Major histocompatibility complex class II-transfected tumor cells present endogenous antigen and are potent inducers of tumor-specific immunity

Rescue of major histocompatibility-DR surface expression in retinoblastoma-defective, non-small cell lung carcinoma cells by the MS-275 histone deacetylase inhibitor

Major histocompatibility (MHC) class II expression is ordinarily inducible by interferon-gamma (IFN-gamma), but the induction is repressed in retinoblastoma protein (Rb)-defective cells. The repression can be rescued by histone deacetylase (HDAC) inhibitor treatment, but this has never been shown for an HDAC inhibitor that is suitable for clinical trials and eventual patient therapy. Here we demonstrate that the HDAC inhibitor, MS-275, can rescue the IFN-gamma inducibility of human leukocyte antigen (HLA)-DR in non-small cell lung cancer cells. This HDAC inhibitor is currently being tested in phase I/II clinical trials for non-small cell lung cancer. We further verified that the MS-275 effect is related to an HDAC tethered to the HLA-DRA promoter by the transcription factor, YY1. HDAC inhibitors that can be used to treat patients may augment the expression of tumor cell MHC class II, and the results suggest an opportunity to determine the immunological consequences of HDAC inhibitor treatment in tumor therapy.

ER stress affects processing of MHC class I-associated peptides

Background

Viral infection and neoplastic transformation trigger endoplasmic reticulum (ER) stress. Thus, a large proportion of the cells that must be recognized by the immune system are stressed cells. Cells respond to ER stress by launching the unfolded protein response (UPR). The UPR regulates the two key processes that control major histocompatibility complex class I (MHC I)-peptide presentation: protein synthesis and degradation. We therefore asked whether and how the UPR impinges on MHC I-peptide presentation.

Results

We evaluated the impact of the UPR on global MHC I expression and on presentation of the H2K^b-associated SIINFEKL peptide. EL4 cells stably transfected with vectors coding hen egg lysozyme (HEL)-SIINFEKL protein variants were stressed with palmitate or exposed to glucose deprivation. UPR decreased surface expression of MHC I but did not affect MHC I mRNA level nor the total amount of intracellular MHC I proteins. Impaired MHC I-peptide presentation was due mainly to reduced supply of peptides owing to an inhibition of overall protein synthesis. Consequently, generation of H2K^b-SIINFEKL complexes was curtailed during ER stress, illustrating how generation of MHC I peptide ligands is tightly coupled to ongoing protein synthesis. Notably, the UPR-induced decline of MHC I-peptide presentation was more severe when the protein source of peptides was localized in the cytosol than in the ER. This difference was not due to changes in the translation rates of the precursor proteins but to increased stability of the cytosolic protein during ER stress.

Conclusion

Our results demonstrate that ER stress impairs MHC I-peptide presentation, and that it differentially regulates expression of ER- vs. cytosol-derived peptides. Furthermore, this work illustrates how ER stress, a typical feature of infected and malignant cells, can impinge on cues for adaptive immune recognition.

The immunogenicity of L1210 lymphoma clones correlates with their ability to function as antigen-presenting cells

Major histocompatibility complex class II (MHCII) antigen expression is directly correlated with immunogenicity, and inversely correlated with tumorigenicity, in clones of the L1210 murine B lymphoma. Moreover, loss of MHCII expression on human diffuse large B-cell lymphoma is associated with dramatic decreases in patient survival. Thus, the role that MHCII antigens play in the progression of B-cell lymphomas is clinically important. In this study, we investigated the basis for the immunogenicity of MHCII(+) L1210 clones. Immunogenic, but not tumorigenic L1210 clones stimulated the proliferation of naïve T cells and their interleukin (IL)-2 production, which indicates that the immunogenic clones can function as antigen-presenting cells (APCs). However, subclonal variants of the immunogenic L1210 clones, which form tumours slowly in mice, could not activate T cells. The costimulatory molecules B7-1, B7-2 and CD40 were expressed on the immunogenic L1210 clones, but not the tumorigenic clones. Importantly, the tumour-forming subclonal variants expressed MHCII and B7-1, but lacked B7-2 and CD40. These results suggest that MHCII and B7-1 expression on L1210 cells is insufficient to activate naïve T cells, and, furthermore, loss of B7-2 and/or CD40 expression contributes to the decreased immunogenicity of L1210 subclones. Blocking B7-1 or B7-2 function on immunogenic L1210 cells reduced their capacity to activate naïve T cells. Furthermore, incubation of immunogenic L1210 cells with CD40 antibodies significantly enhanced APC function. Therefore, the immunogenicity of L1210 cells directly correlates (i) with their ability to stimulate naïve T cells, and (ii) with the concomitant expression of MHCII, B7-1, B7-2, and CD40.

Dendritic cell-based immunotherapy in myeloid leukaemia: translating fundamental mechanisms into clinical applications

Immunotherapy for leukaemia patients, aiming at the generation of anti-leukaemic T cell responses, could provide a new therapeutic approach to eliminate minimal residual disease (MRD) cells in acute myeloid leukaemia (AML). Leukaemic blasts harbour several ways to escape the immune system including deficient MHC class II expression, low levels of co-stimulatory molecules and suppressive cytokines. Therapeutic vaccination with dendritic cells (DC) is now recognized as an important investigational therapy. Due to their unique antigen presenting capacity, immunosuppressive features of the leukaemic blasts can be circumvented. DC can be successfully cultured from leukaemic blasts in 60-70% of patients and show functional potential in vivo. Alternatively, monocyte derived DC obtained at time of complete remission loaded with leukaemia-specific antigens can be used as vaccine. Several sources of leukaemia-associated antigen and different methods of loading antigen onto DC have been used in an attempt to optimize antitumour responses including apoptotic cells, necrotic cell lysates and tumour-associated pep-tides. Currently, the AML-derived cell line MUTZ-3, an immortalized equivalent of CD34(+) DC precursor cells, is under investigation for vaccination purposes. For effective DC vaccination the intrinsic tolerant state of the patient must be overcome. Therefore, the development of efficient and safe adjuvants in antigen specific immunotherapeutic programs should be encouraged.

Linkage of a tumor immune function and cell cycle de-regulation via a gene regulatory network subcircuit

Gene regulatory network (GRN) subcircuits have been described for cell fate progressions in animal development. The hallmark of these subcircuits is the integration of promoters, and positive- and negative-acting promoter binding proteins, such that an alteration in function of any one member of the defined subcircuit, occurring with a change in cell fate, defines a change in status for all other members of the subcircuit. Here we describe a GRN subcircuit that links a tumor immune function with cell cycle de-regulation. All members of this subcircuit have a predictable status change in response to rescue of the growth-controlled phenotype. Given the similarities between the molecular mechanisms underlying cell status changes in tumorigenesis and development, application of GRN paradigms to tumor progression is particularly apt and offers the hope of providing a more concise, reliable, and therapeutically useful series of predictions linking gene regulation and tumor progression.

Methylation of CIITA promoter IV causes loss of HLA-II inducibility by IFN-gamma in promyelocytic cells

The human promyelocytic cell line THP-1 expresses high level of HLA class II (HLA-II) molecules after IFN-gamma treatment. Here, we report a variant of THP-1 that does not express HLA-II after IFN-gamma. The variant's HLA-II phenotype is constant over time in culture and it is not related to a defective IFN-gamma-signalling pathway. Transfection of CIITA, the HLA-II transcriptional activator, under the control of a cytomegalovirus promoter rescues high level of HLA-DR surface expression in the variant indicating that the biosynthetic block resides in the expression of CIITA and not in the CIITA-dependent transactivation of the HLA-II promoters. Treatment of the variant with 5-azacytidine (5-aza), which inhibits CpG methylation, restores inducibility of HLA-II by IFN-gamma both at transcriptional and phenotypic level and antigen presenting and processing function of the variant. DNA studies demonstrate that the molecular defect of the THP-1 variant originates from the methylation of the CIITA promoter IV. Furthermore, treatment with 5-aza produces a substantial demethylation of CIITA promoter IV and a significant increase of IFN-gamma-dependent HLA-II expression in another myelomonocytic cell line, U937. Therefore hyper-methylation of CIITA promoter IV may be a relevant mechanism of epigenetic control preventing HLA-II IFN-gamma inducibility in the myelomonocytic cell lineage.

