We have recently established a method to generate dendritic cells from mouse embryonic stem cells. By introducing exogenous genes into embryonic stem cells and subsequently inducing differentiation to dendritic cells (ES-DC), we can now readily generate transfectant ES-DC expressing the transgenes. A previous study revealed that the transfer of genetically modified ES-DC expressing a model antigen, ovalbumin, protected the recipient mice from a challenge with an ovalbumin-expressing tumor. In the present study, we examined the capacity of ES-DC expressing mouse homologue of human glypican-3, a recently identified oncofetal antigen expressed in human melanoma and hepatocellular carcinoma, to elicit protective immunity against glypican-3-expressing mouse tumors. CTLs specific to multiple glypican-3 epitopes were primed by the in vivo transfer of glypican-3-transfectant ES-DC (ES-DC-GPC3). The transfer of ES-DC-GPC3 protected the recipient mice from subsequent challenge with B16-F10 melanoma, naturally expressing glypican-3, and with glypican-3-transfectant MCA205 sarcoma. The treatment with ES-DC-GPC3 was also highly effective against i.v. injected B16-F10. No harmful side effects, such as autoimmunity, were observed for these treatments. The depletion experiments and immunohistochemical analyses suggest that both CD8+ and CD4+ T cells contributed to the observed antitumor effect. In conclusion, the usefulness of glypican-3 as a target antigen for antimelanoma immunotherapy was thus shown in the mouse model using the ES-DC system. Human dendritic cells expressing glypican-3 would be a promising means for therapy of melanoma and hepatocellular carcinoma. (Cancer Res 2006; 66(4): 2414-22)

To establish effective immunotherapy for cancer, it is absolutely imperative to identify ideal tumor-specific antigens as targets of antitumor immunotherapy. In addition, the development of the methods to direct immune responses toward the antigens is essential. The manipulation of dendritic cells, specialized antigen-presenting cells, is one of the promising strategies to improve the efficacy of immunotherapy for cancer (1). Currently, numerous reports have shown that dendritic cells loaded with dead tumor cells, tumor cell lysates, tumor antigenic proteins, or peptides can induce immunity and clinical responses (25). However, these vaccines often induce a weak immune response that is insufficient for clinical therapy because many tumor antigens are self-antigens against which the immune system has acquired tolerance (6, 7). For loading tumor antigens to dendritic cells for anticancer immunotherapy, the gene-based antigen expression by dendritic cells is considered to be superior to loading antigen as a peptide, protein, or tumor cell lysate (8). For the efficient gene transfer to dendritic cells, the use of virus-based vectors is required because dendritic cells is relatively unsuitable for genetic modification. Clinical trials using dendritic cells genetically modified with virus vectors (e.g., monocyte-derived dendritic cells introduced with adenovirus vectors encoding for tumor antigens) are now under way (911). Considering the broader medical applications of this method, the drawbacks of genetic modification with virus vectors include the potential risk accompanying the use of virus vectors and legal restrictions related to it. As a result, the development of safer and more efficient means is considered to be desirable.

We recently established a novel method for the genetic modification of dendritic cells (12). In this method, we generated dendritic cells from mouse embryonic stem cells by in vitro differentiation. The levels of expression of MHC molecules and costimulatory molecules, CD80 and CD86, in embryonic stem cell–derived dendritic cells (ES-DC) were comparable with those of bone marrow–derived dendritic cells (BM-DC; ref. 12). The capacity of ES-DC to simulate T cells was comparable with that of dendritic cells generated in vitro from BM-DC. We can readily generate genetically modified ES-DC by introducing expression vectors into embryonic stem cells and the subsequent induction of their differentiation into ES-DC (13, 14). The transfection of embryonic stem cells can be done with electroporation using plasmid vectors, and the use of virus-based vectors is not necessary. Once a proper embryonic stem cell transfectant clone is established, it then serves as an infinite source for genetically modified dendritic cells. In a previous study, we showed that the in vivo transfer of ES-DC expressing a model tumor antigen, ovalbumin, potently primed ovalbumin-specific CTLs, thereby eliciting a protective effect against ovalbumin-expressing tumor cells (13).

Many of the genes or gene families encoding many cancer/testis antigen or oncofetal antigens have thus far been identified and regarded as ideal targets for anticancer immunotherapy (1518). However, only a few tumor-associated antigens have been reported as the inducer of both CD8+ and CD4+ T-cell-mediated immune responses (1922). Recently, we and other groups found that an oncofetal protein glypican-3, glycosylphosphatidylinositol (GPI)–anchored membrane protein, is specifically overexpressed in human hepatocellular carcinoma (23, 24). In a subsequent study, we revealed that glypican-3 is overexpressed also in human melanoma (25). An immunohistochemical analysis revealed that the tissue distribution of murine glypican-3 protein was very similar to that in humans. In a previous study, we showed that the in vivo transfer of glypican-3 peptide-pulsed BM-DC or glypican-3-reactive CTL line had a potent effect to protect the recipient mice from the murine glypican-3-transfected Colon 26, a colorectal cancer cell line (17).

In the current study, we found that a mouse melanoma cell line F10, which is a subline of B16, naturally expressed glypican-3. Using this cell line as a target, we elucidated the antitumor effect of therapy with ES-DC genetically modified to express murine glypican-3.

Mice. CBA and C57BL/6 mice were obtained from Clea Animal Co. (Tokyo, Japan) or Charles River (Hamamatsu, Japan) and maintained under specific pathogen-free conditions. Male CBA and female C57BL/6 mice were mated to produce (CBA × C57BL/6) F1 (CBF1) mice and all studies were done with the F1 mice syngeneic to the mouse embryonic stem cell line TT2 at 6 to 8 weeks of age. The mouse experiments met with approval by Animal Research Committee of Kumamoto University.

