Screening of human tumor antigens for CD4 T cell epitopes by combination of HLA-transgenic mice, recombinant adenovirus and antigen peptide libraries

Activated T cell therapy targeting glioblastoma cancer stem cells

Naïve T cells become effector T cells following stimulation by antigen-loaded dendritic cells (DCs) and sequential cytokine activation. We aimed to develop procedures to efficiently activate T cells with tumor-associated antigens (TAAs) to glioblastoma (GBM) stem cells. To remove antigen presentation outside of the immunosuppressive tumor milieu, three different glioma stem cell (GSC) specific antigen sources to load DCs were compared in their ability to stimulate lymphocytes. An activated T cell (ATC) protocol including cytokine activation and expansion in culture to target GSCs was generated and optimized for a planned phase I clinical trial. We compared three different antigen-loading methods on DCs to effectively activate T cells, which were GBM patient-derived GSC-lysate, acid-eluate of GSCs and synthetic peptides derived from proteins expressed in GSCs. DCs derived from HLA-A2 positive blood sample were loaded with TAAs. Autologous T cells were activated by co-culturing with loaded DCs. Efficiency and cytotoxicity of ATCs were evaluated by targeting TAA-pulsed DCs or T2 cells, GSCs, or autologous PHA-blasts. Characteristics of ATCs were evaluated by Flow Cytometry and ELISpot assay, which showed increased number of ATCs secreting IFN-γ targeting GSCs as compared with non-activated T cells and unloaded target cells. Neither GSC-lysate nor acid-eluate loading showed enhancement in response of ATCs but the synthetic peptide pool showed significantly increased IFN-γ secretion and increased cytotoxicity towards target cells. These results demonstrate that ATCs activated using a TAA synthetic peptide pool efficiently enhance cytotoxicity specifically to target cells including GSC.

Therapeutic Cancer Vaccines—Antigen Discovery and Adjuvant Delivery Platforms

For decades, vaccines have played a significant role in protecting public and personal health against infectious diseases and proved their great potential in battling cancers as well. This review focused on the current progress of therapeutic subunit vaccines for cancer immunotherapy. Antigens and adjuvants are key components of vaccine formulations. We summarized several classes of tumor antigens and bioinformatic approaches of identification of tumor neoantigens. Pattern recognition receptor (PRR)-targeting adjuvants and their targeted delivery platforms have been extensively discussed. In addition, we emphasized the interplay between multiple adjuvants and their combined delivery for cancer immunotherapy.

Identification of a novel PD-L1 positive solid tumor transplantable in HLA-A*0201/DRB1*0101 transgenic mice

HLA-A*0201/DRB1*0101 transgenic mice (A2/DR1 mice) have been developed to study the immunogenicity of tumor antigen-derived T cell epitopes. To extend the use and application of this mouse model in the field of antitumor immunotherapy, we described a tumor cell line generated from a naturally occurring tumor in A2/DR1 mouse named SARC-L1. Histological and genes signature analysis supported the sarcoma origin of this cell line. While SARC-L1 tumor cells lack HLA-DRB1*0101 expression, a very low expression of HLA-A*0201 molecules was found on these cells. Furthermore they also weakly but constitutively expressed the programmed death-ligand 1 (PD-L1). Interestingly both HLA-A*0201 and PD-L1 expressions can be increased on SARC-L1 after IFN-γ exposure in vitro. We also obtained two genetically modified cell lines highly expressing either HLA-A*0201 or both HLA-A*0201/ HLA-DRB1*0101 molecules referred as SARC-A2 and SARC-A2DR1 respectively. All the SARC-L1-derived cell lines induced aggressive subcutaneous tumors in A2DR1 mice in vivo. The analysis of SARC-L1 tumor microenvironment revealed a strong infiltration by T cells expressing inhibitory receptors such as PD-1 and TIM-3. Finally, we found that SARC-L1 is sensitive to several drugs commonly used to treat sarcoma and also susceptible to anti-PD-L1 monoclonal antibody therapy in vivo. Collectively, we described a novel syngeneic tumor model A2/DR1 mice that could be used as preclinical tool for the evaluation of antitumor immunotherapies.

