Inhibition of tumor growth with a vaccine based on xenogeneic homologous fibroblast growth factor receptor-1 in mice

Angiogenesis is important for the growth of solid tumors. The breaking of the immune tolerance against the molecule associated with angiogenesis should be a useful approach for cancer therapy. However, the immunity to self-molecules is difficult to elicit by a vaccine based on autologous or syngeneic molecules due to immune tolerance. Basic fibroblast growth factor (bFGF) is a specific and potent angiogenic factor implicated in tumor growth. The biological activity of bFGF is mediated through interaction with its high-affinity receptor, fibroblast growth factor receptor-1 (FGFR-1). In this study, we selected Xenopus FGFR-1 as a model antigen by the breaking of immune tolerance to explore the feasibility of cancer therapy in murine tumor models. We show here that vaccination with Xenopus FGFR-1 (pxFR1) is effective at antitumor immunity in three murine models. FGFR-1-specific autoantibodies in sera of pxFR1-immunized mice could be found in Western blotting analysis. The purified immunoglobulins were effective at the inhibition of endothelial cell proliferation in vitro and at the antitumor activity in vivo. The antitumor activity and production of FGFR-1-specific autoantibodies could be abrogated by depletion of CD4+ T lymphocytes. Histological examination revealed that the autoantibody was deposited on the endothelial cells within tumor tissues from pxFR1-immunized mice, and intratumoral angiogenesis was significantly suppressed. Furthermore, the inhibition of angiogenesis could also be found in alginate-encapsulate tumor cell assay. These observations may provide a new vaccine strategy for cancer therapy through the induction of autoimmunity against FGFR-1 associated with angiogenesis in a cross-reaction.     

Immunotherapy of tumors with xenogeneic endothelial cells as a vaccine

The breaking of immune tolerance against autologous angiogenic endothelial cells should be a useful approach for cancer therapy. Here we show that immunotherapy of tumors using fixed xenogeneic whole endothelial cells as a vaccine was effective in affording protection from tumor growth, inducing regression of established tumors and prolonging survival of tumor-bearing mice. Furthermore, autoreactive immunity targeting to microvessels in solid tumors was induced and was probably responsible for the anti-tumor activity. These observations may provide a new vaccine strategy for cancer therapy through the induction of an autoimmune response against the tumor endothelium in a cross-reaction.     

A DNA vaccine against chimeric AFP enhanced by HSP70 suppresses growth of hepatocellular carcinoma

Alpha-Fetoprotein (AFP) is produced principally in fetal liver, gastrointestinal tract and the yolk sac which is temporarily present during embryonic development. AFP is overexpressed in the majority of Hepatocellular Carcinoma (HCC) and thus offers an attractive target for immunotherapy against this neoplasm. Here, we report that anti-HCC effects were achieved in a therapeutic setting with a DNA vaccine encoding mouse AFP and co-expressing Heat Shock Protein 70 (HSP70) gene. We also demonstrated that this vaccine elicited a marked and highly effective AFP specific CTL response against AFP-positive target cells. This vaccine also induced the prolongation of life span in mice bearing the tumor and the eradication of HCC. It is anticipated that vaccine strategies such as this may contribute to the effective future treatment of Hepatocellular Carcinoma. Ying-hua Lan and Yong-guo Li contributed equally to this work.     

A DNA vaccine against VEGF receptor 2 prevents effective angiogenesis and inhibits tumor growth

Tumor cells are elusive targets for immunotherapy due to their heterogeneity and genetic instability. Here we describe a novel, oral DNA vaccine that targets stable, proliferating endothelial cells in the tumor vasculature rather than tumor cells. Targeting occurs through upregulated vascular-endothelial growth factor receptor 2 (FLK-1) of proliferating endothelial cells in the tumor vasculature. This vaccine effectively protected mice from lethal challenges with melanoma, colon carcinoma and lung carcinoma cells and reduced growth of established metastases in a therapeutic setting. CTL-mediated killing of endothelial cells indicated breaking of peripheral immune tolerance against this self antigen, resulting in markedly reduced dissemination of spontaneous and experimental pulmonary metastases. Angiogenesis in the tumor vasculature was suppressed without impairment of fertility, neuromuscular performance or hematopoiesis, albeit with a slight delay in wound healing. Our strategy circumvents problems in targeting of genetically unstable tumor cells. This approach may provide a new strategy for the rational design of cancer therapies.     

