Expression, purification and immunological characterization of the transforming protein E7, from cervical cancer-associated human papillomavirus type 16

Recombinant Peptide Production Platform Coupled with Site-Specific Albumin Conjugation Enables a Convenient Production of Long-Acting Therapeutic Peptide

The number of therapeutic peptides for human treatment is growing rapidly. However, their development faces two major issues: the poor yield of large peptides from conventional solid-phase synthesis, and the intrinsically short serum half-life of peptides. To address these issues, we investigated a platform for the production of a recombinant therapeutic peptide with an extended serum half-life involving the site-specific conjugation of human serum albumin (HSA). HSA has an exceptionally long serum half-life and can be used to extend the serum half-lives of therapeutic proteins and peptides. We used glucagon-like-peptide 1 (GLP-1) as a model peptide in the present study. A “clickable” non-natural amino acid—p-azido-l-phenylalanine (AzF)—was incorporated into three specific sites (V16, Y19, and F28) of a GLP-1 variant, followed by conjugation with HSA through strain-promoted azide–alkyne cycloaddition. All three HSA-conjugated GLP-1 variants (GLP1_16HSA, GLP1_19HSA, and GLP1_28HSA) exhibited comparable serum half-lives in vivo. However, the three GLP1_HSA variants had different in vitro biological activities and in vivo glucose-lowering effects, demonstrating the importance of site-specific HSA conjugation. The platform described herein could be used to develop other therapeutic peptides with extended serum half-lives.

Exploiting the Plant Secretory Pathway to Improve the Anticancer Activity of a Plant-Derived HPV16 E7 Vaccine

The human papillomavirus 16 (HPV16) E7 oncoprotein can be considered a ‘tumor-specific antigen’ and, therefore, it represents a promising target for a therapeutic vaccine against HPV-associated tumors. Efficient production of E7 protein with a plant-based transient expression system has been already described and it was demonstrated that E7-containing crude plant extracts confer partial protection against tumor challenge in a mouse model system. Before adopting the plant-based system as a cost-effective method for the production of an E7-based anti-cancer vaccine, some aspects, such as the oncoprotein yield, need further investigation. In the present study, we report the transient expression, mediated by a potato virus X (PVX)-derived vector, of the E7 protein targeted to the secretory system of Nicotiana benthamiana plants by using a plant-derived signal sequence. Targeting the antigen to the secretory pathway enhanced the E7 protein expression levels about five-fold. Mice immunized by s.c. administration with crude foliar extracts containing E7 showed strong stimulation of cell-mediated immune response after five boosters, as detected by ELISPOT. After challenging with the E7-expressing C3 tumor cells, tumor growth was completely inhibited in 80% of the vaccinated animals and a drastic reduction of tumor burden was observed in the remaining tumor-affected mice. These data demonstrate that, by enhancing E7 yield, it is possible to improve the anti-cancer activity of the plant-based experimental vaccine and open the way for a large-scale production of the E7 protein which could be purified or used as ‘in planta’ formulation, also suitable for oral therapeutic vaccination.

Purification of recombinant Aβ(1-42) and pGlu-Aβ(3-42) using preparative SDS-PAGE

Recombinant expression and purification of amyloid peptides represents a common basis for investigating the molecular mechanisms of amyloid formation and toxicity. However, the isolation of the recombinant peptides is hampered by inefficient separation from contaminants such as the fusion protein required for efficient expression in E. coli. Here, we present a new approach for the isolation of highly purified Aβ(1-42) and pGlu-Aβ(3-42), which is based on a separation using preparative SDS-PAGE. The method relies on the purification of the Aβ fusion protein by affinity chromatography followed by preparative SDS-PAGE under reducing conditions and subsequent removal of detergents by precipitation. The application of preparative SDS-PAGE represents the key step to isolate highly pure recombinant Aβ, which has been applied for characterization of aggregation and toxicity. Thereby, the yield of the purification strategy was  >60%. To the best of our knowledge, this is the first description of an electrophoresis-based method for purification of a recombinant Aβ peptide. Therefore, the method might be of interest for isolation of other amyloid peptides, which are critical for conventional purification strategies due to their aggregation propensity.

Human papillomavirus vaccines for the treatment of cervical cancer

Human papillomavirus (HPV) infection is a major cause of cervical cancer, the second most common cancer in women worldwide. Currently, a HPV L1-based virus-like particle has been approved as a prophylactic vaccine against HPV infection, which will probably lead to a reduction in cervical cancer incidence within a few decades. Therapeutic vaccines, however, are expected to have an impact on cervical cancer or its precursor lesions, by taking advantage of the fact that the regulatory proteins (E6 and E7) of HPV are expressed constantly in HPV-associated cervical cancer cells. Vaccine types targeting these regulatory proteins include the recombinant protein and DNA vaccines, peptide vaccines, dendritic-cell vaccines, and viral and bacterial vector deliveries of vaccines, and these may provide an opportunity to control cervical cancer. Further approaches incorporating these vaccine types with either conventional therapy modalities or the modulation of CD4(+) regulatory T cells appear to be more promising in achieving increased therapeutic efficacy. In this review, we summarize current and future therapeutic vaccine strategies against HPV-associated malignancies at the animal and clinical levels.

