CIITA-driven MHC-II positive tumor cells: preventive vaccines and superior generators of antitumor CD4+ T lymphocytes for immunotherapy

The NLR member CIITA: Master controller of adaptive and intrinsic immunity and unexpected tool in cancer immunotherapy

Human nucleotide-binding oligomerization domain (NOD)-like receptors (NLR) include a large family of proteins that have important functions in basic physio-pathological processes like inflammation, cell death and regulation of transcription of key molecules for the homeostasis of the immune system. They are all characterized by a common backbone structure (the STAND ATPase module consisting in a nucleotide-binding domain (NBD), an helical domain 1 (HD1) and a winged helix domain (WHD), used by both prokaryotes and eukaryotes as defense mechanism. In this review, we will focus on the MHC class II transactivator (CIITA), the master regulator of MHC class II (MHC-II) gene expression and the founding member of NLR. Although a consistent part of the described NLR family components is often recalled as innate or intrinsic immune sensors, CIITA in fact occupies a special place as a unique example of regulator of both intrinsic and adaptive immunity. The description of the discovery of CIITA and the genetic and molecular characterization of its expression will be followed by the most recent studies that have unveiled this dual role of CIITA, key molecule in intrinsic immunity as restriction factor for human retroviruses and precious tool to induce the expression of MHC-II molecules in cancer cells, rendering them potent surrogate antigen presenting cells (APC) for their own tumor antigens.

Major histocompatibility complex class II in the tumor microenvironment: functions of nonprofessional antigen-presenting cells

Major histocompatibility complex class-II-restricted presentation by nonprofessional antigen-presenting cells in the tumor microenvironment can regulate antitumor T-cell responses. In murine models, tumor cell-specific MHC class II expression decreases in vivo tumor growth, dependent on T cells. Tumor cell-specific MHC class II expression is associated with improved survival and response to immune checkpoint inhibitors in human cancers. Antigen-presenting cancer-associated fibroblasts (apCAF) present MHC class-II-restricted antigens and activate CD4 T cells. The role of MHC class II on apCAFs depends on the cell of origin. MHC class II on tumoral lymphatic endothelial cells leads to expansion of regulatory T cells and increased in vivo tumor growth.

Insight into Cancer Immunity: MHCs, Immune Cells and Commensal Microbiota

Cancer cells circumvent immune surveillance via diverse strategies. In accordance, a large number of complex studies of the immune system focusing on tumor cell recognition have revealed new insights and strategies developed, largely through major histocompatibility complexes (MHCs). As one of them, tumor-specific MHC-II expression (tsMHC-II) can facilitate immune surveillance to detect tumor antigens, and thereby has been used in immunotherapy, including superior cancer prognosis, clinical sensitivity to immune checkpoint inhibition (ICI) therapy and tumor-bearing rejection in mice. NK cells play a unique role in enhancing innate immune responses, accounting for part of the response including immunosurveillance and immunoregulation. NK cells are also capable of initiating the response of the adaptive immune system to cancer immunotherapy independent of cytotoxic T cells, clearly demonstrating a link between NK cell function and the efficacy of cancer immunotherapies. Eosinophils were shown to feature pleiotropic activities against a variety of solid tumor types, including direct interactions with tumor cells, and accessorily affect immunotherapeutic response through intricating cross-talk with lymphocytes. Additionally, microbial sequencing and reconstitution revealed that commensal microbiota might be involved in the modulation of cancer progression, including positive and negative regulatory bacteria. They may play functional roles in not only mucosal modulation, but also systemic immune responses. Here, we present a panorama of the cancer immune network mediated by MHCI/II molecules, immune cells and commensal microbiota and a discussion of prospective relevant intervening mechanisms involved in cancer immunotherapies.

Protective anti-tumor vaccination against glioblastoma expressing the MHC class II transactivator CIITA

Glioblastoma is the most malignant tumor of the central nervous system. Current treatments based on surgery, chemotherapy, and radiotherapy, and more recently on selected immunological approaches, unfortunately produce dismal outcomes, and less than 2% of patients survive after 5 years. Thus, there is an urgent need for new therapeutic strategies. Here, we report unprecedented positive results in terms of protection from glioblastoma growth in an animal experimental system after vaccination with glioblastoma GL261 cells stably expressing the MHC class II transactivator CIITA. Mice injected with GL261-CIITA express de novo MHC class II molecules and reject or strongly retard tumor growth as a consequence of rapid infiltration with CD4+ and CD8+ T cells. Importantly, mice vaccinated with GL261-CIITA cells by injection in the right brain hemisphere strongly reject parental GL261 tumors injected in the opposite brain hemisphere, indicating not only the acquisition of anti-tumor immune memory but also the capacity of immune T cells to migrate within the brain, overcoming the blood–brain barrier. GL261-CIITA cells are a potent anti-glioblastoma vaccine, stimulating a protective adaptive anti-tumor immune response in vivo as a consequence of CIITA-driven MHC class II expression and consequent acquisition of surrogate antigen-presenting function toward tumor-specific CD4+ Th cells. This unprecedented approach for glioblastoma demonstrates the feasibility of novel immunotherapeutic strategies for potential application in the clinical setting.

