Immunisation with modified HPV16 E7 genes against mouse oncogenic TC-1 cell sublines with downregulated expression of MHC class I molecules

Spatial immune heterogeneity in a mouse tumor model after immunotherapy

Cancer immunotherapy is increasingly used in clinical practice, but its success rate is reduced by tumor escape from the immune system. This may be due to the genetic instability of tumor cells, which allows them to adapt to the immune response and leads to intratumoral immune heterogeneity. The study investigated spatial immune heterogeneity in the tumor microenvironment and its possible drivers in a mouse model of tumors induced by human papillomaviruses (HPV) following immunotherapy. Gene expression was determined by RNA sequencing and mutations by whole exome sequencing. A comparison of different tumor areas revealed heterogeneity in immune cell infiltration, gene expression, and mutation composition. While the mean numbers of mutations with every impact on gene expression or protein function were comparable in treated and control tumors, mutations with high or moderate impact were increased after immunotherapy. The genes mutated in treated tumors were significantly enriched in genes associated with ECM metabolism, degradation, and interactions, HPV infection and carcinogenesis, and immune processes such as antigen processing and presentation, Toll-like receptor signaling, and cytokine production. Gene expression analysis of DNA damage and repair factors revealed that immunotherapy upregulated Apobec1 and Apobec3 genes and downregulated genes related to homologous recombination and translesion synthesis. In conclusion, this study describes the intratumoral immune heterogeneity, that could lead to tumor immune escape, and suggests the potential mechanisms involved.

Ethanolic Extract of Salvia officinalis Leaves Affects Viability, Survival, Migration, and the Formation and Growth of 3D Cultures of the Tumourigenic Murine HPV-16+-Related Cancer Cell Line

Salvia officinalis (SO) is one of the most widely used plants in traditional medicine worldwide. In the present study, the effect of an ethanolic extract of S. officinalis leaves on hallmarks of cancer of HPV-16-positive cancer tumorigenic cells, TC-1, was analyzed in vitro. Phytochemical and spectroscopic analysis were performed. Additionally, the extract's flavonoid content, reducing iron, and antioxidant capacity were determined. In regard to the in vitro tests, the cytotoxic activity and its effect on the replicative capacity and on the cell migration of TC-1 cells were analyzed by viability and clonogenic, survival, and wound healing assays. The effect of a pre-treatment or treatment on 3D culture formation, growth, and reversion capacity was also examined. The results of the phytochemical analysis allowed the detection of tannins, saponins, steroids, and flavonoids. The flavonoids content was found to be 153.40 ± 10.68 µg/mg of extract. Additionally, the extract exhibited an antioxidant capacity and a ferric-reducing capacity of around 40% compared to the ascorbic acid. Thin layer chromatographic (TLC) analysis and spectroscopic tests showed the presence of compounds similar to quercetin and catechin flavonoids in the extract. In the in vitro assays, the SO extract induced in a concentration-dependent way changes in cell morphology, the decrease of cell viability, survival, and migration. At a concentration of 125 µg/mL, the extract inhibited spheroid formation, reduced their growth, and affected their reversion to 2D. Ethanolic extract of S. officinalis leaves had inhibitory effects on hallmarks of the cancer line HPV-16+. This suggests that the phytochemicals present in it may be a source of chemotherapeutics against cervical cancer.

Preclinical evaluation of two phylogenetically distant arenavirus vectors for the development of novel immunotherapeutic combination strategies for cancer treatment

BACKGROUND

Engineered arenavirus vectors have recently been developed to leverage the body's immune system in the fight against chronic viral infections and cancer. Vectors based on Pichinde virus (artPICV) and lymphocytic choriomeningitis virus (artLCMV) encoding a non-oncogenic fusion protein of human papillomavirus (HPV)16 E6 and E7 are currently being tested in patients with HPV16+ cancer, showing a favorable safety and tolerability profile and unprecedented expansion of tumor-specific CD8+ T cells. Although the strong antigen-specific immune response elicited by artLCMV vectors has been demonstrated in several preclinical models, PICV-based vectors are much less characterized.

METHODS

To advance our understanding of the immunobiology of these two vectors, we analyzed and compared their individual properties in preclinical in vivo and in vitro systems. Immunogenicity and antitumor effect of intratumoral or intravenous administration of both vectors, as well as combination with NKG2A blockade, were evaluated in naïve or TC-1 mouse tumor models. Flow cytometry, Nanostring, and histology analysis were performed to characterize the tumor microenvironment (TME) and T-cell infiltrate following treatment.

RESULTS

Despite being phylogenetically distant, both vectors shared many properties, including preferential infection and activation of professional antigen-presenting cells, and induction of potent tumor-specific CD8+ T-cell responses. Systemic as well as localized treatment induced a proinflammatory shift in the TME, promoting the infiltration of inducible T cell costimulator (ICOS)+CD8+ T cells capable of mediating tumor regression and prolonging survival in a TC-1 mouse tumor model. Still, there was evidence of immunosuppression built-up over time, and increased expression of H2-T23 (ligand for NKG2A T cell inhibitory receptor) following treatment was identified as a potential contributing factor. NKG2A blockade improved the antitumor efficacy of artARENA vectors, suggesting a promising new combination approach. This demonstrates how detailed characterization of arenavirus vector-induced immune responses and TME modulation can inform novel combination therapies.

CONCLUSIONS

The artARENA platform represents a strong therapeutic vaccine approach for the treatment of cancer. The induced antitumor immune response builds the backbone for novel combination therapies, which warrant further investigation.

A novel type-2 innate lymphoid cell-based immunotherapy for cancer

Cell-based cancer immunotherapy has achieved significant advancements, providing a source of hope for cancer patients. Notwithstanding the considerable progress in cell-based immunotherapy, the persistently low response rates and the exorbitant costs associated with their implementation still present a formidable challenge in clinical settings. In the landscape of cell-based cancer immunotherapies, an uncharted territory involves Type 2 innate lymphoid cells (ILC2s) and interleukin-33 (IL-33) which promotes ILC2 functionality, recognized for their inherent ability to enhance immune responses. Recent discoveries regarding their role in actuating cytolytic T lymphocyte responses, including curbing tumor growth rates and hindering metastasis, have added a new dimension to our understanding of the IL-33/ILC2 axis. These recent insights may hold significant promise for ILC2 cell-based immunotherapy. Nevertheless, the prospect of adoptively transferring ILC2s to confer immune protection against tumors has yet to be investigated. The present study addresses this hypothesis, revealing that ILC2s isolated from the lungs of tumor-bearing mice, and tumor infiltrating ILC2s when adoptively transferred after tumor establishment at a ratio of one ILC2 per sixty tumor cells, leads to an influx of tumor infiltrating CD4+ and CD8+ T lymphocytes as well as tumor infiltrating eosinophils resulting in a remarkable reduction in tumor growth. Moreover, we find that post-adoptive transfer of ILC2s, the number of tumor infiltrating ILC2s is inversely proportional to tumor size. Finally, we find corollaries of the IL-33/ILC2 axis enhancing the infiltration of eosinophils in human prostate carcinomas patients' expressing high levels of IL-33 versus those expressing low levels of IL-33. Our results underscore the heightened efficacy of adoptively transferred ILC2s compared to alternative approaches, revealing an approximately one hundred fifty-fold superiority on a cell-per-cell basis over CAR T-cells in the specific targeting and elimination of tumors within the same experimental model. Overall, this study demonstrates the functional significance of ILC2s in cancer immunosurveillance and provides the proof of concept of the potential utility of ILC2 cell-based cancer immunotherapies.

