Tumor Antigens Discovery: Perspectives for Cancer Therapy

Challenges and new technologies in adoptive cell therapy

Adoptive cell therapies (ACTs) have existed for decades. From the initial infusion of tumor-infiltrating lymphocytes to the subsequent specific enhanced T cell receptor (TCR)-T and chimeric antigen receptor (CAR)-T cell therapies, many novel strategies for cancer treatment have been developed. Owing to its promising outcomes, CAR-T cell therapy has revolutionized the field of ACTs, particularly for hematologic malignancies. Despite these advances, CAR-T cell therapy still has limitations in both autologous and allogeneic settings, including practicality and toxicity issues. To overcome these challenges, researchers have focused on the application of CAR engineering technology to other types of immune cell engineering. Consequently, several new cell therapies based on CAR technology have been developed, including CAR-NK, CAR-macrophage, CAR-γδT, and CAR-NKT. In this review, we describe the development, advantages, and possible challenges of the aforementioned ACTs and discuss current strategies aimed at maximizing the therapeutic potential of ACTs. We also provide an overview of the various gene transduction strategies employed in immunotherapy given their importance in immune cell engineering. Furthermore, we discuss the possibility that strategies capable of creating a positive feedback immune circuit, as healthy immune systems do, could address the flaw of a single type of ACT, and thus serve as key players in future cancer immunotherapy.

Nobel Prize for immune checkpoint inhibitors, understanding the immunological switching between immunosuppression and autoimmunity

INTRODUCTION

Immune checkpoint inhibitors (ICIs) are a revolutionary form of immunotherapy in cancer. However, the percentage of patients responding to therapy is relatively low, while adverse effects occur in a large number of patients. In addition, the therapeutic mechanisms of ICIs are not yet completely described.

AREAS COVERED

The initial view (articles published in PubMed, Scopus, Web of Science, etc.) was that ICIs increase tumor-specific immunity. Recent data (collected from the same databases) suggest that the ICIs pharmacotherapy actually extends beyond the topic of immune reactivity, including additional immune pathways, such as disrupting immunosuppression and increasing tumor-specific autoimmunity. Unfortunately, there is no clear delimitation between these specific autoimmune reactions that are therapeutically beneficial, and nonspecific autoimmune reactions/toxicity that can be extremely severe side effects.

EXPERT OPINION

Immune checkpoint mechanisms perform a non-selective immune regulation, maintaining a dynamic balance between immunosuppression and autoimmunity. By blocking these mechanisms, ICIs actually perform an immunological reset, decreasing immunosuppression and increasing tumor-specific immunity and predisposition to autoimmunity. The predisposition to autoimmunity induces both side effects and beneficial autoimmunity. Consequently, further studies are necessary to maximize the beneficial tumor-specific autoimmunity, while reducing the counterproductive effect of associated autoimmune toxicity.

Implications of Antigen Selection on T Cell-Based Immunotherapy

Many immunotherapies rely on CD8+ effector T cells to recognize and kill cognate tumor cells. These T cell-based immunotherapies include adoptive cell therapy, such as CAR T cells or transgenic TCR T cells, and anti-cancer vaccines which expand endogenous T cell populations. Tumor mutation burden and the choice of antigen are among the most important aspects of T cell-based immunotherapies. Here, we highlight various classes of cancer antigens, including self, neojunction-derived, human endogenous retrovirus (HERV)-derived, and somatic nucleotide variant (SNV)-derived antigens, and consider their utility in T cell-based immunotherapies. We further discuss the respective anti-tumor/anti-self-properties that influence both the degree of immunotolerance and potential off-target effects associated with each antigen class.

Development of neoantigens: from identification in cancer cells to application in cancer vaccines

Introduction: The discovery of neoantigens as mutated proteins specifically expressed in tumor cells but not in normal cells has led to improved cancer vaccines. Targeting neoantigens can induce anti-tumor T-cell responses to destroy tumors without damaging healthy cells. Extensive advances in genome sequencing technology and bioinformatics analysis have made it possible to discover and design effective neoantigens for use in therapeutic cancer vaccines. Neoantigens-based therapeutic personalized vaccines have shown promising results in cancer immunotherapy.Areas covered: We discuss the types of cancer neoantigens that can be recognized by the immune system in this review. We also summarize the detection, identification, and design of neoantigens and their appliction in developing cancer vaccines. Finally, clinical trials of neoantigen-based vaccines, their advantages, and their limitations are reviewed. From 2015 to 2020, the authors conducted a literature search of controlled randomized trials and laboratory investigations that that focused on neoantigens, their use in the design of various types of cancer vaccines.Expert opinion: Neoantigens are cancer cell-specific antigens, which their expression leads to the immune stimulation against tumor cells. The identification and delivery of specific neoantigens to antigen-presenting cells (APCs) with the help of anti-cancer vaccines promise novel and more effective cancer treatments.