Flagellin enhances tumor-specific CD8⁺ T cell immune responses through TLR5 stimulation in a therapeutic cancer vaccine model

Tumor antigen (TA)-specific immunotherapy is an emerging approach for cancer treatment. Potent adjuvants are prerequisites to the immunotherapy for overcoming the low immunogenicity of TAs. We previously demonstrated that a bacterial flagellin, Vibrio vulnificus FlaB, has potent adjuvant activity in various vaccination models. In this study, we investigated whether the FlaB protein could be a potent adjuvant for a human papillomavirus 16 E6 and E7 (E6/E7) peptide-based anticancer immunotherapy. We used an E6/E7-expressing TC-1 carcinoma implantation animal model and tested TA-specific immunomodulation by FlaB. We co-administered the E6/E7 peptide either with or without FlaB into TC-1 tumor-bearing mice and then analyzed the antitumor activity of the peptide. FlaB significantly potentiated specific antitumor immune responses elicited by the peptide immunization, as evidenced by retarded in vivo tumor growth and significantly prolonged survival. We noticed that TC-1 cells do not express Toll-like receptor 5 (TLR5) on their surface and the TLR5 signaling pathway in TC-1 cells was not responsible for the antitumor effect of FlaB. FlaB potentiated the CTL activity and Ag-specific IFN-γ production of CD8(+) T cells from the draining lymph node and spleen. In addition, this antitumor activity was abrogated following the in vivo depletion of CD8(+) T cells and in TLR5 knockout (KO) or MyD88 KO mice. These results suggest that flagellin could enhance TA-specific CD8(+) CTL immune responses through TLR5 stimulation in cancer immunotherapy.

Expression of a recombinant elastin-like protein in pichia pastoris

The translation of highly repetitive gene sequences is often associated with reduced levels of protein expression and may be prone to mutational events. In this report, we describe a modified concatemerization strategy to construct a gene with enhanced sequence diversity that encodes a highly repetitive elastin-like protein polymer for expression in Pichia pastoris. Specifically, degenerate oligonucleotides were used to create a monomer library, which after concatemerization yielded a genetically nonrepetitive DNA sequence that encoded identical pentapeptide repeat sequences. By limiting genetic repetition, the risk of genetic deletions, rearrangements, or premature termination errors during protein synthesis is minimized.

Long-term protection against human papillomavirus e7-positive tumor by a single vaccination of adeno-associated virus vectors encoding a fusion protein of inactivated e7 of human papillomavirus 16/18 and heat shock protein 70

We investigated a gene vaccine strategy against human papillomavirus (HPV)-induced cancer and premalignant diseases, using adeno-associated virus (AAV) vector encoding the viral E7 oncoproteins as the tumor antigens from HPV serotypes 16 (HPV16) and 18 (HPV18). Genetically inactivated E7 proteins were fused with a heat shock protein 70 (hsp70) to minimize the risk of cell transformation and enhance immune responses. The fusion protein gene was packaged in AAV serotype 1 or 2 (AAV1 or 2) for efficient in vivo gene expression. Our results showed that after a single intramuscular injection, the AAV1 vector elicited stronger HPV-specific cytotoxic T lymphocyte (CTL) responses and interferon-gamma secretion when compared with the AAV2 vector. Prophylactic immunization with AAV1 protected 100% of the mice from tumor growth for more than 1 year, whereas all the control mice immunized with either a LacZ vector or saline grew large tumors and died within 6 weeks after inoculation of E7-positive tumor cell line TC-1. In addition, this single-dose AAV1 vaccination completely protected the mice against second and third challenges with higher numbers of TC-1 cells. Despite lower CTL responses against the E7 antigens, AAV2 vector prophylactic immunization was also sufficient to protect 100% of the mice against the initial and second tumor challenges and 70% of the mice against the third challenge. In addition, therapeutic immunization with AAV1 after palpable tumor formation inhibited tumor growth and caused tumor regression in some mice. Thus, our studies support the potential of AAV vectors as a genetic vaccine for the prevention and treatment of HPV-induced malignancies.

Antigen-specific CD8 T cells can eliminate antigen-bearing keratinocytes with clonogenic potential via an IFN-gamma-dependent mechanism

The immune system surveys the skin for keratinocytes (KCs) infected by viruses or with acquired genetic damage. The mechanism by which T cells mediate KC elimination is however undefined. In this study we show that antigen-specific CD8 T cells can eliminate antigen-bearing KCs in vivo and inhibit their clonogenic potential in vitro, independently of the effector molecules perforin and Fas-ligand (Fas-L). In contrast, IFN-gamma receptor expression on KCs and T cells producing IFN-gamma are each necessary and sufficient for in vitro inhibition of KC clonogenic potential. Thus, antigen-specific cytotoxic T lymphocytes (CTLs) may mediate destruction of epithelium expressing non-self antigen by eliminating KCs with potential for self-renewal through an IFN-gamma-dependent mechanism.

Mapping of cytotoxic T lymphocytes epitopes in E7 antigen of human papillomavirus type 11

One of the critical steps in the progression to condyloma acuminatum (CA) is the establishment of a persistent human papillomavirus (HPV) infection, majority of HPV type 6 and 11. Cytotoxic T lymphocytes (CTL), which can be induced by the epitope-based peptides in vitro, are thought to be able to recognize and destroy virus-infected cells. In order to screen and identify HLA-A*0201 restricted HPV-11E7 CTL epitopes, five epitope peptides and tetramers were selected including HPV-11E7 7-15 (TLKDIVLDL), 15-23 (LQPPDPVGL), 47-55 (PLTQHYQIL), 81-89 (DLLLGTLNI) and 82-90 (LLLGTLNIV). Human monocyte-derived dendritic cells (DCs) from HLA-A*0201 healthy individuals were pulsed with these peptides to assess the expression of CD83, CD86, HLA-DR and the secretion of IL-12. The ability of peptide-loaded mature DCs to activate autologous T cells was evaluated by analyzing the frequency of specific tetramer(+) CD8(+) T cells using flow cytometry, and the level of IFN-gamma secretion by ELISA. The ability of the epitope-specific CTLs to kill the target cells was also analysed. It was found that the immature DCs could be fully activated by all the five HPV-11E7 peptides and peptide-loaded mature DCs were able to stimulate the epitope-specific T cells in vitro. There was an increased frequency of CD8(+) T cells specific for the E7 7-15 epitope when compared to other four predicted epitopes of HPV-11E7 (P < 0.05). The epitope-specific CTLs for E7 7-15 induced the strongest cytotoxicity to HPV-11E7 expressing cell line at an E:T ratio of 50:1 (P < 0.05). Taken together, these findings demonstrate that E7 7-15 (TLKDIVLDL) is an HLA-A*0201-restricted CTL epitope of HPV type 11. We propose that this epitope could be more helpful in the characterization of HPV control mechanism and be useful for the development of immunotherapeutic approaches for low-risk HPV infectious diseases such as CA.

