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.

Dendritic cells pulsed with tumor cells killed by high hydrostatic pressure inhibit prostate tumor growth in TRAMP mice.

Dendritic cell (DC)-based vaccines pulsed with high hydrostatic pressure (HHP)-inactivated tumor cells have recently been shown to be a promising tool for prostate cancer chemoimmunotherapy. In this study, DC-based vaccines, both pulsed and unpulsed, were as effective as docetaxel (DTX) in reducing prostate tumors in the orthotopic transgenic adenocarcinoma of the mouse prostate (TRAMP) model. However, we did not observe any additive or synergic effects of chemoimmunotherapy on the tumor growth, while only the combination of DTX and pulsed dendritic cells resulted in significantly lower proliferation detected by Ki67 staining in histological samples. The DC-based vaccine pulsed with HHP-treated tumor cells was also combined with another type of cytostatic, cyclophosphamide, with similar results. In another clinically relevant setting, minimal residual tumor disease after surgery, administration of DC-based vaccines after the surgery of poorly immunogenic transplanted TRAMP-C2, as well as in immunogenic TC-1 tumors, reduced the growth of tumor recurrences. To identify the effector cell populations after DC vaccine application, mice were twice immunized with both pulsed and unpulsed DC vaccine, and the cytotoxicity of the spleen cells populations was tested. The effector cell subpopulations were defined as CD4+ and NK1.1+, which suggests rather unspecific therapeutic effects of the DC-based vaccines in our settings. Taken together, our data demonstrate that DC-based vaccines represent a rational tool for the treatment of human prostate cancer.

Tumor growth accelerated by chemotherapy-induced senescent cells is suppressed by treatment with IL-12 producing cellular vaccines.

Standard-of-care chemo- or radio-therapy can induce, besides tumor cell death, also tumor cell senescence. While senescence is considered to be a principal barrier against tumorigenesis, senescent cells can survive in the organism for protracted periods of time and they can promote tumor development. Based on this emerging concept, we hypothesized that elimination of such potentially cancer-promoting senescent cells could offer a therapeutic benefit. To assess this possibility, here we first show that tumor growth of proliferating mouse TC-1 HPV-16-associated cancer cells in syngeneic mice becomes accelerated by co-administration of TC-1 or TRAMP-C2 prostate cancer cells made senescent by pre-treatment with the anti-cancer drug docetaxel, or lethally irradiated. Phenotypic analyses of tumor-explanted cells indicated that the observed acceleration of tumor growth was attributable to a protumorigenic environment created by the co-injected senescent and proliferating cancer cells rather than to escape of the docetaxel-treated cells from senescence. Notably, accelerated tumor growth was effectively inhibited by cell immunotherapy using irradiated TC-1 cells engineered to produce interleukin IL-12. Collectively, our data document that immunotherapy, such as the IL-12 treatment, can provide an effective strategy for elimination of the detrimental effects caused by bystander senescent tumor cells in vivo.

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.

Dendritic cells pulsed with tumor cells killed by high hydrostatic pressure induce strong immune responses and display therapeutic effects both in murine TC-1 and TRAMP-C2 tumors when combined with docetaxel chemotherapy.

High hydrostatic pressure (HHP) has been shown to induce immunogenic cell death of cancer cells, facilitating their uptake by dendritic cells (DC) and subsequent presentation of tumor antigens. In the present study, we demonstrated immunogenicity of the HHP-treated tumor cells in mice. HHP was able to induce immunogenic cell death of both TC-1 and TRAMP-C2 tumor cells, representing murine models for human papilloma virus-associated tumors and prostate cancer, respectively. HHP-treated cells induced stronger immune responses in mice immunized with these tumor cells, documented by higher spleen cell cytotoxicity and increased IFNγ production as compared to irradiated tumor cells, accompanied by suppression of tumor growth in vivo in the case of TC-1 tumors, but not TRAMP-C2 tumors. Furthermore, HHP-treated cells were used for DC-based vaccine antigen pulsing. DC co-cultured with HHP-treated tumor cells and matured by a TLR 9 agonist exhibited higher cell surface expression of maturation markers and production of IL-12 and other cytokines, as compared to the DC pulsed with irradiated tumor cells. Immunization with DC cell-based vaccines pulsed with HHP-treated tumor cells induced high immune responses, detected by increased spleen cell cytotoxicity and elevated IFNγ production. The DC-based vaccine pulsed with HHP-treated tumor cells combined with docetaxel chemotherapy significantly inhibited growth of both TC-1 and TRAMP-C2 tumors. Our results indicate that DC-based vaccines pulsed with HHP-inactivated tumor cells can be a suitable tool for chemoimmunotherapy, particularly with regard to the findings that poorly immunogenic TRAMP-C2 tumors were susceptible to this treatment modality.