DNA damage induced by CDK4 and CDK6 blockade triggers anti-tumor immune responses through cGAS-STING pathway

CDK4/6 are important regulators of cell cycle and their inhibitors have been approved as anti-cancer drugs. Here, we report a STING-dependent anti-tumor immune mechanism responsible for tumor suppression by CDK4/6 blockade. Clinical datasets show that in human tissues, CDK4 and CDK6 are over-expressed and their expressions are negatively correlated with patients' overall survival and T cell infiltration. Deletion of Cdk4 or Cdk6 in tumor cells significantly reduce tumor growth. Mechanistically, we find that Cdk4 or Cdk6 deficiency contributes to an increased level of endogenous DNA damage, which triggers the cGAS-STING signaling pathway to activate type I interferon response. Knockout of Sting is sufficient to reverse and partially reverse the anti-tumor effect of Cdk4 and Cdk6 deficiency respectively. Therefore, our findings suggest that CDK4/6 inhibitors may enhance anti-tumor immunity through the STING-dependent type I interferon response.

A novel cell-based screen identifies chemical entities that reverse the immune-escape phenotype of metastatic tumours

Genetic and epigenetic events have been implicated in the downregulation of the cellular antigen processing and presentation machinery (APM), which in turn, has been associated with cancer evasion of the immune system. When these essential components are lacking, cancers develop the ability to subvert host immune surveillance allowing cancer cells to become invisible to the immune system and, in turn, promote cancer metastasis. Here we describe and validate the first high-throughput cell-based screening assay to identify chemical extracts and unique chemical entities that reverse the downregulation of APM components in cell lines derived from metastatic tumours. Through the screening of a library of 480 marine invertebrate extracts followed by bioassay-guided fractionation, curcuphenol, a common sesquiterpene phenol derived from turmeric, was identified as the active compound of one of the extracts. We demonstrate that curcuphenol induces the expression of the APM components, TAP-1 and MHC-I molecules, in cell lines derived from both metastatic prostate and lung carcinomas. Turmeric and curcumins that contain curcuphenol have long been utilized not only as a spice in the preparation of food, but also in traditional medicines for treating cancers. The remarkable discovery that a common component of spices can increase the expression of APM components in metastatic tumour cells and, therefore reverse immune-escape mechanisms, provides a rationale for the development of foods and advanced nutraceuticals as therapeutic candidates for harnessing the power of the immune system to recognize and destroy metastatic cancers.

Development of an Orthotopic HPV16-Dependent Base of Tongue Tumor Model in MHC-Humanized Mice

Head and neck squamous cell carcinomas (HNSCC) caused by infections with high-risk human papillomaviruses (HPV) are responsible for an increasing number of head and neck cancers, particularly in the oropharynx. Despite the significant biological differences between HPV-driven and HPV-negative HNSCC, treatment strategies are similar and not HPV targeted. HPV-driven HNSCC are known to be more sensitive to treatment, particularly to radiotherapy, which is at least partially due to HPV-induced immunogenicity. The development of novel therapeutic strategies that are specific for HPV-driven cancers requires tumor models that reflect as closely as possible the characteristics and complexity of human tumors and their response to treatment. Current HPV-positive cancer models lack one or more hallmarks of their human counterpart. This study presents the development of a new HPV16 oncoprotein-dependent tumor model in MHC-humanized mice, modeling the major biologic features of HPV-driven tumors and presenting HLA-A2-restricted HPV16 epitopes. Furthermore, this model was developed to be orthotopic (base of tongue). Thus, it also reflects the correct tumor microenvironment of HPV-driven HNSCC. The cancer cells are implanted in a manner that allows the exact control of the anatomical location of the developing tumor, thereby homogenizing tumor growth. In conclusion, the new model is suited to study HPV16-specific therapeutic vaccinations and other immunotherapies, as well as tumor-targeted interventions, such as surgery or radiotherapy, or a combination of all these modalities.

Tumor-targeted interleukin-12 synergizes with entinostat to overcome PD-1/PD-L1 blockade-resistant tumors harboring MHC-I and APM deficiencies

Background

Immune checkpoint blockade (ICB) has achieved unprecedented success in treating multiple cancer types. However, clinical benefit remains modest for most patients with solid malignancies due to primary or acquired resistance. Tumor-intrinsic loss of major histocompatibility complex class I (MHC-I) and aberrations in antigen processing machinery (APM) and interferon gamma (IFN-γ) pathways have been shown to play an important role in ICB resistance. While a plethora of combination treatments are being investigated to overcome ICB resistance, there are few identified preclinical models of solid tumors harboring these deficiencies to explore therapeutic interventions that can bypass ICB resistance. Here, we investigated the combination of the epigenetic modulator entinostat and the tumor-targeted immunocytokine NHS-IL12 in three different murine tumor models resistant to αPD-1/αPD-L1 (anti-programmed cell death protein 1/anti-programmed death ligand 1) and harboring MHC-I, APM, and IFN-γ response deficiencies and differing tumor mutational burden (TMB).

Methods

Entinostat and NHS-IL12 were administered to mice bearing TC-1/a9 (lung, HPV16 E6/E7⁺), CMT.64 lung, or RVP3 sarcoma tumors. Antitumor efficacy and survival were monitored. Comprehensive tumor microenvironment (TME) and spleen analysis of immune cells, cytokines, and chemokines was performed. Additionally, whole transcriptomic analysis was carried out on TC-1/a9 tumors. Cancer Genome Atlas (TCGA) datasets were analyzed for translational relevance.

Results

We demonstrate that the combination of entinostat and NHS-IL12 therapy elicits potent antitumor activity and survival benefit through prolonged activation and tumor infiltration of cytotoxic CD8⁺ T cells, across αPD-1/αPD-L1 refractory tumors irrespective of TMB, including in the IFN-γ signaling-impaired RVP3 tumor model. The combination therapy promoted M1-like macrophages and activated antigen-presenting cells while decreasing M2-like macrophages and regulatory T cells in a tumor-dependent manner. This was associated with increased levels of IFN-γ, IL-12, chemokine (C-X-C motif) ligand 9 (CXCL9), and CXCL13 in the TME. Further, the combination therapy synergized to promote MHC-I and APM upregulation, and enrichment of JAK/STAT (janus kinase/signal transducers and activators of transcription), IFN-γ-response and antigen processing-associated pathways. A biomarker signature of the mechanism involved in these studies is associated with patients’ overall survival across multiple tumor types.

Conclusions

Our findings provide a rationale for combining the tumor-targeting NHS-IL12 with the histone deacetylase inhibitor entinostat in the clinical setting for patients unresponsive to αPD-1/αPD-L1 and/or with innate deficiencies in tumor MHC-I, APM expression, and IFN-γ signaling.

Specific cannabinoids revive adaptive immunity by reversing immune evasion mechanisms in metastatic tumours

Emerging cancers are sculpted by neo-Darwinian selection for superior growth and survival but minimal immunogenicity; consequently, metastatic cancers often evolve common genetic and epigenetic signatures to elude immune surveillance. Immune subversion by metastatic tumours can be achieved through several mechanisms; one of the most frequently observed involves the loss of expression or mutation of genes composing the MHC-I antigen presentation machinery (APM) that yields tumours invisible to Cytotoxic T lymphocytes, the key component of the adaptive cellular immune response. Fascinating ethnographic and experimental findings indicate that cannabinoids inhibit the growth and progression of several categories of cancer; however, the mechanisms underlying these observations remain clouded in uncertainty. Here, we screened a library of cannabinoid compounds and found molecular selectivity amongst specific cannabinoids, where related molecules such as Δ9-tetrahydrocannabinol, cannabidiol, and cannabigerol can reverse the metastatic immune escape phenotype in vitro by inducing MHC-I cell surface expression in a wide variety of metastatic tumours that subsequently sensitizing tumours to T lymphocyte recognition. Remarkably, H3K27Ac ChIPseq analysis established that cannabigerol and gamma interferon induce overlapping epigenetic signatures and key gene pathways in metastatic tumours related to cellular senescence, as well as APM genes involved in revealing metastatic tumours to the adaptive immune response. Overall, the data suggest that specific cannabinoids may have utility in cancer immunotherapy regimens by overcoming immune escape and augmenting cancer immune surveillance in metastatic disease. Finally, the fundamental discovery of the ability of cannabinoids to alter epigenetic programs may help elucidate many of the pleiotropic medicinal effects of cannabinoids on human physiology.