Vaccination with an adenoviral vector expressing calreticulin-human papillomavirus 16 E7 fusion protein eradicates E7 expressing established tumors in mice

BACKGROUND

Cervical cancer remains a leading cause of cancer-related mortality in women, particularly in developing countries. The causal association between genital human papilloma virus (HPV) infection and cervical cancer has been firmly established, and the oncogenic potential of certain HPV types has been clearly demonstrated. Vaccines targeting the oncogenic proteins, E6 and E7 of HPV-16 and -18 are the focus of current vaccine development. Previous studies have shown that calreticulin (CRT) enhances the MHC class I presentation of linked peptide/protein and may serve as an effective vaccination strategy for antigen-specific cancer treatment.

METHODS

Two replication-deficient adenoviruses, one expressing HPV-16 E7 (Ad-E7) and the other expressing CRT linked to E7 (Ad-CRT/E7), were assessed for their ability to induce cellular immune response and tested for prophylactic and therapeutic effects in an E7-expressing mouse tumor model.

RESULTS

Vaccination with Ad-CRT/E7 led to a dramatic increase in E7-specific T cell proliferation, interferon (IFN)-gamma-secretion, and cytotoxic activity. Immunization of mice with Ad-CRT/E7 was effective in preventing E7-expressing tumor growth, as well as eradicating established tumors with long-term immunological memory.

CONCLUSION

Vaccination with an adenoviral vector expressing CRT-E7 fusion protein represents an effective strategy for immunotherapy of cervical cancer in rodents, with possible therapeutic potential in clinical settings.

Intranasal immunization with synthetic peptides corresponding to the E6 and E7 oncoproteins of human papillomavirus type 16 induces systemic and mucosal cellular immune responses and tumor protection

The E6 and E7 oncoproteins of the high-risk HPV type16 represent ideal targets for HPV vaccine development, they being consistently expressed in cervical cancer lesions. Since HPV-16 is primarily transmitted through genital mucosal route, mucosal immune responses constitute an essential feature for vaccination strategies against HPV-associated lesions. We present here evidence showing that mucosal immunization of mice by the intranasal route with a mixture of peptides E7(44-62) and E6(43-57) from the E7 and E6 oncoproteins of HPV-16, respectively, using a mutant cholera toxin adjuvant (CT-2*), primed strong antigen-specific cellular immune responses in systemic and mucosal tissues. Significant levels of IFN-gamma production by both CD4 and CD8 cells were observed along with CTL responses that were effective against both peptide-pulsed targets as well as syngeneic tumor cells (TC-1) expressing the cognate E6 and E7 proteins. Furthermore, mice immunized with the peptide mixture and CT-2* effectively resisted TC-1 tumor challenge. These results together with our earlier observations that T cell responses to these peptides correlate with recurrence-free survival in women after ablative treatment for HPV-associated cervical intraepithelial neoplasia, support the potential of these E6 and E7 peptides for inclusion in vaccine formulations.

Expression and purification of His-tagged HPV16 E7 protein active in pRb binding

Human papillomavirus type 16 (HPV16) protein E7 is the major oncogenic factor associated with the development of human cervical cancer. The transforming activity of the E7 protein is linked to its interaction with host regulatory proteins such as the retinoblastoma tumor suppressor protein. The recombinant production of E7 protein is a prerequisite for its structural and functional characterization as well as for the development of various preventive and therapeutic strategies. We present an approach to enhance the soluble expression of His-tagged E7 protein by optimization of the E7 gene and the expression conditions in the host Escherichia coli. We also report a detailed protocol for the purification of E7 protein by standard chromatographic methods. The binding of E7 protein to the recombinant non-phosphorylated form of retinoblastoma protein was examined by ELISA and surface plasmon resonance analysis. These studies confirm that the recombinant His-tagged E7 protein retains its conformational properties and biological activity.

Combined prophylactic and therapeutic cancer vaccine: Enhancing CTL responses to HPV16 E2 using a chimeric VLP in HLA-A2 mice

We identified the strategies to induce a CTL response to human papillomavirus (HPV) 16 E2 in HLA-A2 transgenic mice (AAD). A chimeric HPV16 virus-like particle (VLP) that includes full length HPV16 E7 and E2 (VLP-E7E2) was generated. The combination of E2 and E7 has the advantage that E2 is expressed in early dysplasia and neoplasia lesions, where E7 is expressed in more advance lesions. Since T cell response to E2 is less defined, we first evaluated the strategies to enhancing CD8(+) T cell responses to HPV E7, using different combinations of immune-modulators with VLP-E7E2. Data showed that the CTL response to E7 could be significantly enhanced by coinjection of GM-CSF and anti-CD40 antibodies with chimeric VLP-E7E2 without adjuvant. However, using the same combination, a low level of CD8(+) T cell response to E2 was detected. To enhance the CD8+ T cell response to E2, we analyzed T cell epitopes from E2 sequence. A heterogenous prime-boost with chimeric VLP-E7E2 and E2 peptides was performed. The data showed that the priming with chimeric VLP-E7E2, followed by boosting with E2 peptides, gave a better CTL response than 2 immunizations with E2 peptides. The enhanced immunity is due to the increase of CD11c(+) and CD11c(+) CD40(+) double positive dendritic cells in mice that received immune-modulators, GM-CSF and anti-CD40. Furthermore, the level of anti-L1 antibodies remains similar in mice immunized with chimeric VLP with/without immune-modulators. Thus, the data suggested that the chimeric VLP-E7E2 has a therapeutic potential for the treatment of HPV-associated CINs and cancer without diminishing VLPs potential as a prophylactic vaccine by inducing anti-L1 antibodies against free virus.