Gambogic acid induced tumor cell apoptosis by T lymphocyte activation in H22 transplanted mice

Multiple lines of evidence have demonstrated that gambogic acid (GA) is an efficient apoptosis inducing agent. However, the mechanisms of GA induced apoptosis have been controversial, despite the tremendous effort made during recent years. Here we report a novel mechanism through which GA induces cell apoptosis. Instead of dealing with tumor cells directly, GA first activates inactive T lymphocytes, which in turn triggers cancer cell apoptosis. This is supported by the observation that GA inhibited tumor growth and extended the survival time of mice bearing H22 tumor. cDNA microarray analysis indicated that 22.92% of the 48 genes that were affected with GA treatment were immune related genes. RT-PCR assay revealed that GA up-regulated MHC-II and TCR transcriptions, implicating that GA activates T lymphocytes to induce tumor cell apoptosis in vivo. HE staining showed that T lymphocytes penetrated into tumor tissues after GA administration. Western blotting revealed that GA enhanced CD4+ and CD8+ expressions. Annexin-V/PI double-staining and DNA ladder assays confirmed that GA induced tumor cell apoptosis. In summary, this report demonstrated, for the first time, that GA mainly activates T lymphocytes to induce cancer cell apoptosis in H22 transplanted mice.

Enhancement of DNA vaccine potency through coadministration of CIITA DNA with DNA vaccines via gene gun

Administration of DNA vaccines via gene gun has emerged as an important form of Ag-specific immunotherapy. The MHC CIITA is a master regulator of MHC class II expression and also induces expression of class I molecules. We reasoned that the gene gun administration of CIITA DNA with DNA vaccines employing different strategies to improve MHC I and II processing could enhance DNA vaccine potency. We observed that DC-1 cells transfected with CIITA DNA lead to higher expression of MHC I and II molecules, leading to enhanced Ag presentation through the MHC I/II pathways. Furthermore, our data suggested that coadministration of DNA-encoding calreticulin (CRT) linked to human papillomavirus (HPV) 16 E6 Ag (CRT/E6) with CIITA DNA leads to enhanced E6-specific CD8(+) T cell immune responses in vaccinated mice. In addition, coadministration of the combination of CRT/E6 DNA with CIITA DNA and DNA encoding the invariant chain (Ii) linked to the pan HLA-DR-reactive epitope (Ii-PADRE) further enhanced E6-specific CD8(+) T cell immune responses in vaccinated mice. Treatment with the combination vaccine was also shown to enhance the antitumor effects and to prolong survival in TC-1 tumor-bearing mice. Vaccination with the combination vaccine also led to enhanced E6-specific CD8(+) memory T cells and to long-term protection against TC-1 tumors and prolonged survival in vaccinated mice. Thus, our findings suggest that the combination of CIITA DNA with CRT/E6 and Ii-PADRE DNA vaccines represents a potentially effective means to combat tumors in the clinical setting.

Lung cancer patients' CD4(+) T cells are activated in vitro by MHC II cell-based vaccines despite the presence of myeloid-derived suppressor cells

BACKGROUND

Advanced non-small cell lung cancer (NSCLC) remains an incurable disease. Immunotherapies that activate patients' T cells against resident tumor cells are being developed; however, these approaches may not be effective in NSCLC patients due to tumor-induced immune suppression. A major cause of immune suppression is myeloid-derived suppressor cells (MDSC). Because of the strategic role of CD4(+) T lymphocytes in the activation of cytotoxic CD8(+) T cells and immune memory, we are developing cell-based vaccines that activate tumor-specific CD4(+) T cells in the presence of MDSC. The vaccines are NSCLC cell lines transfected with costimulatory (CD80) plus major histocompatibility complex class II (MHC II) genes that are syngeneic to the recipient. The absence of invariant chain promotes the presentation of endogenously synthesized tumor antigens, and the activation of MHC II-restricted, tumor-antigen-specific CD4(+) T cells.

METHODS

Potential vaccine efficacy was tested in vitro by priming and boosting peripheral blood mononuclear cells from ten NSCLC patients who had varying levels of MDSC. CD4(+) T cell activation was quantified by measuring Type 1 and Type 2 cytokine release.

RESULTS

The vaccines activated CD4(+) T cells from all ten patients, despite the presence of CD33(+)CD11b(+) MDSC. Activated CD4(+) T cells were specific for NSCLC and did not cross-react with tumor cells derived from non-lung tissue or normal lung fibroblasts.

CONCLUSIONS

The NSCLC vaccines activate tumor-specific CD4(+) T cells in the presence of potent immune suppression, and may be useful for the treatment of patients with NSCLC.

CIITA mediates interferon-gamma repression of collagen transcription through phosphorylation-dependent interactions with co-repressor molecules

Previously, we have demonstrated that major histocompatibility class II trans-activator (CIITA) is crucial in mediating interferon-gamma (IFN-gamma)-induced repression of collagen type I gene transcription. Here we report that CIITA represses collagen transcription through a phosphorylation-dependent interaction between its proline/serine/threonine domain and co-repressor molecules such as histone deacetylase (HDAC2) and Sin3B. Mutation of a serine (S373A) in CIITA, within a glycogen synthase kinase 3 (GSK3) consensus site, decreases repression of collagen transcription by blocking interaction with Sin3B. In vitro phosphorylation of CIITA by GSK3 relies on a casein kinase I site three amino acids C-terminal to the GSK3 site in CIITA. Both GSK3 and casein kinase I inhibitors alleviate collagen repression and disrupt IFN-gamma-mediated recruitment of Sin3B and HDAC2 to the collagen start site. Therefore, we have identified the region within CIITA responsible for mediating IFN-gamma-induced inhibition of collagen synthesis.

The absence of invariant chain in MHC II cancer vaccines enhances the activation of tumor-reactive type 1 CD4+ T lymphocytes

Activation of tumor-reactive T lymphocytes is a promising approach for the prevention and treatment of patients with metastatic cancers. Strategies that activate CD8(+) T cells are particularly promising because of the cytotoxicity and specificity of CD8(+) T cells for tumor cells. Optimal CD8(+) T cell activity requires the co-activation of CD4(+) T cells, which are critical for immune memory and protection against latent metastatic disease. Therefore, we are developing "MHC II" vaccines that activate tumor-reactive CD4(+) T cells. MHC II vaccines are MHC class I(+) tumor cells that are transduced with costimulatory molecules and MHC II alleles syngeneic to the prospective recipient. Because the vaccine cells do not express the MHC II-associated invariant chain (Ii), we hypothesized that they will present endogenously synthesized tumor peptides that are not presented by professional Ii(+) antigen presenting cells (APC) and will therefore overcome tolerance to activate CD4(+) T cells. We now report that MHC II vaccines prepared from human MCF10 mammary carcinoma cells are more efficient than Ii(+) APC for priming and boosting Type 1 CD4(+) T cells. MHC II vaccines consistently induce greater expansion of CD4(+) T cells which secrete more IFNgamma and they activate an overlapping, but distinct repertoire of CD4(+) T cells as measured by T cell receptor Vbeta usage, compared to Ii(+) APC. Therefore, the absence of Ii facilitates a robust CD4(+) T cell response that includes the presentation of peptides that are presented by traditional APC, as well as peptides that are uniquely presented by the Ii(-) vaccine cells.

