Biochemical nature and mapping of PSMA epitopes recognized by human antibodies induced after immunization with gene-based vaccines

BACKGROUND

A possible new target for immunotherapy is the prostate-specific membrane antigen (PSMA). The aim of the present study was to define potential PSMA epitopes for antibody binding using sera from patients immunized with gene-based anti-PSMA vaccines.

MATERIALS AND METHODS

Sera from prostate cancer patients, immunized repeatedly with plasmid and adenoviral vectors, each encoding for the extracellular portion of human PSMA, were tested for anti-PSMA antibodies by Western blot. PSMA-producing LNCaP cells were used as a control. Recombinant PSMA protein cleaved with different proteinases was used for epitope mapping. Different enzymes were used to cleave the PSMA molecule.

RESULTS

Specific anti-PSMA antibodies were detected in the studied patients' sera, mainly against the PSMA protein core. An alignment of the predicted enzyme-cleavage fragments was compared with Western blot results and several antibody epitopes were determined.

CONCLUSION

These data demonstrate that multiple gene-based vaccinations induce an anti-PSMA humoral immune response. The antibodies are predominantly specific for the PSMA protein core.

Transduction of the gene coding for a human G-protein coupled receptor FPRL1 in mouse tumor cells increases host anti-tumor immunity

Low antigenicity or development of tolerance is believed to be a major contributor to the escape of malignant tumors from immune surveillance of the host. However, anti-tumor responses can be elicited by concomitant immunization of poorly antigenic tumor cells with homologous xenogeneic proteins as 'altered self' proteins. In our study, anti-tumor, but not anti-xenogeneic antigen, immune responses were generated after transduction of the gene coding for a G-protein coupled human formyl peptide receptor like-1 (FPRL1) into a mouse C26 colon cancer cell line. C26 cells transfected with FPRL1 gene exhibited markedly reduced tumorigenicity in syngeneic mice, in association with the appearance of high levels of antibody activity reacting with both FPRL1 containing and wild type C26 cells. The anti-tumor responses required the participation of CD4+ T lymphocytes, since no tumor rejection was observed in nude mice or in syngeneic mice depleted of CD4+ T cells. Furthermore, mice primed with FPRL1 transfected C26 cells were resistant to subsequent challenge by wild type C26 cells. These results indicate that the presence of human FPRL1 is capable of triggering specific anti-tumor host immune responses against poorly antigenic mouse tumor cells.

Reduction of spontaneous metastases through induction of carbohydrate cross-reactive apoptotic antibodies

The selective targeting of tumor-associated carbohydrate Ags by the induction of serum Abs that trigger apoptosis of tumor cells as a means to reduce circulating tumor cells and micrometastases would be an advantage in cancer vaccine development. Some plant lectins like Griffonia simplicifolia lectin I and wheat germ agglutinin mediate the apoptosis of tumor cells. We investigated the possibility of using these lectins as templates to select peptide mimotopes of tumor-associated carbohydrate Ags as immunogens to generate cross-reactive Abs capable of mediating apoptosis of tumor cells. In this study, we show that immunization with a mimotope selected based on its reactivity with Griffonia simplicifolia lectin I and wheat germ agglutinin induced serum IgM Abs in mice that mediated the apoptosis of murine 4T1 and human MCF7 cell lines in vitro, paralleling the apoptotic activity of the lectins. Vaccine-induced anti-carbohydrate Abs reduced the outgrowth of micrometastases in the 4T1 spontaneous tumor model, significantly increasing survival time of tumor-bearing animals. This finding parallels suggestions that carbohydrate-reactive IgM with apoptotic activity may have merit in the adjuvant setting if the right carbohydrate-associated targets are identified.

Targeting of Antigens to Activated Dendritic Cells In vivo Cures Metastatic Melanoma in Mice

Anti (alpha)-DEC-205 antibodies target to the DEC-205 receptor that mediates antigen presentation to T cells by dendritic cells. To exploit these properties for immunization purposes, we conjugated the melanoma antigen tyrosinase-related protein (TRP)-2 to alphaDEC-205 antibodies and immunized mice with these conjugates together with dendritic cell-activating oligonucleotides (CpG). Upon injection of the melanoma cell line B16, alphaDEC-TRP immunized mice were protected against tumor growth. Even more important for clinical applications, we were able to substantially slow the growth of implanted B16 cells by injection of alphaDEC-TRP2 conjugates into tumor bearing hosts. Approximately 70% of the animals were cured from existing tumors by treatment with alphaDEC conjugates carrying two different melanoma antigens (TRP-2 and gp100). This protection was due to induction of melanoma-specific CD4 and CD8 responses. Thus, these data show that targeting of dendritic cells in situ by the means of antibody-antigen conjugates may be a novel way to induce long-lasting antitumor immunity.