Generation of murine tumor cell lines deficient in MHC molecule surface expression using the CRISPR/Cas9 system

In this study, the CRISPR/Cas9 technology was used to establish murine tumor cell lines, devoid of MHC I or MHC II surface expression, respectively. The melanoma cell line B16F10 and the murine breast cancer cell line EO-771, the latter stably expressing the tumor antigen NY-BR-1 (EO-NY), were transfected with an expression plasmid encoding a β₂m-specific single guide (sg)RNA and Cas9. The resulting MHC I negative cells were sorted by flow cytometry to obtain single cell clones, and loss of susceptibility of peptide pulsed MHC I negative clones to peptide-specific CTL recognition was determined by IFNγ ELISpot assay. The β₂m knockout (KO) clones did not give rise to tumors in syngeneic mice (C57BL/6N), unless NK cells were depleted, suggesting that outgrowth of the β₂m KO cell lines was controlled by NK cells. Using sgRNAs targeting the β-chain encoding locus of the IA^b molecule we also generated several B16F10 MHC II KO clones. Peptide loaded B16F10 MHC II KO cells were insusceptible to recognition by OT-II cells and tumor growth was unaltered compared to parental B16F10 cells. Thus, in our hands the CRISPR/Cas9 system has proven to be an efficient straight forward strategy for the generation of MHC knockout cell lines. Such cell lines could serve as parental cells for co-transfection of compatible HLA alleles together with human tumor antigens of interest, thereby facilitating the generation of HLA matched transplantable tumor models, e.g. in HLAtg mouse strains of the newer generation, lacking cell surface expression of endogenous H2 molecules. In addition, our tumor cell lines established might offer a useful tool to investigate tumor reactive T cell responses that function independently from MHC molecule surface expression by the tumor.

Improvement of Peptide-Based Tumor Immunotherapy Using pH-Sensitive Fusogenic Polymer-Modified Liposomes

To establish peptide vaccine-based cancer immunotherapy, we investigated the improvement of antigenic peptides by encapsulation with pH-sensitive fusogenic polymer-modified liposomes for induction of antigen-specific immunity. The liposomes were prepared by modification of egg yolk phosphatidylcholine and l-dioleoyl phosphatidylethanolamine with 3-methyl-glutarylated hyperbranched poly(glycidol) (MGlu-HPG) and were loaded with antigenic peptides derived from ovalbumin (OVA) OVA-I (SIINFEKL), and OVA-II (PSISQAVHAAHAEINEAP_βA), which bind, respectively, to major histocompatibility complex (MHC) class I and class II molecules on dendritic cell (DCs). The peptide-loaded liposomes were taken up efficiently by DCs. The peptides were delivered into their cytosol. Administration of OVA-I-loaded MGlu-HPG-modified liposomes to mice bearing OVA-expressing E.G7-OVA tumors induced the activation of OVA-specific CTLs much more efficiently than the administration of free OVA-I peptide did. Mice strongly rejected E.G7-OVA cells after immunization with OVA-I peptide-loaded MGlu-HPG liposomes, although mice treated with free OVA-I peptide only slightly rejected the cells. Furthermore, efficient suppression of tumor volume was observed when tumor-bearing mice were immunized with OVA-I-peptide-loaded liposomes. Immunization with OVA-II-loaded MGlu-HPG-modified liposomes exhibited much lower tumor-suppressive effects. Results indicate that MGlu-HPG liposomes might be useful for improvement of CTL-inducing peptides for efficient cancer immunotherapy.