Increase of soluble expression in Escherichia coli cytoplasm by a protein disulfide isomerase gene fusion system

Human protein disulfide isomerase (PDI) was selected as a fusion partner to construct a gene expression system to enhance the solubility of recombinant protein in Escherichia coli. DREBIII-1, a plant specific transcriptional factor, was found to mainly form inclusion bodies when expressed in either His-tagged or GST-fusion systems in E. coli. In contrast, when fused with PDI, the expressed DREBIII-1 was in a highly soluble and biologically active form. Two fusion proteins, HDP and HPD, were generated by positioning DREBIII-1 at the N-terminal and C-terminal of PDI, respectively. After purification, HDP exhibited a higher stability and showed only one band on SDS-PAGE, while HPD degraded as several bands. HDP was verified to have the biological function of PDI by isomerase activity assay; meanwhile, it also presented the DNA binding and transcriptional activation characteristic of DREBIII-1 in fluorescence quenching and yeast one-hybrid experiments. The PDI fusion expression system was demonstrated to be highly efficient in generating not only soluble but functional desired proteins.

Both antigen optimization and lysosomal targeting are required for enhanced anti-tumour protective immunity in a human papillomavirus E7-expressing animal tumour model

DNA immunization is a new approach for cancer immune therapy. In this study, we constructed human papillomavirus (HPV) 16 E7 expression vector cassettes and then compared the abilities of these constructs to induce antitumour protection. Lysosome-targeted E7 antigens, and to a lesser degree signal sequence-conjugated and transmembrane region sequence-conjugated E7 antigens in a DNA form, displayed tumour protection significantly higher than wild-type E7 antigens. This enhanced tumour protection was mediated by CD8+ cytotoxic T lymphocytes (CTL), as determined by in vivo T-cell depletion and in vitro interferon-gamma (IFN-gamma) production. Subsequent co-injection with interleukin-12-expressing cDNA showed insignificantly enhanced antitumour protection. However, E7 codon optimization plus lysosomal targeting resulted in a dramatic enhancement in antitumour protection both prophylactically and therapeutically through augmentation of the E7-specific CTL population, compared to either one of them alone. However, wild-type or codonoptimized E7 antigens without intracellular targeting displayed no protection against tumour challenge. Thus, these data suggest that antigen codon optimization plus lysosomal targeting strategy could be important in crafting more efficacious E7 DNA vaccines for tumour protection.

Immunization with adenoviral vectors carrying recombinant IL-12 and E7 enhanced the antitumor immunity to human papillomavirus 16-associated tumor

OBJECTIVE

Human papillomavirus (HPV) infection play a significant role in cervical carcinogenesis, and HPV oncoprotein E7 has important functions in the formation and maintenance of cervical cancers. Interleukin-12 (IL-12) has been reported to induce cellular immune responses, and has also been demonstrated to suppress the growth of tumors and the expression of E7. Here, we investigate the utility of adenovirus E7 (AdE7) and adenovirus IL-12 (AdIL-12) for protection against TC-1 tumor using an animal model.

METHODS

The antitumor effects induced by AdIL-12 and/or E7 were assessed by measurements of tumor size. E7-specific antibody and INF-gamma production in sera were measured, as were T-helper cell proliferative responses. Cytotoxic T-lymphocytes (CTL) and T cell subset depletion studies were also performed.

RESULTS

Infection of tumor sites with a combination of AdIL-12 and AdE7 resulted in an antitumor effect which was significantly more profound than that which resulted from singular infections with either AdIL-12 or AdE7. Combined infection resulted in regression of 9-mm-sized tumors in approximately 80% of our experimental animals as compared to the PBS group. Serum levels of E7-specific antibody and INF-gamma production, as well as T-helper cell proliferative responses, were found to be significantly higher in coinfected with AdIL-12 and AdE7 group than in single infection with either AdIL-12 or AdE7 group. CTL responses only exhibited by the AdIL-12 and AdE7 coinjected group suggested that these tumor suppression effects were mediated primarily by CD8+ and, to a lesser degree, by CD4+ T cells.

CONCLUSION

Combined injection with adenovirus carrying IL-12 and E7 induced significant antitumor immunity against TC-1 tumors. They may prove useful in clinical applications for the treatment of HPV-associated tumors.

Tumour susceptibility to innate and adaptive immunotherapy changes during tumour maturation

Immunotherapy of tumours using T cells expanded in vitro has met with mixed clinical success suggesting that a greater understanding of tumour/T-cell interaction is required. We used a HPV16E7 oncoprotein-based mouse tumour model to study this further. In this study, we demonstrate that a HPV16E7 tumour passes through at least three stages of immune susceptibility over time. At the earliest time point, infusion of intravenous immune cells fails to control tumour growth although the same cells given subcutaneously at the tumour site are effective. In a second stage, the tumour becomes resistant to subcutaneous infusion of cells but is now susceptible to both adjuvant activated and HPV16E7-specific immune cells transferred intravenously. In the last phase, the tumour is susceptible to intravenous transfer of HPV16E7-specific cells, but not adjuvant-activated immune cells. The requirement for IFN-gamma and perforin also changes with each stage of tumour development. Our data suggest that effective adoptive T-cell therapy of tumour will need to be matched with the stage of tumour development.

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.