Class II transactivator induces expression of MHC-I and MHC-II in transmissible Tasmanian devil facial tumours

MHC-I and MHC-II molecules are critical components of antigen presentation and T cell immunity to pathogens and cancer. The two monoclonal transmissible devil facial tumours (DFT1, DFT2) exploit MHC-I pathways to overcome immunological anti-tumour and allogeneic barriers. This exploitation underpins the ongoing transmission of DFT cells across the wild Tasmanian devil population. We have previously shown that the overexpression of NLRC5 in DFT1 and DFT2 cells can regulate components of the MHC-I pathway but not MHC-II, establishing the stable upregulation of MHC-I on the cell surface. As MHC-II molecules are crucial for CD4⁺ T cell activation, MHC-II expression in tumour cells is beginning to gain traction in the field of immunotherapy and cancer vaccines. The overexpression of Class II transactivator in transfected DFT1 and DFT2 cells induced the transcription of several genes of the MHC-I and MHC-II pathways. This was further supported by the upregulation of MHC-I protein on DFT1 and DFT2 cells, but interestingly MHC-II protein was upregulated only in DFT1 cells. This new insight into the regulation of MHC-I and MHC-II pathways in cells that naturally overcome allogeneic barriers can inform vaccine, immunotherapy and tissue transplant strategies for human and veterinary medicine.

Human RNASET2: A Highly Pleiotropic and Evolutionary Conserved Tumor Suppressor Gene Involved in the Control of Ovarian Cancer Pathogenesis

Ovarian cancer represents one of the most malignant gynecological cancers worldwide, with an overall 5-year survival rate, being locked in the 25-30% range in the last decade. Cancer immunotherapy is currently one of the most intensively investigated and promising therapeutic strategy and as such, is expected to provide in the incoming years significant benefits for ovarian cancer treatment as well. Here, we provide a detailed survey on the highly pleiotropic oncosuppressive roles played by the human RNASET2 gene, whose protein product has been consistently reported to establish a functional crosstalk between ovarian cancer cells and key cellular effectors of the innate immune system (the monocyte/macrophages lineage), which is in turn able to promote the recruitment to the cancer tissue of M1-polarized, antitumoral macrophages. This feature, coupled with the ability of T2 ribonucleases to negatively affect several cancer-related parameters in a cell-autonomous manner on a wide range of ovarian cancer experimental models, makes human RNASET2 a very promising candidate to develop a "multitasking" therapeutic approach for innovative future applications for ovarian cancer treatment.

High GILT Expression Is Associated with Improved Survival in Metastatic Melanoma Patients Treated with Immune Checkpoint Inhibition

Simple Summary

Skin cancer is the most common type of cancer, with melanoma being among the deadliest of skin cancers due to its propensity to metastasize. Immune checkpoint inhibitors (ICI) generate anti-tumor immune responses resulting in improved outcomes in patients with metastatic melanoma. However, only a subset of melanoma patients responds to these therapies, which are costly and come with a risk of adverse effects. Therefore, there is a need for biomarkers to predict which patients will respond to ICI. We found that ICI-treated metastatic melanoma patients with high GILT mRNA expression in bulk tumor samples had improved survival. Additionally, high GILT protein expression within metastatic melanoma cells was associated with improved survival in patients treated with ICI. This study suggests that GILT may serve as a biomarker to predict which patients will respond to ICI, which could improve patient care, reduce healthcare costs, and facilitate appropriate selection of therapies for patients with metastatic melanoma.

Abstract

Gamma-interferon-inducible lysosomal thiol reductase (GILT) is critical for MHC class II restricted presentation of multiple melanoma antigens. There is variable GILT protein expression in malignant melanocytes in melanoma specimens. High GILT mRNA expression in melanoma specimens is associated with improved overall survival, before the advent of immune checkpoint inhibitors (ICI). However, the association of GILT in metastatic melanoma with survival in patients treated with ICI and the cell type expressing GILT associated with survival have not been determined. Using RNA sequencing datasets, high GILT mRNA expression in metastatic melanoma specimens was associated with improved progression-free and overall survival in patients treated with ICI. A clinical dataset of metastatic melanoma specimens was generated and annotated with clinical information. Positive GILT immunohistochemical staining in antigen presenting cells and melanoma cells was observed in 100% and 65% of metastatic melanoma specimens, respectively. In the subset of patients treated with ICI in the clinical dataset, high GILT protein expression within melanoma cells was associated with improved overall survival. The association of GILT mRNA and protein expression with survival was independent of cancer stage. These studies support that high GILT mRNA expression in bulk tumor samples and high GILT protein expression in melanoma cells is associated with improved survival in ICI-treated patients. These findings support further investigation of GILT as a biomarker to predict the response to ICI.