Inhibition of a vaccine-induced anti-tumor B cell response by soluble protein antigen in the absence of continuing T cell help

DNA vaccination can elicit the production of anti-tumor antibodies, thus obviating the need to continuously administer passive antibody. This vaccination strategy is particularly important where antibodies have proven to be effective anti-tumor agents. To amplify antibody responses against weak tumor antigens, we previously designed DNA-fusion vaccines incorporating tumor sequences linked to microbial genes. By using a safe idiotypic (Id) antigen from a B cell tumor fused to a fragment C (FrC) sequence from tetanus toxin, we induced both anti-Id and anti-FrC antibodies. It was important to determine whether the antigen itself, either injected or released from residual tumor cells, would boost the antibody response. Id protein not only failed to boost the response, but permanently and rapidly inhibited it by ablating Id-specific memory B cells. In contrast, an Id protein-FrC conjugate boosted both Id-specific and FrC-specific responses. Strikingly, the depletion of CD4+ T cells converted the Id protein-FrC conjugate vaccine into an inhibitor. These findings support the hypothesis that the activation of memory B cells by a DNA vaccine encoding a protein antigen, in the presence of the protein itself, depends completely on T cell help. Furthermore, by using knockout mice, we have shown that inhibition of the Id-specific memory B cells by the Id protein is largely independent of the FcgammaRIIB and, hence, independent of immune complexes. The principles revealed by using a DNA vaccine have implications for all cancer vaccines designed to induce and maintain antibody responses against weak autologous tumor antigens.

Using antibodies in tumour immunotherapy

The role of antibodies as therapeutic cancer vaccines includes two distinct approaches, which are summarised in this review, namely anti-idiotypic vaccines and antigen-antibody complex therapies. Bispecific antibodies directed against T cells or antigen-presenting cells are also referenced. The report focuses on theoretical issues, laboratory data on the mechanism of action, examples of humoral and cellular immune induction, and novel therapeutic advances in vaccine development. The biology of antigen processing and recent advances in the field of dendritic cell biology are critical to understanding the potent immune response induction. Future directions include combination therapies to manipulate immune regulatory mechanisms and to enhance clinical effects. Additional applications of antibodies targeting costimulatory or regulatory receptors on antigen-presenting cells and T cells, neutralising immune suppressive cytokines, and depleting T regulatory cells hold promise for future mono- and particularly combination therapies.

Electroporation as a "prime/boost" strategy for naked DNA vaccination against a tumor antigen

We have developed novel DNA fusion vaccines encoding tumor Ags fused to pathogen-derived sequences. This strategy activates linked T cell help and, using fragment C of tetanus toxin, amplification of anti-tumor Ab, CD4(+), and CD8(+) T cell responses is achievable in mice. However, there is concern that simple DNA vaccine injection may produce inadequate responses in larger humans. To overcome this, we tested electroporation as a method to increase the transfection efficiency and immune responses by these tumor vaccines in vivo in mice. Using a DNA vaccine expressing the CTL epitope AH1 from colon carcinoma CT26, we confirmed that effective priming and tumor protection in mice are highly dependent on vaccine dose and volume. However, suboptimal vaccination was rendered effective by electroporation, priming higher levels of AH1-specific CD8(+) T cells able to protect mice from tumor growth. Electroporation during priming with our optimal vaccination protocol did not improve CD8(+) T cell responses. In contrast, electroporation during boosting strikingly improved vaccine performance. The prime/boost strategy was also effective if electroporation was used at both priming and boosting. For Ab induction, DNA vaccination is generally less effective than protein. However, prime/boost with naked DNA followed by electroporation dramatically increased Ab levels. Thus, the priming qualities of DNA fusion vaccines, integrated with the improved Ag expression offered by electroporation, can be combined in a novel homologous prime/boost approach, to generate superior antitumor immune responses. Therefore, boosting may not require viral vectors, but simply a physical change in delivery, facilitating application to the cancer clinic.