Cell lines. The embryonic stem cell line TT2, derived from CBF1 blastocysts (26), was maintained as described previously (12). The method for induction of differentiation in vitro of embryonic stem cells into dendritic cells was done as described previously (12), and ES-DC prepared from a 14-day culture in bacteriologic Petri dishes in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) were used for in vivo and in vitro assays. C57BL/6-derived tumor cell lines, F1 and F10 sublines of B16 melanoma, a fibrosarcoma cell line MCA205 (MCA), Lewis lung cancer (3LL) and a thymoma cell line EL4, and a human hepatocellular carcinoma cell line HepG2 were provided by the Cell Resource Center for Biomedical Research Institute of Development, Aging, and Cancer, Tohoku University (Sendai, Japan). The cells were cultured in RPMI 1640 supplemented with 10% FCS. To produce glypican-3-expressing MCA (MCA-GPC3), MCA cells were transfected with pCAGGS-GPC3-internal ribosomal entry site (IRES)-puromycin-resistant (puro-R) by using LipofectAMINE 2000 reagent (Invitrogen Corp., Carlsbad, CA), selected with puromycin, and then subjected to cloning by limiting dilution in drug-free medium using 96-well culture plates (27, 28).

Generation of ES-DC expressing glypican-3. A full-length murine glypican-3 cDNA clone was purchased from Invitrogen. A cDNA fragment encoding total glypican-3 protein was isolated from that and transferred to a mammalian expression vector pCAGGS-IRES-puro-R, containing the CAG promoter and an IRES-puro-R N-acetyltransferase gene cassette (29, 30), to generate an expression vector for glypican-3, pCAGGS-GPC3-IRES-puro-R. To generate glypican-3-transfected embryonic stem cell clones, TT2 embryonic stem cells were introduced with pCAGGS-GPC3-IRES-puro-R by electroporation and selected with puromycin as described previously (12). Glypican-3-transfectant embryonic stem cell clones were subjected to a differentiation culture to generate ES-DC as described previously (1214). No maturation stimuli, such as lipopolysaccharide or tumor necrosis factor-α, were given to ES-DC before in vivo transfer. The expression of glypican-3 in transfectant ES-DC was confirmed by reverse transcription-PCR (RT-PCR).

RT-PCR and Northern blotting. Total cellular RNA was extracted and RT-PCR was done as described previously (13, 14). Briefly, total RNA was converted into cDNA and PCR was done for 33 cycles for the quantification of glypican-3 mRNA and for 30 cycles for the quantification of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA. The primer sequences were as follows: glypican-3, sense 5′-CTGACTGACCGCGTTACTCCCACA-3′ and antisense 5′-TAGCAGCATCGCCACCAGCAAGCA-3′ and GAPDH, sense 5′-GGAAAGCTGTGGCGTGATG-3′ and antisense 5′-CTGTTGCTGTAGCCGTATTC-3′. The sense strand primer used for detection of transgene-derived mRNA was corresponding to the 5′ untranslated region included in the vector DNA. PCR products were visualized by ethidium bromide staining after separation over a 1% agarose gel. A Northern blot analysis was done as described previously (31). In brief, RNA samples (20 μg total RNA per lane) were subjected to electrophoresis in formalin-MOPS gels, blotted onto nylon membranes (Hybond N+, Amersham, Piscataway, NJ), and probed with 32P-labeled DNA probe. A human glypican-3 cDNA fragment (bp 1,639-2,139) was used as a probe. Human and murine glypican-3 have a 90% similarity in nucleotide sequence and human cDNA probe hybridized to both human and murine glypican-3 mRNA.

Peptides, protein, and cytokines. Eleven kinds of 9- to 10-mer glypican-3-derived peptides predicted to bind with H2-Db or Kb were selected based on the binding score as calculated by the BIMAS software package (BioInformatics and Molecular Analysis Section, Center for Information Technology, NIH, Bethesda, MD). The peptides were synthesized by the F-MOC method on an automatic peptide synthesizer (PSSM8; Shimadzu, Kyoto, Japan) and subsequently purified by high-performance liquid chromatography. The synthetic peptides were designated as murine glypican-3-1 to -11 in ascending order of high binding score. Their amino acid sequences are as follows: murine glypican-3-1, AMFKNNYPSL; murine glypican-3-2, LGSDINVDDM; murine glypican-3-3, LTARINMEQL; murine glypican-3-4, SVLDINECL; murine glypican-3-5, TLCWNGQEL; murine glypican-3-6, YVQKNGGKL; murine glypican-3-7, GMVKVKNQL; murine glypican-3-8, RNGMKNQFNL; murine glypican-3-9, AMLLGLGCL; murine glypican-3-10, ASMELKFLI; and murine glypican-3-11, LFPVIYTQM. Murine glypican-3-11 is predicted to be restricted to H2-Kb and the others to H2-Db. Recombinant human glypican-3 protein was purchased from R&D Systems (Minneapolis, MN). Recombinant murine GM-CSF and IFN-γ were purchased from PeproTech (London, United Kingdom).