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.

DNA demethylating agent 5-azacytidine inhibits myeloid-derived suppressor cells induced by tumor growth and cyclophosphamide treatment.

MDSCs represent one of the key players mediating immunosuppression. These cells accumulate in the TME, lymphoid organs, and blood during tumor growth. Their mobilization was also reported after CY therapy. DNMTi 5AC has been intensively studied as an antitumor agent. In this study, we examined, using two different murine tumor models, the modulatory effects of 5AC on TU-MDSCs and CY-MDSCs tumor growth and CY therapy. Indeed, the percentage of MDSCs in the TME and spleens of 5AC-treated mice bearing TRAMP-C2 or TC-1/A9 tumors was found decreased. The changes in the MDSC percentage were accompanied by a decrease in the Arg-1 gene expression, both in the TME and spleens. CY treatment of the tumors resulted in additional MDSC accumulation in the TME and spleens. This accumulation was subsequently inhibited by 5AC treatment. A combination of CY with 5AC led to the highest tumor growth inhibition. Furthermore, in vitro cultivation of spleen MDSCs in the presence of 5AC reduced the percentage of MDSCs. This reduction was associated with an increased percentage of CD11c+ and CD86+/MHCII+ cells. The observed modulatory effect on MDSCs correlated with a reduction of the Arg-1 gene expression, VEGF production, and loss of suppressive capacity. Similar, albeit weaker effects were observed when MDSCs from the spleens of tumor-bearing animals were cultivated with 5AC. Our findings indicate that beside the direct antitumor effect, 5AC can reduce the percentage of MDSCs accumulating in the TME and spleens during tumor growth and CY chemotherapy, which can be beneficial for the outcome of cancer therapy.

Administration of anti-CD25 mAb leads to impaired α-galactosylceramide-mediated induction of IFN-γ production in a murine model.

CD4(+)CD25(+)Foxp3(+) T regulatory cells (Tregs) and CD1d-restricted invariant natural killer T (iNKT) cells are two cell types that are known to regulate immune reactions. Depletion or inactivation of Tregs using specific anti-CD25 antibodies in combination with immunostimulation is an attractive modality especially in anti-tumour immunotherapy. However, CD25 is not expressed exclusively on Tregs but also on subpopulations of activated lymphocytes. Therefore, the modulatory effects of the specific anti-CD25 antibodies can also be partially attributed to their interactions with the effector cells. Here, the effector functions of iNKT cells were analysed in combination with anti-CD25 mAb PC61. Upon PC61 administration, α-galactosylceramide (α-GalCer)-mediated activation of iNKT cells resulted in decreased IFN-γ but not IL-4 production. In order to determine whether mutual interactions between Tregs and iNKT cells take place, we compared IFNγ production after α-GalCer administration in anti-CD25-treated and "depletion of regulatory T cell" (DEREG) mice. Since no profound effects on IFNγ induction were observed in DEREG mice, deficient in FoxP3(+) Tregs, our results indicate that the anti-CD25 antibody acts directly on CD25(+) effector cells. In vivo experiments demonstrated that although both α-GalCer and PC61 administration inhibited TC-1 tumour growth in mice, no additive/synergic effects were observed when these substances were used in combination therapy.

Cyclophosphamide-induced myeloid-derived suppressor cell population is immunosuppressive but not identical to myeloid-derived suppressor cells induced by growing TC-1 tumors.

