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.

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.

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.

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.

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.

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.

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.

Chemotherapy, IL-12 gene therapy and combined adjuvant therapy of HPV 16-associated MHC class I-proficient and -deficient tumours.

Moderately immunogenic HPV 16-associated murine tumour cell line mimicking human HPV 16-associated neoplasms TC-1 (MHC class I(+)) and its variants, TC-1/P3C10 and TC-1/A9, with a marked down-regulation of MHC I molecules, were used to examine the effect of local interleukin 12 (IL-12) gene therapy for the treatment of early tumour transplants and minimal residual tumour disease obtained after cytoreductive chemotherapy (CMRTD). Experiments were designed to examine whether down-regulation of MHC class I molecules plays a role during chemotherapy and gene therapy of early tumour transplants. It was found that peritumoral administration of IL-12-producing tumour cell vaccines (single dose, day 8 after tumour cell administration) inhibited the growth of both TC-1 (MHC class I positive) tumours and their MHC class I-deficient variants. To investigate the antitumour effects in a clinically relevant setting, IL-12 gene therapy was utilised for the treatment of minimal residual tumour disease after cytoreductive chemotherapy. Intra-peritoneal treatment of tumour-bearing mice with ifosfamide derivative, CBM-4A, produced a significant tumour-inhibitory effect. This treatment was followed by peritumoral s.c. administration of genetically modified TC-1 (MHC class I positive) or MK16/I/IIIABC (MHC class I negative) vaccines producing IL-12 (single dose, day 7 after chemotherapy) or with recombinant interleukin 12 (rIL-12) in two cycles of 5 daily doses (days 8-19) after chemotherapy. This combined therapy significantly inhibited the growth of TC-1 and TC-1/A9 (MHC class I-) tumours. When the combined therapy of TC-1 (MHC class I positive) tumours was followed by peritumoral administration of bone marrow dendritic cell (BMDC) vaccines, the IL-12-mediated inhibitory effect was significantly boosted. In the next set of experiments, the impacts of chemotherapy and IL-12 adjuvant therapy on MHC class I surface expression were assessed. Chemotherapy and gene therapy of tumours led to the up-regulation of MHC I expression on MHC class I-deficient tumours (TC-1/A9 and TC-1/P3C10) and to down-regulation on MHC I-proficient tumours (TC-1). These findings indicate that the MHC I phenotype is not stable during tumour progression and treatment. Collectively, these results illustrate the efficacy of IL-12 gene therapy in combination with chemotherapy on HPV-associated tumours regardless of the level of MHC class I expression on the tumour cells.

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.

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.

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.

Immune escape phenotype of HPV16-associated tumours: MHC class I expression changes during progression and therapy.

Malignant transformation of somatic cells followed by selection of the transformed cell populations can give rise to tumours that display an immune escape phenotype, MHC class I deficient neoplasms. Experiments were designed to examine whether the immune escape phenotype of HPV16-associated tumours is stable or whether the MHC class I expression can change during tumour progression and therapy. It has been found that temporary growth of MHC class I- tumour MK16/1/IIIABC in syngeneic mice can lead to up-regulation of the low MHC class I expression, both in the subcutaneous tumour inocula and in their lung metastases. Mimicking this process in vitro by co-cultivation of tumour and spleen cell populations revealed that the spleen cells produce IFNgamma, which upregulates MHC class I expression on the MK16/1/IIIABC cells as well as their sensitivity to T cell-mediated cytolysis (CTLs). The up-regulation could be prevented by admixture of anti-IFNgamma antibody to the tumour/spleen cell mixtures. Similar up-regulation of the MHC class I expression was observed in HPV16-associated tumour cell lines, MK16/1/IIIABC, MK16/MET/M1, TC-1, TC-1/A9 and TC-1/P3C10 grown in vitro in the presence of IFNgamma. The up-regulation was found to be IFNgamma dose-dependent and the level of the MHC class I expression required for in vitro cytolysis of the tumour cells by CTLs could be characterized in cytofluorometry with anti-H-2 antibody. After removal of the IFNgamma from the cultivation medium or after injection of the IFNgamma-treated cells into syngeneic mice the MHC class I expression gradually dropped back to the original level or to the level observed on the tumours growing in vivo. These findings indicate that the immune escape phenotype of at least some HPV16-associated tumours is not stable and that up-regulation of the MHC class I expression can occur in vivo during progression of the MHC I- tumours, apparently due to production of IFNgamma by the immune cells in the tumour microenviroment and its vicinity. In vitro irradiation of HPV16-associated MHC class I-deficient tumour cell lines MK16/MET/M1 and TC-1/P3C10 with a dose of 150 Gy up-regulated their MHC class I expression. Similarly, substantial up-regulation of the MHC class I expression was observed in TC-1/A9 tumour recurrences after surgery. The up-regulation observed in the recurrences after surgery or after irradiation has reached the level required for in vitro cytolysis of the tumour cells by CTLs. If confirmed also with other tumour types and in human tumour systems, the up-regulation of MHC class I molecule expression during radiotherapy and in tumour recurrences after surgery may have important implications in the development of immunotherapeutic strategies.