Immunohistochemical and flow cytometric analysis. An immunofluorescence analysis to detect the expression of glypican-3 was done as described previously (16). Anti-human glypican-3 polyclonal antibody was purchased from Santa Cruz Biotechnology (Santa Cruz, CA). FITC-labeled goat anti-rabbit IgG (clone ALI4408; Biosource, Camarillo, CA) was used as a second antibody and propidium iodide for nuclear DNA staining. Stained samples were subjected to microscopic analysis on a confocal microscope (Fluoview FV300, Olympus, Tokyo, Japan). Immunohistochemical analysis of frozen tissue sections was done as described previously (13, 23) using monoclonal antibody (mAb) specific to CD4 (L3T4; BD PharMingen, San Diego, CA) or CD8 (Ly-2; BD PharMingen). In the flow cytometric analysis, cell samples were stained and analyzed on a flow cytometer (FACScan; BD Biosciences, Japan) as described previously (12, 14). Antibodies used for staining were as follows: FITC-conjugated mouse anti-mouse H2-Db (clone CTDb; mouse IgG2a; Caltag, Burlingame, CA), anti-H2-Kb (clone CTKb; mouse IgG2a; Caltag) and anti-I-Ab (clone 3JP; mouse IgG2a; Caltag), R-phycoerythrin (R-PE)–conjugated anti-mouse CD11c (clone N148; hamster IgG; Chemicon, Temecula, CA), R-PE-conjugated anti-mouse CD86 (clone RMMP-2; rat IgG2a; Caltag), FITC-conjugated goat anti-mouse Ig (BD PharMingen), mouse IgG2a control (clone G155-178; BD PharMingen), FITC-conjugated mouse IgG2a control (clone G155-178; BD PharMingen), and R-PE-conjugated hamster IgG control (Immunotech, Marseille, France).

Generation of BM-DC. Generation of dendritic cells from bone marrow cells was done as described previously (17). For loading of synthetic peptides, BM-DC were incubated with a mixture of three kinds of glypican-3 peptides, murine glypican-3-2, -8, and -11 (10 μmol/L each), at 37°C for 2 hours. For loading of recombinant glypican-3 protein, BM-DC were cultured in the presence of glypican-3 protein (2 μg/mL) at 37°C for 12 hours. No maturation stimuli were given to BM-DC before in vivo transfer.

Induction of glypican-3-specific CTLs and cytotoxicity assay. The mice were i.p. immunized with 1 × 105 ES-DC twice with a 7-day interval. Seven days after the second immunization, spleen cells were isolated from the mice and cultured (2.5 × 106 per well) with ES-DC (1 × 105 per well) in 24-well culture plates in RPMI supplemented with 10% horse serum, recombinant human interleukin (IL)-2 (100 units/mL), and 2-mercaptoethanol (50 μmol/L). After the culture for 5 days, the cells were recovered and their cytotoxic activity was analyzed by 51Cr release assays using MCA, MCA-GPC3, B16-F1, and B16-F10 as target cells basically by the same method as described previously (12). B16 cells were pretreated with recombinant murine IFN-γ (1,000 units/mL) before use as target cells as reported previously (32). In some experiments, CD8+ T cells and natural killer (NK) cells were isolated from effector cell preparations by using a magnetic cell sorting system (Miltenyi, Bergisch Gladbach, Germany). Positively selected cells were 95% pure as determined by flow cytometry.

ELISPOT analysis. Glypican-3-specific T cells were induced by a culture of splenocytes isolated from mice immunized with ES-DC-GPC3 by the same way as described above, except that glypican-3-derived peptides (10 μmol/L) were added to the culture instead of ES-DC-GPC3. After 5 days, the frequency of cells producing IFN-γ on stimulation with target cells (EL4 or EL4 pulsed with each peptide, MCA or MCA-GPC3) was assessed by an ELISPOT assay as described previously (33). The spots were automatically counted and subsequently analyzed using the Eliphoto system (Minerva Tech, Tokyo, Japan).

Tumor prevention and treatment. ES-DC-GPC3 or BM-DC (1 × 105) loaded with glypican-3 peptide or protein were transferred i.p. into mice twice on days −14 and −7, and B16-F10 or MCA-GPC3 cells were challenged s.c. into the shaved back region on day 0. The tumor sizes were determined biweekly in a blinded fashion and survival rate or disease free rate was monitored. Tumor index was calculated as follows: tumor index (mm2) = (length × width). For the i.v. challenge experiments, tumor cells (B16-F10) were injected i.v. on day 0, and 1 × 105 ES-DC-GPC3 were injected i.p. twice on days 3 and 10 as described previously (34).

In vivo depletion of CD4+ and CD8+ T cells. The mice were transferred i.p. twice with 1 × 105 ES-DC-GPC3 on days −14 and −7 and challenged s.c. with 5 × 103 B16-F10 cells on day 0. For the depletion of T-cell subsets in vivo, mice were given a total of six i.p. transfers of the ascites (0.1 mL/mouse/transfer) from hybridoma-bearing nude mice or anti–asialo GM1 on days −18, −15, −11, −8, −4, and −1. Antibodies used were rat anti-mouse CD4 mAb (clone GK1.5), rat anti-mouse CD8 mAb (clone 2.43), and rabbit anti–asialo GM1 polyclonal antibody (Wako Japan; 20 μL/mouse/transfer). Normal rat IgG (Sigma-Aldrich, St. Louis, MO; 200 μg/mouse/transfer) was used as a control. The depletion of T-cell subsets by treatment with antibodies was confirmed by a flow cytometric analysis of spleen cells, which showed a >90% specific depletion.

Statistical analysis. The two-tailed Student's t test was used to determine the statistical significance of differences in the cytolytic activity and tumor growth between the treatment groups. P < 0.05 was considered to be significant. The Kaplan-Meier plot for survival was assessed for significance in the tumor challenge experiments using the Breslow-Gehan-Wilcoxon test. Statistical analyses were made using the StatView 5.0 software package (Abacus Concepts, Calabasas, CA).

Generation of ES-DC expressing glypican-3. TT2 embryonic stem cells were introduced with a murine glypican-3 expression vector, pCAGGS-GPC3-IP, driven by the CAG promoter and containing the IRES-puro-R marker gene (Fig. 1A), and several transfectant clones were isolated. The transfectant embryonic stem cell clones were subjected to differentiation to ES-DC, and a transfectant clone 12 expressing the highest level of glypican-3 was selected based on the RT-PCR analysis (Fig. 1B). ES-DC differentiated from parental embryonic stem cell line TT2 without transfection were designated as ES-DC-TT2, and ES-DC differentiated from glypican-3-transfectant embryonic stem cells were designated as ES-DC-GPC3. No significant difference was observed in the morphology and levels of the surface expression of H2-Db, H2-Kb, I-Ab, CD11c, and CD86 between ES-DC-TT2 and ES-DC-GPC3 (Fig. 1C). As a result, the transfection of the glypican-3 gene has little influence on the differentiation of ES-DC.