Distinct Responsiveness of Tumor-Associated Macrophages to Immunotherapy of Tumors with Different Mechanisms of Major Histocompatibility Complex Class I Downregulation

Simple Summary

Tumor-associated macrophages (TAMs) are one of the major cell subpopulations in the tumor microenvironment (TME) where they can either be pro-tumorigenic or contribute to an anti-tumor immunity. The TME and TAM phenotype were analyzed after combined immuno-therapy (IT) in tumor models characterized by distinct expression of major histocompatibility class I complex (MHC-I) molecules, i.e., tumors induced with TC-1 (MHC-I-proficient), TC-1/A9 (reversibly downregulated), and TC-1/dB2m (irreversibly downregulated) cells. We found out that combined IT highly activated immune reactions in the TME of TC-1 and TC-1/A9 tumors, but the TME of TC-1/dB2m tumors remained almost unchanged. Correspondingly, TAMs from TC-1/A9 tumors were able to destroy tumor cells in vitro, while TAMs isolated from TC-1/dB2m tumors showed profoundly decreased cytotoxicity. Hence, various capabilities of TAMs in tumors with distinct expression of MHC-I molecules should be considered when applying IT, particularly IT focused on TAMs.

Abstract

Tumor-associated macrophages (TAMs) plentifully infiltrate the tumor microenvironment (TME), but their role in anti-tumor immunity is controversial. Depending on the acquired polarization, they can either support tumor growth or participate in the elimination of neoplastic cells. In this study, we analyzed the TME by RNA-seq and flow cytometry and examined TAMs after ex vivo activation. Tumors with normal and either reversibly or irreversibly decreased expression of major histocompatibility complex class I (MHC-I) molecules were induced with TC-1, TC-1/A9, and TC-1/dB2m cells, respectively. We found that combined immunotherapy (IT), composed of DNA immunization and the CpG oligodeoxynucleotide (ODN) ODN1826, evoked immune reactions in the TME of TC-1- and TC-1/A9-induced tumors, while the TME of TC-1/dB2m tumors was mostly immunologically unresponsive. TAMs infiltrated both tumor types with MHC-I downregulation, but only TAMs from TC-1/A9 tumors acquired the M1 phenotype upon IT and were cytotoxic in in vitro assay. The anti-tumor effect of combined IT was markedly enhanced by a blockade of the colony-stimulating factor-1 receptor (CSF-1R), but only against TC-1/A9 tumors. Overall, TAMs from tumors with irreversible MHC-I downregulation were resistant to the stimulation of cytotoxic activity. These data suggest the dissimilarity of TAMs from different tumor types, which should be considered when utilizing TAMs in cancer IT.

Abrogation of IFN-γ Signaling May not Worsen Sensitivity to PD-1/PD-L1 Blockade

Programmed cell death protein 1 (PD-1)/PD-1 ligand 1 (PD-L1) blockade is a promising therapy for various cancer types, but most patients are still resistant. Therefore, a larger number of predictive biomarkers is necessary. In this study, we assessed whether a loss-of-function mutation of the interferon (IFN)-γ receptor 1 (IFNGR1) in tumor cells can interfere with anti-PD-L1 therapy. For this purpose, we used the mouse oncogenic TC-1 cell line expressing PD-L1 and major histocompatibility complex class I (MHC-I) molecules and its TC-1/A9 clone with reversibly downregulated PD-L1 and MHC-I expression. Using the CRISPR/Cas9 system, we generated cells with deactivated IFNGR1 (TC-1/dIfngr1 and TC-1/A9/dIfngr1). In tumors, IFNGR1 deactivation did not lead to PD-L1 or MHC-I reduction on tumor cells. From potential inducers, mainly IFN-α and IFN-β enhanced PD-L1 and MHC-I expression on TC-1/dIfngr1 and TC-1/A9/dIfngr1 cells in vitro. Neutralization of the IFN-α/IFN-β receptor confirmed the effect of these cytokines in vivo. Combined immunotherapy with PD-L1 blockade and DNA vaccination showed that IFNGR1 deactivation did not reduce tumor sensitivity to anti-PD-L1. Thus, the impairment of IFN-γ signaling may not be sufficient for PD-L1 and MHC-I reduction on tumor cells and resistance to PD-L1 blockade, and thus should not be used as a single predictive marker for anti-PD-1/PD-L1 cancer therapy.

Experimental Combined Immunotherapy of Tumours with Major Histocompatibility Complex Class I Downregulation

Combined immunotherapy constitutes a novel, advanced strategy in cancer treatment. In this study, we investigated immunotherapy in the mouse TC-1/A9 model of human papillomavirus type 16 (HPV16)-associated tumors characterized by major histocompatibility complex class I (MHC-I) downregulation. We found that the induction of a significant anti-tumor response required a combination of DNA vaccination with the administration of an adjuvant, either the synthetic oligodeoxynucleotide ODN1826, carrying immunostimulatory CpG motifs, or α-galactosylceramide (α-GalCer). The most profound anti-tumor effect was achieved when these adjuvants were applied in a mix with a one-week delay relative to DNA immunization. Combined immunotherapy induced tumor infiltration with various subsets of immune cells contributing to tumor regression, of which cluster of differentiation (CD) 8⁺ T cells were the predominant subpopulation. In contrast, the numbers of tumor-associated macrophages (TAMs) were not markedly increased after immunotherapy but in vivo and in vitro results showed that they could be repolarized to an anti-tumor M1 phenotype. A blockade of T cell immunoglobulin and mucin-domain containing-3 (Tim-3) immune checkpoint had a negligible effect on anti-tumor immunity and TAMs repolarization. Our results demonstrate a benefit of combined immunotherapy comprising the activation of both adaptive and innate immunity in the treatment of tumors with reduced MHC-I expression.

The role of immune cell subpopulations in the growth and rejection of TC-1/A9 tumors in novel mouse strains differing in the H2-D haplotype and NKC domain

The present study aimed to elucidate the role of cluster of differentiation (CD)8+, CD4+, natural killer (NK), and myeloid (CD11b+) cells in the course of the growth and rejection of experimental major histocompatibility complex (MHC) class I-deficient, HPV16 E6/E7-associated TC-1/A9 tumors in mice. Stable mouse lines (F₃₀) generated by inbreeding of Balb/c and C57BL/6 strains, which were characterized by H-2Db+d-NK1.1neg (B6-neg) and H-2Db-d+NK1.1high (Balb-high) phenotypes, were used for the present study. The novel strains spontaneously regressed tumors in 70–90% of cases. Ex vivo histological analysis of the tumor microenvironment in cryosections showed an indirect correlation between the growth of the transplanted tumor (progressor vs. regressor mice) and the proportion of immunocompetent cell infiltration in the tumors. The regressor mice exhibited a higher infiltration of tumors with CD4+ and CD8+ cells, and in Balb-high with NK cells as well, compared with the progressors. All tumor transplants also indicated a huge infiltration of CD11b+ cells, but this infiltration was not dependent on the stage of the TC-1/A9 tumor development. Depletion of individual cell subpopulations in vivo exhibited different effects on the tumor development in the two strains. Elimination of CD8-positive cells enhanced growth of TC-1/A9 tumor transplants in both hybrid stains, whereas CD4+ cell depletion affected rejection of TC-1/A9 tumors in the B6-neg mice only. Depletion of NK cells with anti-asialo GM1 antibody in the Balb-high strain led to enhancement of tumor growth, which was more pronounced after depletion of the NK1.1+ subpopulation. On the other hand, depletion of NK cells with anti-asialo GM1 in B6-neg mice did not affect the regression of TC-1/A9 tumor transplants, but increased the CD11b+ cell infiltration. In summary, these results indicate that co-operation of particular subsets of immunocompetent cells is essential for the rejection of TC-1/A9 tumor transplants. In B6-neg mice, the co-operative action of CD8+ and CD4+ cells is required, whereas in Balb-high mice, the synergy of CD8+ and NK1.1+ cells is of major importance.