Myeloid-derived suppressor cells (MDSC) play an important role in tumor escape from antitumor immunity. MDSC accumulate in the lymphoid organs and blood during tumor growth and their mobilization was also reported after cyclophosphamide (CY) administration. In this communication, spleen MDSC accumulating after CY therapy (CY-MDSC) were compared with those expanded in mice bearing human papilloma viruses 16-associated TC-1 carcinoma (TU-MDSC). Although both CY-MDSC and TU-MDSC accelerated growth of TC-1 tumors in vivo, their phenotype and immunosuppressive function differed. CY-MDSC consisted of higher percentage of monocyte-like subpopulation and this was accompanied by lower relative expression of immunosuppressive genes and lower suppression of T-cell proliferation. After interferon-γ stimulation, the expression of immunosuppressive genes increased, but the suppressive ability of CY-MDSC did not reach that of TU-MDSC. The phenotype and function of MDSC obtained from mice bearing TC-1 tumors treated with CY was, in general, found to lie between CY-MDSC and TU-MDSC. After in vitro cultivation of MDSC in the presence of interleukin 12 (IL-12), the percentage of CD11b+/Gr-1+ cells decreased and was accompanied by an increase in the percentage of CD86+/MHCII+ cells. The strongest modulatory effect was noticed in the group of CY-MDSC. The susceptibility of CY-MDSC to all-trans-retinoic acid (ATRA) was also evaluated. In vitro cultivation with ATRA resulted in MDSC differentiation, and ATRA inhibited MDSC accumulation induced by CY administration. Our findings identified differences between CY-MDSC and TU-MDSC and supported the rationale for utilization of ATRA or IL-12 to alter MDSC accumulation after CY chemotherapy with the aim to improve its antitumor effect.

Genetically modified tumour vaccines producing IL-12 augment chemotherapy of HPV16-associated tumours with gemcitabine.

Genetically modified tumour cells producing cytokines such as interleukin 12 (IL-12) are potent activators of the antitumour immune responses and represent a promising therapeutic modality when combined with chemotherapy. The objective of this study was to examine whether IL-12-producing cellular vaccines can augment chemotherapy of human papilloma virus (HPV) 16-associated murine tumours with the cytostatic agent gemcitabine (GEM). We found that peritumoral administration of IL-12-producing tumour vaccines enhanced the effect of cytoreductive therapy with GEM both in non-metastasizing murine carcinoma TC-1 and in metastasizing murine carcinoma MK16. The percentage of mice with MK16 metastases and the number of lung metastatic nodules was substantially decreased. In another clinically relevant setting, surgical minimal residual tumour disease, the administration of IL-12-producing tumour vaccine and GEM after the MK16 tumour surgery reduced the percentage of mice with tumour recurrences; similarly, the percentage of metastasis-bearing mice and the number of metastatic nodules was decreased. Tumour inhibitory effects exerted by GEM plus IL-12 were associated with high production of interferon-γ (IFNγ) by splenocytes. Our results suggest that the IL-12-producing vaccine can enhance the effect of GEM chemotherapy in some HPV16-associated murine tumour models.

NK1.1+ cells are important for the development of protective immunity against MHC I-deficient, HPV16-associated tumours.

Loss or downregulation of MHC class I molecules on tumour cells is a common mechanism by which tumours can escape T-cell mediated immune responses. In this study, we examined the role of different immune cell lineages in the development of immunity against tumours of the same aetiology but with different MHC class I expression. In vivo depletion of CD8+ cells, but not of CD4+ or NK1.1+ cells in the immunization period resulted in complete elimination of the protective effects of immunization with irradiated TC-1 cells (MHC class I-positive cell line) against the TC-1 tumour challenge. After immunization with irradiated TC-1/A9 or with MK16 tumour cells (MHC class I-deficient sublines) a remarkable dependence on the presence of NK1.1+ cells was observed, while the tumour growth inhibition after CD4+ or CD8+ depletion was not efficient. Cytotoxic activity induced by TC-1 cell immunization was significantly abrogated in the CD8+ and CD4+ but not NK1.1+ cell-depleted mice, as compared to the immunized only controls. After MK16 or TC-1/A9 cell immunization, NK1.1+ but not CD8+ and CD4+ cell-depleted mice displayed significant reduction of specific cytotoxicity. Mice immunized with TC-1 cells showed similar percentage of IFNγ producing cells in CD8+, CD4+ and NK1.1+ cell populations. On the other hand, the highest proportion of IFNγ producing cells after immunization with TC-1/A9 or MK16 cells was concentrated into the NK1.1-positive spleen cell population. Our data demonstrate that the development of immunity against MHC class I-deficient tumours is highly dependent on the activity NK1.1+ cell population.

Dendritic cell-based vaccines for the therapy of experimental tumors.

Dendritic cells (DCs) are believed to be the most potent antigen-presenting cells able to link the innate and adaptive immune systems. Many studies have focused on different immunotherapeutic approaches to applying DCs as tools to improve anticancer therapy. Although a number of investigations suggesting the benefit of DC-based vaccination during anticancer therapy have been reported, the general knowledge regarding the ultimate methods of DC-vaccine preparation is still unsatisfactory. In this article, the perspectives of DC-based anti-tumor immunotherapy and optimizing strategies of DC vaccination in humans in light of results obtained in mouse models are discussed.