Figure 1.

Establishment of ES-DC genetically modified to express murine glypican-3. A, structure of pCAGGS-GPC3-IRES-puro-R vector. To obtain pCAGGS-GPC3-IRES-puro-R, a cDNA fragment, including a full-length cDNA of murine glypican-3, was inserted into a mammalian expression vector pCAGGS-IRES-puro-R containing the CAG promoter and an IRES-puromycin N-acetyltransferase gene cassette. B, expression of glypican-3 mRNA detected by RT-PCR analysis in transfectant ES-DC (ES-DC-GPC3). Primer sets (arrows in A) were designed to span the intron (917 bp) in the CAG promoter sequence to distinguish PCR products of mRNA origin (249 bp) from the genome-integrated vector DNA origin (1,166 bp). Black boxes in (A) indicate the 5′-untranslated region of the rabbit β-actin gene included in the CAG promoter. PCR was done at the cycles indicated for quantification of glypican-3 mRNA and GAPDH mRNA. C, surface phenotype of genetically modified ES-DC. The expression of the cell surface H2-Db, H2-Kb, I-Ab, CD11c, and CD86 on transfectant ES-DC was analyzed by a flow cytometric analysis. The staining patterns of ES-DC-GPC3 (thick line) closely coincided with those of parental ES-DC (thin line). Dotted lines, findings for isotype-matched control staining.

Figure 1.

Establishment of ES-DC genetically modified to express murine glypican-3. A, structure of pCAGGS-GPC3-IRES-puro-R vector. To obtain pCAGGS-GPC3-IRES-puro-R, a cDNA fragment, including a full-length cDNA of murine glypican-3, was inserted into a mammalian expression vector pCAGGS-IRES-puro-R containing the CAG promoter and an IRES-puromycin N-acetyltransferase gene cassette. B, expression of glypican-3 mRNA detected by RT-PCR analysis in transfectant ES-DC (ES-DC-GPC3). Primer sets (arrows in A) were designed to span the intron (917 bp) in the CAG promoter sequence to distinguish PCR products of mRNA origin (249 bp) from the genome-integrated vector DNA origin (1,166 bp). Black boxes in (A) indicate the 5′-untranslated region of the rabbit β-actin gene included in the CAG promoter. PCR was done at the cycles indicated for quantification of glypican-3 mRNA and GAPDH mRNA. C, surface phenotype of genetically modified ES-DC. The expression of the cell surface H2-Db, H2-Kb, I-Ab, CD11c, and CD86 on transfectant ES-DC was analyzed by a flow cytometric analysis. The staining patterns of ES-DC-GPC3 (thick line) closely coincided with those of parental ES-DC (thin line). Dotted lines, findings for isotype-matched control staining.

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Expression of glypican-3 in a F10 subline of B16 melanoma. We recently revealed that the oncofetal protein glypican-3 is specifically overexpressed in human hepatocellular carcinomas and melanomas (23, 25). To establish a mouse model system to evaluate the glypican-3 as a target antigen for anticancer immunotherapy, we searched for a transplantable mouse tumor cell line naturally expressing glypican-3. We examined the expression of glypican-3 in several mouse cell lines and found that B16-F10, a subline of B16 melanoma, expressed glypican-3. In a Northern blot analysis, as shown in Fig. 2A, where a human hepatocellular carcinoma cell line HepG2 was used as a positive control, glypican-3 mRNA was evidently detected in a mouse melanoma cell line B16-F10 but not in B16-W.T., B16-F1, 3LL, MCA205, or EL4. The expression of glypican-3 mRNA was also detected in a glypican-3-transfected MCA, MCA-GPC3. Figure 2B shows an immunofluorescence analysis to detect expression of glypican-3 protein. In accordance with the result of the Northern blot analysis, evident expression of glypican-3 protein was detected in B16-F10 and MCA-GPC3. On the other hand, MCA205 and B16-F1 cells did not express glypican-3 protein. Glypican-3 is a GPI-anchored membrane protein, and the results shown in Fig. 2B indicated that glypican-3 protein localized at or around cell membrane is consistent with this, although some differences in the staining patterns among the cells were observed.

Figure 2.

Expression of glypican-3 in cancer cell lines. A, Northern blot analysis of glypican-3 mRNA in a human hepatocellular carcinoma cell line HepG2 (positive control) and various cancer cell lines of C57BL/6 origin. The same filters were stripped and rehybridized with GAPDH cDNA to assess the loading of equal amounts of RNA. B, immunofluorescence staining analysis of murine glypican-3 protein expressed in B16 variants F1, F10, MCA205, and MCA-GPC3. These cells were stained with rabbit anti-human glypican-3 polyclonal antibody cross-reactive to murine glypican-3 (green). Chromosome DNA was visualized by propidium iodide staining (red).

Figure 2.

Expression of glypican-3 in cancer cell lines. A, Northern blot analysis of glypican-3 mRNA in a human hepatocellular carcinoma cell line HepG2 (positive control) and various cancer cell lines of C57BL/6 origin. The same filters were stripped and rehybridized with GAPDH cDNA to assess the loading of equal amounts of RNA. B, immunofluorescence staining analysis of murine glypican-3 protein expressed in B16 variants F1, F10, MCA205, and MCA-GPC3. These cells were stained with rabbit anti-human glypican-3 polyclonal antibody cross-reactive to murine glypican-3 (green). Chromosome DNA was visualized by propidium iodide staining (red).