Immunization with adenoviral vectors carrying recombinant IL-12 and E7 enhanced the antitumor immunity against human papillomavirus 16-associated tumor

PURPOSE

Human papillomavirus (HPV) infection has a significant role in cervical carcinogenesis, and HPV oncoprotein E7 plays an important part in the formation and maintenance of cervical cancer. Interleukin-12 (IL-12) has been reported to induce a cellular immune response, and to suppress the tumor growth and the E7 production. Here we describe the use of adenoviral delivery of the HPV 16 E7 subunit (AdE7) along with adenoviral delivery of IL-12 (AdIL-12) in mice with HPV-associated tumors.

MATERIALS AND METHODS

Mice were injected with TC-1 cells to establish TC-1 tumor, and then they were immunized with AdIL-12 and/or AdE7 intratumorally. The anti tumor effects induced by AdIL-12 and/or E7 were evaluated by measuring the size of the tumor. E7-specific antibody and INF-gamma production in sera, and the T-helper cell proliferative responses were then measured. Cytotoxic T-lymphocyte (CTL) and T cell subset depletion studies were also performed.

RESULTS

Combined AdIL-12 and AdE7 infection at the tumor sites significantly enhanced the antitumor effects more than that of AdIL-12 or AdE7 single infection. This combined infection resulted in regression of the 9 mm sized tumors in 80% of animals as compare to the PBS group. E7-specific antibody and INF-gamma production in the sera, and the T-helper cell proliferative responses were significantly higher with coinfection of AdIL-12 and AdE7 than with AdIL-12 or AdE7 alone. CTL response induced by AdIL-12 and AdE7 in the coinjected group suggested that tumor suppression was mediated by mostly CD8+ and only a little by the CD4+ T cells.

CONCLUSION

IL-12 and E7 application using adenovirus vector showed antitumor immunity effects against TC-1 tumor, and this system could be use in clinical applications for HPV-associated cancer.

Impaired antigen presentation and effectiveness of combined active/passive immunotherapy for epithelial tumors

BACKGROUND

Although immunization with tumor antigens can eliminate many transplantable tumors in animal models, immune effector mechanisms associated with successful immunotherapy of epithelial cancers remain undefined.

METHODS

Skin from transgenic mice expressing the cervical cancer-associated tumor antigen human papillomavirus type 16 (HPV16) E6 or E7 proteins from a keratin 14 promoter was grafted onto syngeneic, non-transgenic mice. Skin graft rejection was measured after active immunization with HPV16 E7 and adoptive transfer of antigen-specific T cells. Cytokine secretion of lymphocytes from mice receiving skin grafts and immunotherapy was detected by enzyme-linked immunosorbent assay, and HPV16 E7-specific memory CD8+ T cells were detected by flow cytometry and ELISPOT.

RESULTS

Skin grafts containing HPV16 E6-or E7-expressing keratinocytes were not rejected spontaneously or following immunization with E7 protein and adjuvant. Adoptive transfer of E7-specific T-cell receptor transgenic CD8+ T cells combined with immunization resulted in induction of antigen-specific interferon gamma-secreting CD8+ T cells and rejection of HPV16 E7-expressing grafts. Specific memory CD8+ T cells were generated by immunotherapy. However, a further HPV16 E7 graft was rejected from animals with memory T cells only after a second E7 immunization.

CONCLUSIONS

Antigen-specific CD8+ T cells can destroy epithelium expressing HPV16 E7 tumor antigen, but presentation of E7 antigen from skin is insufficient to reactivate memory CD8+ T cells induced by immunotherapy. Thus, effective cancer immunotherapy in humans may need to invoke sufficient effector as well as memory T cells.

ISCOMATRIX™ adjuvant: an adjuvant suitable for use in anticancer vaccines

Human Papillomavirus type 16 (HPV16) E6 and E7 oncoproteins are associated with cervical cancer development and progression and can therefore be used as target antigens for cancer immunotherapy. In this study we evaluated the immunogenicity in mice, of different vaccine formulations using recombinant HPV16 derived E6E7 or E7GST fusion proteins. When co-administered with ISCOMATRIX adjuvant, these E6E7 proteins consistently induced E7 specific CTL, in vivo tumor protection, antibody and DTH responses. ISCOMATRIX adjuvant has been developed for use in the formulation of novel human vaccines and has been evaluated for safety and toxicity in human trials. A formulation containing aluminum hydroxide (Al(OH)3) gave a lesser degree of E7 specific antibody, and no local E7 specific CTL response but similar DTH and tumor protection. These findings demonstrate the potential of ISCOMATRIX adjuvant to stimulate both cellular and humoral immune responses to endogenously processed target antigens, and hence is the preferred adjuvant when CTL responses are desirable.

Recombinant NY-ESO-1 protein with ISCOMATRIX adjuvant induces broad integrated antibody and CD4(+) and CD8(+) T cell responses in humans

NY-ESO-1 is a "cancer-testis" antigen expressed in many cancers. ISCOMATRIX is a saponin-based adjuvant that induces antibody and T cell responses. We performed a placebo-controlled clinical trial evaluating the safety and immunogenicity of recombinant NY-ESO-1 protein with ISCOMATRIX adjuvant. Forty-six evaluable patients with resected NY-ESO-1-positive tumors received three doses of vaccine intramuscularly at monthly intervals. The vaccine was well tolerated. We observed high-titer antibody responses, strong delayed-type hypersensitivity reactions, and circulating CD8(+) and CD4(+) T cells specific for a broad range of NY-ESO-1 epitopes, including known and previously unknown epitopes. In an unplanned analysis, vaccinated patients appeared to have superior clinical outcomes to those treated with placebo or protein alone. The vaccine is safe and highly potent immunologically.