Among B cell non-Hodgkin's lymphomas, MALT lymphomas express a unique antibody repertoire with frequent rheumatoid factor reactivity

We analyzed the structure of antigen receptors of a comprehensive panel of mature B non-Hodgkin's lymphomas (B-NHLs) by comparing, at the amino acid level, their immunoglobulin (Ig)V_H-CDR3s with CDR3 sequences present in GenBank. Follicular lymphomas, diffuse large B cell lymphomas, Burkitt's lymphomas, and myelomas expressed a CDR3 repertoire comparable to that of normal B cells. Mantle cell lymphomas and B cell chronic lymphocytic leukemias (B-CLLs) expressed clearly restricted albeit different CDR3 repertoires. Lymphomas of mucosa-associated lymphoid tissues (MALTs) were unique as 8 out of 45 (18%) of gastric- and 13 out of 32 (41%) of salivary gland-MALT lymphomas expressed B cell antigen receptors with strong CDR3 homology to rheumatoid factors (RFs). Of note, the RF-CDR3 homology without exception included N-region–encoded residues in the hypermutated IgV_H genes, indicating that they were stringently selected for reactivity with auto-IgG. By in vitro binding studies with 10 MALT lymphoma–derived antibodies, we showed that seven of these cases, of which four with RF-CDR3 homology, indeed possessed strong RF reactivity. Of one MALT lymphoma, functional proof for selection of subclones with high RF affinity was obtained. Interestingly, RF-CDR3 homology and t(11;18) appeared to be mutually exclusive features and RF-CDR3 homology was not encountered in any of the 19 pulmonary MALT lymphomas studied.

Immunotherapy of ovarian cancer with antibodies: a focus on oregovomab

Recent advances in the molecular and cellular biology of malignancy and tumour immunology have stimulated significant progress in the application of immunotherapies as adjuvant treatments in cancer. Oregovomab (OvaRex, AltaRex) is a murine monoclonal antibody with high affinity to the ovarian cancer associated antigen CA125. Infusion of low-dose antibody results in formation of circulating immune complexes which can trigger a cellular immune response targeting CA125 and the ovarian cancer. Oregovomab has activity following initial chemotherapy and in recurrent disease settings and is in Phase III trials to establish its efficacy to prolong time to relapse in patients with advanced ovarian cancer and favourable outcomes to their front-line treatment. Additional studies of antigen processing and combination chemo-immunotherapy are ongoing. The treatment shows promise as a potential new addition to the standard care of ovarian cancer.

Cancer vaccines and immunotherapies: emerging perspectives

Research efforts over the last two decades studying immune responses to human carcinomas have demonstrated that antigens expressed by tumor cells can elicit specific cellular and humoral immune responses. Unfortunately, despite the observation that existent immune responses to these antigens are present in some patients with cancer, the tumors continue to progress. Thus, there has been considerable interest to augment these immune responses by immunization. Some of the clinical trials of the first cancer vaccines have provided evidence of clinical benefit thus encouraging the development of other vaccines. Challenges to development of such cancer vaccines include the identification and characterization of the antigen(s) to be targeted, the definition of the desired immune response to be elicited by the vaccine, and the choice of the appropriate vaccine delivery system.

Intermediate filament protein synemin is present in human reactive and malignant astrocytes and associates with ruffled membranes in astrocytoma cells