A novel vaccine containing EphA2 epitope and LIGHT plasmid induces robust cellular immunity against glioma U251 cells

EphA2 is a receptor tyrosine kinase and can be acted as an attractive antigen for glioma vaccines. In addition, LIGHT plays an important role on enhancing T cell proliferation and cytokine production. To improve the CTL mediated immune response against glioma cells, we prepared the novel vaccine containing EphA2_883–891 peptide (TLADFDPRV) and LIGHT plasmid and utilized it to immunize the HLA-A2 transgenic HHD mice. In addition, trimera mice were immunized with the novel vaccine to elicit the antitumor immune response. The results demonstrated that the novel vaccine could induce robust cellular immunity against glioma U251 cells without lysing autologous lymphocytes. Moreover, the novel vaccine could significantly inhibit the tumor growth and prolong the life span of tumor bearing mice. These findings suggested that the novel vaccine containing EphA2 epitope and LIGHT plasmid could induce anti-tumor immunity against U251 cells expressing EphA2, and provided a promising strategy for glioma immunotherapy.     

HSP110-HER2/neu chaperone complex vaccine induces protective immunity against spontaneous mammary tumors in HER-2/neu transgenic mice

Heat shock proteins (HSPs) are shown to be strong immunoadjuvants, eliciting both innate and adaptive immune responses against cancers. HSP110 is related in sequence to HSP70 and is approximately 4-fold more efficient in binding to and stabilizing denatured protein substrates compared with HSP70. In the present study we evaluated the ability of a heat shock complex of HSP110 with the intracellular domain (ICD) of human HER-2/neu to elicit effective antitumor immune responses and to inhibit spontaneous mammary tumors in FVB-neu (FVBN202) transgenic mice. The HSP110-ICD complex was capable of breaking tolerance against the rat neu protein and inhibiting spontaneous mammary tumor development. This vaccine induced ICD-specific IFN-gamma and IL-4 production. Depletion studies revealed that CD8(+) T cells were involved in protection against challenge with mouse mammary tumors, whereas CD4(+) T cells revealed partial protection. Increased IgG2a Ab titer in the sera of tumor-free animals after vaccination and elevated CD4(+) CD25(+) regulatory T cells in the PBL of tumor-bearing animals suggested that IFN-gamma-producing Th1 cells may be responsible for partial protection of CD4(+) T cells against the mammary tumor challenge, whereas CD4(+)CD25(+) regulatory T cells (Th2 cells) may suppress the antitumor immune responses. Together, these results suggest that HSP110-ICD complex can elicit effective IFN-gamma-producing T cells against spontaneous mammary tumors and that up-regulation of CD4(+) CD25(+) regulatory T cells may prevent complete eradication of the tumor following immunotherapy.     

Immunogene therapy of tumors with vaccine based on xenogeneic epidermal growth factor receptor

The breaking of immune tolerance against self epidermal growth factor receptor (EGFr) should be a useful approach for the treatment of receptor-positive tumors with active immunization. To test this concept, we constructed a plasmid DNA encoding extracellular domain of xenogeneic (human) EGFr (hEe-p) or corresponding control mouse EGFr (mEe-p) and empty vector (c-p). Mice immunized with hEe-p showed both protective and therapeutic antitumor activity against EGFr-positive tumor. Sera isolated from the hEe-p-immunized mice exhibited positive staining for EGFr-positive tumor cells in flow cytometric analysis and recognized a single 170-kDa band in Western blot analysis. Ig subclasses responded to rEGFr proteins were elevated in IgG1, Ig2a, and Ig2b. There was the deposition of IgG on the tumor cells. Adoptive transfer of the purified Igs showed the antitumor activity. The increased killing activity of CTL against EGFr-positive tumor cells could be blocked by anti-CD8 or anti-MHC class I mAb. In vivo depletion of CD4(+) T lymphocytes could completely abrogate the antitumor activity, whereas the depletion of CD8(+) cells showed partial abrogation. The adoptive transfer of CD4-depleted (CD8(+)) or CD8-depleted (CD4(+)) T lymphocytes isolated from mice immunized with hEe-p vaccine showed the antitumor activity. In addition, the increase in level of both IFN-gamma and IL-4 was found. Taken together, these findings may provide a new vaccine strategy for the treatment of EGFr-positive tumors through the induction of the autoimmune response against EGFr in a cross-reaction between the xenogeneic homologous and self EGFr.     

