biological modifiers, gene therapy, and cell therapy will hopefully provide efficient means to combat inoperable neoplasms in a not-very-distant future.

Steroidogenic acute regulatory (StAR)-directed immunotherapy protects against tumor growth of StAR-expressing Sp2-0 cells in a rodent adrenocortical carcinoma model

Adrenocortical carcinoma (ACC) is a highly malignant tumor with poor response to classical antitumor therapy. Steroidogenic acute regulatory (StAR) protein is expressed in most human ACCs. The aim of this study was to induce antitumoral T cells directed against StAR in a murine tumor model. Because a suitable syngenic adrenocortical mouse tumor model is lacking, we established a clone of the mouse myeloma Sp2-0 tumor cell line stably expressing murine StAR (Sp2-mStAR). Using repeated im injections of plasmid DNA encoding mStAR followed by infection with a recombinant vaccinia virus (rVV) expressing mStAR, we induced a cytotoxic T-cell response as measured by enzyme-linked immunospot assay. To demonstrate antitumor activity of the vaccination procedure, mice were treated as follows: group A, mice immunized with plasmids and rVV encoding mStAR receiving Sp2-mStAR cells; control group B, mice immunized with the empty plasmid and the empty rVV receiving Sp2-mStAR cells; control group C, mice immunized with the empty plasmid and rVV encoding P450 side-chain cleavage enzyme receiving Sp2-mStAR cells; and control group D, mice immunized with plasmid and rVV encoding mStAR receiving parental Sp2-0 cells. A high proportion (89-100%) of the control groups B, C, and D developed subcutaneous tumors. In contrast, immunization specific for mStAR (group A) was highly protective against tumor growth (percentage of tumor-free animals, 67%; P < 0.001 vs. controls). In summary, these results show that T-cell tolerance toward mStAR can be broken, resulting in antitumoral immunity. Thus, StAR represents a candidate target antigen for immunotherapeutic strategies against ACC.

Construction and identification of the eukaryotic expression vector of murine AFP-CTLA4 fusion protein

AIM: To clone the murine α-fetoprotein gene and to construct the eukaryotic expression vector of AFP-CTLA4 fusion protein.

METHODS: Total RNAs were extracted from Hepa1-6 cells, then the murine α-fetoprotein gene was amplified by RT-PCR and cloned into the eukaryotic expression vector pcDNA3.1. The extramembrane domain of mouse CTLA4 gene was amplified from plasmid pmCTLA4-Ig, followed by the addition of a linker using overlap PCR. The PCR product was subcloned into pmAFP and fused in frame with the AFP. The recombinant of vector was transformed into E. coli. DH5α, the positive clones were selected and the plasmid DNA was identified by restriction enzyme analysis and sequencing. After transient transfection of CHO-K1 cells with the recombinant of vector, Western blotting was used to detect the expression of fusion protein.

RESULTS: The 1.8 kb murine α-fetoprotein gene was successfully cloned from the total RNA of Hepa1-6 cells. The result obtained from the restriction enzyme analysis showed that the extramembrane domain of mouse CTLA4 gene was successfully inserted into pmAFP. Result of sequencing assertained that the orientation of the ligations and the reading frame were correct, and Western blotting indicated that the recombinant of vector could express murine AFP-CTLA4 fusion protein in CHO-K1 cells.

CONCLUSION: We successfully construct eukaryotic expression vector of AFP-CTLA4 fusion protein, which forms an important basis for the research of immunotherapy of hepatocellular carcinoma with pmAFP-CTLA4.

Antitumor immunopreventive effect in mice induced by DNA vaccine encoding a fusion protein of α-fetoprotein and CTLA4

AIM: To develop a tumor DNA vaccine encoding a fusion protein of murine AFP and CTLA4, and to study its ability to induce specific CTL response and its protective effect against AFP-producing tumor.