Synemin, a very unique type VI intermediate filament (IF) protein, exhibits alternative splice variants termed alpha and beta. Unlike other IF proteins, synemin binds to actin-associated proteins, including alpha-actinin, vinculin, and alpha-dystrobrevin. Our previous work has demonstrated the presence of synemin in differentiating astrocytes. In this study, we have examined the presence of synemin in human astrocytes under pathological conditions, using rabbit antibodies raised against the C-terminal domain of human synemin produced in bacteria. Western blotting shows that astrocytic tumors contain greater amounts of alpha-synemin than do normal brain tissues. These tumors also contain beta-synemin, which is not detectable in normal brain. Immunohistochemistry demonstrates that, while synemin is present in normal adult brain only in vascular smooth muscle cells, it is newly synthesized by reactive and neoplastic astrocytes. Alpha- and beta-Synemins have also been detected by Western blotting and polymerase chain reaction in several human glioblastoma cell lines. In these cell lines, surprisingly, synemin is associated with ruffled membranes in addition to being distributed along the IF network. In ruffled membranes, synemin was found to co-localize with alpha-actinin. This unusual cellular localization for an IF protein is maintained after nocodazole-induced perinuclear coiling of the vimentin IF network. In addition, immunoprecipitation experiments demonstrate that synemin forms a complex with alpha-actinin in glioblastoma cells. Taken together with synemin localization within ruffled membranes, this finding suggests that synemin plays a role in motility of glioblastoma cells.

In vitro simian virus 40 large tumor antigen expression correlates with differential immune responses following DNA immunization

Simian virus 40 (SV40) contains an essential protein, large tumor antigen (Tag), which assists in viral replication and causes cell transformation and immortalization. Our laboratory has examined plasmid DNA, expressing SV40 Tag under two different promoters, for use in potential cancer vaccination strategies. One plasmid, pSV3-neo, failed to induce SV40 Tag antibody, produced a weak cell-mediated response, and only partial protection in murine experimental tumor challenge systems. The second plasmid, pCMV-Tag, induced antibodies to SV40 Tag, produced a robust cell-mediated response, and invoked complete tumor immunity in vivo. The induction of CD4+ and CD8+ T cell responses following plasmid DNA immunization and tumor cell challenge reflected a type 1 cytokine secretion profile. Our hypothesis for this differential immune response is that pCMV-Tag exhibits a higher level of transgene expression due to a more efficient promoter. We determined that pCMV-Tag levels of SV40 Tag mRNA and protein expression were higher when compared to pSV3-neo. A threshold amount of SV40 Tag may be required to stimulate antibody production and provide complete systemic tumor immunity.

The adjuvant activity of BAT antibody enables DNA vaccination to inhibit the progression of established autochthonous Her-2/neu carcinomas in BALB/c mice

Over the course of 33 weeks from birth, the mammary glands of virgin female BALB/c mice transgenic for the transforming rat Her-2/neu oncogene progress from atypical hyperplasia to invasive carcinoma. By week 12, all their mammary glands display many foci of in situ carcinoma. DNA vaccination at weeks 12 and 14 through in vivo electroporation of a plasmid encoding for the extracellular and transmembrane domain of the protein product of rat Her-2/neu oncogene kept 33% of mice tumor-free until week 35, when the experiment ended. To improve its efficacy the vaccine was combined with a T cell stimulatory monoclonal antibody (BAT). When each plasmid electroporation was followed by intravenous administration of 10 microg of BAT monoclonal antibody at weeks 13 and 15, 55% of mice remained tumor free (p < 0.0001) and stronger T cell and antibody-mediated immune responses were elicited. These data suggest that costimulation by BAT monoclonal antibody enables DNA vaccination to establish an effective protection against incipient carcinomas.

[Secretory expression of chimeric Fab antibody HAb18 against human hepatocellular carcinoma in Pichia pastoris]

AIM

To express secretively chimeric Fab antibody HAb18 (cFab) against human hepatocellular carcinoma in Pichia pastoris.

METHODS

Genes encoding CL chain and Fd fragment of cFab antibody HAb18 were subcloned into vectors pPIC9K and pPICZalphaA, respectively. After confirmed by DNA sequence analysis, the recombinant plasmids pPIC9K/CL and pPICZalphaA/Fd were transformed into the genome of Pichia pastoris GS115. Mut(+) multiple insert transformants were screened by G418 and Zeocin and then induced with 5 mL/L methanol to express cFab.

RESULTS

4 days after methanol induction, 26 mg/L of the cFab fragment was detected in the culture supernatant. Western blot proved that the expressed protein could specifically bind with HAb18GEF antigen.

CONCLUSION

The successful expression of cFab/HAb18 in Pichia pastoris lays the foundation for large-scale production and further application of the antibody.