Efficient Expression of Modified Human Papillomavirus 16 E6/E7 Fusion Protein and the Antitumor Efficacy in a Mouse Model

Infection with human papillomavirus, particularly type 16 (HPV16), is highly associated with the development of cervical intraepithelial neoplasia and cervical cancer. The two early viral oncogenes, E6 and E7, are selectively retained and constitutively expressed in tumor cells and are therefore attractive immunotherapeutic targets. Thus a vaccine strategy based on recombinant HPV16 E6/E7 fusion protein represents an efficient approach against HPV16-associated tumors. Although the expression level of HPV16 E6/E7 fusion protein was presumed to be low, direct experimental proof in vivo was lacking. To enhance the expression level and investigate its antitumor efficacy in vivo, we constructed a modified HPV16 E6/E7 fusion gene with three point-mutations and expressed it in Escherichia coli. The encoded protein, denoted mE6(1-120)/mE7(1-60), comprises 120 N-terminus amino acids of E6 and 60 N-terminus amino acids of E7 plus a histine tag, was purified on an affinity column, and subsequently characterized by Western blotting. Immunization of mice with mE6(1-120)/mE7(1-60) completely protected them against subsequent challenge and rechallenge with TC-1 tumor cells expressing HPV16 E6 and E7 proteins. In the therapeutic experiments, most mice eliminated the preexisting tumors and had a long-term protection. Consistent with the results of in vivo experiments, the splenocytes from immunized mice elicited cytotoxic T lymphocytes and specifically lysed TC-1 cells in vitro. More importantly, the expression level of mE6(1-120)/mE7(1-60) was significantly improved, meeting the necessary quantity required for a vaccine clinical trial. In conclusion, these data provide a scientific basis for the use of modified mE6(1-120)/mE7(1-60) in future human trials.

A Therapy Modality Using Recombinant IL-12 Adenovirus plus E7 Protein in a Human Papillomavirus 16 E6/E7-Associated Cervical Cancer Animal Model

Interleukin (IL)-12 has been reported to induce cellular immune responses for protection against tumor formation. Here we investigate the utility of adenoviral delivery of IL-12 as an adjuvant for a human papillomavirus E7 subunit vaccine in a mouse tumor challenge model. Direct intratumoral injection of AdIL-12 resulted in a significant suppression of tumor growth compared to the control group. Injection of E7 protein into either a tumor site or the distance site along with AdIL-12 further enhanced antitumor effects significantly higher than either AdIL-12 or E7 injection alone. This combined injection resulted in complete regression of 9-mm-sized tumor in 40% of animals as well as lasting antitumor immunity against tumor recurrence. We also evaluated immune responses induced by these injections. AdIL-12 plus E7 enhanced E7-specific antibody responses significantly higher than AdIL-12 or E7 injection. In particular, the production level of interferon (IFN)-gamma from E7-specific CD4(+) T cells was similar between AdIL-12 group and AdIL-12 + E7 group. However, IFN-gamma production from E7-specific CD8(+) T cells was the most significant when injected with AdIL-12 + E7. This was consistent with intracellular IFN-gamma staining levels of CD8(+) T cells, suggesting that AdIL-12 + E7 injection enhances antitumor immunity in the human papillomavirus (HPV) 16 tumor model through increased expansion of the cytotoxic T-lymphocyte (CTL) subset. This enhanced protection appeared to be mediated by CD8(+) T cells, as determined by in vivo T-cell subset deletion. Thus, these studies demonstrate that E7 vaccines can induce CTL responses responsible for antitumor effects in the presence of IL-12 delivered via adenovirus vectors. This likely provides one additional approach for immune therapy against cervical cancers.

A critical review of the methods for cleavage of fusion proteins with thrombin and factor Xa

Expression and purification of proteins in recombinant DNA systems is a powerful and widely used technique. Frequently there is the need to express the protein of interest as a fusion protein or chimeric protein. Fusion protein technology is frequently used to attach a "signal" which can be used for subsequent localization of the protein or a "carrier" which can be used to deliver a "therapeutic" such as a radioactive molecule to a specific site. In addition to these applications, fusion protein technology can be employed for several other useful purposes. Of these, the most frequent reason is to provide a 'tag' or 'handle' which will aid in the purification of the protein. Another useful purpose is to improve the expression or folding of the protein of interest. In these latter two situations, it is often necessary to remove the fusion partner before the recombinant protein of interest can be used for further studies. This removal process involves the insertion of a unique amino acid sequence that is susceptible to cleavage by a highly specific protease. Thrombin and factor Xa are the most frequently used proteases for this application. The purpose of this review is to discuss the application of thrombin and factor Xa for the cleavage of fusion proteins. It is emphasized that while these enzymes are quite specific for cleavage at the inserted cleavage site, proteolysis can frequently occur at other site(s) in the protein of interest. It is necessary to characterize the protein of interest after cleavage from the affinity label to assure that there are no changes in the covalent structure of the protein of interest. Examples are presented which describe the proteolysis of the protein of interest by either factor Xa or thrombin.

Paucity of functional CTL epitopes in the E7 oncoprotein of cervical cancer associated human papillomavirus type 16

Many specific antiviral and antitumour immune responses have been attributed to the protective effects of antigen-specific CD8+ cytotoxic T lymphocytes (CTL). Recognition of virus infected or tumour cells by CTL requires presentation of at least one peptide epitope from a virus or tumour-specific antigen by the relevant MHC Class I molecule. Viral genes with mutations which remove CTL epitopes may thus be favoured for survival. Human cervical cancers are caused by papillomavirus infection, and these cancers consistently express the E7 protein of the oncogenic papillomavirus. We therefore investigated the MHC Class I restricted T cell epitopes of the human papillomavirus type 16 E7 oncoprotein using mice of five different genetic backgrounds, and an IFN-gamma ELISPOT assay, to determine the frequency with which MHC Class I epitopes might be expected in this small oncoprotein (98 amino acids). No MHC Class I restricted responses were detected in E7 immunized BALB/c (H-2d), CBA/CaH (H-2 k), FVB/N (H-2q) or A2KbH2b human HLA2.1 transgenic mice. In C57BL/6 J (H-2b) mice, a previously identified single antigenic epitope was detected. Therefore, we conclude that there is a paucity of MHC Class I restricted T cell epitopes in HPV16 E7 protein because of its small size. This might be advantageous to the virus. Furthermore here we present a quick and easy method to exhaustively determine CD8 T cell epitopes in proteins using a unique set of overlapping 8, 9 and 10 mer synthetic peptides.