Targeting the MHC Class II antigen presentation pathway in cancer immunotherapy

The success of immunotherapy relies on the participation of all arms of the immune system and the role of CD4+ T lymphocytes in preventing tumor growth is now well established. Understanding how tumors evade immune responses holds the key to the development of cancer immunotherapies. In this review, we discuss how MHC Class II expression varies in cancer cells and how this influences antitumor immune responses. We also discuss the means that are currently available for harnessing the MHC Class II antigen presentation pathway for the development of efficient vaccines to activate the immune system against cancer.

CIITA-Transduced Glioblastoma Cells Uncover a Rich Repertoire of Clinically Relevant Tumor-Associated HLA-II Antigens

CD4+ T cell responses are crucial for inducing and maintaining effective anticancer immunity, and the identification of human leukocyte antigen class II (HLA-II) cancer-specific epitopes is key to the development of potent cancer immunotherapies. In many tumor types, and especially in glioblastoma (GBM), HLA-II complexes are hardly ever naturally expressed. Hence, little is known about immunogenic HLA-II epitopes in GBM. With stable expression of the class II major histocompatibility complex transactivator (CIITA) coupled to a detailed and sensitive mass spectrometry-based immunopeptidomics analysis, we here uncovered a remarkable breadth of the HLA-ligandome in HROG02, HROG17, and RA GBM cell lines. The effect of CIITA expression on the induction of the HLA-II presentation machinery was striking in each of the three cell lines, and it was significantly higher compared with interferon gamma (IFNɣ) treatment. In total, we identified 16,123 unique HLA-I peptides and 32,690 unique HLA-II peptides. In order to genuinely define the identified peptides as true HLA ligands, we carefully characterized their association with the different HLA allotypes. In addition, we identified 138 and 279 HLA-I and HLA-II ligands, respectively, most of which are novel in GBM, derived from known GBM-associated tumor antigens that have been used as source proteins for a variety of GBM vaccines. Our data further indicate that CIITA-expressing GBM cells acquired an antigen presenting cell-like phenotype as we found that they directly present external proteins as HLA-II ligands. Not only that CIITA-expressing GBM cells are attractive models for antigen discovery endeavors, but also such engineered cells have great therapeutic potential through massive presentation of a diverse antigenic repertoire.

Unveiling the Hidden Treasury: CIITA-Driven MHC Class II Expression in Tumor Cells to Dig up the Relevant Repertoire of Tumor Antigens for Optimal Stimulation of Tumor Specific CD4+ T Helper Cells

Despite the recent enthusiasm generated by novel immunotherapeutic approaches against cancer based on immune checkpoint inhibitors, it becomes increasingly clear that single immune-based strategies are not sufficient to defeat the various forms and types of tumors. Within this frame, novel vaccination strategies that are based on optimal stimulation of the key cell governing adaptive immunity, the CD4+ T helper cell, will certainly help in constructing more efficient treatments. In this review, we will focus on this aspect, mainly describing our past and recent contributions that, starting with a rather unorthodox approach, have ended up with the proposition of a new idea for making available an unprecedented extended repertoire of tumor antigens, both in quantitative and qualitative terms, to tumor-specific CD4+ T helper cells. Our approach is based on rendering the very same tumor cells antigen presenting cells for their own tumor antigens by gene transfer of CIITA, the major transcriptional coordinator of MHC class II expression discovered in our laboratory. CIITA-driven MHC class II-expressing tumor cells optimally stimulate in vivo tumor specific MHC class II-restricted CD4 T cells generating specific and long lasting protective immunity against the tumor. We will discuss the mechanism underlying protection and elaborate not only on the applicability of this approach for novel vaccination strategies amenable to clinical setting, but also on the consequence of our discoveries on sedimented immunological dogmas that are related to antigen presentation.