MHC class II-transduced tumor cells originating in the immune-privileged eye prime and boost CD4(+) T lymphocytes that cross-react with primary and metastatic uveal melanoma cells

Uveal melanoma, the most common malignancy of the eye, has a 50% rate of liver metastases among patients with large primary tumors. Several therapies prolong survival of metastatic patients; however, none are curative and no patients survive. Therefore, we are exploring immunotherapy as an alternative or adjunctive treatment. Uveal melanoma may be particularly appropriate for immunotherapy because primary tumors arise in an immune-privileged site and may express antigens to which the host is not tolerized. We are developing MHC class II (MHC II)-matched allogeneic, cell-based uveal melanoma vaccines that activate CD4(+) T lymphocytes, which are key cells for optimizing CD8(+) T-cell immunity, facilitating immune memory, and preventing tolerance. Our previous studies showed that tumor cells genetically modified to express costimulatory and MHC II molecules syngeneic to the recipient are potent inducers of antitumor immunity. Because the MHC II-matched allogeneic vaccines do not express the accessory molecule, Invariant chain, they present MHC II-restricted peptides derived from endogenously encoded tumor antigens. We now report that MHC II-matched allogeneic vaccines, prepared from primary uveal melanomas that arise in the immune-privileged eye, prime and boost IFNgamma-secreting CD4(+) T cells from the peripheral blood of either healthy donors or uveal melanoma patients that cross-react with primary uveal melanomas from other patients and metastatic tumors. In contrast, vaccines prepared from metastatic cells in the liver are less effective at activating CD4(+) T cells, suggesting that tumor cells originating in immune-privileged sites may have enhanced capacity for inducing antitumor immunity and for serving as immunotherapeutic agents.

Suppression of major histocompatibility complex class II-associated invariant chain enhances the potency of an HIV gp120 DNA vaccine

Summary One function of the major histocompatibility complex (MHC) class II-associated invariant chain (Ii) is to prevent MHC class II molecules from binding endogenously generated antigenic epitopes. Ii inhibition leads to MHC class II presentation of endogenous antigens by APC without interrupting MHC class I presentation. We present data that in vivo immunization of BALB/c mice with HIV gp120 cDNA plus an Ii suppressive construct significantly enhances the activation of both gp120-specific T helper (Th) cells and cytotoxic T lymphocytes (CTL). Our results support the concept that MHC class II-positive/Ii-negative (class II(+)/Ii(-)) antigen-presenting cells (APC) present endogenously synthesized vaccine antigens simultaneously by MHC class II and class I molecules, activating both CD4(+) and CD8(+) T cells. Activated CD4(+) T cells locally strengthen the response of CD8(+) CTL, thus enhancing the potency of a DNA vaccine.

MHC class II molecules in tumour immunology: prognostic marker and target for immune modulation

MHC class II molecules presenting MHC class II restricted antigens play an important role in the activation of CD4+ T cells, which are the central orchestrating cells of an immune response. This review focuses on the particular role of MHC class II molecules in tumour immunology. The MHC class II antigen presentation pathway and the expression of MHC class II molecules on tumour cells related to clinical outcome is discussed. Improving the MHC class II tumour antigen presentation pathway, for instance by downregulation of the invariant chain or modulation of HLA-DO expression, offers many opportunities for developing new modalities of immunotherapy.

Challenge with mammary tumor cells expressing MHC class II and CD80 prevents the development of spontaneously arising tumors in MMTV-neu transgenic mice

The HER-2/Neu oncogene has been implicated in human and mouse breast cancer. Indeed, transgenic MMTV-neu mice expressing this oncogene from the mammary tumor virus long terminal repeat develop spontaneous mammary tumors and die within 1 year of life. We have expressed the class II transactivator (CIITA) and/or the costimulatory molecule CD80 (B7.1) in a mammary carcinoma cell line (MCNeuA) derived from these mice. Class II transactivator directs the expression of MHC class II and the machinery for antigen processing and presentation by this pathway. When injected into MMTV-neu mice, tumor cells expressing CD80 or CD80 and CIITA, were rejected completely. In addition, following the rejection of dual expressing cells, 75% of the mice were protected against the development of subsequent spontaneous tumors. Cells expressing only CD80 or CIITA were not as effective as antitumor vaccines in preventing the development of spontaneous tumors. Thus, converting cancer cells into antigen presenting cells could represent an effective immunotherapy for breast cancer.

Tumor-specific CD4+ T cells are activated by "cross-dressed" dendritic cells presenting peptide-MHC class II complexes acquired from cell-based cancer vaccines

Tumor cells that constitutively express MHC class I molecules and are genetically modified to express MHC class II (MHC II) and costimulatory molecules are immunogenic and have therapeutic efficacy against established primary and metastatic cancers in syngeneic mice and activate tumor-specific human CD4+ T lymphocytes. Previous studies have indicated that these MHC II vaccines enhance immunity by directly activating tumor-specific CD4+ T cells during the immunization process. Because dendritic cells (DCs) are considered to be the most efficient APCs, we have now examined the role of DCs in CD4+ T cell activation by the MHC II vaccines. Surprisingly, we find that DCs are essential for MHC II vaccine immunogenicity; however, they mediate their effect through "cross-dressing." Cross-dressing, or peptide-MHC (pMHC) transfer, involves the generation of pMHC complexes within the vaccine cells, and their subsequent transfer to DCs, which then present the intact, unprocessed complexes to CD4+ T lymphocytes. The net result is that DCs are the functional APCs; however, the immunogenic pMHC complexes are generated by the tumor cells. Because MHC II vaccine cells do not express the MHC II accessory molecules invariant chain and DM, they are likely to load additional tumor Ag epitopes onto MHC II molecules and therefore activate a different repertoire of T cells than DCs. These data further the concept that transfer of cellular material to DCs is important in Ag presentation, and they have direct implications for the design of cancer vaccines.

Tumor cells transduced with the MHC class II Transactivator and CD80 activate tumor-specific CD4+ T cells whether or not they are silenced for invariant chain

The specificity and potency of the immune system make immunotherapy a potential strategy for the treatment of cancer. To exploit this potential, we have developed cell-based cancer vaccines consisting of tumor cells expressing syngeneic MHC class II and costimulatory molecules. The vaccines mediate tumor regression in mice and activate human CD4+ T cells in vitro. Previous vaccines were generated by transducing MHC II negative tumor cells with a single HLA-DR allele. Because expression of multiple MHC II alleles would facilitate presentation of a broader repertoire of tumor antigens, we have now transduced tumor cells with the MHC class II transactivator (CIITA), a regulatory gene that coordinately increases expression of all MHC II alleles. Previous studies in mice indicated that coexpression of the MHC II accessory molecule invariant chain (Ii) inhibited presentation of endogenously synthesized tumor antigens and reduced vaccine efficacy. To determine if Ii expression affects presentation of MHC class II-restricted endogenously synthesized tumor antigens in human tumor cells, HLA-DR-MCF10 breast cancer cells were transduced with the CIITA, CD80 costimulatory molecule gene, and with or without small interfering RNAs (siRNA) specific for Ii. Ii expression is silenced >95% in CIITA/CD80/siRNA transductants; down-regulation of Ii does not affect HLA-DR expression or stability; and Ii(+) and Ii(-) transductants activate human CD4+ T cells to DRB1*0701-restricted HER-2/neu epitopes. Therefore, tumor cells transduced with the CIITA, CD80, and with or without Ii siRNA present endogenously synthesized tumor antigens and are potential vaccines for activating tumor-specific CD4+ T cells.