Limitations of HLA-transgenic mice in presentation of HLA-restricted cytotoxic T-cell epitopes from endogenously processed human papillomavirus type 16 E7 protein

We investigated the use of mice transgenic for human leucocyte antigen (HLA) A*0201 antigen-binding domains to test vaccines composed of defined HLA A*0201-restricted cytotoxic T-lymphocyte (CTL) epitopes of human papillomavirus (HPV) type 16 E7 oncoprotein. HPV is detected in >90% of cervical carcinomas. HPV16 E7 oncoprotein transforms cells of the uterine cervix and functions as a tumour-associated antigen to which immunotherapeutic strategies may be directed. We report that although the HLA A*0201 E7 epitope peptides function both to prime for E7 CTL responses, and to sensitize target cells for E7-directed CTL killing in situations where antigen processing is not required, the epitopes are not processed out of either endogenously expressed or immunization-introduced E7, by the mouse antigen-processing and presentation machinery. Thus (1) CTL induced by HLA A*0201 peptide immunization killed E7 peptide-pulsed target cells, but did not kill target cells expressing whole E7; (2) immunization with whole E7 protein did not elicit CTL directed to HLA A*0201-restricted E7 CTL epitopes; (3) HLA A*0201-restricted CTL epitopes expressed in the context of a DNA polytope vaccine did not activate E7-specific T cells either in 'conventional' HLA A*0201 transgenic (A2.1Kb) mice, or in HHD transgenic mice in which expression of endogenous H-2 class 1 is precluded; and (4) HLA A*0201 E7 peptide epitope immunization was incapable of preventing the growth of an HLA A*0201- and E7-expressing tumour. There are generic implications for the universal applicability of HLA-class 1 transgenic mice for studies of human CTL epitope presentation in murine models of human infectious disease where recognition of endogenously processed antigen is necessary. There are also specific implications for the use of HLA A2 transgenic mice for the development of E7-based therapeutic vaccines for cervical cancer.

Regression of established human papillomavirus type 16 (HPV-16) immortalized tumors in vivo by vaccinia viruses expressing different forms of HPV-16 E7 correlates with enhanced CD8(+) T-cell responses that home to the tumor site

Using vaccinia virus as a live vector, we show that the expression of human papillomavirus type 16 (HPV-16) E7 fused to a nonhemolytic portion of the Listeria monocytogenes virulence factor, listeriolysin O (LLO), induces an immune response that causes the regression of established HPV-16 immortalized tumors in C57BL/6 mice. The vaccinia virus construct expressing LLO fused to E7 (VacLLOE7) was compared with two previously described vaccinia virus constructs: one that expresses unmodified E7 (VacE7) and another that expresses E7 in a form designed to direct it to intracellular lysosomal compartments and improve major histocompatibility complex class II-restricted responses (VacSigE7LAMP-1). C57BL/6 mice bearing established HPV-16 immortalized tumors of 5 or 8 mm were treated with each of these vaccines. Fifty percent of the mice treated with VacLLOE7 remained tumor free 2 months after tumor inoculation, whereas 12 to 25% of the mice were tumor free after treatment with VacSigE7LAMP-1 (depending on the size of the tumor). No mice were tumor free in the group given VacE7. Compared to VacE7, VacSigE7LAMP-1 and VacLLOE7 resulted in increased numbers of H2-D(b)-specific tetramer-positive CD8(+) T cells in mouse spleens that produced gamma interferon and tumor necrosis factor alpha upon stimulation with RAHYNIVTF peptide. In addition, the highest frequency of tetramer-positive T cells was seen in the tumor sites of mice treated with VacLLOE7. An increased efficiency of E7-specific lysis by splenocytes from mice immunized with VacLLOE7 was also observed. These results indicate that the fusion of E7 with LLO not only enhances antitumor therapy by improving the tumoricidal function of E7-specific CD8(+) T cells but may also increase the number of antigen-specific CD8(+) T cells in the tumor, the principle site of antigen expression.

Modified HPV16 E7 Genes as DNA Vaccine against E7-Containing Oncogenic Cells

Therapeutic vaccines against tumors associated with human papillomaviruses (HPV) should elicit cellular immune responses against early HPV antigens, primarily the oncoproteins E7 and E6. Because of safety concerns, the direct use of an unmodified oncogene is impossible in human DNA vaccination. Therefore, we introduced three point mutations into the pRb-binding site of HPV16 E7 oncogene to eliminate its transformation potential. The resultant gene was denoted E7GGG. The rates of expression and the cellular localization of E7 and E7GGG proteins were comparable. In immunization-challenge experiments, the efficacy of plasmids containing the E7, E7GGG, or fusion genes of HPV16 E7, viz. L1DeltaCE7(1-60) (M. Muller et al., 1997, Virology 234, 93-111), and Sig/E7/LAMP-1 (T. C. Wu et al., 1995, Proc. Natl. Acad. Sci. USA 92, 11671-11675), was compared. While tumors developed in all animals immunized with the wild-type E7 gene, a significant proportion of mice remained tumor-free after vaccination with the E7GGG gene. The fusion gene L1DeltaCE7(1-60) induced negligible protection, but Sig/E7/LAMP-1 conferred the highest protection. Intradermal immunization by gene gun proved superior to i.m. inoculation. In "therapeutic" experiments, a 1-day delay between inoculation of oncogenic cells and the start of DNA immunization resulted in partial therapeutic effect, but a 3-day delay produced a substantially lower immunization effect. A combination of Sig/E7/LAMP-1 and E7GGG genes did not enhance the immune response. These results demonstrate a significant enhancement of HPV16 E7 immunogenicity after mutagenesis of the pRb-binding site, but the mutated E7 gene did not excel the Sig/E7/LAMP-1 fusion gene.