Alphavirus-based DNA vaccine breaks immunological tolerance by activating innate antiviral pathways

Cancer vaccines targeting 'self' antigens that are expressed at consistently high levels by tumor cells are potentially useful in immunotherapy, but immunological tolerance may block their function. Here, we describe a novel, naked DNA vaccine encoding an alphavirus replicon (self-replicating mRNA) and the self/tumor antigen tyrosinase-related protein-1. Unlike conventional DNA vaccines, this vaccine can break tolerance and provide immunity to melanoma. The vaccine mediates production of double-stranded RNA, as evidenced by the autophosphorylation of dsRNA-dependent protein kinase R (PKR). Double-stranded RNA is critical to vaccine function because both the immunogenicity and the anti-tumor activity of the vaccine are blocked in mice deficient for the RNase L enzyme, a key component of the 2',5'-linked oligoadenylate synthetase antiviral pathway involved in double-stranded RNA recognition. This study shows for the first time that alphaviral replicon-encoding DNA vaccines activate innate immune pathways known to drive antiviral immune responses, and points the way to strategies for improving the efficacy of immunization with naked DNA.     

Combined alpha tumor necrosis factor gene therapy and engineered dendritic cell vaccine in combating well-established tumors

BACKGROUND: Although current immunotherapeutic strategies including adenovirus (AdV)-mediated gene therapy and dendritic cell (DC) vaccine can all stimulate antitumor cytotoxic T lymphocyte (CLT) responses, their therapeutic efficiency has still been limited to generation of prophylactic antitumor immunity against re-challenge with the parental tumor cells or growth inhibition of small tumors in vivo. However, it is the well-established tumors in animal models that mimic clinical patients with existing tumor burdens. Alpha tumor necrosis factor (TNF-alpha) is a multifunctional and immunoregulatory cytokine that induces antitumor activity and activates immune cells such as DCs and T cells. We hypothesized that a combined immunotherapy including gene therapy and DC vaccine would have some advantages over each modality administered as a monotherapy. METHODS: We investigated the antitumor immunotherapeutic efficiency of gene therapy by intratumoral injection of AdVTNF-alpha and DC vaccine using subcutaneous injection of TNF-alpha-gene-engineered DC(TNF-alpha) cells, and further developed a combined AdV-mediated TNF-alpha-gene therapy and TNF-alpha-gene-engineered DC(TNF-alpha) vaccine in combating well-established MO4 tumors expressing the ovalbumin (OVA) gene in an animal model. RESULTS: Our data show that vaccination of DC(TNF-alpha) cells pulsed with the OVA I peptide can (i) stimulate type 1 immune response with enhanced antitumor CTL activities, (ii) induce protective immunity against challenge of 5 x 10(5) MO4 tumor cells, and (iii) reduce growth of the small (3-4 mm in diameter), but not large, established MO4 tumors (6-8 mm in diameter). Our data also show that AdVTNF-alpha-mediated gene therapy can completely eradicate small tumors in 6 out of 8 (75%) mice due to the extensive tumor necrosis formation, but not the large tumors (0%). Interestingly, a combined AdVTNF-alpha-mediated gene therapy and TNF-alpha-gene-engineered DC(TNF-alpha) vaccine is able to cure 3 out of 8 (38%) mice bearing large MO4 tumors, indicating that the combined immunotherapy strategy is much more efficient in combating well-established tumors than monotherapy of either gene therapy or DC vaccine alone. CONCLUSIONS: This novel combined immunotherapy may become a tool of considerable conceptual interest in the implementation of future clinical objectives.     

Danger signals and nonself entity of tumor antigen are both required for eliciting effective immune responses against HER-2/neu positive mammary carcinoma: implications for vaccine design

Using parental FVB mice and their neu transgenic counterparts, FVBN202, we showed for the first time that dangerous hyperplasia of mammary epithelial cells coincided with breaking immunological tolerance to the neu "self" tumor antigen, though such immune responses failed to prevent formation of spontaneous neu-overexpressing mammary carcinoma (MMC) or reject transplanted MMC in FVBN202 mice. On the other hand, neu-specific immune responses appeared to be effective against MMC in parental FVB mice because of the fact that rat neu protein was seen as "nonself" antigen in these animals and the protein was dangerously overexpressed in MMC. Interestingly, low/intermediate expression of the neu "nonself" protein in tumors induced immune responses but such immune responses failed to reject the tumor in FVB mice. Our results showed that self-nonself (SNS) entity of a tumor antigen or danger signal alone, while may equally induce an antigen-specific immune response, will not warrant the efficacy of immune responses against tumors. On the other hand, entity of antigen in the context of dangerous conditions, i.e. abnormal/dangerous overexpression of the neu nonself protein, will warrant effective anti-tumor immune responses in FVB mice. This unified "danger-SNS" model suggests focusing on identification of naturally processed cryptic or mutated epitopes, which are considered semi-nonself by the host immune system, along with novel dangerous adjuvant in vaccine design.     