Induction of protective immunity against MHC class I-deficient, HPV16-associated tumours with peptide and dendritic cell-based vaccines.

Downregulation of MHC class I expression on the cell surface is a common mechanism by which tumour cells, including cervical carcinoma, can escape the T cell-mediated anti-tumour immunity. This downregulation represents an obstacle for the efficacy of anti-tumour vaccines. In this study, we investigated the efficacy of prophylactic peptide and peptide-pulsed dendritic cell-based vaccines in a murine model of experimental MHC class I-deficient tumours (TC-1/A9), expressing E6/E7 oncogenes derived from HPV16, and compared the efficacy of particular vaccination settings to anti-tumour protection against parental MHC class I-positive TC-1 tumours. Peptide vaccine based on the 'short' peptide E749-57 harbouring solely the CTL epitope and co-administered to the C57BL/6 mice with CpG oligodeoxynucleotide (CpG ODN) 1826 was effective against MHC class I-positive but not -deficient tumours, while the 'longer' peptide E744-62 (peptide 8Q, harbouring CTL and Th epitopes)-based vaccines were also effective against MHC class I-deficient tumours. We have compared the adjuvant efficacies of two CpG ODN, CpG ODN 1826 and CpG ODN 1585. The 8Q peptide immunisation combined with CpG ODN 1585 inhibited growth of the TC-1/A9 tumours more effectively as compared to CpG ODN 1826. Further, we investigated the efficacy of cellular vaccines based on ex vivo cultured dendritic cells pulsed with either E749-57 or E744-62 peptides and matured with CpG ODN 1826. Unlike in the peptide immunisation setting, treatment with dendritic cells pulsed with a 'short' peptide resulted in the tumour growth inhibition, albeit weaker as compared to the immunisation with the longer peptide. Our data demonstrate that peptide and dendritic cell-based vaccines can be designed to elicit protective immunity against MHC class I-deficient tumours.

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.

HPV 16-associated tumours: IL-12 can repair the absence of cytotoxic and proliferative responses of tumour infiltrating cells after chemotherapy.

We have examined the effect of IL-12-producing cellular vaccines on the cytotoxicity and proliferative potential of CD45+ tumour-infiltrating cells (TIL) in mice carrying syngeneic TC-1 and TC-1/A9 HPV 16-associated tumours after chemotherapy with CBM-4A ifosfamide derivative. The chemotherapy resulted in the decrease of the CD4+ and CD8+ TIL, increase of the Gr-1+/CD11b+ TIL, no changes in the infiltration with CD4+/CD25+ Treg TIL, and decrease of the cytolytic and proliferative potential of the CD45+ TIL. Subsequent immunotherapy with the IL-12-producing, genetically modified TC-1 (TC-1-IL-12) cells increased tumour infiltration with CD8+ and CD4+ cells, decreased the Gr-1+/CD11b+ cells, and increased the cytolytic and proliferative potential of the CD45+ TIL. Taken together, these findings suggest that peritumoral administration of the IL-12-producing cellular vaccine can restore the cytolytic potential and inhibit immunosuppressive TIL-dependent mechanisms in the individuals bearing HPV 16-associated tumours, and explain our previously described tumour-inhibitory effects of the vaccine in mice with minimal residual disease after the tumour chemotherapy.

IL-12 immunotherapy of minimal residual disease in murine models of HPV16-associated tumours: induction of immune responses, cytokine production and kinetics of immune cell subsets.

We have established animal models of HPV16-associated tumours with distinct levels of MHC class I expression. This model was used for examination of immune responses, production of cytokines and kinetics of immune cell subsets after IL-12 therapy of minimal residual tumour disease induced by CBA-4A (cyclophosphamide derivative) treatment. Upregulation of cytokine production was detected, compared to control animals without tumours. No differences in Th1/Th2 polarization of the immune responses after immunotherapy in animals bearing tumours with different surface expression of MHC class I molecules were observed. In the spleens of TC-1 (MHC class I+) but not of TC-1/A9 (MHC class I-) treated tumour-bearing animals, the cytotoxic CD8+ cells detectable in 51Cr microcytotoxicity assay, were found. In the spleens of TC-1/A9 but not of TC-1 tumour-treated animals, the NK activity measured as the lysis of NK-sensitive YAC-1 targets was detected. Down-regulation of the CD4+ and CD8+ subpopulations in spleens of tumour-bearing animals were not restored after therapy. The percentage of CD25+/CD4+ T regulatory (Treg) cells in lymph nodes remained unchanged. The cytoreductive chemotherapy led to strong upregulation and accumulation of immunosuppressive immature myeloid Gr-1+/CD11b+ cells (IMC) in the spleens of treated animals. The accumulation of Gr-1+/CD11b+ cells was significantly decreased after subsequent IL-12 immunotherapy. These data suggest that elimination of IMC after IL-12 immunotherapy may be responsible for the improvement of antitumour responses after adjuvant IL-12 vaccination for the treatment of CMRTD.