Type 2 Innate Lymphocytes Actuate Immunity Against Tumours and Limit Cancer Metastasis

Type 2 innate lymphoid cells (ILC2) potentiate immune responses, however, their role in mediating adaptive immunity in cancer has not been assessed. Here, we report that mice genetically lacking ILC2s have significantly increased tumour growth rates and conspicuously higher frequency of circulating tumour cells (CTCs) and resulting metastasis to distal organs. Our data support the model that IL-33 dependent tumour-infiltrating ILC2s are mobilized from the lungs and other tissues through chemoattraction to enter tumours, and subsequently mediate tumour immune-surveillance by cooperating with dendritic cells to promote adaptive cytolytic T cell responses. We conclude that ILC2s play a fundamental, yet hitherto undescribed role in enhancing anti-cancer immunity and controlling tumour metastasis.

Combined Cancer Immunotherapy Against Aurora Kinase A

Aurora kinase A (AURKA) is a centrosomal protein that is overexpressed in a number of human malignancies and can contribute to tumor progression. As we used this protein as a target of DNA immunization, we increased its immunogenicity by the addition of the PADRE helper epitope and decreased its potential oncogenicity by mutagenesis of the kinase domain. For in vitro analysis of induced immune responses in mice, we identified the Aurka(220-228) nonapeptide representing an H-2Kb epitope. As DNA vaccination against the Aurka self-antigen by a gene gun did not show any antitumor effect, we combined DNA immunization with anti-CD25 treatment that depletes mainly regulatory T cells. Whereas 1 anti-CD25 dose injected before DNA vaccination did not enhance the activation of Aurka-specific splenocytes, 3 doses administered on days of immunizations augmented about 10-fold immunity against Aurka. However, an opposite effect was found for antitumor immunity-only 1 anti-CD25 dose combined with DNA vaccination reduced tumor growth. Moreover, the administration of 3 doses of anti-CD25 antibody alone accelerated tumor growth. Analysis of tumor-infiltrating cells showed that 3 anti-CD25 doses not only efficiently depleted regulatory T cells but also activated helper T cells and CD3(-)CD25(+) cells. Next, we found that blockade of the PD-1 receptor initiated 1 week after the first immunization was necessary for significant inhibition of tumor growth with therapeutic DNA vaccination against Aurka combined with depletion of CD25 cells. Our results suggest that combined cancer immunotherapy should be carefully evaluated to achieve the optimal antitumor effect.

Discovery of a Metastatic Immune Escape Mechanism Initiated by the Loss of Expression of the Tumour Biomarker Interleukin-33

A new paradigm for understanding immune-surveillance and immune escape in cancer is described here. Metastatic carcinomas express reduced levels of IL-33 and diminished levels of antigen processing machinery (APM), compared to syngeneic primary tumours. Complementation of IL-33 expression in metastatic tumours upregulates APM expression and functionality of major histocompatibility complex (MHC)-molecules, resulting in reduced tumour growth rates and a lower frequency of circulating tumour cells. Parallel studies in humans demonstrate that low tumour expression of IL-33 is an immune biomarker associated with recurrent prostate and kidney renal clear cell carcinomas. Thus, IL-33 has a significant role in cancer immune-surveillance against primary tumours, which is lost during the metastatic transition that actuates immune escape in cancer.

Resistance of novel mouse strains different in MHC class I and the NKC domain to the development of experimental tumors

To elucidate the immunological mechanisms critical for tumor progression, we bred novel mouse strains, different in the NKC and H-2D domains. We used inbreeding to generate hybrids of Balb/c and C57BL/6 of stable H-2Db+d-NK1.1neg and H-2Db-d+NK1.1high phenotypes. We analyzed the growth of three established MHC class I-deficient tumor cell lines: TC-1/A9 tumor (HPV-associated) and B16F10 melanoma, both syngeneic to C57BL/6, and the MCB8 (3-methycholanthrene-induced tumor) syngeneic to Balb/c. Furthermore, we induced colorectal carcinoma by azoxymethane-DSS treatment to test the susceptibility to chemically-induced primary cancer. We found that the novel strains spontaneously regressed the tumor transplants syngeneic to both Balb/c (MCB8) and C57BL/6 (B16F10 and TC-1/A9) mice. The H2-Db+d-NK1.1neg, but not the H2-Db-d+NK1.1high strain was also highly resistant to chemically-induced colorectal cancer in comparison to the parental mice. The immune changes during TC-1/A9 cancer development involved an increase of the NK cell distribution in the peripheral blood and spleen along with higher expression of NKG2D activation antigen; this was in correlation with the time-dependent rise of cytotoxic activity in comparison to C57BL/6 mice. The TC-1/A9 cancer regression was accompanied by higher proportion of B cells in the spleen and B220+/CD86+ activated antigen-presenting B cells distributed in the lymphoid organs, as well as in the periphery. The changes in the T-cell population were represented mainly by the prevalence of T helper cells reflected by grown CD4/CD8 ratio, most prominent in the b+d-NK1.1neg strain. The results of the present study imply usefulness of the two novel mouse strains as an experimental model for further studies of tumor resistance mechanisms.

Epigenetic regulations in the IFNγ signalling pathway: IFNγ-mediated MHC class I upregulation on tumour cells is associated with DNA demethylation of antigen-presenting machinery genes

Downregulation of MHC class I expression on tumour cells, a common mechanism by which tumour cells can escape from specific immune responses, can be associated with coordinated silencing of antigen-presenting machinery genes. The expression of these genes can be restored by IFNγ. In this study we documented association of DNA demethylation of selected antigen-presenting machinery genes located in the MHC genomic locus (TAP-1, TAP-2, LMP-2, LMP-7) upon IFNγ treatment with MHC class I upregulation on tumour cells in several MHC class I-deficient murine tumour cell lines (TC-1/A9, TRAMP-C2, MK16 and MC15). Our data also documented higher methylation levels in these genes in TC-1/A9 cells, as compared to their parental MHC class I-positive TC-1 cells. IFNγ-mediated DNA demethylation was relatively fast in comparison with demethylation induced by DNA methyltransferase inhibitor 5-azacytidine, and associated with increased histone H3 acetylation in the promoter regions of APM genes. Comparative transcriptome analysis in distinct MHC class I-deficient cell lines upon their treatment with either IFNγ or epigenetic agents revealed that a set of genes, significantly enriched for the antigen presentation pathway, was regulated in the same manner. Our data demonstrate that IFNγ acts as an epigenetic modifier when upregulating the expression of antigen-presenting machinery genes.

Anti-tumor effects of genetic vaccines against HPV major oncogenes

Expression of HPV E5, E6 and E7 oncogenes are likely to overcome the regulation of cell proliferation and to escape immunological control, allowing uncontrolled growth and providing the potential for malignant transformation. Thus, their three oncogenic products may represent ideal target antigens for immunotherapeutic strategies. In previous attempts, we demonstrated that genetic vaccines against recombinant HPV16 E7 antigen were able to affect the tumor growth in a pre-clinical mouse model. To improve this anti-HPV strategy we developed a novel approach in which we explored the effects of E5-based genetic immunization. We designed novel HPV16 E5 genetic vaccines based on two different gene versions: whole E5 gene and E5Multi. The last one is a long multi epitope gene designed as a harmless E5 version. Both E5 genes were codon optimized for mammalian expression. In addition, we demonstrated that HPV 16 E5 oncogene is expressed in C3 mouse cell line making it an elective model for the study of E5 based vaccine. In this mouse model the immunological and biological activity of the E5 vaccines were assessed in parallel with the activity of anti-E7 and anti-E6 vaccines already reported to be effective in an immunotherapeutic setting. These E7 and E6 vaccines were made with mutated oncogenes, the E7GGG mutant that does not bind pRb and the E6F47R mutant that is less effective in inhibiting p53, respectively. Results confirmed the immunological activity of genetic formulations based on attenuated HPV16 oncogenes and showed that E5-based genetic immunization provided notable anti-tumor effects.