Enhancement of DNA vaccine potency through linkage of antigen gene to ER chaperone molecules,ER-60, tapasin,and calnexin

DNA vaccines have emerged as an attractive approach for generating antigen-specific immunotherapy. Strategies that enhance antigen presentation may potentially be used to enhance DNA vaccine potency. Previous experiments showed that chimeric DNA vaccines utilizing endoplasmic reticulum (ER) chaperone molecules, such as Calreticulin (CRT), linked to an antigen were capable of generating antigen-specific CD8⁺ T cell immune responses in vaccinated mice. In this study, we tested DNA vaccines encoding the ER chaperone molecules ER-60, tapasin (Tap), or calnexin (Cal), linked to human papillomavirus type 16 (HPV-16) E7 for their abilities to generate E7-specific T cell-mediated immune responses and antitumor effects in vaccinated mice. Our results demonstrated that vaccination with DNA encoding any of these chaperone molecules linked to E7 led to a significant increase in the frequency of E7-specific CD8⁺ T cell precursors and generated stronger antitumor effects against an E7-expressing tumor in vaccinated mice compared to vaccination with wild-type E7 DNA. Our data suggest that DNA vaccines employing these ER chaperone molecules linked to antigen may enhance antigen-specific CD8⁺ T cell immune responses, resulting in a significantly more potent DNA vaccine.     

Immunosensitization with a Bcl-2 small molecule inhibitor

Several tumor immunotherapy approaches result in a low percentage of durable responses in selected cancers. We hypothesized that the insensitivity of cancer cells to immunotherapy may be related to an anti-apoptotic cancer cell milieu, which could be pharmacologically reverted through the inhibition of antiapoptotic Bcl-2 family proteins in cancer cells. ABT-737, a small molecule inhibitor of the antiapoptotic proteins Bcl-2, Bcl-w and Bcl-x_L, was tested for the ability to increase antitumor immune responses in two tumor immunotherapy animal models. The addition of systemic therapy with ABT-737 to the immunization of BALB/c mice with tumor antigen peptide-pulsed dendritic cells (DC) resulted in a significant delay in CT26 murine colon carcinoma tumor growth and improvement in survival. However, the addition of ABT-737 to either a vaccine strategy involving priming with TRP-2 melanoma antigen peptide-pulsed DC and boosting with recombinant Listeria monocytogenes expressing the same melanoma antigen, or the adoptive transfer of TCR transgenic cells, did not result in superior antitumor activity against B16 murine melanoma. In vitro studies failed to demonstrate increased cytotoxic lytic activity when testing the combination of ABT-737 with lymphokine activated killer (LAK) cells, or the death receptor agonists Fas, TRAIL-ligand or TNF-alpha against the CT26 and B16 cell lines. In conclusion, the Bcl-2 inhibitor ABT-737 sensitized cancer cells to the antitumor effect of antigen-specific immunotherapy in a vaccine model for the CT26 colon carcinoma in vivo but not in two immunotherapy strategies against B16 melanoma.     

Human T lymphocyte responses against lung cancer induced by recombinant truncated mouse EGFR

The induction of active cellular responses against EGFR should be a promising approach for the treatment of those receptor-positive tumors. However, the immunity against EGFR is presumably difficult to elicit by vaccine based on self or syngeneic EGFR due to the immune tolerance acquired during the development in immune system. We proposed a model to break immune tolerance against self-EGFR through an altered immunogen source based on xenogeneic homologous EGFR. We have previously shown human EGFR as a xenoantigen could induce specific immune responses in mouse and cross-react with mouse EGFR, and resulted in therapeutic benefits for EGFR-positive mouse tumor. Here, we show a recombinant form of extracellular domain of mouse EGFR, in the presence of DCs, could activate human peripheral T cells to proliferate, secret IFN-γ, the induced responses could cross-react with human EGFR and kill autologous EGFR-positive lung cancer cells which could be blocked by anti-CD8 and anti-MHC class I antibody. There is no detectable cytotoxical activity against lung tissue, liver tissue and kidney tissue derived from paracancerous normal tissue. These observations suggest that antitumor immunity induced by the truncated mouse EGFR may be provoked in a cross-reaction between mouse EGFR and self-EGFR, and may provide insight into treatment of EGFR-positive tumors through induction of the autoimmune responses against EGFR.     