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.

Immunization with MHC class I-negative but not -positive HPV16-associated tumour cells inhibits growth of MHC class I-negative tumours.

Loss or downregulation of MHC class I molecules on tumour cells is a common mechanism by which tumours can escape from T-cell mediated immune responses. In this study we have investigated the immunologic crossreactivity between murine tumour cell lines expressing human papilloma virus (HPV) 16-derived E6/E7 oncoproteins with distinct surface expression of MHC class I molecules. The aims of this study were to demonstrate whether immune responses capable of coping with MHC class I-positive tumours can also be effective against their MHC class I-deficient derivatives and whether it is possible to induce immunity against MHC class I-deficient tumours by cellular vaccines based on MHC class I-deficient tumour cell lines. Our data showed that immunization with MHC class I-deficient but not with MHC class I positive tumour cells inhibited the growth of MHC class I-deficient tumours. In vivo depletion studies revealed that the mechanisms underlying effective immune responses against MHC class I-negative tumours in animals immunized with MHC class I-deficient tumour cells involved natural killer cells. The presented findings are of particular clinical relevance in the sense of construction of vaccines directed against a broad spectrum of HPV-associated tumours.

CpG oligodeoxynucleotides are effective in therapy of minimal residual tumour disease after chemotherapy or surgery in a murine model of MHC class I-deficient, HPV16-associated tumours.

Oligodeoxynucleotides containing guanine-cytidine dimers (CpG ODN) are potent inducers of anti-tumour immune responses. In this study, we analyzed the capacity of CpG ODN to inhibit the growth of both MHC class I-positive and -deficient tumours after debulking the tumour mass by chemotherapy or surgery. We employed an animal model resembling human papillomavirus (HPV) 16-associated tumours. Tumour cell lines with distinct cell surface expression of the MHC class I molecules were injected into syngeneic C57BL/6 mice, and the growing tumours were either subjected to cytoreductive chemotherapy with ifosfamide derivative, CBM-4A, or surgically removed. Subsequent treatment with synthetic CpG ODN significantly blocked the growth of the recurrent tumours. Our results indicate that the therapy with CpG ODN can be effective for the treatment of minimal residual tumour disease of the tumours that have escaped from the immune surveillance by downmodulating the MHC class I expression.

Differences in pathogenicity among strains of the same or different avian leukosis virus subgroups.

An efficient induction of wasting disease in chickens by avian leukosis virus (ALV), particularly ALV subgroup C, requires >102 infectious units virus inoculated in mid embryogenesis. The most conspicuous symptoms of the disease were induced by ALV subgroup C; however, significant differences in the occurrence of wasting disease were found among individual members of this subgroup. Almost comparable pathogenicity was exhibited by ALV subgroup D, whereas viruses of subgroups B and A proved to be moderately and almost non-pathogenic, respectively. Using antibodies to cellular antigens, tissue alterations were shown clearly in ALV-C-infected chickens. An essential feature was depletion of lymphocytes in the thymus, bursa and spleen. While the number of dendritic cells in the bursa was increased, their representation in the thymus and spleen was reduced. In the spleen, however, the reduction of dendritic cells concerned only an ellipsoid compartment, which in itself was also markedly reduced. An increased number of macrophages in the thymus and spleen corresponded with the observed general activation of the monocyte-macrophage system. In the spleen, CD4+ T cells were reduced while CD8+ T cells were increased. In agreement with this finding was a failure of chickens to respond to Brucella antigen and an inability of their splenocytes to respond to Concanavalin A, both of which pointed to the damage of immune reactivity. Variation in the pathogenicity among individual ALV strains provides ground for depicting gene sequences playing an important role in ALV acute pathogenicity.