Drafting the proteome landscape of myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of cells that are defined by their myeloid origin, immature state, and ability to potently suppress T-cell responses. They regulate immune responses and the population significantly increases in the tumor microenvironment of patients with glioma and other malignant tumors. For their study, MDSCs are usually isolated from the spleen or directly of tumors from a large number of tumor-bearing mice although promising ex vivo differentiated MDSC production systems have been recently developed. During the last years, proteomics has emerged as a powerful approach to analyze MDSCs proteomes using shotgun-based mass spectrometry (MS), providing functional information about cellular homeostasis and metabolic state at a global level. Here, we will revise recent proteome profiling studies performed in MDSCs from different origins. Moreover, we will perform an integrative functional analysis of the protein compilation derived from these large-scale proteomic studies in order to obtain a comprehensive view of MDSCs biology. Finally, we will also discuss the potential application of high-throughput proteomic approaches to study global proteome dynamics and post-translational modifications (PTMs) during the differentiation process of MDSCs that will greatly boost the identification of novel MDSC-specific therapeutic targets to apply in cancer immunotherapy.

Identification of NY-BR-1-specific CD4(+) T cell epitopes using HLA-transgenic mice

Breast cancer represents the second most common cancer type worldwide and has remained the leading cause of cancer-related deaths among women. The differentiation antigen NY-BR-1 appears overexpressed in invasive mammary carcinomas compared to healthy breast tissue, thus representing a promising target antigen for T cell based tumor immunotherapy approaches. Since efficient immune attack of tumors depends on the activity of tumor antigen-specific CD4(+) effector T cells, NY-BR-1 was screened for the presence of HLA-restricted CD4(+) T cell epitopes that could be included in immunological treatment approaches. Upon NY-BR-1-specific DNA immunization of HLA-transgenic mice and functional ex vivo analysis, a panel of NY-BR-1-derived library peptides was determined that specifically stimulated IFNγ secretion among splenocytes of immunized mice. Following in silico analyses, four candidate epitopes were determined which were successfully used for peptide immunization to establish NY-BR-1-specific, HLA-DRB1*0301- or HLA-DRB1*0401-restricted CD4(+) T cell lines from splenocytes of peptide immunized HLA-transgenic mice. Notably, all four CD4(+) T cell lines recognized human HLA-DR-matched dendritic cells (DC) pulsed with lysates of NY-BR-1 expressing human tumor cells, demonstrating natural processing of these epitopes also within the human system. Finally, CD4(+) T cells specific for all four CD4(+) T cell epitopes were detectable among PBMC of breast cancer patients, showing that CD4(+) T cell responses against the new epitopes are not deleted nor inactivated by self-tolerance mechanisms. Our results present the first NY-BR-1-specific HLA-DRB1*0301- and HLA-DRB1*0401-restricted T cell epitopes that could be exploited for therapeutic intervention against breast cancer.

PolyI:C and mouse survivin artificially embedding human 2B peptide induce a CD4+ T cell response to autologous survivin in HLA-A*2402 transgenic mice

CD4(+) T cell effectors are crucial for establishing antitumor immunity. Dendritic cell maturation by immune adjuvants appears to facilitate subset-specific CD4(+) T cell proliferation, but the adjuvant effect for CD4 T on induction of cytotoxic T lymphocytes (CTLs) is largely unknown. Self-antigenic determinants with low avidity are usually CD4 epitopes in mutated proteins with tumor-associated class I-antigens (TAAs). In this study, we made a chimeric version of survivin, a target of human CTLs. The chimeric survivin, where human survivin-2B containing a TAA was embedded in the mouse survivin frame (MmSVN2B), was used to immunize HLA-A-2402/K(b)-transgenic (HLA24(b)-Tg) mice. Subcutaneous administration of MmSVN2B or xenogeneic human survivin (control HsSNV2B) to HLA24(b)-Tg mice failed to induce an immune response without co-administration of an RNA adjuvant polyI:C, which was required for effector induction in vivo. Although HLA-A-2402/K(b) presented the survivin-2B peptide in C57BL/6 mice, 2B-specific tetramer assays showed that no CD8(+) T CTLs specific to survivin-2B proliferated above the detection limit in immunized mice, even with polyI:C treatment. However, the CD4(+) T cell response, as monitored by IFN-γ, was significantly increased in mice given polyI:C+MmSVN2B. The Th1 response and antibody production were enhanced in the mice with polyI:C. The CD4 epitope responsible for effector function was not Hs/MmSNV13-27, a nonconserved region between human and mouse survivin, but region 53-67, which was identical between human and mouse survivin. These results suggest that activated, self-reactive CD4(+) helper T cells proliferate in MmSVN2B+polyI:C immunization and contribute to Th1 polarization followed by antibody production, but hardly participate in CTL induction.