HPV16-associated tumours: therapy of surgical minimal residual disease with dendritic cell-based vaccines.

Dendritic cell (DC)-based vaccines are being intensively investigated for the treatment of a variety of human neoplasms. However, little attention has until now been paid to the use of DC-based vaccines for immunotherapy of tumour residua after surgery. In this communication, an animal model mimicking human HPV16-associated neoplasms was employed to examine the effect of DC-based vaccines for the treatment of surgical minimal residual tumour disease. Mice were subcutaneously inoculated with syngeneic TC-1 tumour cells of HPV16 origin. When the tumours reached approximately 1 cm in diameter, they were surgically removed and the operated mice were injected into the site of the operation with bone marrow-derived DC, which were either pulsed with TC-1 cell lysates or co-cultured with irradiated TC-1 cells. It has been found that the growth of TC-1 tumour recurrences in the mice treated with these vaccines was substantially suppressed, as compared to the operated-only controls. The phenotypic analysis of the spleen cells has shown that the percentage of CD3+ cells was diminished in the operated-only and vaccinated mice carrying recurrent tumours, in comparison with healthy control mice and with operated tumour-free mice. Moreover, accumulation of immature myeloid cells (CD11b+/Gr-1+) was observed in spleens of the tumour-bearing mice. These findings indicate that the immune system of the tumour-bearing individuals was compromised, as compared to that of normal individuals or tumour regressors. To our knowledge, this is the first report that has demonstrated the positive effect of local administration of the DC-based, HPV16 E6/E7 oncoprotein-containing, tumour lysate-loaded vaccines in the treatment of surgical minimal residual tumour disease.

Treatment of minimal residual disease after surgery or chemotherapy in mice carrying HPV16-associated tumours: Cytokine and gene therapy with IL-2 and GM-CSF.

Moderately immunogenic HPV16-associated tumours TC-1 (MHC class I+, HPV16 E6/E7+, G12V Ha-ras+) and MK16/1/IIIABC (MK16, MHC class I-, HPV16 E6/E7+, G12V Ha-ras+), both of the H-2b haplotype and transplanted in syngeneic mice, were used to examine the effects of local IL-2 and GM-CSF cytokine or gene therapy in the treatment of minimal residual tumour disease. The mice carrying MHC class I+ TC-1 tumour residua after surgery were injected into the site of the surgery either with irradiated, IL-2 gene-modified MK16 tumour cells, or with recombinant IL-2. It has been found that both, the recombinant IL-2 and the IL-2 gene-modified tumour vaccine substantially reduced the percentage of tumour recurrences in the operated mice. Similarly, when the mice carrying TC-1 tumour residua after surgery were injected with recombinant GM-CSF, the recombinant GM-CSF inhibited growth of the tumour residua in the operated mice. Gene therapy with irradiated, GM-CSF secreting MK16 cells did not produce any tumour-inhibitory effect. In further experiments, mice bearing s.c. TC-1 tumours were injected i.p. with ifosfamide derivative CBM-4A and 8 days later, peritumourally, either with IL-2 gene-modified and IL-2-producing MK16 cells, or with recombinant IL-2. It has been found that both, the recombinant IL-2 and the IL-2 gene therapy substantially reduced the percentage of tumour-bearing mice. When the mice bearing s.c. TC-1 tumours were injected i.p. with ifosfamide derivative CBM-4A and then, peritumourally, either with irradiated, GM-CSF gene-modified and GM-CSF-producing MK16 cells, or with recombinant GM-CSF, it was found that both, the recombinant GM-CSF and GM-CSF gene therapy inhibited growth of tumour residua. Comparative experiments were performed with the MHC class I-, metastasizing tumour MK16. It has been found that both, recombinant IL-2 and GM-CSF, can inhibit growth of the tumour residua after surgery or chemotherapy. The lung metastases in mice with surgical minimal residual tumour disease or in mice with tumour residua after chemotherapy were inhibited by IL-2 but not by GM-CSF. The MK16 tumour vaccine producing IL-2 inhibited growth of tumour residua after chemotherapy, but not the tumour residua after surgery. The GM-CSF-producing vaccine was without significant effect in both, surgically- and chemotherapeutically-induced minimal residual MK16 tumour disease. In conclusion, the MHC class I+ and MHC class I-, HPV16-associated tumours were found to be sensitive to IL-2 and GM-CSF therapy after surgery or after cytoreductive chemotherapy. It is yet to be addressed if this is more general case with HPV16-associated experimental tumours. If so, it would be of interest to further investigate whether such adjuvant therapy can also help to eradicate the residua after surgery and chemotherapy in patients carrying HPV16-associated neoplasms.