Presentation of Endogenously Synthesized MHC Class II-Restricted Epitopes by MHC Class II Cancer Vaccines Is Independent of Transporter Associated with Ag Processing and the Proteasome

Cell-based vaccines consisting of invariant chain-negative tumor cells transfected with syngeneic MHC class II (MHC II) and costimulatory molecule genes are prophylactic and therapeutic agents for the treatment of murine primary and metastatic cancers. Vaccine efficacy is due to direct presentation of endogenously synthesized, MHC II-restricted tumor peptides to CD4+ T cells. Because the vaccine cells lack invariant chain, we have hypothesized that, unlike professional APC, the peptide-binding groove of newly synthesized MHC II molecules may be accessible to peptides, allowing newly synthesized MHC II molecules to bind peptides that have been generated in the proteasome and transported into the endoplasmic reticulum via the TAP complex. To test this hypothesis, we have compared the Ag presentation activity of multiple clones of TAP-negative and TAP-positive tumor cells transfected with I-Ak genes and the model Ag hen egg white lysozyme targeted to the endoplasmic reticulum or cytoplasm. Absence of TAP does not diminish Ag presentation of three hen egg white lysozyme epitopes. Likewise, cells treated with proteasomal and autophagy inhibitors are as effective APC as untreated cells. In contrast, drugs that block endosome function significantly inhibit Ag presentation. Coculture experiments demonstrate that the vaccine cells do not release endogenously synthesized molecules that are subsequently endocytosed and processed in endosomal compartments. Collectively, these data indicate that vaccine cell presentation of MHC II-restricted endogenously synthesized epitopes occurs via a mechanism independent of the proteasome and TAP complex, and uses a pathway that overlaps with the classical endosomal pathway for presentation of exogenously synthesized molecules.

Curative Antitumor Immune Response Is Optimal with Tumor Irradiation Followed by Genetic Induction of Major Histocompatibility Complex Class I and Class II Molecules and Suppression of Ii Protein

Transfecting genes into tumors, to upregulate major histocompatibility complex (MHC) class I and class II molecules and inhibit MHC class II associated invariant chain (Ii), induces a potent anti-tumor immune response when preceded by tumor irradiation, in murine RM-9 prostate carcinoma. The transfected genes are cDNA plasmids for interferon-gamma (pIFN-gamma), MHC class II transactivator (pCIITA), an Ii reverse gene construct (pIi-RGC), and a subtherapeutic dose of adjuvant IL-2 (pIL-2). Responding mice rejected challenge with parental tumor and demonstrated tumor-specific cytotoxic T lymphocytes (CTLs). We have extended our investigation to determine the relative roles of each one of the four plasmids pIFN-gamma, pCIITA, pIi-RGC, and pIL-2 in conjunction with radiation for the induction of a curative immune response. Upregulation of MHC class I with pIFN-gamma or class II with pCIITA, separately, does not lead to a complete response even if supplemented with pIL-2 or pIi-RGC. An optimal and specific antitumor response is achieved in more than 50% of the mice when, after tumor irradiation, tumor cells are converted in situ to a MHC class I+/class II+/Ii- phenotype with pIFN-gamma, pCIITA, pIi-RGC, and pIL-2. We demonstrate further that both CD4+ helper T cells and CD8+ cytotoxic T cells are essential for induction of an antitumor response because in vivo depletion of either subset abrogates the response. The radiation contributes to the gene therapy by causing tumor debulking and increasing the permeability of tumors to infiltration of inflammatory cells.

Engineered fusion hybrid vaccine of IL-18 gene-modified tumor cells and dendritic cells induces enhanced antitumor immunity

Dendritic cell (DC)-tumor fusion hybrid vaccines that facilitate antigen presentation represent a novel powerful strategy in cancer immunotherapy. In our study, we investigated the antitumor immunity derived from the vaccination of fusion hybrids between engineered J558/IL-18 myeloma cells secreting Th1 cytokine IL-18 and DCs. DC/J558/IL-18 could secret a higher level of IL-18 than DCs, efficiently expressed J558 tumor antigen P1A, and enhanced ability of allogeneic T cell stimulation when compared to J558/IL-18. Our data showed that the immunization of BALB/c mice with DC/J558/IL-18 hybrids induced the most potent protective immunity against 1 x 10(6) cells with a J558 tumor challenge, compared to those immunized with the mixture of DCs and J558/IL-18, J558/IL-18, or J558. Furthermore, the immunization of mice with engineered DC/J558/IL-18 hybrids elicited stronger NK activity and J558 tumor-specific cytotoxic T lymphocyte (CTL) responses in vitro. In addition, DC/J558/IL-18 tumor cells into syngeneic mice induced a Th1 dominant immune response to J558 and resulted in tumor regression, which indicated that the antitumor effect mediated by DC/J558/IL-18 appeared to be dependent on TH1 cytokine production. These results demonstrate that the engineered fusion hybrid vaccines that combine Th1 gene-modified tumor with DCs may be an attractive strategy for cancer immunotherapy.

Epigenetic inactivation of class II transactivator (CIITA) is associated with the absence of interferon-gamma-induced HLA-DR expression in colorectal and gastric cancer cells

Tightly regulated at the level of transcription, expression of MHC class II molecules varies significantly among gastrointestinal cancers. High levels of MHC class II expression are often associated with a better prognosis, which is indicative of the involvement of CD4+ lymphocytes in tumor suppression, but the molecular mechanism by which MHC class II expression is regulated remains unclear. In the present study, we investigated the expression of one inducible MHC class II molecule, HLA-DR, and its coactivators in a panel of colorectal and gastric cancer cell lines. Interferon-gamma induced expression of HLA-DR in 14 of 20 cell lines tested; the remaining six cell lines did not express HLA-DR. Analysis of the expression of transcription factors and coactivators associated with HLA-DR revealed that the loss of CIITA expression was closely associated with the absence of HLA-DR induction. Moreover, DNA methylation of the 5' CpG island of CIITA-PIV was detected in all cancer cells that lacked CIITA. The methylation and resultant silencing of CIITA-PIV depended on the activities of two DNA methyltransferases, DNMT1 and DNMT3B, and their genetic inactivation restored CIITA-PIV expression. It thus appears that CIITA methylation is a key mechanism that enables some gastrointestinal cancer cells to escape immune surveillance.

Class II-Associated Invariant Chain Peptide Expression on Myeloid Leukemic Blasts Predicts Poor Clinical Outcome

Effective antitumor responses need the activation of CD4+ T cells. MHC class II antigen presentation requires the release of class II-associated invariant chain peptide (CLIP) from the antigen-binding site. In antigen-presenting cells, human leukocyte antigen DM (HLA-DM; abbreviated DM in this article) catalyzes CLIP dissociation. In B cells, HLA-DO (DO) down-modulates DM function. Cell surface CLIP:HLA-DR (DR) ratio correlates to DO:DM ratio and the efficacy of antigen presentation. We examined 111 blood and bone marrow samples of patients with newly diagnosed acute myeloid leukemia (AML) for the expression of CLIP, DR, DM, and DO by flow cytometry. Patients with DR+/CLIP- blasts had a significant longer disease-free survival than patients with DR+/CLIP+ blasts. DO, until now believed to be restricted to lymphoid cells, could be demonstrated at protein level as well as by reverse transcription-PCR. DO:DM ratio correlated to CLIP:DR ratio, suggesting that, unlike in other antigen-presenting cells of the nonlymphoid cell type, both DO and DM mediate regulation of CLIP expression in AML blasts. We hypothesize that DR+/CLIP- AML blasts are able to present leukemia-specific antigens to CD4+ T helper cells initiating an effective and long-lasting antitumor response resulting in a prolonged disease-free survival.