CIITA-Driven MHC Class II Expressing Tumor Cells as Antigen Presenting Cell Performers: Toward the Construction of an Optimal Anti-tumor Vaccine

Construction of an optimal vaccine against tumors relies on the availability of appropriate tumor-specific antigens capable to stimulate CD4+ T helper cells (TH) and CD8+ cytolytic T cells (CTL). CTL are considered the major effectors of the anti-tumor adaptive immune response as they recognize antigens presented on MHC class I (MHC-I) molecules usually expressed in all cells and thus also in tumors. However, attempts to translate in clinics vaccination protocols based only on tumor-specific MHC-I-bound peptides have resulted in very limited, if any, success. We believe failure was mostly due to inadequate triggering of the TH arm of adaptive immunity, as TH cells are necessary to trigger and maintain the proliferation of all the immune effector cells required to eliminate tumor cells. In this review, we focus on a novel strategy of anti-tumor vaccination established in our laboratory and based on the persistent expression of MHC class II (MHC-II) molecules in tumor cells. MHC-II are the restricting elements of TH recognition. They are usually not expressed in solid tumors. By genetically modifying tumor cells of distinct histological origin with the MHC-II transactivator CIITA, the physiological controller of MHC-II gene expression discovered in our laboratory, stable expression of all MHC class II genes was obtained. This resulted in tumor rejection or strong retardation of tumor growth in vivo in mice, mediated primarily by tumor-specific TH cells as assessed by both depletion and adoptive cell transfer experiments. Importantly these findings led us to apply this methodology to human settings for the purification of MHC-II-bound tumor specific peptides directly from tumor cells, specifically from hepatocarcinomas, and the construction of a multi-peptide (MHC-II and MHC-I specific) immunotherapeutic vaccine. Additionally, our approach unveiled a noticeable exception to the dogma that dendritic cells are the sole professional antigen presenting cells (APC) capable to prime naïve TH cells, because CIITA-dependent MHC-II expressing tumor cells could also perform this function. Thus, our approach has served not only to select the most appropriate tumor specific peptides to activate the key lymphocytes triggering the anti-tumor effector functions but also to increase our knowledge of intimate mechanisms governing basic immunological processes.

A Multigene Assay Determines Risk of Recurrence in Patients with Triple-Negative Breast Cancer

Approximately 40% of patients with stage I-III triple-negative breast cancer (TNBC) recur after standard treatment, whereas the remaining 60% experience long-term disease-free survival (DFS). There are currently no clinical tests to assess the risk of recurrence in TNBC patients. We previously determined that TNBC patients with MHC class II (MHCII) pathway expression in their tumors experienced significantly longer DFS. To translate this discovery into a clinical test, we developed an MHCII Immune Activation assay, which measures expression of 36 genes using NanoString technology. Preanalytical testing confirmed that the assay is accurate and reproducible in formalin-fixed paraffin-embedded (FFPE) tumor specimens. The assay measurements were concordant with RNA-seq, MHCII protein expression, and tumor-infiltrating lymphocyte counts. In a training set of 44 primary TNBC tumors, the MHCII Immune Activation Score was significantly associated with longer DFS (HR = 0.17; P = 0.015). In an independent validation cohort of 56 primary FFPE TNBC tumors, the Immune Activation Score was significantly associated with longer DFS (HR = 0.19; P = 0.011) independent of clinical stage. An Immune Activation Score threshold for identifying patients with very low risk of relapse in the training set provided 100% specificity in the validation cohort. The assay format enables adoption as a standardized clinical prognostic test for identifying TNBC patients with a low risk of recurrence. Correlative data support future studies to determine if the assay can identify patients in whom chemotherapy can be safely deescalated and patients likely to respond to immunotherapy. SIGNIFICANCE: The MHCII Immune Activation assay identifies TNBC patients with a low risk of recurrence, addressing a critical need for prognostic biomarker tests that enable precision medicine for TNBC patients.

Biological Consequences of MHC-II Expression by Tumor Cells in Cancer

Immunotherapy has emerged as a key pillar of cancer treatment. To build upon the recent successes of immunotherapy, intense research efforts are aimed at a molecular understanding of antitumor immune responses, identification of biomarkers of immunotherapy response and resistance, and novel strategies to circumvent resistance. These studies are revealing new insight into the intricacies of tumor cell recognition by the immune system, in large part through MHCs. Although tumor cells widely express MHC-I, a subset of tumors originating from a variety of tissues also express MHC-II, an antigen-presenting complex traditionally associated with professional antigen-presenting cells. MHC-II is critical for antigen presentation to CD4+ T lymphocytes, whose role in antitumor immunity is becoming increasingly appreciated. Accumulating evidence demonstrates that tumor-specific MHC-II associates with favorable outcomes in patients with cancer, including those treated with immunotherapies, and with tumor rejection in murine models. Herein, we will review current research regarding tumor-enriched MHC-II expression and regulation in a range of human tumors and murine models, and the possible therapeutic applications of tumor-specific MHC-II.