Antitumor DNA vaccination against the Sox2 transcription factor

As cancer stem cells (CSCs) are resistant to chemotherapy, radiotherapy and targeted molecular therapy, immunotherapy of tumors could be aimed at their elimination. Markers specific for CSCs have not been identified to date, but microarray analyses have shown that CSCs and embryonic stem cells use similar transcriptional programs, thus suggesting the production of shared transcription factors. In this study, we developed an experimental DNA vaccine against the transcription factor Sox2 that is important for self-renewal of stem cells and is overexpressed in numerous human cancers. The Sox2 gene was codon optimized for the expression in human cells, its sequences encoding two nuclear localization signals (NLSs) were mutagenized, and the sequence coding for the PADRE helper epitope was fused with its 5' terminus. While codon optimization did not increase Sox2 production and mutagenesis in NLSs only partially reduced nuclear localization of Sox2, the addition of the PADRE epitope was crucial for the enhancement of Sox2 immunogenicity. The antitumor effect was shown after immunization against mouse oncogenic TC-1/B7 cells derived from the lung cancer cell line TC-1 and characterized by high Sox2 production. Sox2-specific reactivity in an ELISPOT assay was further augmented by the depletion of regulatory T (Treg) cells, but this depletion did not enhance the antitumor effect. These data demonstrated the induction of immune responses against the Sox2 self-antigen, but did not confirm the usefulness of Treg depletion when combined with antitumor vaccination.

The effect of helper epitopes and cellular localization of an antigen on the outcome of gene gun DNA immunization

In DNA vaccination, CD4(+) T-cell help can be enhanced by fusion of a gene encoding an immunization protein with a foreign gene or its part providing T(h) epitopes. To study the effect of helper epitope localization in a protein molecule, the influence of the vicinity of the helper epitope, and the impact of chimeric protein cellular localization, we fused the helper epitope p30 from tetanus toxin (TT, aa 947-967) with the N- or C-terminus of the mutated E7 oncoprotein (E7GGG) of human papillomavirus type 16, enlarged the p30 epitope with the flanking residues containing potential protease-sensitive sites and altered the cellular localization of the fusion constructs by signal sequences. The p30 epitope enhanced the E7-specific response, but only in constructs without added signal sequences. After localization of the fusion proteins into the endoplasmic reticulum and endo/lysosomal compartment, the TT-specific T(h)2 response was increased. The synthetic Pan DR epitope (PADRE) induced a stronger E7-specific response than the p30 epitope and its stimulatory effect was not limited to nuclear/cytoplasmic localization of the E7 antigen. These results suggest that in the optimization of immune responses by adding helper epitopes to DNA vaccines delivered by the gene gun, the cellular localization of the antigen needs to be taken into account.

Biolistic DNA vaccination against cervical cancer

The development of cervical cancer is associated with infection by oncogenic human papillomaviruses (HPVs), of which type 16 (HPV16) is the most prevalent in HPV-induced malignant diseases. The viral oncoproteins E6 and E7 are convenient targets for anti-tumor immunization. To adapt the corresponding genes for DNA vaccination, their oncogenicity needs to be reduced and immunogenicity enhanced. The main modifications for achieving these aims include mutagenesis, rearrangement of gene parts, and fusion with supportive cellular or viral/bacterial genes or their functional parts. As HPVs are strictly human specific, an animal model of HPV infection does not exist. Therefore, immunization against HPV-induced tumors is most frequently tested in mouse models utilizing transplantable syngeneic tumor cells producing the HPV16 E6/E7 oncoproteins. In this chapter, one such cell line designated TC-1 is characterized and the effect of immunization with the modified E7 fusion gene against TC-1-induced subcutaneous tumors is described. As down-regulation of MHC class I molecules is one of the most important escape mechanisms of cervical carcinoma cells, the TC-1/A9 clone with reversibly reduced MHC class I expression has been developed and, herein, its response to DNA vaccination is also shown and compared with that of the TC-1 cells.

Immunotherapy augments the effect of 5-azacytidine on HPV16-associated tumours with different MHC class I-expression status

BACKGROUND

Epigenetic mechanisms have important roles in the tumour escape from immune responses, such as in MHC class I downregulation or altered expression of other components involved in antigen presentation. Chemotherapy with DNA methyltransferase inhibitors (DNMTi) can thus influence the tumour cell interactions with the immune system and their sensitivity to immunotherapy.

METHODS

We evaluated the therapeutic effects of the DNMTi 5-azacytidine (5AC) against experimental MHC class I-deficient and -positive tumours. The 5AC therapy was combined with immunotherapy, using a murine model for HPV16-associated tumours.

RESULTS

We have demonstrated 5AC additive effects against MHC class I-positive and -deficient tumours when combined with unmethylated CpG oligodeoxynucleotides or with IL-12-producing cellular vaccine. The efficacy of the combined chemoimmunotherapy against originally MHC class I-deficient tumours was partially dependent on the CD8(+)-mediated immune responses. Increased cell surface expression of MHC class I cell molecules, associated with upregulation of the antigen-presenting machinery-related genes, as well as of genes encoding selected components of the IFNγ-signalling pathway in tumours explanted from 5AC-treated animals, were observed.

CONCLUSION

Our data suggest that chemotherapy of MHC class I-deficient tumours with 5AC combined with immunotherapy is an attractive setting in the treatment of MHC class I-deficient tumours.

Systemic administration of CpG oligodeoxynucleotide and levamisole as adjuvants for gene-gun-delivered antitumor DNA vaccines

DNA vaccines showed great promise in preclinical models of infectious and malignant diseases, but their potency was insufficient in clinical trials and is needed to be improved. In this study, we tested systemic administration of two conventional adjuvants, synthetic oligodeoxynucleotide carrying immunostimulatory CpG motifs (CpG-ODN) and levamisole (LMS), and evaluated their effect on immune reactions induced by DNA vaccines delivered by a gene gun. DNA vaccination was directed either against the E7 oncoprotein of human papillomavirus type 16 or against the BCR-ABL1 oncoprotein characteristic for chronic myeloid leukemia. High doses of both adjuvants reduced activation of mouse splenic CD8(+) T lymphocytes, but the overall antitumor effect was enhanced in both tumor models. High-dose CpG-ODN exhibited a superior adjuvant effect in comparison with any combination of CpG-ODN with LMS. In summary, our results demonstrate the benefit of combined therapy with gene-gun-delivered antitumor DNA vaccines and systemic administration of CpG-ODN or LMS.

Regulation of immune responses to HPV infection and during HPV-directed immunotherapy

The recent development of vaccines prophylactic against human papillomavirus (HPV) infection has the potential to reduce the incidence of cervical cancer globally by up to 70% over the next 40 years, if universal immunization is adopted. As these prophylactic vaccines do not alter the natural history of established HPV infection, immunotherapies to treat persistent HPV infection and associated precancers would be of benefit to assist with cervical cancer control. Efforts to develop immuno-therapeutic vaccines have been hampered by the relative non-immunogenicity of HPV infection, by immunoregulatory processes in skin, and by subversion of immune response induction and immune effector functions by papillomavirus proteins. This review describes HPV-specific immune responses induced by viral proteins, their regulation by host and viral factors, and highlights some conclusions from our own recent research.