Turning tumor cells in situ into T-helper cell-stimulating, MHC class II tumor epitope-presenters: immuno-curing and immuno-consolidation

Immunological control or cure of tumors depends on initiating a robust T helper cell response to MHC class II epitopes of tumor-associated antigens. T helper cells regulate the potency of cytotoxic T lymphocyte and antibody responses. We have developed a novel approach to stimulate T helper cells by converting tumor cells into MHC class II molecule-positive, antigen presenting cells. Furthermore, using antisense methods, we suppress expression of the Ii protein, that normally blocks the antigenic peptide binding site of MHC class II molecules during synthesis in the endoplasmic reticulum. In such gene-engineered tumor cells, the MHC class II molecules pick up antigenic peptides, which have been transported into the endoplasmic reticulum for binding to MHC class I molecules. All nucleated cells create such "surveys of self" to detect viral or malignant transformation. Our method extends that survey of self to MHC class II endogenous tumor-associated antigens. Simultaneous presentation of tumor antigens by both MHC class I and II generates a robust and long-lasting antitumor immune response. Injecting murine tumors with genes, which induce MHC class II molecules and suppress Ii protein, cures a significant number of animals with renal and prostate tumors. We have developed analogous human gene vectors that are suitable for most patients and cancers, because they are monomorphic and active in all HLA-DR alleles. We review our findings, and analyze remaining issues for preclinical study and the design of clinical trials.

Surgical removal of primary tumor reverses tumor-induced immunosuppression despite the presence of metastatic disease

Immunotherapy is a promising approach for the management of malignancies. It may be particularly useful for tumors that do not respond to conventional therapies, such as many metastatic cancers. The efficacy of immunotherapy will depend on many factors, one of which is the immunocompetence of the host. Patients with large primary tumors frequently are immunosuppressed, making them poor candidates for immunotherapy. Although a few studies have reported that surgical removal of primary tumor reverses immunosuppression, it is not known whether metastatic disease in postsurgery patients inhibits this recovery. To determine the role of metastatic disease, we examined tumor-free mice versus mice with primary tumor and metastatic disease versus mice whose primary tumors were removed surgically but who had metastatic disease. We have used the mouse 4T1 mammary carcinoma, a BALB/c-derived transplantable tumor that shares many characteristics with human breast cancer and is an established model for spontaneous, metastatic cancer. Cell-mediated and humoral adaptive immunity, as measured by rejection of allogeneic tumor, antigen-specific T-cell proliferation, and antigen-specific antibody responses, was suppressed in 4T1-bearing nonsurgery mice relative to tumor-free mice. Surgical removal of primary tumor resulted in rebounding of antibody and cell-mediated responses, even in mice with metastatic disease. Macrophage activity, as measured by lipopolysaccharide responsiveness, and dendritic cell function, as measured by nominal and alloantigen presentation, were not suppressed in tumor-bearing mice. Therefore, the presence of primary tumor suppresses T-cell and antibody responses; however, surgical removal of primary tumor restores immunocompetence even when disseminated metastatic disease is present.

Activation of Tumor-specific CD4+ T Lymphocytes by Major Histocompatibility Complex Class II Tumor Cell Vaccines

Mouse tumor cells transfected with syngeneic MHC class II and costimulatory molecule genes are therapeutic vaccines in mice, provided they do not coexpress the class II-associated invariant chain (Ii). We demonstrated previously that the vaccine cells present tumor peptides via the endogenous antigen presentation pathway to activate CD4(+) and CD8(+) T cells. Because of their efficacy in mice, we are translating this vaccine strategy for clinical use. To obtain MHC class II(+)CD80(+)Ii(-) human tumor cells, we developed retroviruses encoding HLA-DR and CD80. The HLA-DR virus encodes the DRalpha and DRbeta0101 chains using an internal ribosomal entry site to coordinate expression. SUM159PT mammary carcinoma and Mel 202 ocular melanoma cells transduced with the retroviruses DRB1/CD80 express high levels of DRB0101 and CD80 on the cell surface in the absence of Ii. Irradiated SUM159PT/DR1/CD80 vaccines stimulate proliferation of non-HLA-DRB0101 peripheral blood mononuclear cells and present an exogenous DR1-restricted tetanus toxoid (TT) peptide, indicating that the transduced DRB0101 is functional. SUM159PT/DR1/CD80 vaccines were further transduced with a retrovirus encoding the TT fragment C gene, as a model tumor antigen. These cells stimulate IFN-gamma release from TT-primed human DRB0101 peripheral blood mononuclear cells, demonstrating their ability to present "endogenous" tumor antigen. Depletion and antibody blocking experiments confirm that MHC class II-restricted, endogenously synthesized epitopes are presented to CD4(+) T cells. Therefore, the MHC class II vaccines are efficient antigen-presenting cells that activate tumor-specific MHC class II-restricted, CD4(+) T lymphocytes, and they are a novel and potential immunotherapeutic for metastatic cancers.

Mutations and regulatory anomalies effecting tumor cell immune functions

The immune system is capable of interacting with tumor cells in such a way as to lead to tumor cell death, and this knowledge has inspired therapies to manipulate patient immune systems to eradicate cancer. However, tumor cells are able to mitigate the antitumor immune response, a fact that has rarely been addressed in the design of immunotherapies. There are many different tumor cell immune functions that play a role in mitigating the antitumor immune response. In some cases, these functions appear to be intimately associated with the tumor cell abnormalities that lead to loss of growth control, such as the cases where classical tumor suppressor proteins regulate tumor cell immune function genes. In other cases, tumor cell mutations appear to affect only the antitumor response, such as tumor cell mutations that eliminate MHC class I expression. Here I review the bases for tumor cell immune functions, noting in particular where tumor cell mutations, the gold standard for identifying a tumor-specific function, are known to be responsible for the tumor cell immune function. This review also discusses other known regulatory anomalies, in the absence of a known mutation, that are apparently important for tumor development and that regulate tumor cell immune functions. Surprisingly, in many cases where the tumor cell immune function is well understood in terms of its effect on the antitumor immune response, the tumor abnormality underlying the tumor cell immune function is completely uncharacterized.

Different levels of control prevent interferon-gamma-inducible HLA-class II expression in human neuroblastoma cells

The HLA class II expression is controlled by the transcriptional activator CIITA. The transcription of CIITA is controlled by different promoters, among which promoter-IV is inducible by IFN-gamma. We analysed the regulation of HLA class II molecules by IFN-gamma in a large series of human neuroblastoma cell lines. No induction of surface or intracellular HLA class II molecules and of specific mRNA was observed, in all neuroblastomas, with the exception of a nonprototypic cell line, ACN. In a large subset of neuroblastomas IFN-gamma induced expression of CIITA mRNA, derived from promoter-IV, which was not methylated. In contrast, in another subset of neuroblastomas, CIITA was not inducible by IFN-gamma and CIITA promoter-IV was either completely or partially methylated. Interestingly, the use of DNA demethylating agents restored CIITA gene transcriptional activation by IFN-gamma, but not HLA class II expression. The defect of HLA class II was not related to alterations in RFX or NF-Y transcription factors, as suggested by EMSA or RFX gene transfection experiments. In addition, the transfection of a functional CIITA cDNA failed to induce HLA class II expression in typical neuroblastoma cells. Confocal microscopy and Western blot analysis suggested a defective nuclear translocation and/or reduced protein synthesis in CIITA-transfected NB cells. Altogether, these data point to multiple mechanisms preventing HLA class II expression in the neuroblastoma, either involving CIITA promoter-IV silencing, or acting at the CIITA post-transcriptional level.

Inhibition of invariant chain expression in dendritic cells presenting endogenous antigens stimulates CD4+ T-cell responses and tumor immunity

Induction of potent and sustained antiviral or antitumor immunity is dependent on the efficient activation of CD8+ and CD4+ T cells. While dendritic cells constitute a powerful platform for stimulating cellular immunity, presentation of endogenous antigens by dendritic cells transfected with nucleic acid-encoded antigens favors the stimulation of CD8+ T cells over that of CD4+ T cells. A short incubation of mRNA-transfected dendritic cells with antisense oligonucleotides directed against the invariant chain enhances the presentation of mRNA-encoded class II epitopes and activation of CD4+ T-cell responses in vitro and in vivo. Immunization of mice with the antisense oligonucleotide-treated dendritic cells stimulates a more potent and longer lasting CD8+ cytotoxic T-cell (CTL) response and enhances the antitumor efficacy of dendritic cell-based tumor vaccination protocols. Transient inhibition of invariant chain expression represents a simple and general method to enhance the stimulation of CD4+ T-cell responses from endogenous antigens.