Paradigm Shift in Dendritic Cell-Based Immunotherapy: From in vitro Generated Monocyte-Derived DCs to Naturally Circulating DC Subsets

Dendritic cell (DC)-based immunotherapy employs the patients’ immune system to fight neoplastic lesions spread over the entire body. This makes it an important therapy option for patients suffering from metastatic melanoma, which is often resistant to chemotherapy. However, conventional cellular vaccination approaches, based on monocyte-derived DCs (moDCs), only achieved modest response rates despite continued optimization of various vaccination parameters. In addition, the generation of moDCs requires extensive ex vivo culturing conceivably hampering the immunogenicity of the vaccine. Recent studies, thus, focused on vaccines that make use of primary DCs. Though rare in the blood, these naturally circulating DCs can be readily isolated and activated thereby circumventing lengthy ex vivo culture periods. The first clinical trials not only showed increased survival rates but also the induction of diversified anti-cancer immune responses. Upcoming treatment paradigms aim to include several primary DC subsets in a single vaccine as pre-clinical studies identified synergistic effects between various antigen-presenting cells.

Involvement of HLA class I molecules in the immune escape of urologic tumors

CONTEXT AND OBJECTIVE

To analyze the influence of different alterations in human leukocyte antigen class I molecules (HLA I) in renal cell carcinoma, as well as in bladder and prostate cancer. We also study the correlation between HLA I expression and the progression of the disease and the response after immunotherapy protocols.

EVIDENCES ACQUISITION

It has been shown, experimentally, that the immune system can recognize and kill neoplastic cells. By analyzing the expression of HLA I molecules on the surface of cancer cells, we were able to study the tumor escape mechanisms against the immune system.

EVIDENCES SYNTHESIS

Alteration or irreversible damage in HLA I molecules is used by the neoplastic cells to escape the immune system. The function of these molecules is to recognize endogenous peptides and present them to T cells of the immune system. There is a clear relationship between HLA I reversible alterations and success of therapy. Irreversible lesions also imply a lack of response to treatment. The immune system activation can reverse HLA I molecules expression in tumors with reversible lesions, whereas tumors with irreversible ones do not respond to such activation. Determine the type of altered HLA I molecules in tumors is of paramount importance when choosing the type of treatment to keep looking for therapeutic success. Those tumors with reversible lesions can be treated with traditional immunotherapy; however, tumour with irreversible alterations should follow alternative protocols, such as the use of viral vectors carrying the HLA genes to achieve damaged re-expression of the protein.

CONCLUSION

From studies in urologic tumors, we can conclude that the HLA I molecules play a key role in these tumors escape to the immune system.