Therapy for minimal residual tumor disease: beta-galactosylceramide inhibits the growth of recurrent HPV16-associated neoplasms after surgery and chemotherapy

Natural killer T (NKT) cells are potent modulators of antitumor immunity. Their protective effects can be achieved upon their activation by glycolipid ligands presented in the context of the CD1d molecule. These CD1d-binding glycolipid antigens have been described as potent therapeutic agents against tumors, infections, as well as autoimmune diseases. Immunoregulatory and therapeutic effects of glycolipid ligands depend on their structure and modes of administration. Therefore, more studies are needed for optimization of the particular therapeutic settings. This study was focused on the tumor-inhibitory effects of 12 carbon acyl chain beta-galactosyl ceramide (C12 beta-D-Galactosyl Ceramide; beta-GalCer(C12)) on the growth of human papillomavirus type 16 (HPV16)-associated neoplasms transplanted in syngeneic mice. Treatment of tumor-bearing mice with beta-GalCer(C12) 3-14 days after tumor cell transplantation significantly inhibited the growth of the major histocompatibility complex (MHC) Class I-positive (TC-1), as well as MHC Class I-deficient (TC-1/A9) HPV16-associated tumors. Moreover, administration of beta-GalCer(C12) after surgical removal of TC-1 tumors inhibited the growth of tumor recurrences. Similar results were obtained in the treatment of tumors after chemotherapy. beta-GalCer(C12) treatment turned out to be also synergistic with immunotherapy based on administration of IL-12-producing cellular vaccines. These results suggest that beta-GalCer(C12), whose antitumor effects have so far not been studied in detail, can be effective for the treatment of minimal residual tumor disease as well as an adjuvant for cancer immunotherapy.

Molecular mechanisms of IFN-gamma to up-regulate MHC class I antigen processing and presentation

IFN-gamma up-regulates MHC class I expression and antigen processing and presentation on cells, since IFN-gamma can induce multiple gene expressions that are related to MHC class I antigen processing and presentation. MHC class I antigen presentation-associated gene expression is initiated by IRF-1. IRF-1 expression is initiated by phosphorylated STAT1. IFN-gamma binds to IFN receptors, and then activates JAK1/JAK2/STAT1 signal transduction via phosphorylation of JAK and STAT1 in cells. IFN-gamma up-regulates MHC class I antigen presentation via activation of JAK/STAT1 signal transduction pathway. Mechanisms of IFN-gamma to enhance MHC class I antigen processing and presentation were summarized in this literature review.

Epigenetic enhancement of antigen processing and presentation promotes immune recognition of tumors

Histone deacetylase inhibitors (HDACi) have been hailed as a powerful new class of anticancer drugs. The HDACi, trichostatin A (TSA), is thought to interfere with epigenetic control of cell cycle progression in G1 and G2-M phase, resulting in growth arrest, differentiation, or apoptosis. Here, we describe a novel mechanism of action of HDACis in promoting immune responses against tumors. We report that treatment of carcinoma cells with TSA increases the expression of many components of the antigen processing machinery, including TAP-1, TAP-2, LMP-2, and Tapasin. Consistent with this result, we found that treatment of metastatic carcinoma cells with TSA also results in an increase in MHC class I expression on the cell surface that functionally translates into an enhanced susceptibility to killing by antigen-specific CTLs. Finally, we observed that TSA treatment suppresses tumor growth and increases tap-1 promoter activity in TAP-deficient tumor cells in vivo. Intriguingly, this in vivo anti-tumoral effect of TSA is entirely mediated by an increase in immunogenicity of the tumor cells, as it does not occur in immunodeficient mice. These novel insights into the molecular mechanisms controlling tumor immune escape may help revise immunotherapeutic modalities for eradicating cancers.

Mutation in the immunodominant epitope of the HPV16 E7 oncoprotein as a mechanism of tumor escape

Infection with high-risk types of human papillomavirus (HPV) can cause the development of malignant tumors. To study mechanisms responsible for immune escape of tumor cells infected with HPV16, we previously used mouse oncogenic TC-1 cells producing HPV16 E6 and E7 oncoproteins to derive TC-1 clones resistant to immunization against E7. We have found immunoresistance of the clones to correlate with the point mutation in the E7 oncogene, which resulted in the N53S substitution in the immunodominant epitope RAHYNIVTF (aa 49-57). Here, we have shown that this mutation reduced stabilization of H-2D(b) molecules on RMA-S cells and eliminated immunogenicity of E7. The resistance of TC-1 clones was E7-specific as immunization against E6 inhibited tumor growth. Transduction of the TC-1/F9 clone carrying the mutated epitope with the wild-type E7 gene restored susceptibility to immunization against E7. Our results suggest that mutagenesis of tumor antigens can lead to the escape of malignant cells and should be considered in the development and evaluation of cancer immunotherapy.

Gene expression profiling for the prediction of lymph node metastasis in patients with cervical cancer

We investigated whether gene expression profiling of primary cervical tumor tissue could be used to predict lymph node (LN) metastasis and compared this with conventional magnetic resonance imaging. We obtained 43 primary cervical cancer samples (16 with LN metastasis and 27 without LN metastasis) for microarray analysis. A prediction model for LN metastasis from the training set was developed by support vector machine methods using a 10-fold cross-validation. The 'LN prediction model' derived from the signature of 156 distinctive genes (P < 0.01) had a prediction accuracy of 77%. Correlation between mRNA expressions measured by microarray and semiquantitative reverse transcription-polymerase chain reaction was ascertained in four (RBM8A, SDHB, SERPINB13, and gamma-interferon) out of 10 genes. Magnetic resonance imaging showed accuracy (69%) for the prediction of LN metastasis. These results suggest that gene expression profiling allows reliable prediction of LN metastasis in cervical cancer.

Epigenetic control of the immune escape mechanisms in malignant carcinomas

Downregulation of the transporter associated with antigen processing 1 (TAP-1) has been observed in many tumors and is closely associated with tumor immunoevasion mechanisms, growth, and metastatic ability. The molecular mechanisms underlying the relatively low level of transcription of the tap-1 gene in cancer cells are largely unexplained. In this study, we tested the hypothesis that epigenetic regulation plays a fundamental role in controlling tumor antigen processing and immune escape mechanisms. We found that the lack of TAP-1 transcription in TAP-deficient cells correlated with low levels of recruitment of the histone acetyltransferase, CBP, to the TAP-1 promoter. This results in lower levels of histone H3 acetylation at the TAP-1 promoter, leading to a decrease in accessibility of the RNA polymerase II complex to the TAP-1 promoter. These observations suggest that CBP-mediated histone H3 acetylation normally relaxes the chromatin structure around the TAP-1 promoter region, allowing transcription. In addition, we found a hitherto-unknown mechanism wherein interferon gamma up-regulates TAP-1 expression by increasing histone H3 acetylation at the TAP-1 promoter locus. These findings lie at the heart of understanding immune escape mechanisms in tumors and suggest that the reversal of epigenetic codes may provide novel immunotherapeutic paradigms for intervention in cancer.

Induction of MHC class I molecule cell surface expression and epigenetic activation of antigen-processing machinery components in a murine model for human papilloma virus 16-associated tumours

Epigenetic events play an important role in tumour progression and also contribute to escape of the tumour from immune surveillance. In this study, we investigated the up-regulation of major histocompatibility complex (MHC) class I surface expression on tumour cells by epigenetic mechanisms using a murine tumour cell line expressing human E6 and E7 human papilloma virus 16 (HPV16) oncogenes and deficient in MHC class I expression, as a result of impaired antigen-presenting machinery (APM). Treatment of the cells with the histone deacetylase inhibitor Trichostatin A, either alone or in combination with the DNA demethylating agent 5-azacytidine, induced surface re-expression of MHC class I molecules. Consequently, the treated cells became susceptible to lysis by specific cytotoxic T lymphocytes. Further analysis revealed that epigenetic induction of MHC class I surface expression was associated with the up-regulation of APM genes [transporter associated with antigen processing 1 (TAP-1), TAP-2, low-molecular-mass protein 2 (LMP-2) and LMP-7]. The results demonstrate that expression of the genes involved in APM are modulated by epigenetic mechanisms and suggest that agents modifying DNA methylation and/or histone acetylation have the potential to change the effectiveness of antitumour immune responses and therapeutically may have an impact on immunological output.