Active specific immunotherapy of melanoma with a GM3 ganglioside-based vaccine: a report on safety and immunogenicity

A novel cancer vaccine was obtained by combining GM3 ganglioside with Neisseria meningitidis outer membrane protein complex to obtain very-small-size proteoliposomes (GM3/VSSP). The authors report the results of a phase 1 study of intramuscular administration of GM3/VSSP/Montanide ISA 51 to patients with metastatic melanoma. Twenty-six patients were included in three dose-level cohorts of 120, 240, and 360 mug. The first five doses (induction phase) were given at 2-week intervals, and the remaining four doses were given monthly. Patients were evaluated for dose-related toxicities and antitumor effects. In addition, serum and peripheral blood mononuclear cells were obtained at baseline and throughout treatment to evaluate humoral and cellular immune responses. One episode of severe hypotension and fever was observed in a patient included at the highest dose level. Other toxicities consisted of local reactions at the site of injection and mild fever and chills. Five doses of GM3/VSSP induced an anti-GM3 IgM response in 44% of patients. Serum reactivity was also observed against melanoma cell lines and tumor biopsies. GM3/VSSP was shown to induce very strong in vitro IFNgamma secretion in all evaluated melanoma patients. Furthermore, in one patient IFNgamma secretion was shown to be GM3-specific. A 62% reduction of a mediastinal mass was documented in one patient (partial response), while a second patient benefited from initial disease stabilization followed by tumor reduction in nonmeasurable soft tissue lesions accompanied by vitiligo.

A method to generate antigen-specific mAb capable of staining formalin-fixed, paraffin-embedded tissue sections

Abnormalities in HLA class I antigen expression are frequently found in malignant tumors. Their potential role in the clinical course of the disease and in the outcome of T cell-based immunotherapy has stimulated interest in the characterization of the molecular mechanisms underlying HLA class I antigen abnormalities in malignant cells. Multiple mechanisms have been identified. Among them are abnormalities in antigen processing machinery (APM) component expression. In spite of this information, APM component expression in malignant lesions has been investigated only to a limited extent because of the lack of availability, for most APM components, of monoclonal antibodies (mAb) which stain formalin-fixed, paraffin-embedded tissues. The latter are the substrate of choice in immunohistochemical (IHC) reactions. To overcome this limitation, we have developed a simple and reproducible method to generate APM component-specific mAb which stain formalin-fixed, paraffin-embedded tissue sections. This method involves five steps: (i) immunogenic amino acid sequences, which display low homology with their mouse counterparts when possible, are identified in APM components and utilized to synthesize peptides; (ii) BALB/c mice are immunized with keyhole limpet hemocyanin (KLH)-conjugated synthetic peptides and with sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE)-purified recombinant APM component proteins; (iii) immunized mice, which develop high titer APM component-specific antibodies, are utilized to generate hybridomas which are screened for APM component-specific antibody production by Western blotting assays, with lymphoid cell lysates; (iv) identified APM component-specific mAb are characterized in their specificity and in their reactivity with permeabilized cells in ELISA and/or flow cytometry; and (v) mAb, with the appropriate reactivity pattern, are tested in IHC reactions with formalin-fixed, paraffin-embedded tissue sections. The use of the methodology we have developed resulted in the generation of a panel of APM component-specific mAb capable of staining formalin-fixed, paraffin-embedded tissue sections in IHC reactions. These reagents will facilitate the analysis of APM component expression in tissues under physiological and pathological conditions. In addition, the methodology we have described is likely to be applicable to other antigenic systems to develop mAb capable of detecting protein components of interest in formalin-fixed, paraffin-embedded tissue sections.

One NY-ESO-1-derived epitope that promiscuously binds to multiple HLA-DR and HLA-DP4 molecules and stimulates autologous CD4+ T cells from patients with NY-ESO-1-expressing melanoma