Chemoimmunotherapy in mice carrying HPV16-associated, MHC class I+ and class I- tumours: Effects of CBM-4A potentiated with IL-2, IL-12, GM-CSF and genetically modified tumour vaccines.

The effectiveness of chemoimmunotherapy with ifosfamide derivative CBM-4A and recombinant IL-2, IL-12, GM-CSF, or genetically modified, cytokine-producing tumour vaccines was examined in mice carrying HPV16-associated, MHC class I+ (TC-1), and MHC class I- (MK16) tumours. Intraperitoneal treatment of TC-1 or MK16 tumour-bearing mice with CBM-4A produced a significant tumour-inhibitory effect. When the i.p. treatment of the MHC class I+ TC-1 tumour-bearing mice with CBM-4A was followed by peritumoral s.c. administration of IL-2, IL-12, or both cytokines, the growth of TC1 tumours was inhibited more vigorously than after the chemotherapy alone. In contrast, when the i.p. treatment ofEthe MHC class I- MK16 tumour-bearing mice with CBM-4A was followed by peritumoral s.c. administration of IL-2 or IL-12, the cytokine therapy had no potentiating effect. The only potentiating effect of the MK16 tumour immunotherapy was obtained when the i.p. CBM-4A pretreatment was followed by peritumoral s.c. administration of IL-2 plus IL-12. InEfurther experiments, the TC-1 and MK16 tumour-bearing mice were i.p. pretreated with CBM-4A and then injected s.c., peritumorally, with genetically modified, IL-2 or GM-CSF-producing MK16 tumour vaccines. Whereas both genetically modified tumour vaccines produced a substantial tumour-inhibitory effect in mice carrying TC-1 tumours, no effect of the vaccines was observed in mice carrying MK16 tumour inocula. The systemic effects of local cytokine treatment were examined in mice carrying s.c. MK16 neoplasms, which were pretreated i.p. with CBM-4A, and then injected peritumorally with IL-2 or GM-CSF. Peritumoral administration of GM-CSF had no antimetastatic effect, whereas peritumoral IL-2 administration produced substantial reduction of lung metastases. The systemic antimetastatic effect of IL-2 contrasted with the negligible effect of IL-2 on the s.c. MK16 tumour inoculum. Taken collectively, the results indicate that in mice carrying the MK16 (MHC class I-) tumour, the effects of the adjuvant cytokine therapy were substantially weaker than in mice carrying the TC-1 (MHC class I+) tumour inoculum.

Tumour-inhibitory and antimetastatic effects of IL-2 in mice carrying MHC class I- tumours of HPV16 origin.

Oncogenic, moderately immunogenic, MHC class I- and class II-, B7-, MK16/1/III ABC (MK16) cells were previously established by co-transfection of HPV16 E6/E7 and activated H-ras oncogene DNA into C57BL/6 kidney cells. Subcutaneous transplantation of these cells produced progressively growing local neoplasms which metastasized spontaneously to lungs and lymph nodes. The MK16 cells were implanted into syngeneic mice and used to examine whether the tumour lacking the signal molecules required for the induction of and sensitivity to T cell immunity is susceptible to local IL-2 treatment and IL-2 gene therapy. Peritumoural administration of human rIL-2 or murine IL-2 gene-modified MK16 tumour vaccine inhibited growth of subcutaneous MK16 tumour transplants and reduced the number of their lung metastases. Spleen cells from MK16 tumour-immunized mice were not cytolytic when allowed to react with the MK16 target cells, although they efficiently lysed the MHC class I+ malignant TC1 cells, obtained from C57BL/6 lung cell cultures after transfection with the same plasmids as those used for the derivation of the MK16 cells. However, when the MK16 cells were cultivated in vitro in the presence of IFNgamma, they acquired, together with the expression of MHC class I molecules, the sensitivity to the cytolytic effect of spleen cells from the MK16 tumour-immunized mice. These results indicate that experimental tumours which are MHC class I- and mimick in this respect a high proportion of human HPV16-associated carcinomas are suitable for IL-2 treatment.

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.

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.

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.