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Priming of antigen-specific cytotoxic T cells with genetically modified ES-DC-GPC3. We analyzed the capacity of ES-DC-GPC3 to prime glypican-3-specific CTLs. The mice were immunized i.p. twice with ES-DC-GPC3 or ES-DC-TT2 on days −14 and −7. On day 0, the spleen cells were isolated and restimulated in vitro with ES-DC-GPC3 in the presence of exogenous recombinant human IL-2 (100 units/mL). After 5 days, the cells were recovered and their killing activity against target cells with or without expression of glypican-3 was analyzed. As shown in Fig. 3A and B, the effector cells primed by ES-DC-GPC3 showed a significantly higher killing activity against B16-F10 than against B16-F1, and also against MCA-GPC3 than nontransfectant MCA cells. These results suggest that the effector cells included CTLs recognizing glypican-3. In the experiments shown in Fig. 3C, we separated the effector cells into CD8+ T cells and NK cells before the killing assay. NK cells showed activity to kill MCA and MCA-GPC3 in a similar magnitude and to kill B16-F1 and F10 in a similar magnitude, indicating that they killed target cells regardless of glypican-3 expression. On the other hand, for the CD8+ fraction, the cytotoxic activity against B16-F10 was higher than that against B16-F1, and the cytotoxic activity against MCA-GPC3 was higher than that against MCA. On the contrary, spleen cells isolated from mice transferred with ES-DC-TT2 and cocultured in vitro with ES-DC-GPC3 exhibited the similar basal levels of killing activities directed against both B16-F1 and F10 as well as MCA and MCA-GPC3 (data not shown).

Figure 3.

Priming of antigen-specific CTLs with ES-DC-GPC3. The mice were transferred i.p. twice with 1 × 105 ES-DC-GPC3 on days −14 and −7. On day 0, spleen cells from immunized mice were isolated and cultured with 1 × 105 ES-DC-GPC3 per well in the presence of recombinant human IL-2 (100 units/mL) for 5 days. 51Cr release assays were done with the obtained resultant cells to evaluate the capacity to kill IFN-γ pretreated B16-F1 and B16-F10 cells (A) and MCA and MCA-GPC3 cells (B). Results are expressed as % specific lysis from triplicate assays. C, in addition, the resultant cells obtained in the same way were sorted to the fraction of NK cells and CD8+ T cells with microbeads, and another assay was done using the targets in the same condition as in (A and B). D, spleen cells from mice transferred twice with 1 × 105 ES-DC-GPC3 or ES-DC-TT2, respectively, were isolated and restimulated in vitro with 1 × 105 ES-DC-GPC3 per well for 5 days. The resultant cells were used for IFN-γ ELISPOT assay. The assay was done in triplicate using the same targets as in (A and B). Columns, mean number of IFN-γ-positive spots. E, identification of glypican-3-derived and H2-Db- or H2-Kb-restricted CTL epitopes by IFN-γ ELISPOT assays. The mice were immunized with 1 × 105 ES-DC-GPC3 twice with a 7-day interval. Spleen cells from mice immunized were restimulated in vitro with each glypican-3 peptide (10 μmol/L) and cultured for 5 days with 100 units/mL recombinant human IL-2. ELISPOT assays for 16 hours were examined against EL4 pulsed with or without each peptide and MCA or MCA-GPC3. Columns, mean total number of spots from quadruplicate assays. Data are representative of three independent experiments with similar results in (A-E). *, P < 0.05, differences in the responses are statistically significant between two values in (C-E).

Figure 3.

Priming of antigen-specific CTLs with ES-DC-GPC3. The mice were transferred i.p. twice with 1 × 105 ES-DC-GPC3 on days −14 and −7. On day 0, spleen cells from immunized mice were isolated and cultured with 1 × 105 ES-DC-GPC3 per well in the presence of recombinant human IL-2 (100 units/mL) for 5 days. 51Cr release assays were done with the obtained resultant cells to evaluate the capacity to kill IFN-γ pretreated B16-F1 and B16-F10 cells (A) and MCA and MCA-GPC3 cells (B). Results are expressed as % specific lysis from triplicate assays. C, in addition, the resultant cells obtained in the same way were sorted to the fraction of NK cells and CD8+ T cells with microbeads, and another assay was done using the targets in the same condition as in (A and B). D, spleen cells from mice transferred twice with 1 × 105 ES-DC-GPC3 or ES-DC-TT2, respectively, were isolated and restimulated in vitro with 1 × 105 ES-DC-GPC3 per well for 5 days. The resultant cells were used for IFN-γ ELISPOT assay. The assay was done in triplicate using the same targets as in (A and B). Columns, mean number of IFN-γ-positive spots. E, identification of glypican-3-derived and H2-Db- or H2-Kb-restricted CTL epitopes by IFN-γ ELISPOT assays. The mice were immunized with 1 × 105 ES-DC-GPC3 twice with a 7-day interval. Spleen cells from mice immunized were restimulated in vitro with each glypican-3 peptide (10 μmol/L) and cultured for 5 days with 100 units/mL recombinant human IL-2. ELISPOT assays for 16 hours were examined against EL4 pulsed with or without each peptide and MCA or MCA-GPC3. Columns, mean total number of spots from quadruplicate assays. Data are representative of three independent experiments with similar results in (A-E). *, P < 0.05, differences in the responses are statistically significant between two values in (C-E).