Tumor immunotherapy by converting tumor cells to MHC class II-positive, Ii protein-negative phenotype

A potent antitumor CD4(+) T-helper cell immune response is created by inducing tumor cells in vivo to a MHC class II(+)/Ii(- )phenotype. MHC class II and Ii molecules were induced in tumor cells in situ following tumor injection of a plasmid containing the gene for the MHC class II transactivator (CIITA). Ii protein was suppressed by the antisense effect of an Ii-reverse gene construct (Ii-RGC) in the same or another co-injected plasmid. The MHC class II(+)/Ii(- )phenotype of the tumor cells was confirmed by FACS analysis of cells transfected in vitro and by immunostaining of tumor nodules transfected by injections in vivo. Subcutaneous Renca tumors in BALB/c mice were treated by intratumoral injection with CIITA and Ii-RGC, in combination with a subtherapeutic dose of IL-2, to up-regulate the activation of T cells. Significant tumor shrinkage and decrease in rates of progression of established Renca tumors were seen in the groups injected with Ii-RGC, compared with groups in which only IL-2 plus empty plasmid controls were injected. Our method provides an effective immunotherapy warranting further development for human cancers.

Generating MHC Class II+/Ii- phenotype after adenoviral delivery of both an expressible gene for MHC Class II inducer and an antisense Ii-RNA construct in tumor cells

Tumor cells engineered by gene transduction to be MHC Class II+/Ii- are novel APCs capable of presenting endogenous tumor antigen epitopes to activate T helper cells. The MHC Class II+/Ii- tumor cell phenotype is created by transfecting genes for either CIITA or IFN-gamma, and inhibiting induced Ii mRNA by an Ii reverse gene construct (Ii-RGC). Adenoviral vectors are preferred for the delivery of such genes because of high infection efficiency and ubiquity of the adenoviral receptor on many cell types and tumors. Here we show that at 5 MOI (multiplicity of infection), recombinant adenoviruses with CIITA or IFN-gamma genes converted virtually all MC-38 colon adenocarcinoma cells and Renca renal carcinoma cells in culture to MHC Class II+/Ii+ cells. A single recombinant adenovirus with both genes for IFN-gamma and Ii-RGC (rAV/IFN-gamma/Ii-RGC) efficiently induced the MHC Class II+/Ii- phenotype. Injection of tumor nodules with rAV/Ii-RGC and rAV/CIITA/IFN-gamma combined with a suboptimal dose of rAV/IL-2 induced a potent antitumor immune response. The methods are adaptable for producing enhanced genetic vaccines, attenuated virus vaccines (eg, vaccinia), and ex vivo cell-based vaccines (dendritic and tumor cells).

Intracytoplasmic domains of MHC class II molecules are essential for lipid-raft-dependent signaling

In addition to their role in antigen presentation, major histocompatibility complex (MHC) class II molecules have been widely described as signaling proteins in diverse antigen-presenting cells (APCs) including B cells and dendritic cells. By contrast, little is known of the signaling function of MHC class II molecules expressed in solid tumors. We describe the functional organization and signaling ability of I-Ak expressed in a sarcoma, and report the recruitment of I-Ak to lipid rafts after MHC class II engagement. Lipid raft integrity was required for I-Ak-mediated reorganization of the actin cytoskeleton and translocation of protein kinase C-alpha(PKC-alpha) to the precise site of stimulation via I-Ak. Truncation of the intracytoplasmic domains of I-Ak did not perturb I-Ak recruitment to lipid rafts but abrogated PKC-alpha translocation and actin rearrangement. PKC-alpha was detected in lipid microdomains and enrichment of activated PKC-alphain lipid rafts was induced by I-Ak signaling. Ordering of the molecular events following engagement of the MHC class II molecules revealed that I-Ak recruitment to lipid rafts precedes signaling. This is consistent with the absence of a requirement for the intracytoplasmic tails for localization to lipid rafts. These data reveal that lipid-rich microdomains play a key role in MHC class II-mediated signaling in a solid tumor.

Radiation improves intratumoral gene therapy for induction of cancer vaccine in murine prostate carcinoma

Our goal was to convert murine RM-9 prostate carcinoma cells in vivo into antigen-presenting cells capable of presenting endogenous tumor antigens and triggering a potent T-helper cell-mediated immune response essential for the generation of a specific antitumor response. We showed that generating the major histocompatibility complex (MHC) class I+/class II+/Ii- phenotype, within an established subcutaneous RM-9 tumor nodule, led to an effective immune response limiting tumor growth. This phenotype was created by intratumoral injection of plasmid cDNAs coding for interferon gamma, MHC class II transactivator, and an antisense reverse gene construct (RGC) for a segment of the gene for Ii protein (-92,97). While this protocol led to significant suppression of tumor growth, there were no disease-free survivors. Nevertheless, irradiation of the tumor nodule on the day preceding initiation of gene therapy yielded 7 of 16 mice that were disease-free in a long-term follow up of 57 days compared to 1 of 7 mice receiving radiotherapy alone. Mice receiving radiotherapy and gene therapy rejected challenge with parental RM-9 cells and demonstrated specific cytotoxic T-cell activity in their splenocytes but not the mouse cured by radiation alone. These data were reproduced in additional experiments and confirmed that tumor irradiation prior to gene therapy resulted in complete tumor regression and specific tumor immunity in more than 50% of the mice. Increasing the number of plasmid injections after tumor irradiation induced tumor regression in 70% of the mice. Administering radiation before this novel gene therapy approach, that creates an in situ tumor vaccine, holds promise for the treatment of human prostate carcinoma.

On the biological relevance of MHC class II and B7 expression by tumour cells in melanoma metastases

A large number of studies have indicated that specific immune reactivity plays a crucial role in the control of malignant melanoma. In this context, expression of MHC I, MHC II and B7 molecules by melanoma cells is seen as relevant for the immune response against the tumour. For a better understanding of the biological relevance of MHC II and B7 expression by tumour cells in metastatic melanoma, we studied the expression of these molecules in melanoma metastases in relation to the inflammatory response, regression of the tumour and survival from 27 patients treated with biochemotherapy (30 mg m(-2) Cisplatin and 250 mg m(-2) decarbazine (dimethyl-triazene-imidazole-carboxamide, DTIC) on days 1-3 i.v., and 10(7) IU IFN-alpha 2b 3 days a week s.c., q. 28d). In 19 out of 27 lesions studied, we found expression of MHC II by the tumour cells, while only in one out of 11 tumour biopsies obtained from untreated metastatic melanoma patients, MHC II expression was detected. Expression of B7.1 and B7.2 by tumour cells was found in nine out of 24 and 19 out of 24 lesions, respectively. In all cases where B7.1 expression was found, expression of B7.2 by the tumour cells was also seen. In general, no or only few inflammatory cells positive for B7 were found. Expression of MHC II by tumour cells was positively correlated with the presence of tumour-infiltrating lymphocytes, regression of the lesion, and with time to progression (TTP) and overall survival (OS) of the patient. However, no significant correlation between B7.1 or B7.2 expression and regression of the tumour, TTP or OS was found. In light of other recent findings, these data altogether do support a role as biomarker for MHC II expression by tumour cells; however, its exact immunological pathomechanism(s) remain to be established.