Modified HPV16 E7/HSP70 DNA vaccine with high safety and enhanced cellular immunity represses murine lung metastatic tumors with downregulated expression of MHC class I molecules

OBJECTIVE

To explore whether the modified E7-HSP70, which has been introduced mutations in two zinc-binding motifs of E7, will eliminate its transformation potential and enhance the immunogenicity of fusion protein and repress E7 containing tumors with a low level of MHC-I molecules to lung metastatic in murine model.

METHODS

In this study, we examined the transforming properties of mutant E7 oncoprotein by the soft agar colony-formation assays, explored the immunogenicity of modified E7-HSP70 gene by various cellular and humor immune responses and evaluated the effect of treating lung metastatic tumor with a low expressing MHC-I molecules by tumor challenge assay and therapeutic experiment.

RESULTS

The mutant E7 oncoprotein has completely lost its transforming properties as measured in the soft agar colony-formation assays. Modified E7-HSP70 gene inducted stronger E7-specific cellular immune response than that induced by unmodified E7-HSP70. More importantly, the new construct significantly reduced the number of B16-HPV16E7 lung metastases.

CONCLUSION

The modified E7-HSP70 gene may be as a powerful and safe DNA vaccine in controlling the hematogenous spread of HPV16E7-associated tumors with low expression of MHC-I molecules. In addition, the B16-HPV16E7 lung metastasis model can be used to test the efficacy of various E7-specific vaccines and immunotherapeutic strategies in settings more relevant to clinical requirements.

Inhibitory effects of unmethylated CpG oligodeoxynucleotides on MHC class I-deficient and -proficient HPV16-associated tumours

Unmethylated oligodeoxynucleotides containing guanine-cytidine dimers (CpG ODN) have been described as potent inducers of selected antitumour immune responses and the immunotherapeutic efficacy of CpG ODN has been examined either alone or as a vaccine adjuvant. We hypothesized that CpG ODN therapy could be an effective tool for immunotherapy of not only conventional MHC class I(+) tumours but also of those tumours that have lost MHC class I expression during their progression. To address this hypothesis, we employed the animal model resembling MHC class I-proficient and -deficient human papilloma virus (HPV) 16-associated tumours. A cell line transformed with HPV16 E6 and E7 oncogenes, TC-1, as a prototype of MHC class I-positive line, and its MHC class I-deficient sublines TC-1/A9 and TC-1/P3C10 were injected into syngeneic C57BL/6 mice and the growing tumours were subjected to immunotherapy with CpG ODN 1826. The therapy started either 1 day after the challenge with the tumour cells or later, when the tumours had reached a palpable size. In both settings, CpG ODN 1826 significantly reduced the growth of MHC class I-proficient and -deficient tumours. Furthermore, we demonstrated that CpG ODN 1585, whose mechanism of action preferably involves indirect activation of the natural killer cells, induced regression of the MHC class I-deficient tumours TC1/A9 but not of the MHC class I-proficient tumours TC-1. This study infers that synthetic CpG ODN have a potential for the therapy of both MHC class I-proficient and -deficient tumours and thus could be also used against tumours that tend to down-regulate their MHC class I expression.

Plasmid encoding papillomavirus Type 16 (HPV16) DNA constructed with codon optimization improved the immunogenicity against HPV infection

Human papillomavirus Type 16 (HPV16) infections can cause neoplasia, which is thought to be closely associated with the development of cervical cancers. In the study, we attempted to construct a DNA plasmid encoding a HPV16 capsid protein (L1) and a HPV16 oncoprotein (E7), which was capable of preventing HPV16 infection and eliminating HPV16-infected cells. A plasmid, L1E7hpSCA1, encoding the L1 and E7 genes with the codon usage optimized for mammalian cell expression, was constructed. Mutations were introduced into the E7 gene sequence for reducing its oncogenicity. C57BL/6 mice were intramuscularly immunized at tibialis anterior (TA) muscles with the newly constructed L1E7hpSCA1 plasmid. The immune responses induced by the L1E7hpSCA1 plasmid (with codon optimization) and a control L1E7pSCA1 plasmid (without codon optimization) were compared. It is shown that the L1E7hpSCA1 was able to induce much stronger immune responses than the L1E7pSCA1. Sera obtained from immunized animals were found to contain anti-HPV16 antibodies as detected by ELISA and hemagglutination inhibition (HAI) assays. Cytotoxicity and interferon-gamma assays showed that spleenocytes from immunized animals were able to recognize and lyze E7 expressing tumor TC-1 cells. Moreover, the growth of E7 expressing tumor mass was inhibited in vaccinated mice. In vivo tumor protection test indicated that tumor formation was prevented in the experimental animals (67%) after vaccination with L1E7hpSCA1, while for the control group injected with L1E7pSCA1 only and the animal group injected with pSCA1 only, tumor formation was observed in all experimental animals. Our results suggest that the L1E7h gene (with codon optimization) is more effective against HPV16 than the L1E7 gene (without codon optimization). The L1E7hpSCA1 plasmid was able to provide protection against E7 expressing tumor, and it might have the potential to be a vaccine candidate for HPV prevention.

Tumor sensitivity to IFN-gamma is required for successful antigen-specific immunotherapy of a transplantable mouse tumor model for HPV-transformed tumors

PURPOSE

Many human tumors lose responsiveness to IFN-gamma, providing a possible mechanism for the tumor to avoid immune recognition and destruction. Here we investigate the importance of tumor responsiveness to IFN-gamma in the successful immunotherapy of TC1 tumors that were immortalized with human papillomavirus proteins E6 and E7.

METHODS

To investigate the role of IFN-gamma in vivo, we constructed a variant of TC1, TC1.mugR, that is unresponsive to IFN-gamma due to overexpression of a dominant negative IFN-gamma receptor.

RESULTS

Using recombinant Listeria monocytogenes that express HPV-16 E7 (Lm-LLO-E7) to stimulate an antitumor response, we demonstrate that sensitivity to IFN-gamma is required for therapeutic efficacy in that Lm-LLO-E7 induces regression of TC1 tumors but not TC1.mugR. In addition, we show that tumor sensitivity to IFN-gamma is not required for inhibition of tumor angiogenesis by Lm-LLO-E7 or for trafficking of CD4+ and CD8+ T cells to the tumor. However, it is required for penetration of lymphocytes into the tumor mass in vivo.

CONCLUSIONS

Our findings identify a role for IFN-gamma in immunity to TC1 tumors and show that loss of tumor responsiveness to IFN-gamma poses a challenge to antigen-based immunotherapy.

Enhancement of immunogenicity of HPV16 E7 oncogene by fusion with E. coli beta-glucuronidase

BACKGROUND

Human papillomavirus type 16 (HPV16) E7 is an unstable oncoprotein with low immunogenicity. In previous work, we prepared the E7GGG gene containing point mutations resulting in substitution of three amino acids in the pRb-binding site of the HPV16 E7 protein.