METHODS: Murine α-fetoprotein (mAFP) gene was cloned from total RNA of Hepa1-6 cells by RT-PCR. A DNA vaccine was constructed by fusion murine α-fetoprotein gene and extramembrane domain of murine CTLA4 gene. The DNA vaccine was identified by restriction enzyme analysis, sequencing and expression. EL-4 (mAFP) was developed by stable transfection of EL-4 cells with pmAFP. The frequency of cells producing IFN-γ in splenocytes harvested from the immunized mice was measured by ELISPOT. Mice immunized with DNA vaccine were inoculated with EL-4 (mAFP) cells in back to observe the protective effect of immunization on tumor. On the other hand, blood samples were collected from the immunized mice to check the functions of liver and kidney.

RESULTS: 1.8 kb mAFP cDNA was cloned from total RNA of Hepa1-6 cells by RT-PCR. The DNA vaccine encoding a fusion protein of mAFP-CTLA4 was constructed and confirmed by restriction enzyme analysis, sequencing and expression. The expression of mAFP mRNA in EL-4 (mAFP) was confirmed by RT-PCR. The ELISPOT results showed that the number of IFN-γ-producing cells in pmAFP-CTLA4 group was significantly higher than that in pmAFP, pcDNA3.1 and PBS group. The tumor volume in pmAFP-CTLA4 group was significantly smaller than that in pmAFP, pcDNA3.1 and PBS group, respectively. The hepatic and kidney functions in each group were not altered.

CONCLUSION: AFP-CTLA4 DNA vaccine can stimulate potent specific CTL responses and has distinctive antitumor effect on AFP-producing tumor. The vaccine has no impact on the function of mouse liver and kidney.

Gene therapy of hepatocarcinoma: a long way from the concept to the therapeutical impact

Hepatocellular carcinoma (HCC), the most prevalent histological form of primary liver cancer is one of the most frequent cancer worldwide. This pathology still requires the development of new therapeutical approaches. Gene therapy strategies focusing on the genetic manipulation of accessory cells involved in the immune reaction against cancer cells, or on the direct transduction of tumor cells with transgenes able to "suicide" cancer cells have been largely developed for more than ten years.

Construction and expression of recombined human AFP eukaryotic expression vector

AIM: To construct a recombined human AFP eukaryotic expression vector for the purpose of gene therapy and target therapy of hepatocellular carcinoma (HCC).

METHODS: The full length AFP-cDNA of prokaryotic vector was digested, and subcloned to the multi-clony sites of the eukaryotic vector. The constructed vector was confirmed by enzymes digestion and electrophoresis, and the product expressed was detected by electrochemiluminescence and immunofluorescence methods.

RESULTS: The full length AFP-cDNA successfully cloned to the eukaryotic vector through electrophoresis, 0.9723 IU/mL AFP antigen was detected in the supernatant of AFP-CHO by electrochemiluminescence method. Compared with the control groups, the differences were significant (P < 0.05). AFP antigen molecule was observed in the plasma of AFP-CHO by immunofluorescence staining.

CONCLUSION: The recombined human AFP eukaryotic expression vector can express in CHO cell line. It provides experimental data for gene therapy and target therapy of hepatocellular carcinoma.

Gene therapy of neoplastic liver diseases

Since advanced liver cancer lacks effective therapy in most cases, a considerable interest has been drawn towards gene therapy. Natural or chimerical genes can be transferred to the tumour itself, the non-tumoral liver, or even distant tissues using a variety of vectors administered by intratumoral or intravascular routes. The desired selectivity in gene expression can be achieved by increasing the specificity of gene delivery or by controlling gene expression with tumour-specific promoters, such as alpha-fetoprotein or carcinoembryonic antigen. There are two main approaches to gene therapy of liver cancer aiming at killing directly malignant cells or at improving the host's defensive systems, respectively. The former include replacing the lost function of tumour suppressor genes, inhibiting the action of activated oncogenes, sensitising tumour cells to prodrugs, or infecting the tumoral tissue with viruses that replicate selectively in cancer cells. Host defences can be improved by stimulating the antitumoral immune response, or by interfering with tumour vessel formation. Progress in gene therapy of liver cancer depends very much on information collected from well-designed clinical trials. This information includes knowledge of whether an efficient gene transfer has been achieved and what is the duration and magnitude of gene expression in the transduced tissues. Hopefully, magnetic resonance or positron emission tomography (PET) may turn out to be reliable procedures for tracing transgene expression in humans. Pre-clinical evidence and early clinical trials strongly suggest that there is a place for gene therapy of liver malignancies.