CIITA-related block of HLA class II expression, upregulation of HLA class I, and heterogeneous expression of immune checkpoints in hepatocarcinomas: implications for new therapeutic approaches

Hepatocellular carcinoma (HCC) is the second cause of death for cancer worldwide, justifying the urgent need for novel therapeutic approaches. Immunotherapeutic strategies based on triggering and/or rescuing tumor antigen-specific T cells may be promising particularly if combined together. As preliminary step toward this goal, we have investigated the expression of antigen presenting molecules (HLA class I and class II) and immune checkpoints (PD-1 and PD-L1) in 43 HCC samples from distinct patients and in HCC cell lines. While normal hepatocytes did not express HLA class I and II, HCC cells strongly upregulated HLA class I while remaining negative for HLA class II. The absence of HLA class II expression in HCC cell lines correlated with lack of expression of the HLA class II transactivator, CIITA, which could not be rescued even after interferon-gamma treatment. This was due to high methylation levels of interferon-gamma-sensitive CIITA promoter IV strongly suggesting a biologically relevant developmental silencing of HLA-II expression in liver cell lineage. HCC tumor tissues showed a variable degree of leukocyte infiltration. Infiltrating lymphocytes expressed PD-1, while PD-L1 was expressed in cells with monocyte-macrophage morphology mostly localized at the tumor margin, but not in tumor cells. De novo expression of HLA class I, instrumental for presenting tumor antigens to cytotoxic T lymphocytes, and the correct characterization of the cells expressing checkpoint inhibitors in the tumor tissue should be the ground for setting novel strategies of combined approaches of immunotherapy in HCC based on tumor peptide vaccines and anti-checkpoint inhibitor antibodies.

Fowlpoxvirus recombinants coding for the CIITA gene increase the expression of endogenous MHC-II and Fowlpox Gag/Pro and Env SIV transgenes

A complete eradication of an HIV infection has never been achieved by vaccination and the search for new immunogens that can induce long-lasting protective responses is ongoing. Avipoxvirus recombinants are host-restricted for replication to avian species and they do not have the undesired side effects induced by vaccinia recombinants. In particular, Fowlpox (FP) recombinants can express transgenes over long periods and can induce protective immunity in mammals, mainly due to CD4-dependent CD8⁺ T cells. In this context, the class II transactivator (CIITA) has a pivotal role in triggering the adaptive immune response through induction of the expression of class-II major histocompatibility complex molecule (MHC-II), that can present antigens to CD4⁺ T helper cells. Here, we report on construction of novel FPgp and FPenv recombinants that express the highly immunogenic SIV Gag-pro and Env structural antigens. Several FP-based recombinants, with single or dual genes, were also developed that express CIITA, driven from H6 or SP promoters. These recombinants were used to infect CEF and Vero cells in vitro and determine transgene expression, which was evaluated by real-time PCR and Western blotting. Subcellular localisation of the different proteins was evaluated by confocal microscopy, whereas HLA-DR or MHC-II expression was measured by flow cytometry. Fowlpox recombinants were also used to infect syngeneic T/SA tumour cells, then injected into Balb/c mice to elicit MHC-II immune response and define the presentation of the SIV transgene products in the presence or absence of FPCIITA. Antibodies to Env were measured by ELISA. Our data show that the H6 promoter was more efficient than SP to drive CIITA expression and that CIITA can enhance the levels of the gag/pro and env gene products only when infection is performed by FP single recombinants. Also, CIITA expression is higher when carried by FP single recombinants than when combined with FPgp or FPenv constructs and can induce HLA-DR cell surface expression. However, in-vivo experiments did not show any significant increase in the humoral response. As CIITA already proved to elicit immunogenicity by improving antigen presentation, further in-vivo experiments should be performed to increase the immune responses. The use of prime/boost immunisation protocols and the oral administration route of the recombinants may enhance the immunogenicity of Env peptides presented by MHC-II and provide CD4⁺ T-cell stimulation.

Tumor Immunology meets…Immunology: Modified cancer cells as professional APC for priming naïve tumor-specific CD4+ T cells

Although recent therapeutic approaches have revitalized the enthusiasm of the immunological way to combat cancer, still the comprehension of immunity against tumors is largely incomplete. Due to their specific function, CD8+ T cells with cytolytic activity (CTL) have attracted the attention of most investigators because CTL are considered the main effectors against tumor cells. Nevertheless, CTL activity and persistence is largely dependent on the action of CD4+ T helper cells (TH). Thus establishment of tumor-specific TH cell response is key to the optimal response against cancer. Here we describe emerging new strategies to increase the TH cell recognition of tumor antigens. In particular, we review recent data indicating that tumor cells themselves can act as surrogate antigen presenting cells for triggering TH response and how these findings can help in constructing immunotherapeutic protocols for anti-cancer vaccine development.