The effects of DNA formulation and administration route on cancer therapeutic efficacy with xenogenic EGFR DNA vaccine in a lung cancer animal model

Background

Tyrosine kinase inhibitor gefitinib is effective against lung cancer cells carrying mutant epidermal growth factor receptor (EGFR); however, it is not effective against lung cancer carrying normal EGFR. The breaking of immune tolerance against self epidermal growth factor receptor with active immunization may be a useful approach for the treatment of EGFR-positive lung tumors. Xenogeneic EGFR gene was demonstrated to induce antigen-specific immune response against EGFR-expressing tumor with intramuscular administration.

Methods

In order to enhance the therapeutic effect of xenogeneic EGFR DNA vaccine, the efficacy of altering routes of administration and formulation of plasmid DNA was evaluated on the mouse lung tumor (LL2) naturally overexpressing endogenous EGFR in C57B6 mice. Three different combination forms were studied, including (1) intramuscular administration of non-coating DNA vaccine, (2) gene gun administration of DNA vaccine coated on gold particles, and (3) gene gun administration of non-coating DNA vaccine. LL2-tumor bearing C57B6 mice were immunized four times at weekly intervals with EGFR DNA vaccine.

Results

The results indicated that gene gun administration of non-coating xenogenic EGFR DNA vaccine generated the strongest cytotoxicty T lymphocyte activity and best antitumor effects. CD8(+) T cells were essential for anti-tumor immunityas indicated by depletion of lymphocytes in vivo.

Conclusion

Thus, our data demonstrate that administration of non-coating xenogenic EGFR DNA vaccine by gene gun may be the preferred method for treating EGFR-positive lung tumor in the future.     

Induction of antitumor immunity by indomethacin

Irradiated tumor cells given, together with indomethacin, to syngeneic mice induced an antitumor response and conferred protection against a challenge of a lethal dose of murine mammary (4T1) and lung (3LL) carcinoma cells. Continuous administration of indomethacin was crucial throughout the entire period of immunization and challenge, as no protection was achieved when the drug was given during only one of these procedures. Antitumor immunity was long-lasting and, when tested in the 4T1 model, 48% of mice were resistant to a second challenge of lethal tumor cells. Tumor-free immune mice that were given indomethacin for more than 300 days remained healthy with normal white blood cell counts and normal spleen size. Cells isolated from immune mice were able to kill tumor cells in culture after in vitro activation by interleukin-2, in a manner similar to cells from naive normal control mice. In addition, the mitogenic response of their T cells was as high as that of the control naive mice. While indomethacin was able to induce antitumor immunity to 4T1 and 3LL murine carcinoma cells, both of which contain a high concentration of endogenic prostaglandin E₂ (PGE2), no such immunity was achieved to murine tumor cells with a low concentration of endogenic PGE2. These results suggest a correlation between PGE2 concentration and the ability of indomethacin to induce antitumor immunity. We therefore suggest that an immunotherapy protocol with long-term dispensation of a tolerable dose of an immunomodulator, given together with irradiated autologous tumor cells, may stimulate antitumor responses to tumors containing high concentrations of endogenic PGE2. Received: 12 August 1999 / Accepted: 21 September 1999     

A crucial role for dendritic cell (DC) IL-10 in inhibiting successful DC-based immunotherapy: superior antitumor immunity against hepatocellular carcinoma evoked by DC devoid of IL-10

The dendritic cell (DC)-based tumor immunotherapy has been a new promise of cure for cancer patients, but animal studies and clinical trials have thus far only shown limited success, especially in treating established tumors. Certain immunosuppressive mechanisms triggered by tumor cells or the derivatives are believed to be a major obstacle. We studied the role of DC-derived IL-10 and its negative impact on vaccine efficacy in mouse models. Liver tumor cells were injected via the portal vein, giving rise to disseminated intrahepatic tumors, or s.c. to form solid but extrahepatic tumors. Bone marrow-derived DCs were generated from normal or IL-10-deficient mice and used as the vector to deliver tumor Ags. We demonstrate here that DCs devoid of IL-10, a potent immunosuppressive cytokine, are superior over conventional DCs in triggering antitumor immunity. The IL-10(-/-)DCs were highly immunogenic, expressed enhanced levels of surface MHC class II molecules, and secreted increased amounts of Th1-related cytokines. By inducing tumor-specific killing and through the establishment of immunological memory, the vaccines delivered by IL-10(-/-)DCs could evoke strong therapeutic and protective immunity against hepatocellular carcinoma in the mouse models. These findings will have great clinical impact once being translated into the treatment of malignant, and potentially infectious, diseases in humans.     