NY-ESO-1 is expressed by a broad range of human tumors and is often recognized by Abs in the sera of cancer patients with NY-ESO-1-expressing tumors. The NY-ESO-1 gene also encodes several MHC class I- and class II-restricted tumor epitopes recognized by T lymphocytes. In this study we report one novel pan-MHC class II-restricted peptide sequence, NY-ESO-1 87-111, that is capable of binding to multiple HLA-DR and HLA-DP4 molecules, including HLA-DRB1*0101, 0401, 0701, and 1101 and HLA-DPB1*0401 and 0402 molecules. We also demonstrate that peptide NY-ESO-1 87-111 stimulates Th1-type and Th-2/Th0-type CD4(+) T cells and clones when presented in the context of these HLA-DR and HLA-DP4 molecules. Both bulk CD4(+) T cells and CD4(+) T cell clones were capable of recognizing not only peptide-pulsed APCs, but also autologous dendritic cells, either loaded with the NY-ESO-1 protein or transfected with NY-ESO-1 cDNAs. Using IFN-gamma and IL-5 ELISPOT assays and PBL from patients with NY-ESO-1-expressing tumors, we observed the existence of Th1-type circulating CD4(+) T cells recognizing peptide NY-ESO-1 87-111 in the context of HLA-DP4 molecules. Taken together, these data represent the first report of an HLA-DR- and HLA-DP-restricted epitope from a tumor Ag. They also support the relevance of cancer vaccine trials with peptides NY-ESO-1 87-111 in the large number of cancer patients with NY-ESO-1-expressing tumors.

Human papillomavirus type 16 E7 peptide(38-61) linked with an immunoglobulin G fragment provides protective immunity in mice

OBJECTIVE

To explore whether the recombinant protein (Human papillomavirus (HPV) type16 E7 peptide(38-61) linked with an immunoglobulin G fragment) will generate protective immunity in mouse model.

METHODS

In our study, we combined the HPV16 E7 peptide(38-61) with a murine IgG heavy chain constant region to construct a chimeric protein compound, which was highly expressed as inclusion bodies in a bacterial expression system with Escherichia coli. The purified chimeric protein was injected into C57BL/6 mice and the efficiency of the chimeric vaccine candidate was evaluated by antibody response assay, T cell proliferation assay, CTL assay, tumor challenge assay and therapeutic experiment.

RESULTS

The chimeric vaccine candidate was able to induce anti-HPV antibodies as well as to elicit HPV16 E7-specific CTLs and T cell proliferation in a pre-clinical mouse model. It was also able to effectively protect mice against the challenge of HPV16-positive tumor cells, and to eradicate HPV16-expressing tumors in mice.

CONCLUSIONS

The chimeric protein vaccine can induce E7-specific immune responses and protect mice against challenge of HPV16-positive tumor, even eradicate developed tumor. The results indicated a possibility to use the chimeric protein vaccine to protect human against HPV infection.

Construction and expression of intracellular anti-ATF-1 single chain Fv fragment: a modality to inhibit melanoma tumor growth and metastasis

The expression of the transcriptional regulators activating transcription factor-1 (ATF-1) and cAMP-responsive element (CRE)-binding protein (CREB) is upregulated in metastatic melanoma cells. However, how overexpression of ATF-1/CREB contributes to the acquisition of the metastatic phenotype is unclear. Monoclonal antibodies against ATF-1 have previously been used to inhibit the transcriptional activity of ATF-1 and its associated proteins. Here, the effect of disrupting ATF-1 activity was investigated using intracellular expression of an inhibitory anti-ATF-1 single chain antibody fragment (ScFv). Intracellular expression of ScFv anti-ATF-1 in human melanoma cells caused significant reduction in CRE-dependent promoter activation. In addition, expression of ScFv anti-ATF-1 in melanoma cells suppressed their tumorigenicity and metastatic potential in nude mice. Furthermore, expression of ScFv anti-ATF-1 rendered the melanoma cells susceptible to thapsigargin-induced apoptosis in vitro and caused massive apoptosis in vivo in tumors transplanted subcutaneously into nude mice. These studies demonstrate the potential usage of ScFv anti-ATF-1 as an inhibitor of tumor growth and metastasis of solid tumors overexpressing ATF-1/CREB.

[Anti-tumor effect of anti-dsDNA autoantibodies]

OBJECTIVE

To investigate effects of anti-dsDNA autoantibodies on growth of tumor in vitro and in vivo.

METHODS

BALB/c mice were inoculated with inactivated tumor cells and challenged s.c. with SP 2/0 and Wehi 164 tumor cells four weeks after the last inoculation. The naïve mice were inoculated with SP 2/0 tumor cells immediately after incubating with sera derived from the immunized mice at week 6. Then the tumor size was examined. In vitro, the cytotoxicity of anti-dsDNA autoantibodies to tumor cells was analysed. Furthermore, apoptosis of SP 2/0 and Wehi 164 tumor cells induced by anti-dsDNA autoantibodies was examined by FACS.