Development of potent class II transactivator gene delivery systems capable of inducing de novo MHC II expression in human cells, in vitro and ex vivo

Class II transactivator (CIITA) induces transcription of major histocompatibility complex (MHC) II genes and can potentially be used to improve genetic immunotherapies by converting non-immune cells into cells capable of presenting antigens to CD4⁺ T cells. However, CIITA expression is tightly controlled and it remains unclear whether distinct non-immune cells differ in this transactivator regulation. Here we describe the development of gene delivery systems capable of promoting the efficient CIITA expression in non-immune cell lines and in primary human cells of an ex vivo skin explant model. Different human cell types undergoing CIITA overexpression presented high-level de novo expression of MHC II, validating the delivery systems as suitable tools for the CIITA evaluation as a molecular adjuvant for gene therapies.

CIITA-driven MHC class II expressing tumor cells can efficiently prime naive CD4+ TH cells in vivo and vaccinate the host against parental MHC-II-negative tumor cells

Our previous studies showed that non-immunogenic H-2^d tumor cells of distinct epithelial histotypes can become highly immunogenic, induce a protective CD4⁺ T cell response and vaccinate the animals against parental MHC-II-negative cells if they are rendered MHC class II-positive by stable transfection with the Air-1-encoded MHC-II transcriptional activator CIITA. These studies did not establish, however, whether tumor immunity was the consequence of a direct priming of naive CD4⁺ T lymphocytes by CIITA-driven MHC-II-expressing tumor cells or by MHC-II-tumor antigen complexes engulfed by dendritic cells (DC) and exposed on the surface of these professional antigen presenting cells (APC). In the present investigation, we provide definitive evidence that CIITA-tumor cells are the crucial APC in vivo for CD4⁺ T cell priming. By using a transgenic H-2^b mouse model, the CD11c.DTR C57BL/6 mice, in which DC can be functionally deleted by administration of diphteria toxin, we show that CIITA-tumor cells of two distinct histotypes can be rejected or strongly retarded in their growth in DC-deleted mice. To rule out that in absence of DC, other professional APC could prime naive CD4⁺ T cells, we deleted the macrophages in CD11c.DTR C57BL/6 mice by administration of liposome Clodronate and still obtained rejection or strong retardation in tumor growth of CIITA-tumor cells. Our results challenge the diffuse belief that non-professional APC cannot efficiently prime naive T cells in vivo. Moreover, the demonstration of the general validity of our approach in different genetic backgrounds may open a way for new strategies of antitumor treatment in clinical settings.

Class II transactivator-induced MHC class II expression in pancreatic cancer cells leads to tumor rejection and a specific antitumor memory response

OBJECTIVES

The loss of major histocompatibility complex (MHC) classes I and II is a well-known mechanism by which cancer cells are able to escape from immune recognition. In this study, we analyzed the expression of antigen processing and presenting molecules in 2 cell lines derived from mouse models of pancreatic ductal adenocarcinoma (PDA) and the effects of the re-expression of MHC class II on PDA rejection.

METHODS

The PDA cell lines were analyzed for the expression of MHC class I, II, and antigen-processing molecules by flow cytometry or polymerase chain reaction. We generated stable PDA-MHC class II transactivator (CIITA) cells and injected them into syngeneic mice. The CD4 and CD8 T-cell role was analyzed in vitro and in vivo.

RESULTS

Murine PDA cell lines were negative for MHC and antigen-processing molecules, but their expression was restored by exogenous interferon-γ. CIITA-tumor cells were rejected in 80% to 100% of injected mice, which also developed long-lasting immune memory. In vitro assays and immunohistochemical analyses revealed the recruitment of T effector cells and CD8 T cells into the tumor area.

CONCLUSIONS

Overall, these data confirm that immunotherapy is a feasible therapeutic approach to recognize and target an aggressive cancer such as PDA.

Exosomes from CIITA-transfected CT26 cells enhance anti- tumor effects

AIM

To study anti-tumor effects of exosomes from class II transactivator (CIITA) gene transfected CT26 cells.

METHODS

In this study, we established an MHC class II molecule-expressing murine colon cancer cell line (CT26-CIITA) by transduction of the CIITA gene. Immune effects in vitro and tumor protective results in vivo were tested and monitored.