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We next compared the efficiency of the induction of glypican-3-specific and IFN-γ-producing T cells primed by ES-DC-GPC3 with that primed by ES-DC-TT2. The mice were immunized twice with ES-DC-TT2 or ES-DC-GPC3 based on the above described schedule, and the splenocytes isolated from both group of mice were cocultured with ES-DC-GPC3 for 5 days. Thereafter, the frequency of glypican-3-specific T cells was analyzed by an ELISPOT analysis to detect cells producing IFN-γ. As shown in Fig. 3D, in vivo priming with ES-DC-GPC3 and ES-DC-TT2 resulted in the induction of similar frequency of cells producing IFN-γ on stimulation with cells with no expression of glypican-3, MCA or B16-F1. On the other hand, in vivo priming with ES-DC-GPC3 led to the induction of significantly larger number of T cells producing IFN-γ on stimulation with cells expressing glypican-3, MCA-GPC3 or B16-F10, compared with priming with ES-DC-TT2. Collectively, these results showed that glypican-3-specific CTLs were primed in vivo only when mice were transferred with ES-DC-GPC3, further confirming that ES-DC-GPC3 have the capacity to prime the glypican-3-specific CTLs in vivo.

Identification of glypican-3-derived and H2-Db- or Kb-restricted CTL epitopes. To identify the H-2b-restricted CTL epitopes of glypican-3, we synthesized 11 glypican-3-derived peptides carrying the binding peptide motifs for H2-Db or Kb and designated as murine glypican-3-1 to -11 in turn. Spleen cells of the mice immunized with ES-DC-GPC3 by the same procedure as described above were stimulated in vitro with each of the peptides instead of ES-DC-GPC3 for 5 days. Subsequently, the frequency of glypican-3-specific CTLs was analyzed by IFN-γ ELISPOT assays. As shown in Fig. 3E, cells stimulated in vitro with murine glypican-3-2, -8, or -11 showed specific IFN-γ production on restimulation with EL4 cells prepulsed with the same peptide or MCA-GPC3. These results indicate that glypican-3-specific CTLs primed in vivo with ES-DC-GPC3 included those recognizing multiple glypican-3 epitopes.

Tumor preventive effects of immunization with ES-DC-GPC3. We next asked whether ES-DC-GPC3 could induce a protective immunity against tumor cells expressing glypican-3 in vivo. We immunized mice by the i.p. transfer of ES-DC on days −14 and −7, and the mice were challenged s.c. with 5 × 103 B16-F10 cells or 1 × 105 MCA-GPC3 on day 0. We then monitored the growth of tumors and survival of the mice. As shown in Fig. 4, immunizations with ES-DC-GPC3 provided a significant degree of protection against both B16-F10 and MCA-GPC3. On the other hand, the transfer of ES-DC-TT2 gave no significant protection compared with mice without dendritic cell transfer. Immunization with ES-DC-GPC3 did not show a protective effect against MCA or B16-F1 with no glypican-3 expression (data not shown). Collectively, the in vivo administration of ES-DC-GPC3 induced antitumor immunity against glypican-3-expressing tumor cells, thus resulting in a significant inhibition of the growth of tumor and prolongation of the survival time of the treated mice.

Figure 4.

Suppression of tumor growth and prolongation of survival by preimmunization with ES-DC-GPC3. The mice were transferred i.p. twice with 1 × 105 ES-DC-GPC3 or ES-DC-TT2 on days −14 and −7. On day 0, the mice were challenged s.c. with 5 × 103 B16-F10 (A and B) or 1 × 105 MCA-GPC3 (C and D) expressing glypican-3. The tumor index, survival rate, or disease-free rate was monitored. *, P < 0.05, differences in these three indexes between the groups treated with ES-DC-GPC3 and ES-DC-TT2 were statistically significant. E, mice were injected i.p. with ES-DC-GPC3 or BM-DC loaded with a mixture of glypican-3 peptides, murine glypican-3-2, -8, and -11, or glypican-3 protein on the same schedule as in (A-D) and challenged s.c. with 5 × 103 B16-F10. Subsequently, the mice were monitored for the growth of tumor.

Figure 4.

Suppression of tumor growth and prolongation of survival by preimmunization with ES-DC-GPC3. The mice were transferred i.p. twice with 1 × 105 ES-DC-GPC3 or ES-DC-TT2 on days −14 and −7. On day 0, the mice were challenged s.c. with 5 × 103 B16-F10 (A and B) or 1 × 105 MCA-GPC3 (C and D) expressing glypican-3. The tumor index, survival rate, or disease-free rate was monitored. *, P < 0.05, differences in these three indexes between the groups treated with ES-DC-GPC3 and ES-DC-TT2 were statistically significant. E, mice were injected i.p. with ES-DC-GPC3 or BM-DC loaded with a mixture of glypican-3 peptides, murine glypican-3-2, -8, and -11, or glypican-3 protein on the same schedule as in (A-D) and challenged s.c. with 5 × 103 B16-F10. Subsequently, the mice were monitored for the growth of tumor.

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Next, we compared ES-DC-GPC3 with BM-DC preloaded with glypican-3 peptide or protein in their capacity to induce antitumor effect. We generated BM-DC from bone marrow cells of CBF1 mice and loaded them with mixture of the three major H2-Db-restricted epitopes, murine glypican-3-2, -8, and -11 (Fig. 3E), or recombinant glypican-3 protein. As shown in Fig. 4E, ES-DC-GPC3 and peptide or protein antigen-loaded BM-DC elicited similar magnitude of protective effect against challenge with B16-F10.

Protective effect of ES-DC-GPC3 against i.v. challenge with tumor cells. We next examined the antitumor effect of ES-DC-GPC3 against i.v. challenge with B16-F10. As shown in Fig. 5A, the mice were i.v. inoculated with B16-F10 cells on day 0, and the mice were treated with ES-DC-TT2 or ES-DC-GPC3 twice on days 3 and 10. On day 30, mice were sacrificed and macroscopically analyzed. As shown in Fig. 5B and C, treatment with ES-DC-GPC3 significantly reduced the pulmonary and liver metastases in comparison with the treatment with ES-DC-TT2 (P < 0.05). Some of the mice treated with ES-DC-TT2, but not those treated with ES-DC-GPC3, died before they were scheduled to be sacrificed. Thus, the survival time of the mice treated with ES-DC-GPC3 was prolonged in comparison with those treated with ES-DC-TT2.