The role of the MHC class II transactivator in class II expression and antigen presentation by astrocytes and in susceptibility to central nervous system autoimmune disease

The role of the MHC class II transactivator (CIITA) in Ag presentation by astrocytes and susceptibility to experimental autoimmune encephalomyelitis (EAE) was examined using CIITA-deficient mice and newly created transgenic mice that used the glial fibrillary acidic protein promoter to target CIITA expression in astrocytes. CIITA was required for class II expression on astrocytes. Like class II-deficient mice, CIITA-deficient mice were resistant to EAE by immunization with CNS autoantigen, although T cells from immunized CIITA-deficient, but not class II-deficient, mice proliferated and secreted Th1 cytokines. CIITA-deficient splenic APC presented encephalitogenic peptide to purified wild-type encephalitogenic CD4(+) T cells, indicating that CIITA-independent mechanisms can be used for class II-restricted Ag presentation in lymphoid tissue. CIITA-deficient mice were also resistant to EAE by adoptive transfer of encephalitogenic class II-restricted CD4(+) Th1 cells, indicating that CIITA-dependent class II expression was required for CNS Ag presentation. Despite constitutive CIITA-driven class II expression on astrocytes in vivo, glial fibrillary acidic protein-CIITA transgenic mice were no more susceptible to EAE than controls. CIITA-transfected astrocytes presented peptide Ag, but in contrast to IFN-gamma-activated astrocytes, they could not process and present native Ag. CIITA-transfected astrocytes did not express cathepsin S without IFN-gamma activation, indicating that CIITA does not regulate other elements that may be required for Ag processing by astrocytes. Although our results demonstrate that CIITA-directed class II expression is required for EAE induction, CIITA-directed class II expression by astrocytes does not appear to increase EAE susceptibility. These results do not support the role of astrocytes as APC for class II-restricted Ag presentation during the induction phase of EAE.

Engineered fusion hybrid vaccine of IL-4 gene-modified myeloma and relative mature dendritic cells enhances antitumor immunity

Dendritic cell (DC)-tumor fusion hybrid vaccine which facilitates antigen presentation represents a new powerful strategy in cancer therapy. In the present study, we investigated the antitumor immunity derived from vaccination of fusion hybrids between wild-type J558 or engineered J558-IL-4 myeloma cells secreting cytokine interleukin-4 (IL-4) and immature DCs (DC(IMAT)) or relative mature DCs (DC(RMAT)). DC(RMAT) displayed an up-regulated expression of immune molecules (Ia(d), CD40, CD54, CD80 and CD86) and certain cytokines/chemokines, and enhanced ability of allogeneic T cell stimulation when compared to DC(IMAT). These DCs were fused with myeloma cells by polyethylene glycol (PEG). The fusion efficiency was approximately 20%. Our data showed that immunization of C57BL/6 mice with DC(RMAT)/J558 hybrids induced protective immunity against a high dose of J558 tumor challenge (1x10(6) cells) in 3 out of 10 immunized mice, compared with no protection seen in mice immunized with DC(IMAT)/J558 hybrids. Furthermore, immunization of mice with engineered DC(RMAT)/J558-IL-4 hybrids elicited stronger J558 tumor-specific cytotoxic T lymphocyte (CTL) responses in vitro and induced more efficient protective immunity (10/10 mice; tumor free) against J558 tumor challenge in vivo than DC(RMAT)/J558 hybrid vaccines. The results demonstrate the importance of DC maturation in DC-tumor hybrid vaccines and indicate that the engineered fusion hybrid vaccines which combine gene-modified tumor and DC vaccines may be an attractive strategy for cancer immunotherapy.

Absence of gamma-interferon-inducible lysosomal thiol reductase in melanomas disrupts T cell recognition of select immunodominant epitopes

Long-lasting tumor immunity requires functional mobilization of CD8+ and CD4+ T lymphocytes. CD4+ T cell activation is enhanced by presentation of shed tumor antigens by professional antigen-presenting cells (APCs), coupled with display of similar antigenic epitopes by major histocompatibility complex class II on malignant cells. APCs readily processed and presented several self-antigens, yet T cell responses to these proteins were absent or reduced in the context of class II+ melanomas. T cell recognition of select exogenous and endogenous epitopes was dependent on tumor cell expression of gamma-interferon-inducible lysosomal thiol reductase (GILT). The absence of GILT in melanomas altered antigen processing and the hierarchy of immunodominant epitope presentation. Mass spectral analysis also revealed GILT's ability to reduce cysteinylated epitopes. Such disparities in the profile of antigenic epitopes displayed by tumors and bystander APCs may contribute to tumor cell survival in the face of immunological defenses.

MHC class II-deficient tumor cell lines with a defective expression of the class II transactivator

MHC class II expression defects have been evidenced in several human tumor cell lines originating from lung cancers or retinoblastoma. Accordingly, the mouse adenocarcinoma and fibrosarcoma cell lines, RAG and L(tk-), do not express I-A and I-E molecules even when treated with IFN-gamma. Here we show that fusion of both cell lines restores the inducible expression of MHC class II, thereby demonstrating that they present different and recessive alterations outside the MHC class II locus. CIITA, the MHC class II transactivator, controls the tissue-specific expression of MHC class II genes and creates the architecture of the transcriptional complex that binds to the MHC class II gene promoters. In L(tk-) cells, C2ta transcripts, expressed from the gene encoding CIITA, were indeed detected in severely limited amounts, with a defect in C2ta transcription initiation. In agreement we show here that the L(tk-) cell line does not express the CIITA protein. In contrast, in the RAG cell line, C2ta transcripts were expressed at normal levels, from the proper initiation site. The nucleotide sequencing of the CIITA cDNA from RAG did not reveal any mutation. However, the CIITA protein was not detected. These data evidence a new type of defect in a MHC class II-defective tumor cell line, as we show here that the alteration in the RAG cells occurs downstream of C2ta transcription. The RAG mutation might therefore reside in the C2ta transcript nuclear export or translation, or in the stability of the CIITA protein.

Genetic control of MHC class II expression

The presentation of peptides to T cells by MHC class II molecules is of critical importance in specific recognition by the immune system. Expression of class II molecules is exquisitely controlled at the transcriptional level. A large set of proteins interact with the promoters of class II genes. The most important of these is CIITA, a master controller that orchestrates expression but does not bind directly to the promoter. The transcriptosome complex formed at class II promoters is a model for induction of gene expression.

Innovative cancer vaccine strategies based on the identification of tumour-associated antigens

The identification of tumour-associated antigens has opened up new approaches to cancer immunotherapy. While past research focused on CD8+ cytotoxic T-cell responses, accumulating evidence suggests that CD4+ T cells also play an important role in orchestrating the host immune response against cancer. In this article, we summarise new strategies for the identification of major histocompatibility complex (MHC) class II-associated tumour antigens and discuss the importance of engaging both CD4+ and CD8+ T cells in cancer immunotherapy. The cloning of MHC class I- or class II-associated antigens has made it possible to develop synthetic and recombinant cancer vaccines that express specific tumour antigens. There are three major types of synthetic and recombinant cancer vaccines: recombinant viral and bacterial vaccines; naked DNA or RNA vaccines; and recombinant protein and peptide vaccines. In this article, we also discuss a new generation of recombinant cancer vaccines, 'self-replicating' DNA and RNA vaccines. Studies on the mechanisms of 'self-replicating' nucleic acid vaccines revealed that the enhanced immunogenicity was not due to an enhanced antigen expression, suggesting that the quantitative difference may not be as important as the qualitative difference in antigen presentation. The presence of the RNA replicase in the 'self-replicating' nucleic acid vaccines mimics alphavirus infection, which triggers the innate antiviral pathways of the host cells. Studies on how viral and cellular modulators of the innate antiviral pathways affect vaccine function should provide molecular insights crucial to future vaccine design.

Diversity in MHC class II antigen presentation

Processing exogenous and endogenous proteins for presentation by major histocompatibility complex (MHC) molecules to T cells is the defining function of antigen-presenting cells (APC) as major regulatory cells in the acquired immune response. MHC class II-restricted antigen presentation to CD4 T cells is achieved by an essentially common pathway that is subject to variation with regard to the location and extent of degradation of protein antigens and the site of peptide binding to MHC class II molecules. These subtle variations reveal a surprising flexibility in the ways a diverse peptide repertoire is displayed on the APC surface. This diversity may have profound consequences for the induction of immunity to infection and tumours, as well as autoimmunity and tolerance.