RESULTS

Exosomes from CT26-CIITA cells were found to contain a high level of MHC class II protein. When loaded on dendritic cells (DCs), exosomes from CT26-CIITA cells significantly increased expression of MHC class II molecules, CD86 and CD80, as compared to exosomes from CT26 cells. In vitro assays using co-culture of immunized splenocytes and exosome-loaded DCs demonstrated that CIITA- Exo enhanced splenocyte proliferation and IFN-γ production of CD4+T cells, while inhibiting IL-10 secretion. In addition, compared to exosomes from CT26 cells, CT26-CIITA-derived exosomes induced higher TNF-α and IL-12 mRNA levels. A mouse tumour preventive model showed that CT26-CIITA derived exosomes significantly inhibited tumour growth in a dose-dependent manner and significantly prolonged the survival time of tumour- bearing mice.

CONCLUSION

Our findings indicate that CT26-CIITA-released exosomes are more efficient to induce anti-tumour immune responses, suggesting a potential role of MHC class II-containing tumour exosomes as cancer vaccine candidates.

Boosting the MHC Class II-Restricted Tumor Antigen Presentation to CD4+ T Helper Cells: A Critical Issue for Triggering Protective Immunity and Re-Orienting the Tumor Microenvironment Toward an Anti-Tumor State

Although the existence of an immune response against tumor cells is well documented, the fact that tumors take off in cancer patients indicates that neoplastic cells can circumvent this response. Over the years many investigators have described strategies to rescue the anti-tumor immune response with the aim of creating specific and long-lasting protection against the disease. When exported to human clinical settings, these strategies have revealed in most cases a very limited, if any, positive outcome. We believe that the failure is mostly due to the inadequate triggering of the CD4+ T helper (TH) cell arm of the adaptive immunity, as TH cells are necessary to trigger all the immune effector mechanisms required to eliminate tumor cells. In this review, we focus on novel strategies that by stimulating MHC class II-restricted activation of TH cells generate a specific and persistent adaptive immunity against the tumor. This point is of critical importance for both preventive and therapeutic anti-tumor vaccination protocols, because adaptive immunity with its capacity to produce specific, long-lasting protection and memory responses is indeed the final goal of vaccination. We will discuss data from our as well as other laboratories which strongly suggest that triggering a specific and persistent anti-tumor CD4+ TH cell response stably modify not only the tumor microenvironment but also tumor-dependent extratumor microenvironments by eliminating and/or reducing the blood-derived tumor infiltrating cells that may have a pro-tumor growth function such as regulatory CD4+/CD25+ T cells and myeloid-derived-suppressor cells. Within this frame, therefore, we believe that the establishment of a pro-tumor environment is not the cause but simply the consequence of the tumor strategy to primarily counteract components of the adaptive cellular immunity, particularly TH lymphocytes.

Adequate antigen availability: a key issue for novel approaches to tumor vaccination and tumor immunotherapy

A crucial parameter for activation of the anti-tumor immune response is an adequate antigen availability (AAA) defined here as the optimal tumor antigen dose and related antigen processing and MHC-II-restricted presentation necessary to efficiently trigger tumor-specific TH cells. We will discuss two distinct experimental systems: a) a preventive anti-tumor vaccination system; b) a therapy-induced anti-tumor vaccination approach. In the first case tumor cells are rendered constitutively MHC-II+ by transfecting them with the MHC-II transcriptional activator CIITA. Here AAA is generated by the function of tumor's newly expressed MHC-II molecules to present tumor-associated antigens to tumor-specific TH cells. In the second case, AAA is generated by treating established tumors with neovasculature-targeted TNFα. In conjuction with Melphalan, targeted TNFα delivery produces extensive areas of tumor necrosis that generate AAA capable of optimally activate tumor-specific TH cells which in turn activate CTL immune effectors. In both experimental systems tumor rejection and persistent and long-lived TH cell anti-tumor memory, responsible of defending the animals from subsequent challenges with tumor cells, are achieved. Based on these and other investigators' results we propose that AAA is a key element for triggering adaptive immune functions resulting in subversion from a pro-tumor to an anti-tumor microenvironment, tumor rejection and acquisition of anti-tumor immune memory. Hypotheses of neuro-immune networks involved in these approaches are discussed. These considerations are important also for the comprehension of how chemotherapy and/or radiation therapies may help to block and/or to eradicate the tumor and for the construction of suitable anti-tumor vaccine strategies.