METHODS AND RESULTS

To increase E7GGG immunogenicity we constructed fusion genes of E. coli beta-glucuronidase (GUS) with one or three copies of E7GGG. Furthermore, a similar construct was prepared with partial E7GGG (E7GGGp, 41 amino acids from the N-terminus). The expression of the fusion genes was examined in human 293T cells. Quantification of GUS activity and the amount of E7 antigen showed substantially reduced GUS activity of fusion proteins with complete E7GGG that was mainly caused by decrease of their steady-state level in comparison with GUS or E7GGGpGUS. Still, the steady-state level of E7GGG.GUS was about 20-fold higher than that of the E7GGG protein. The immunogenicity of the fusion genes with complete E7GGG was tested by DNA immunisation of C57BL/6 mice with a gene gun. TC-1 cells and their clone TC-1/A9 with down-regulated MHC class I expression were subcutaneously (s.c.) inoculated to induce tumour formation. All mice were protected against challenge with TC-1 cells and most animals remained tumour-free in therapeutic-immunisation experiments with these cells, in contrast to immunisation with unfused E7GGG and the fusion with the lysosome-associated membrane protein 1 (Sig/E7GGG/LAMP-1). Significant protection was also recorded against TC-1/A9 cells. Both tetramer staining and ELISPOT assay showed substantially higher activation of E7-specific CD8+ lymphocytes in comparison with E7GGG and Sig/E7GGG/LAMP-1. Deletion of 231 bp in the GUS gene eliminated enzymatic activity, but did not influence the immunogenicity of the E7GGG.GUS gene.

CONCLUSIONS

The findings demonstrate the superior immunisation efficacy of the fusion genes of E7GGG with GUS when compared with E7GGG and Sig/E7GGG/LAMP-1. The E7GGG.GUS-based DNA vaccine might also be efficient against human tumour cells with reduced MHC class I expression.

Combined immunization with fusion genes of mutated E7 gene of human papillomavirus type 16 did not enhance antitumor effect

BACKGROUND

The E7 oncoprotein of human papillomavirus type 16 (HPV16) is frequently used as a model tumor-associated antigen. Its immunogenicity has been substantially enhanced by fusion with several proteins of various origins and functions. Different mechanisms have been responsible for increased vaccination efficacy of fusion proteins.

METHODS AND RESULTS

We linked E7 and its mutated form (E7GGG) with the mouse heat-shock protein 70.1 (HSP70.1). Enhanced immunogenicity of both fusion genes administered via a gene gun was demonstrated by protection of C57BL/6 mice against oncogenic MHC class I positive TC-1 cells producing the HPV16 E7 oncoprotein but not against the MHC class I negative TC-1/A9 subline. To assess if the efficacy of E7-based DNA vaccines could be increased by combination of various fusion genes, we combined the HSP70.1 fusion genes (i.e. E7HSP or E7GGGHSP) with the fusion construct linking E7GGG with targeting signals of lysosome-associated membrane protein 1 (Sig/E7GGG/LAMP-1). Treatment of mice 4 days after TC-1 cell inoculation showed moderately higher immunization potency of HSP70.1 fusion genes in comparison with the Sig/E7GGG/LAMP-1 gene. Any combination of two fusion genes given in the same gene gun shot neither was more effective compared with single genes nor protected mice against TC-1/A9 cells. As fusion of E7GGG with E. coli glucuronidase (E7GGG.GUS) had been previously proven to provide partial protection from TC-1/A9-induced tumors, we also combined E7GGGHSP with E7GGG.GUS. The genes were inoculated either in mix in two gene gun shots or separately each gene in one shot into opposite sides of the abdomen. Neither mode of combined immunization induced higher protection than E7GGG.GUS alone. However, doubling the DNA dose considerably enhanced the antitumor efficacy of E7GGG.GUS.

CONCLUSIONS

We constructed highly immunogenic fusions of HPV16 E7 and E7GGG with mouse HSP70.1. Furthermore, we substantially enhanced protection against TC-1/A9 cells with downregulated MHC class I expression by doubling the pBSC/E7GGG.GUS dose, but we failed to demonstrate a beneficial effect of any combination of two fusion genes with different mechanisms causing enhancement of HPV16 E7 immunogenicity.

Expression library immunization to discover and improve vaccine antigens

Genetic immunization is a novel method for vaccination in which DNA is delivered into the host to drive both cellular and humoral immune responses against its protein product. While genetic immunization can be potent, it requires that one have, in hand, a gene that encodes a protective protein antigen. Therefore, for many diseases, one cannot make a genetic vaccine because no protective antigen is known or no gene for this antigen is available. This lack of candidate antigens and their genes is a considerable bottleneck in developing new vaccines against old infectious agents, new emerging pathogens, and bioweapons. To address this limitation, we developed expression library immunization (ELI) as a high-throughput technology to discover vaccine candidate genes at will, by using the immune system to screen the entire genome of a pathogen for vaccine candidate. To date, ELI has discovered new vaccine candidates from a diverse set of bacterial, fungal, and parasitic pathogens. In addition, the process of applying ELI to the genome of pathogens allows one to genetically re-engineer these antigens to convert immunoevasive pathogen proteins into immunostimulatory vaccine antigens. Therefore, ELI is a potent technology to discover new vaccines and also generate genomic vaccines with amplified, multivalent immunostimulatory capacities.

Vaccination strategies for the treatment and prevention of cervical cancer

PURPOSE OF REVIEW

Immunotherapy of HPV-induced premalignant anogenital lesions and cervical cancer has made impressive progress. HPV as causative agent is targeted by prophylactic and therapeutic vaccination strategies. Preclinical and clinical studies have shown induction of natural and/or vaccine-induced immune responses. This review will summarize the status of vaccine development and clinical testing published since March 2003.

RECENT FINDINGS

For prophylactic vaccines there is first clinical evidence of effectivity (ie, 100% protection from HPV infection and dysplasia by virus-like particle (VLP) vaccine-induced neutralizing antibodies). Also, therapeutic vaccines have entered clinical evaluation. While prophylactic VLP vaccines are immunogenic per se, therapeutic vaccines will need further adjuvants to guide T cell differentiation, expansion, survival, and homing to tumor sites. To enhance clinical outcome of successful T cell induction in patients, the susceptibility of the tumor cells for lysis must be addressed in the future, since tumor immune evasion is a severe problem in cervical cancer.

SUMMARY

While successful prophylactic HPV vaccines have entered large clinical trials, therapeutic HPV vaccines, in spite of T cell induction, lack clinical responses due to the problem of tumor immune evasion. Adjuvants for systemic and local immune modulation will be mandatory for effective therapy.

Anogenital neoplasia in AIDS

PURPOSE OF REVIEW

We review the recent literature on anogenital neoplasms in AIDS, with emphasis on cancers associated with HPV infection. Immune reactivity to HPV as well as novel immunotherapeutic and preventative strategies are discussed.

RECENT FINDINGS

Many AIDS-associated neoplasms are associated with HPV infection. Whether cervical cancer is truly an AIDS-associated neoplasm has recently been questioned, while the association of anal cancer with AIDS in both males and females is more convincing. Recent reports cast doubt on the efficacy of HAART therapy for HPV-induced anogenital neoplasms, despite efficacy in improving disease caused by other infectious agents. We include here new data on humoral and cellular immune responses to HPV. VLP serology has been reported to be associated with outcome of cervical cancer. VLP seropositivity has been reported to be a favorable prognostic sign in women with HPV 16 positive cervical carcinoma. Several investigators have questioned the immunogenicity of the oncogenic HPV type 16 compared with other HPV types. It has recently been found that in HIV-infected patients, lymphoproliferative cellular immune responses (CMI) to HPV 16 peptides are not associated with CD4 counts, whereas responses to recall antigens and mitogens are associated with CD4 counts. CD4 + T cells may not be responsible for protective cellular immune responses to HPV. VLP serology and CMI responses may be the future intermediate surrogate biomarkers for HPV-associated anogenital neoplasia trials. Several new therapeutic vaccine strategies for management of HPV-induced neoplasia are reviewed.

SUMMARY

Most anogenital neoplasms occurring with increased frequency in patients with HIV/AIDS are associated with HPV infections. Current treatment strategies are not effective in clearing anogenital HPV infection and need improvement. Immunotherapy with novel vaccines will provide both prevention and therapy for these common malignancies.