Figure 5.

Suppression of tumor growth in the metastatic tumor model of B16-F10. The protocol for therapeutic immunotherapy model was indicated in (A). All mice were injected into tail vein with 1 × 105 F10 cells on day 0. On days 3 and 10, mice were injected i.p. with 1 × 105 ES-DC-TT2 or ES-DC-GPC3. On day 30, the mice were sacrificed and the numbers of pulmonary and liver metastases were macroscopically calculated. Columns, mean number of total metastases in the lung (B) and liver (C) using five mice per group. *, P < 0.05, differences in the number of metastases are statistically significant between the two values.

Figure 5.

Suppression of tumor growth in the metastatic tumor model of B16-F10. The protocol for therapeutic immunotherapy model was indicated in (A). All mice were injected into tail vein with 1 × 105 F10 cells on day 0. On days 3 and 10, mice were injected i.p. with 1 × 105 ES-DC-TT2 or ES-DC-GPC3. On day 30, the mice were sacrificed and the numbers of pulmonary and liver metastases were macroscopically calculated. Columns, mean number of total metastases in the lung (B) and liver (C) using five mice per group. *, P < 0.05, differences in the number of metastases are statistically significant between the two values.

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Identification of effector cells involved in the protection against F10 and MCA-GPC3 induced by ES-DC-GPC3. To determine the subsets of the effector cells involved in the observed protective effect against tumor cells induced by ES-DC-GPC3, we depleted CD4+ or CD8+ T cells in the mice by treatments with either anti-CD4 or anti-CD8 mAb. By this treatment, >90% of CD4+ or CD8+ T cells were depleted (data not shown). The NK cells were depleted by the treatment with anti–asialo GM1 antibody. During this procedure, the mice were immunized with ES-DC-GPC3 and challenged s.c. with B16-F10 cells. As shown in Fig. 6, depletion of CD4+ T cells, CD8+ T cells, or NK cells almost totally abrogated the protective immunity induced by ES-DC-GPC3, suggesting that all of three effector cell subsets were essential for the protective effect.

Figure 6.

Involvement of both CD4+ and CD8+ T cells in antitumor immunity induced by ES-DC-GPC3. A, CD4+ or CD8+ T cells were depleted in vivo by the inoculation of anti-CD4 or anti-CD8 mAbs during immunization with ES-DC-GPC3. The mice were challenged s.c. with 5 × 103 F10 tumor cells, and the tumor size was measured and the tumor volume was represented as the tumor index. In immunization with ES-DC-GPC3, the differences in the tumor index between the mice inoculated with rat IgG and those with anti-CD4 mAb or those with anti-CD8 mAb are statistically significant (*, P < 0.05). The mice inoculated with anti-CD4 mAb or anti-CD8 mAb showed tumors that were the same size as those in the mice with no transfer with dendritic cells. Points, mean tumor index (n = 10 per group); bars, SD. B, infiltration of both CD4+ and CD8+ T cells into pulmonary metastatic tumor tissues. After the challenge with 1 × 105 F10 tumor cells as well as the pulmonary metastatic model in Fig. 5, the mice were treated twice with 1 × 105 ES-DC-TT2 or ES-DC-GPC3. Twenty days after the second treatment, frozen sections of tumor tissue were made and stained with the Giemsa method or immunostained with anti-CD4 or anti-CD8 mAb. In mice treated with ES-DC-GPC3, both CD8+ and CD4+ T cells apparently infiltrated into and/or around the pulmonary metastatic tumor. However, in the mice treated with ES-DC-TT2, neither CD8+ nor CD4+ T cells were detected in the tissue specimens. Magnification, ×400.

Figure 6.

Involvement of both CD4+ and CD8+ T cells in antitumor immunity induced by ES-DC-GPC3. A, CD4+ or CD8+ T cells were depleted in vivo by the inoculation of anti-CD4 or anti-CD8 mAbs during immunization with ES-DC-GPC3. The mice were challenged s.c. with 5 × 103 F10 tumor cells, and the tumor size was measured and the tumor volume was represented as the tumor index. In immunization with ES-DC-GPC3, the differences in the tumor index between the mice inoculated with rat IgG and those with anti-CD4 mAb or those with anti-CD8 mAb are statistically significant (*, P < 0.05). The mice inoculated with anti-CD4 mAb or anti-CD8 mAb showed tumors that were the same size as those in the mice with no transfer with dendritic cells. Points, mean tumor index (n = 10 per group); bars, SD. B, infiltration of both CD4+ and CD8+ T cells into pulmonary metastatic tumor tissues. After the challenge with 1 × 105 F10 tumor cells as well as the pulmonary metastatic model in Fig. 5, the mice were treated twice with 1 × 105 ES-DC-TT2 or ES-DC-GPC3. Twenty days after the second treatment, frozen sections of tumor tissue were made and stained with the Giemsa method or immunostained with anti-CD4 or anti-CD8 mAb. In mice treated with ES-DC-GPC3, both CD8+ and CD4+ T cells apparently infiltrated into and/or around the pulmonary metastatic tumor. However, in the mice treated with ES-DC-TT2, neither CD8+ nor CD4+ T cells were detected in the tissue specimens. Magnification, ×400.

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In a histologic analysis of the tumor tissue specimens, we observed more intense infiltration of inflammatory cells into and/or around tumor tissues of mice immunized with ES-DC-GPC3 than those of mice immunized with ES-DC-TT2. In the metastatic B16-F10 tumor tissue specimens, the infiltrating cells were found to consist of both CD4+ and CD8+ T cells (Fig. 6). These results also suggest that both CD4+ and CD8+ T cells were involved in the antitumor effect against the B16-F10 induced by ES-DC-GPC3.