The pharmacologic inhibition of the xc- antioxidant system improves the antitumor efficacy of COX inhibitors in the in vivo model of 3-MCA tumorigenesis

The chemopreventive and therapeutic efficacy of the cyclooxygenase (COX) inhibitor ibuprofen (IB) and of sulfasalazine (SASP), a drug that targets the antioxidant xc- system, were exploited in the experimental model of 3-methylcholantrene (3-MCA)-induced mouse sarcoma. The chemopreventive treatments gave unsatisfactory results because administration of IB one day after the 3-MCA injection only slightly delayed the tumor development, whereas SASP dispensed under the same conditions resulted in accelerated tumorigenesis. Similarly, the therapeutic treatment with either drug, administrated daily from the tumor detection, decreased the proliferation rate of tumor cells and increased the survival of treated mice only at a low extent. Remarkably, the combined chemopreventive treatment with IB and therapeutic treatment with SASP displayed a better efficacy, with strong delay of sarcoma growth, reduced tumor size and increased survival of treated mice. The two drugs target not only tumor cells but also tumor-associated macrophages that were dramatically decreased in the tumor infiltrate of mice subjected to the combined treatment. The synergistic effects of the association between a broad anti-inflammatory compound, such as IB, and a redox-directed drug, such as SASP, shed new light in the role of inflammation and of the redox response in chemical tumorigenesis and point to the combined chemopreventive plus therapeutic treatment with IB and SASP as a promising novel approach for antitumor therapy.

Optimal MHC-II-restricted tumor antigen presentation to CD4+ T helper cells: the key issue for development of anti-tumor vaccines

Present immunoprevention and immunotherapeutic approaches against cancer suffer from the limitation of being not “sterilizing” procedures, as very poor protection against the tumor is obtained. Thus newly conceived anti-tumor vaccination strategies are urgently needed. In this review we will focus on ways to provide optimal MHC class II-restricted tumor antigen presentation to CD4+ T helper cells as a crucial parameter to get optimal and protective adaptive immune response against tumor. Through the description of successful preventive or therapeutic experimental approaches to vaccinate the host against the tumor we will show that optimal activation of MHC class II-restricted tumor specific CD4+ T helper cells can be achieved in various ways. Interestingly, the success in tumor eradication and/or growth arrest generated by classical therapies such as radiotherapy and chemotherapy in some instances can be re-interpreted on the basis of an adaptive immune response induced by providing suitable access of tumor-associated antigens to MHC class II molecules. Therefore, focussing on strategies to generate better and suitable MHC class II–restricted activation of tumor specific CD4+ T helper cells may have an important impact on fighting and defeating cancer.

T cells and adoptive immunotherapy: recent developments and future prospects in gastrointestinal oncology

Gastrointestinal oncology is one of the foremost causes of death: the gastric cancer accounts for 10.4% of cancer deaths worldwide, the pancreatic cancer for 6%, and finally, the colorectal cancer for 9% of all cancer-related deaths. For all these gastrointestinal cancers, surgical tumor resection remains the primary curative treatment, but the overall 5-year survival rate remains poor, ranging between 20-25%; the addition of combined modality strategies (pre- or postoperative chemoradiotherapy or perioperative chemotherapy) results in 5-year survival rates of only 30-35%. Therefore, many investigators believe that the potential for making significant progress lies on understanding and exploiting the molecular biology of gastrointestinal tumors to investigate new therapeutic strategies such as specific immunotherapy. In this paper we will focus on recent knowledge concerning the role of T cells and the use of T adoptive immunotherapy in the treatment of gastrointestinal cancers.

New strategies of mammary cancer vaccination

A new strategy of vaccination against mammary tumors, extendible to tumors of distinct histological origin, based on the administration of tumor cells genetically modified to express major histocompatibility complex (MHC) class II gene products, will be described. Expression of MHC class II molecules in solid tumors, generally lacking these molecules, is achieved by transfecting tumor cells with the MHC class II transactivator (CIITA), the major regulator of the entire family of MHC class II genes. CIITA is encoded by the AIR-1 locus, discovered in our laboratory. The rationale underlying this approach consists in making the tumor cells a sort of surrogate antigen presenting cells for MHC-II-restricted CD4 + T helper (TH) cells. Indeed, it is known that an efficient adaptive immune response against cancer cells can only be achieved if tumor-specific TH cells, the key lymphocyte subpopulation required to trigger both humoral and cellular effector mechanisms, are optimally stimulated. Results from our group show that: (a) CIITA-modified tumor cells can be rejected in vivo by syngeneic immunocompetent mice; (b) this rejection is mediated primarily by CD4 + TH lymphocytes that activate cytolytic CD8 + T cell effectors ; (c) tumor-rejecting mice are resistant to challenge with parental unmodified tumor cells and display long term immune memory; (d) anti-tumor vaccination can be reproduced by using inactivated, nonreplicating CIITA-transfected tumor cells; (e) immune effectors and particularly primed CD4 + TH cells can be used successfully in approaches of immunotherapy of established tumors. These results open the way to envisage a possible use of CIITA-modified mammary tumor cells as a vaccine for increasing both the inducing and the effector phase of the anti-tumor immune response in human settings.