RESULTS

In vivo study showed that the growth of SP 2/0 and Wehi 164 tumors were inhibited in mice with anti-dsDNA autoantibodies, but not in mice lack of anti-dsDNA autoantibodies. In vitro, apoptosis of SP 2/0 and Wehi 164 tumor cells was induced when the tumor cells were incubated with the sera containing anti-dsDNA autoantibodies. Statistical analysis showed that the ability of anti-dsDNA autoantibodies to induce apoptosis of SP 2/0 and Wehi 164 tumor cells was significantly correlated with affinity (r = 0.990, P < 0.01 and r = 0.901, P < 0.05).

CONCLUSION

Anti-dsDNA autoantibodies have inhibitory effect on tumor cells via inducing apoptosis.

Endogenous anti-HER2 antibodies block HER2 phosphorylation and signaling through extracellular signal-regulated kinase

Immunologic targeting of the oncoprotein HER2/neu with monoclonal antibodies is an important component of current therapeutic strategies for patients with locally and systemically advanced breast cancer. Engineered antibodies targeting HER2 may have agonist or antagonist effects on HER2, but little is known about whether endogenous antibodies modulate HER2 activity. Vaccination of patients with HER2 peptides successfully induced antibodies in a minority of patients with HER2-expressing malignancy. A subset of antibodies specifically suppressed phosphorylation of HER2 on tyrosine Y1248, a residue critical for HER2 signaling through extracellular signal-regulated kinase. These antibodies also suppressed extracellular signal-regulated kinase phosphorylation and inhibited colony formation in soft agar. The majority of the antibodies that suppressed HER2 phosphorylation displayed specificity for amino acids 328 to 345 and 369 to 384. The isotype of anti-HER2 antibodies was predominantly IgG3 of low avidity, suggesting a Th1 response to peptide vaccine. Endogenous anti-HER2 antibodies can effectively suppress HER2 kinase activity and downstream signaling to inhibit the transformed phenotype of HER2-expressing tumor cells.

Quality of Recombinant Protein Determines the Amount of Autoreactivity Detected against the Tumor-Associated Epithelial Cell Adhesion Molecule Antigen: Low Frequency of Antibodies against the Natural Protein

The human epithelial cell adhesion molecule (EpCAM) is expressed on normal epithelial cells and is overexpressed in most carcinomas. EpCAM-targeted immunotherapy has been tried in several clinical studies. High titers of autoantibodies against EpCAM have been reported by different authors. We have generated large amounts of purified protein in S2 Drosophila cells (S2-EpCAM) with a purity of >96%. In contrast, the protein produced in baculovirus-dependent systems (baculo-EpCAM) that has been used in previous studies shows a purity of 79%. (1)H nuclear magnetic resonance spectrum of S2-EpCAM is typical of folded protein, whereas the baculo-EpCAM sample shows a spectrum corresponding to a partially unfolded protein. Using S2-EpCAM, denatured S2-EpCAM, and baculo-EpCAM, we measured EpCAM Abs of different isotypes in the serum of healthy controls and cancer patients. We found Ab titers against EpCAM in a much lower percentage of sera as published previously, and support the hypothesis that Ab reactivity in some published studies might be due to reactivity against denatured protein, to contaminating proteins in the baculovirus preparations, and to reactivity with BSA. Tetanus toxoid-reactive IgG Abs are present in 1000-fold higher titers compared with EpCAM-reactive Abs. Only IgA Abs were found in higher proportions and in higher concentrations than tetanus toxoid-specific Abs. Our study shows that EpCAM only rarely induces autoantibodies against native protein and emphasizes the importance of using extremely purified Ag preparations when evaluating Abs against tumor-associated Ags.