We investigated the antitumor effect of immunization with ES-DC genetically engineered to express a mouse oncofetal antigen glypican-3 against mouse tumor cells naturally expressing GPC3-F10, a subline of B16 melanoma. In vivo transfer of ES-DC-GPC3 primed CTL reactive to multiple glypican-3-derived epitopes. The treatment of mice with ES-DC-GPC3 elicited potent protective effect against B16-F10 in both preventive and therapeutic conditions with no evidence of any side effects, such as autoimmunity. The antitumor effect induced by ES-DC-GPC3 was specific to the tumor cells expressing glypican-3, because this treatment was not effective against B16-F1, another subline of B16 with no glypican-3 expression. The glypican-3 specificity of the antitumor effect induced by ES-DC-GPC3 was further confirmed by the observation that the treatment was effective against glypican-3-transfectant MCA205 sarcoma but not against parental MCA 205 cells. The depletion experiments and immunohistochemical analyses showed that CD8+ T cells, CD4+ T cells, and NK cells contributed to the observed antitumor effect.

The tumor cell lines used in this study, MCA205 and B16-F10, were derived from C57BL/6 mice and may be recognized by some fraction of NK cells of CBF1 mice. Thus, the tumor cells must be more immunogenic to CBF1 mice, used as the recipient mice in the present experiments, than to C57BL/6 mice. However, under the current experimental condition, all of the CBF1 mice challenged with B16-F10 or MCA-GPC3 died unless the recipient mice were treated with ES-DC-GPC3 (Fig. 4B and D), indicating that these tumor cells are invasive enough also to CBF1 mice.

In the 51Cr release assay shown in Fig. 3A, to C, CTL primed with ES-DC-GPC3 or ES-DC-TT2 (data not shown) exhibited weak killing activity against MCA or B16-F1 cells. Similar weak responses of spleen cells primed with ES-DC-GPC3 or ES-DC-TT2 to MCA or B16-F1 cells were also observed in the ELISPOT assay shown in Fig. 3D. At present, we have not yet clarified the effector cells and the target antigens that cause these “background” responses. However, such responses observed in vitro did not contribute to the in vivo antitumor effect, because the treatment with ES-DC-TT2 had no antitumor effects as shown in Fig. 4.

There was a considerable difference in the effect of treatment with ES-DC-GPC3 between the challenge with B16-F10 and that with MCA-GPC3 cells. This may be partly due to the lower expression of MHC class I on B16 compared with MCA205. B16 does not express MHC class I unless they are stimulated with IFN-γ. The indispensable role of NK cells in the antitumor effect (Fig. 6A) suggests that NK cells recognized B16 cells expressing a very low level of MHC class I; subsequently, NK cells produced IFN-γ to up-regulate MHC class I molecules on B16-F10 cells and to make B16-F10 cells sensitive to an attack by glypican-3-specific CTLs (35, 36).

As shown in Fig. 4, the protection against B16-F10 elicited by ES-DC-GPC3 was not complete. Treatment of the ES-DC with some maturation stimuli or loading of α-galactosylceramide, a ligand for NKT cells, to ES-DC before in vivo administration may have some effect to enhance the antitumor effect (37). As a future project, we are planning to generate ES-DC genetically engineered to produce cytokines, such as IL-15 or IL-21, along with glypican-3 to improve the antitumor effect.

We reported previously that the induction of immune response to glypican-3 protected the mice from a challenge with Colon 26 colon tumor cells genetically modified to overexpress glypican-3 (17). In the present study, we found the natural overexpression of glypican-3 in B16-F10 and showed that the immunization of mice with glypican-3 protected the mice from the challenge with B16-F10. Glypican-3 is one of the oncofetal proteins and the expression in normal human tissues is limited to the placenta and fetal liver (17). In addition, the tissue distribution of glypican-3 expression is very similar in mice and humans (17). As a result, our results strongly suggest that anti-melanoma and anti–hepatocellular carcinoma immunotherapy with glypican-3 seems to be an effective and safe method, and it should therefore be tested clinically.

To enable to the future clinical application of ES-DC, we recently established a method for generating ES-DC from embryonic stem cells of nonhuman primate, cynomolgus monkey, and also for genetic modification of them.3

3

In preparation.

Considering the future clinical application of ES-DC technology, allogenicity (i.e., differences in the genetic background between the patients to be treated and the embryonic stem cells as the source for dendritic cells), we expected to cause problems. However, it is expected that human embryonic stem cells sharing some of HLA alleles with patients are available in most cases. We recently found that antigen-expressing ES-DC could potently prime antigen-specific CTL on the adoptive transfer to semiallogeneic mice, thus sharing some MHC alleles with the ES-DC and also protecting the recipient mice from subsequent challenge with tumor cells bearing the antigen (38). Immunotherapy with human ES-DC expressing glypican-3 may therefore be clinically useful as an immunotherapy of melanoma and hepatocellular carcinoma.

Grant support: Ministry of Education, Science, Technology, Sports, and Culture, Japan, grants-in-aid 12213111, 14370115, 14570421, and 14657082; Ministry of Health, Labor and Welfare, Japan, Research Grant for Intractable Diseases; Tokyo Biochemical Research Foundation; Uehara Memorial Foundation; Oncotherapy Science Co.; Eisai Pharmasential Co.; and Meiji Institute of Health Science.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

We thank Dr. S. Aizawa (Riken Center for Developmental Biology, Kobe, Japan) for TT2, Drs. N. Takakura (Kanazawa University, Kanazawa, Japan) and T. Suda (Keio University, Tokyo, Japan) for OP9, Dr. H. Niwa (Riken Center for Developmental Biology) for pCAG-IP, and T. Kubo for technical assistance.

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