Bypassing tumor-specific and bispecific antibodies: triggering of antitumor immunity by expression of anti-FcgammaR scFv on cancer cell surface

We have developed a novel immunostimulatory molecule against tumor cells, composed of an anti-FcgammaRIII (CD16) scFv fused to the platelet-derived growth factor receptor (PDGFR) transmembrane region. This fusion molecule was stably expressed on the tumor cell surface and retained the ability of the parental antibody to bind soluble CD16. Tumor cells expressing anti-CD16 scFv triggered the release of IL-2 by Jurkat-CD 16/gamma cells and of TNFalpha by monocytes when co-cultured with these cells. Furthermore, NK cells could kill scFv-transfected HLA+ class I H1299 lung carcinoma tumor cells, but not the parental cells, indicating that anti-CD16 scFv tumor expression prevents the killer inhibitory receptor (KIR)-mediated inhibition of NK cell cytotoxicity. This anti-CD16 scFv tumor expression also enhanced tumor phagocytosis by IFNgamma-activated macrophages, a mechanism known to induce a protective long-term adaptative immunity to tumors. In vivo Winn tests performed in SCID mice showed that the expression of anti-CD16 scFv on tumor cells, but not of the negative control anti-phOx scFv, prevented tumor cell growth. Thus, expression of FcR antibodies or other FcR-specific ligands on tumor cells represents a novel and potent antibody-based gene therapy approach, which may have clinical applications in cancer

Loss of MHC class II inducibility in hyperplastic tissue in Rb-defective mice

Retinoblastoma gene (Rb) defects occur frequently in human tumors. Studies of Rb-defective human tumor cell lines and Rb-/- murine embryonic fibroblasts demonstrate that Rb is required for interferon-gamma (IFN-gamma) induced major histocompatibility complex (MHC) class II expression. MHC class II expressing tumors generate anti-tumor immune responses associated with tumor-specific infiltrating lymphocytes. The role of Rb in IFN-gamma induced MHC class II expression on an endogenous tumor was examined by immunohistochemical staining for IAbeta and Rb on tissues from Rb+/- mice. MHC class II IAbeta is not induced by IFN-gamma in Rb-deficient neoplastic cells, but remains inducible in related normal tissue.

Histone deacetylase activity represses gamma interferon-inducible HLA-DR gene expression following the establishment of a DNase I-hypersensitive chromatin conformation

Expression of the retinoblastoma tumor suppressor protein (Rb) is required for gamma interferon (IFN-gamma)-inducible major histocompatibility complex class II gene expression and transcriptionally productive HLA-DRA promoter occupancy in several human tumor cell lines. Treatment of these Rb-defective tumor cell lines with histone deacetylase (HDAC) inhibitors rescued IFN-gamma-inducible HLA-DRA and -DRB mRNA and cell surface protein expression, demonstrating repression of these genes by endogenous cellular HDAC activity. Additionally, Rb-defective, transcriptionally incompetent tumor cells retained the HLA-DRA promoter DNase I-hypersensitive site. Thus, HDAC-mediated repression of the HLA-DRA promoter occurs following the establishment of an apparent nucleosome-free promoter region and before transcriptionally productive occupancy of the promoter by the required transactivators. Repression of HLA-DRA promoter activation by HDAC activity likely involves a YY1 binding element located in the first exon of the HLA-DRA gene. Chromatin immunoprecipitation experiments localized YY1 to the HLA-DRA gene in Rb-defective tumor cells. Additionally, mutation of the YY1 binding site prevented repression of the promoter by HDAC1 and partially prevented activation of the promoter by trichostatin A. Mutation of the octamer element also significantly reduced the ability of HDAC1 to confer repression of inducible HLA-DRA promoter activation. Treatment of Rb-defective tumor cells with HDAC inhibitors greatly reduced the DNA binding activity of Oct-1, a repressor of inducible HLA-DRA promoter activation. These findings represent the first evidence that HDAC activity can repress IFN-gamma-inducible HLA class II gene expression and also demonstrate that HDAC activity can contribute to promoter repression following the establishment of a DNase I-hypersensitive chromatin conformation.

HLA class II-restricted antigen presentation of endogenous bcr-abl fusion protein by chronic myelogenous leukemia-derived dendritic cells to CD4(+) T lymphocytes

Bcr-abl fusion peptide-specific CD4+ T-lymphocyte clones have recently been shown to augment colony formation by chronic myelogenous leukemia (CML) cells in a bcr-abl type-specific and HLA class II-restricted manner without addition of exogenous antigen. These findings suggest that CML cells can naturally process and present endogenous bcr-abl fusion protein to CD4+ T lymphocytes in the context of HLA class II molecules. To verify this possibility, the ability of CML-derived dendritic cells (DCs) to present endogenous bcr-abl fusion protein to bcr-abl fusion peptide-specific CD4+ T-lymphocyte clones was investigated. The bcr-abl b3a2 peptide-specific and HLA-DRB1*0901-restricted CD4+ T-lymphocyte clones produced interferon-gamma in response to stimulation with monocyte-derived DCs from HLA-DRB1*0901+ patients with b3a2 type CML. In contrast, DCs from patients with HLA-DRB1*0901- or b2a2 type CML and those from healthy individuals did not exert stimulatory activity on bcr-abl-specific CD4+ T-lymphocyte clones. The response of CD4+ T-lymphocyte clones to CML-derived mature DCs was higher than that to immature DCs and was inhibited by anti-HLA-DR monoclonal antibody. These data suggest that CML-derived DCs can process and present endogenous bcr-abl fusion protein to CD4+ T lymphocytes.

H2-O inhibits presentation of bacterial superantigens, but not endogenous self antigens

H2-O/HLA-DO are MHC class II accessory molecules that modulate exogenous Ag presentation. Most class II accessory molecules are expressed in all professional APC; however, H2-O is only expressed in B cells and medullary thymic epithelial cells. Because B cells present exogenous Ags and superantigens (SAgs), and medullary thymic epithelial cells are specialized APC for self Ags during negative selection in the thymus, we have hypothesized that H2-O might play a role in MHC class II-restricted SAg and self Ag presentation. In this study, we demonstrate that H2-O expression inhibits presentation of the bacterial SAgs staphylococcal enterotoxins A and B to four SAg-reactive T hybridoma cells. In contrast, H2-O has no effect on presentation of endogenous self Ags, as measured by tumorigenicity in vivo and Ag presentation to three self Ag-specific T hybridoma cells. Additional experiments suggest that H2-O inhibits presentation of exogenous Ags by both newly synthesized and recycling MHC class II molecules. These data suggest H2-O may have a physiological role in tolerance induction and SAg-mediated toxic shock.

Signalling via MHC class II molecules modifies the composition of GEMs in APC

Major histocompatibility complex (MHC) class II molecules are responsible for peptide presentation to helper T lymphocytes and as such play an essential role in the immune response. These molecules transmit intracellular signals leading to diverse consequences in B lymphocytes including proliferation and apoptosis. Recent studies have revealed that glycolipid enriched membrane microdomains (GEMs) behave as signalling platforms for a variety of lymphocyte receptors. We have quantified human leucocyte antigen (HLA)-DR molecules localized in GEMs in human B lymphocytes. Use of a model imitating the interaction of HLA-DR with a T-cell receptor (TCR) modified the constituents of the HLA-DR-enriched GEMs. Confocal microscopy demonstrated a recruitment of HLA-DR and the ganglioside GM1 at the site of HLA-DR interaction with the stimulating ligand. Moreover, cholesterol depletion efficiently impaired this recruitment. Co-localizing proteins detected in HLA-DR-enriched GEMs include protein kinase C (PKC)-delta and actin. These data reveal that MHC class II antigens are localized in GEMs in mature human B lymphocytes and indicates that the formation of the immunological synapse regulates the composition of HLA-DR enriched GEMs in the antigen presenting cell (APC).