Vaccination with a Human High Molecular Weight Melanoma-Associated Antigen Mimotope Induces a Humoral Response Inhibiting Melanoma Cell Growth In Vitro

Peptide mimics of a conformational epitope that is recognized by a mAb with antitumor activity are promising candidates for formulations of anticancer vaccines. These mimotope vaccines are able to induce a polyclonal Ab response focused to the determinant of the mAb. Such attempts at cancer immunotherapy are of special interest for malignant melanoma that is highly resistant to chemotherapy and radiotherapy. In this study, we describe for the first time the design and immunogenicity of a vaccine containing a mimotope of the human high m.w. melanoma-associated Ag (HMW-MAA) and the biological potential of the induced Abs. Mimotopes were selected from a pVIII-9mer phage display peptide library with the anti-HMW-MAA mAb 225.28S. The mimotope vaccine was then generated by coupling the most suitable candidate mimotope to tetanus toxoid as an immunogenic carrier. Immunization of rabbits with this vaccine induced a specific humoral immune response directed toward the epitope recognized by the mAb 225.28S on the native HMW-MAA. The induced Abs inhibited the in vitro growth of the melanoma cell line 518A2 up to 62%. In addition, the Abs mediated 26% lysis of 518A2 cells in Ab-dependent cellular cytotoxicity. Our results indicate a possible application of this mimotope vaccine as a novel immunotherapeutic agent for the treatment of malignant melanoma.

Osteoclast-like giant cell tumor in mucinous cystadenocarcinoma of the pancreas: an immunohistochemical and molecular analysis

Osteoclast-like giant cell tumors (OLGT) are rare neoplasms of the pancreas and mostly associated with ductal adenocarcinomas. In this report, we present the rare case of OLGT associated with mucinous cystadenocarcinoma (MCC). We investigated the expression profile of both tumors by methods of molecular biology and immunohistochemistry. The panel of markers included osteopontin, her2/neu, mismatch repair genes, K-ras, p53, E-cadherin, VEGF-C, and podoplanin. Osteopontin was expressed by the osteoclast-like giant cells but not by the mononuclear tumor cells of the OLGT. We detected an amplification and overexpression of her2/neu in the MCC but not in the OLGT. Although we observed an immunohistochemical expression of hMSH2 and hMLH1 in the OLGT, we were not able to confirm this result by western blot analysis. We also did not find any microsatellite instability (D2S123, BAT26). While mutation of K-ras codon 12 was found in both tumor components, there was wild-type DNA of p53. E-cadherin was expressed in MCC but not in OLGT. VEGF-C was only positive in osteoclast-like giant cells and some of the mononuclear cells of OLGT. The vessel-rich stroma of OLGT did not present any podoplanin-positive lymphatic vessel. The observation of our case and others in the published literature may indicate separating OLGT with undifferentiated carcinoma from OLGT with MCC for the better clinical outcome of the latter.

Immune responses of breast cancer patients to mutated epidermal growth factor receptor (EGF-RvIII, Delta EGF-R, and de2-7 EGF-R)

Mutated epidermal growth factor receptor (EGF-RvIII, DeltaEGF-R, and de2-7 EGF-R) is the result of an 801-bp deletion within the extracellular domain of wild-type EGF-R and is expressed by breast carcinomas, but not by normal breast tissues. EGF-RvIII is expressed both on the surface and in the cytoplasm of tumor cells. Thus, EGF-RvIII is a potential tumor-specific target for both Abs and T cells. However, it is not known whether breast cancer patients can raise immune responses to EGF-RvIII expressed by their tumors. The demonstration of EGF-RvIII-specific immune responses in patients would suggest that immunization of patients with EGF-RvIII vaccines is feasible, because these vaccines may boost a pre-existing immune response. We have evaluated humoral and cellular immune responses to EGF-RvIII in 16 breast cancer patients and three healthy donors. Seven of 16 patients developed EGF-RvIII-specific Abs that bound to isolated EGF-RvIII protein or the protein expressed by EGF-RvIII-transfected mouse fibroblasts. The Abs that bound to EGF-RvIII did not bind to wild-type EGF-R, and anti-EGF-RvIII Abs were not found in the sera of healthy donors. Three patients had EGF-RvIII peptide-specific lymphoproliferative responses, and two of these patients also had humoral immune responses. Humoral and cellular immune responses correlated with EGF-RvIII expression by patients' tumors in most cases. These studies demonstrate that breast cancer patients specifically recognize EGF-RvIII with an overall immune response rate of 50%, suggesting that patients may benefit from vaccination against EGF-RvIII, boosting pre-existing immune responses.