Cervical cancer vaccines: emerging concepts and developments

Certain human cancers are linked to infection by oncogenic viruses that are able to cause transformation of the normal host cell into a cancerous cell. Human papillomavirus (HPV) DNA and expression of viral transforming proteins are found in virtually all cervical cancer cells, indicating an important role of this virus in the pathogenesis of the disease. Evidence exists that the immune response to cancer cells can play a major role in determining the outcome of disease. The fact that HPV is a necessary cause for cervical cancer provides a clear opportunity to develop a therapeutic vaccine against the virus to treat patients with cervical cancer at its early and late stages. Development of a prophylactic vaccine for HPV would also reduce the incidence of cervical neoplasias by preventing virus infection. Various candidate HPV vaccines are being developed and tested in animal models and/or in human clinical trials. These HPV vaccines, both preventive and therapeutic, are the subjects of this review.

Preventive and therapeutic vaccines for human papillomavirus-associated cervical cancers

'High risk' genotypes of the human papillomavirus (HPV), particularly HPV type 16, are the primary etiologic agent of cervical cancer. Thus, HPV-associated cervical malignancies might be prevented or treated by induction of the appropriate virus-specific immune responses in patients. Sexual transmission of HPV may be prevented by the generation of neutralizing antibodies that are specific for the virus capsid. In ongoing clinical trials, HPV virus-like particles (VLPs) show great promise as prophylactic HPV vaccines. Since the capsid proteins are not expressed at detectable levels by basal keratinocytes, therapeutic vaccines generally target other nonstructural viral antigens. Two HPV oncogenic proteins, E6 and E7, are important in the induction and maintenance of cellular transformation and are coexpressed in the majority of HPV-containing carcinomas. Therefore, therapeutic vaccines targeting these proteins may provide an opportunity to control HPV-associated malignancies. Various candidate therapeutic HPV vaccines are currently being tested whereby E6 and/or E7 are administered in live vectors, in peptides or protein, in nucleic acid form, as components of chimeric VLPs, or in cell-based vaccines. Encouraging results from experimental vaccination systems in animal models have led to several prophylactic and therapeutic vaccine clinical trials. Should they fulfill their promise, these vaccines may prevent HPV infection or control its potentially life-threatening consequences in humans.

T-helper epitopes identified within the E6 transforming protein of cervical cancer-associated human papillomavirus type 16

The E6 oncoprotein of human papillomavirus type 16 (HPV16 E6) produced by tumor cells of HPV16-associated cervical carcinoma is poorly immunogenic in patients, but nonetheless is a tumor-specific antigen to which therapeutic vaccine strategies may be directed. To investigate the subunit immunogenicity of E6 protein at the T-helper cell level, we immunized mice with overlapping peptides spanning the entire 158 amino acid sequence. Two peptides recalled a proliferative response in lymph node cells (LNC) from C57BL/6 (H-2b)-immunized mice. One of these peptides also recalled proliferative responses in the context of 5/5 other major histocompatibility complex (MHC) class II haplotypes, indicating a "promiscuous" T-epitope. Minimal consensus motif analysis identified the epitopes as 60VYRDGNPYA68 and 98GYNKPLCDLL107. LNC from mice immunized with T-epitope proliferated in response to challenge with whole E6 protein. Immunization with E6 T-epitopes linked to B-epitopes of HPV16 E7 protein elicited specific antibody indicating that T-cells recognizing the T-epitopes provided cognate "help" for B-cells. LNC from mice co-immunized with E6 T-epitope and the major T-helper epitope of HPV16 E7 (48DRAHYNI54) proliferated comparably when challenged with the peptides individually indicating co-dominance of the two T-epitopes. The findings have implications for incorporation of E6 into a therapeutic vaccine.

Expression of human papilloma virus E7 protein causes apoptosis and inhibits DNA synthesis in primary hepatocytes via increased expression of p21(Cip-1/WAF1/MDA6)

The impact of human papilloma virus (HPV16) E7 proteins and retinoblastoma (RB) antisense oligonucleotides upon mitogen-activated protein kinase (MAPK)-mediated inhibition of DNA synthesis via p21(Cip-1/WAF1/MDA6) (p21) was determined in primary hepatocytes. Prolonged activation of the MAPK pathway in p21(+/+) or p21(-/-) hepatocytes caused a large decrease and increase, respectively, in DNA synthesis. Either transfection with RB antisense oligonucleotides, expression of wild type E7, or RB binding mutant E7 (C24S) proteins increased p21 levels and reduced DNA synthesis in p21(+/+) hepatocytes. RB antisense oligonucleotides and E7 proteins increased apoptosis in p21(+/+), but not p21(-/-), hepatocytes. Expression of wild type E7 increased DNA synthesis above control levels in p21(-/-) cells, which was additive with prolonged MAPK activation. In contrast, expression of mutant E7 did not alter DNA synthesis above control levels in p21(-/-) cells and was supra-additive with prolonged MAPK activation. Antisense ablation of RB in p21(-/-) hepatocytes had a weak stimulatory effect upon DNA synthesis itself but enhanced the capacity of mutant E7 protein to stimulate DNA synthesis to the same level observed using wild type E7. The ability of prolonged MAPK activation to stimulate DNA synthesis in the presence of mutant E7 and antisense RB was additive. Collectively, the present data demonstrate that loss of RB function together with loss of p21 function plays an important role in the E7- and MAPK-dependent modulation of apoptosis and DNA synthesis in primary hepatocytes.