Unmasking of alpha-fetoprotein-specific CD4(+) T cell responses in hepatocellular carcinoma patients undergoing embolization

Necrosis of tumor cells can activate both innate and adaptive antitumor immunity. However, there is little information on the effects of necrosis-inducing cancer treatments on tumor-specific T cell immune responses in humans. We studied the effects of a necrosis-inducing treatment (embolization) on anti-alpha-fetoprotein (AFP)-specific CD4(+) T cell responses in hepatocellular carcinoma (HCC) patients and controls using an array of AFP-derived peptides. In this study, we show that AFP-specific CD4(+) T cell responses to three immunodominant epitopes in HCC patients were significantly expanded during (p < 0.0001) and after embolization (p < 0.002). The development of higher frequencies of AFP-specific CD4(+) T cells after treatment were significantly associated with the induction of >50% necrosis of tumor and an improved clinical outcome (p < 0.007). In addition, we identified two novel HLA-DR-restricted AFP-derived CD4(+) T cell epitopes (AFP(137-145) and AFP(249-258)) and showed that the CD4(+) T cells recognizing these epitopes produce Th1 (IFN-gamma and TNF-alpha) but not Th2 (IL-5)-type cytokines. AFP(137-145)-, AFP(249-258)-, and AFP(364-373)-specific CD4(+) T cells were detected in HCC patients but not in patients with chronic liver diseases or healthy donors. In conclusion; our study shows that induction of tumor necrosis by a conventional cancer treatment can unmask tumor rejection Ag cell-mediated immunity and provides a rationale for combining embolization with immunotherapy in HCC patients.     

Tumor-specific idiotype vaccines. II. Analysis of the tumor-related network response induced by the tumor and by internal image antigens (Ab2 beta)

In this study the tumor-specific immuneresponse induced by irradiated tumor cells (L1210/GZL) and by anti-idiotype antibodies was analyzed. The anti-idiotype antibodies (Ab2) were made against the paratope of a monoclonal antitumor antibody (11C1) that recognizes a tumor-associated antigen which cross-reacts with the mouse mammary tumor virus-encoded envelope glycoprotein 52. Two Ab2, 2F10 and 3A4, induced idiotypes expressed by the monoclonal antitumor antibodies 11C1 and 2B2. Cytotoxic T cells, generated by immunization with irradiated tumor cells, lyse 2F10 and 3A4 hybridoma cells. Furthermore, immunization with Ab2 induces tumor-specific cytotoxic T lymphocytes. The frequency of tumor-reactive cytotoxic T lymphocyte was found to be similar in mice immunized with Ab2 or irradiated tumor cells when examined at the precursor level. However, only 2F10 induces protective immunity against the growth of L1210/GZL tumor cells. The depletion of a L3T4+ T cell population from 2F10 immune mice was found to increase the effectiveness of transferred T cells to induce inhibition of tumor growth. The inability of 3A4 to induce antitumor immunity could be correlated with the presence of a population of Lyt2+ regulatory T cells. Collectively, these results demonstrate the existence of a regulatory network controlling the expression of effective tumor immunity. Our results demonstrate that selection of binding site-related Ab2 may not be a sufficient criteria for the development of an idiotype vaccine. A better understanding of the regulatory interactions induced by anti-idiotypes is needed for the design of effective antitumor immunotherapy.     

Alpha-fetoprotein impairs APC function and induces their apoptosis

alpha-Fetoprotein (AFP) is a tumor-associated Ag, and its serum level is elevated in patients with hepatocellular carcinoma (HCC). In vitro, AFP induces functional impairment of dendritic cells (DCs). This was demonstrated by the down-regulation of CD40 and CD86 molecules and the impairment of allostimulatory function. Also, AFP was found to induce significant apoptosis of DCs, and AFP-treated DCs produced low levels of IL-12 and TNF-alpha, a cytokine pattern that could hamper an efficient antitumor immune response. Ex vivo, APCs of patients with HCC and high levels of AFP produced lower levels of TNF-alpha than that of healthy individuals. In conclusion, these results illustrate that AFP induces dysfunction and apoptosis of APCs, thereby offering a mechanism by which HCC escapes immunological control.