Tumour immunogenicity, antigen presentation and immunological barriers in cancer immunotherapy

Since the beginning of the 20^th century, scientists have tried to stimulate the anti-tumour activities of the immune system to fight against cancer. However, the scientific effort devoted on the development of cancer immunotherapy has not been translated into the expected clinical success. On the contrary, classical anti-neoplastic treatments such as surgery, radiotherapy and chemotherapy are the first line of treatment. Nevertheless, there is compelling evidence on the immunogenicity of cancer cells, and the capacity of the immune system to expand cancer-specific effector cytotoxic T cells. However, the effective activation of anti-cancer T cell responses strongly depends on efficient tumour antigen presentation from professional antigen presenting cells such as dendritic cells (DCs). Several strategies have been used to boost DC antigen presenting functions, but at the end cancer immunotherapy is not as effective as would be expected according to preclinical models. In this review we comment on these discrepancies, focusing our attention on the contribution of regulatory T cells and myeloid-derived suppressor cells to the lack of therapeutic success of DC-based cancer immunotherapy.

Establishment of HLA-DR4 transgenic mice for the identification of CD4+ T cell epitopes of tumor-associated antigens

Reports have shown that activation of tumor-specific CD4⁺ helper T (Th) cells is crucial for effective anti-tumor immunity and identification of Th-cell epitopes is critical for peptide vaccine-based cancer immunotherapy. Although computer algorithms are available to predict peptides with high binding affinity to a specific HLA class II molecule, the ability of those peptides to induce Th-cell responses must be evaluated. We have established HLA-DR4 (HLA-DRA*01:01/HLA-DRB1*04:05) transgenic mice (Tgm), since this HLA-DR allele is most frequent (13.6%) in Japanese population, to evaluate HLA-DR4-restricted Th-cell responses to tumor-associated antigen (TAA)-derived peptides predicted to bind to HLA-DR4. To avoid weak binding between mouse CD4 and HLA-DR4, Tgm were designed to express chimeric HLA-DR4/I-E^d, where I-E^d α1 and β1 domains were replaced with those from HLA-DR4. Th cells isolated from Tgm immunized with adjuvant and HLA-DR4-binding cytomegalovirus-derived peptide proliferated when stimulated with peptide-pulsed HLA-DR4-transduced mouse L cells, indicating chimeric HLA-DR4/I-E^d has equivalent antigen presenting capacity to HLA-DR4. Immunization with CDCA1_55-78 peptide, a computer algorithm-predicted HLA-DR4-binding peptide derived from TAA CDCA1, successfully induced Th-cell responses in Tgm, while immunization of HLA-DR4-binding Wilms' tumor 1 antigen-derived peptide with identical amino acid sequence to mouse ortholog failed. This was overcome by using peptide-pulsed syngeneic bone marrow-derived dendritic cells (BM-DC) followed by immunization with peptide/CFA booster. BM-DC-based immunization of KIF20A_494-517 peptide from another TAA KIF20A, with an almost identical HLA-binding core amino acid sequence to mouse ortholog, successfully induced Th-cell responses in Tgm. Notably, both CDCA1_55-78 and KIF20A_494-517 peptides induced human Th-cell responses in PBMCs from HLA-DR4-positive donors. Finally, an HLA-DR4 binding DEPDC1_191-213 peptide from a new TAA DEPDC1 overexpressed in bladder cancer induced strong Th-cell responses both in Tgm and in PBMCs from an HLA-DR4-positive donor. Thus, the HLA-DR4 Tgm combined with computer algorithm was useful for preliminary screening of candidate peptides for vaccination.

Database of T cell-defined human tumor antigens: the 2013 update

The plethora of tumor antigens that have been--and are still being--defined required systematization to provide a comprehensive overview of those tumor antigens that are the most relevant targets for cancer immunotherapy approaches. Here, we provide a new update of a peptide database resource that we initiated many years ago. This database compiles all human antigenic peptides described in the literature that fulfill a set of strict criteria needed to ascertain their actual "tumor antigen" nature, as we aim at guiding scientists and clinicians searching for appropriate cancer vaccine candidates (www.cancerimmunity.org/peptide). In this review, we revisit those criteria in light of recent findings related to antigen processing. We also introduce the 29 new tumor antigens that were selected for this 2013 update. Two of the new peptides show unusual features, which will be briefly discussed. The database now comprises a total of 403 tumor antigenic peptides.