The immunotherapeutic effect of dendritic cells vaccine modified with interleukin-18 gene and tumor cell lysate on mice with pancreatic carcinoma

AIM: To estimate the effect of a therapeutic vaccine against pancreatic carcinoma based on dendritic cell (DC) vaccine modified with tumor lysate and Interleukin-18 gene.

METHODS: The BALB/C mice model of pancreatic carcinoma was induced with DMBA. DC vaccine was constructed through pulsed with tumor lysate and transfected by the recombinant adenoviral vector encoding IL-18 gene. The immnotherapeutic effects of DC vaccine on mice with pancreatic carcinoma were assessed (divided into DC-IL18-Lysate group, DC-Lysate group, DC-IL18 group, DC group, PBS group).

RESULTS: After vaccination of the DC vaccine, the concentration of IL-18 and IFN-γ were 2161 ± 439 ng·L^-1 and 435 ± 72 ng·L^-1 in DC-IL18-Lysate group and there was significant difference compared with other groups (P < 0.01). After vaccination of the DC vaccine, the transplanted tumors were observed on 30 d in DC-Lysate groups, on 16 d in DC-IL18 groups, on 3 d in control group, but mice remained tumor-free for at least 50 d in DC-IL18-Lysate group and there was significant difference between DC-IL18-Lysate group and other groups (P < 0.01). The median survival exceeds 62 d in DC-IL18-Lysate group. But the median survival was 48.6 d in DC-Lysate group, 33 d in DC-IL18 group, 17 d in PBS group. The survival period was obviously prolonged in DC-IL18-Lysate group than in other groups (P < 0.05, P < 0.01). The weight of pancreatic tumor was 0.22 ± 0.083 g in DC-IL18-Lysate group, 1.45 ± 0.74 g in DC-Lysate group, 1.89 ± 1.34 g in DC-IL18 group, 3.0 ± 1.6 g in DC group, 2.9 ± 2.0 g in PBS group and the weight of tumor obviously reduced in DC-IL18-Lysate group than in other groups (P < 0.05, P < 0.01).

CONCLUSION: DC vaccine modified with tumor lysate and Interleukin-18 gene can induce a specific and effective immune response against pancreatic carcinoma cell.

DNA vaccination with AFP-encoding plasmid DNA prevents growth of subcutaneous AFP-expressing tumors and does not interfere with liver regeneration in mice

The oncofetal alpha-fetoprotein (AFP) is reexpressed in the majority of hepatocellular carcinomas and may be used as a target molecule for an immunotherapy or prophylaxis against this tumor. We investigated the potential of DNA vaccination with AFP-expressing plasmid DNA to induce an immune response against AFP-expressing tumor cells in DBA/2 mice. 62.5% of mice vaccinated with AFP-expressing plasmid DNA, rejected subcutaneous syngeneic AFP-expressing P815 tumors, whereas only 16.7% of mice vaccinated with control plasmid rejected these tumor cells (P=.03). Mean survival of mice after challenge with subcutaneous AFP-expressing tumor cells was prolonged for 8 days in mice vaccinated with AFP-expressing DNA (35 days) compared to mice vaccinated with control plasmid (27 days). To rule out possible autoimmune reactions against regenerating liver, which also reexpresses AFP, we evaluated the influence of AFP-specific DNA vaccination on liver regeneration in DBA/2 mice. Histologic quantification of proliferating hepatocytes and of the amount of necrotic liver tissue in carbon tetrachloride-damaged liver did not reveal statistically significant differences in mice vaccinated with AFP-expressing plasmid compared to control mice. These data suggest that AFP-specific DNA vaccination represents a useful tool to inhibit growth of AFP-expressing tumors in mice that does not affect liver regeneration.

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 in mice

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.