Coley's immunotherapy revived: Innate immunity as a link in priming cancer cells for an attack by adaptive immunity

There is no doubt that immunotherapy lies in the spotlight of current cancer research and clinical trials. However, there are still limitations in the treatment response in certain types of tumors largely due to the presence of the complex network of immunomodulatory and immunosuppressive pathways. These limitations are not likely to be overcome by current immunotherapeutic options, which often target isolated steps in immune pathways preferentially involved in adaptive immunity. Recently, we have developed an innovative anti-cancer immunotherapeutic strategy that initially elicits a strong innate immune response with subsequent activation of adaptive immunity in mouse models. Robust primary innate immune response against tumor cells is induced by toll-like receptor ligands and anti-CD40 agonistic antibodies combined with the phagocytosis-stimulating ligand mannan, anchored to a tumor cell membrane by biocompatible anchor for membrane. This immunotherapeutic approach results in a dramatic therapeutic response in large established murine subcutaneous tumors including melanoma, sarcoma, pancreatic adenocarcinoma, and pheochromocytoma. Additionally, eradication of metastases and/or long-lasting resistance to subsequent re-challenge with tumor cells was also accomplished. Current and future advantages of this immunotherapeutic approach and its possible combinations with other available therapies are discussed in this review.

Antigenic GM3 Lactone Mimetic Molecule Integrated Mannosylated Glycopeptide Nanofibers for the Activation and Maturation of Dendritic Cells

The ability of dendritic cells to coordinate innate and adaptive immune responses makes them essential targets for vaccination strategies. Presentation of specific antigens by dendritic cells is required for the activation of the immune system against many pathogens and tumors, and nanoscale materials can be functionalized for active targeting of dendritic cells. In this work, we integrated an immunogenic, carbohydrate melanoma-associated antigen-mimetic GM3-lactone molecule into mannosylated peptide amphiphile nanofibers to target dendritic cells through DC-SIGN receptor. Based on morphological and functional analyses, when dendritic cells were treated with peptide nanofiber carriers, they showed significant increase in antigen internalization and a corresponding increase in the surface expression of the activation and maturation markers CD86, CD83 and HLA-DR, in addition to exhibiting a general morphology consistent with dendritic cell maturation. These results indicate that mannosylated peptide amphiphile nanofiber carriers are promising candidates to target dendritic cells for antigen delivery.

Experimental discovery of T-cell epitopes: combining the best of classical and contemporary approaches

T cells specifically recognize antigens as peptide epitope-MHC complexes on the surface of target cells. The inherent complexities of antigen processing and presentation, the polygenic and polymorphic nature of MHC and the technical hurdles in working with T cells have made epitope discovery challenging. Here, we review significant experimental advances in recent years. These include new and sensitive assays and the availability of human cells and high numbers of synthetic peptides for screening, which have allowed for the first time comprehensive analysis of antigens and whole virus genomes. Such studies have provided important insights into the immunobiology of a number of diseases. The newly gathered detailed information on T-cell epitopes will aid vaccine design and immunological monitoring in clinical trials.

Cancer immunotherapy using dendritic/tumour-fusion vaccine induces elevation of serum anti-nuclear antibody with better clinical responses

Dendritic cell (DC) vaccines might induce both anti-tumour immunity and autoimmunity. In this report, we demonstrate elevated levels of anti-nuclear antibody (ANA) in the sera of patients with cancer who had received immunotherapy with a dendritic/tumour-fusion vaccine. Twenty-two patients were treated with DC vaccine of fusion cells composed of autologous DCs and tumour cells (DC/tumour-fusion vaccine), which was generated by treating each cell type with polyethylene glycol. Nine of the 22 patients were treated with both the DC/tumour-fusion vaccine and systemic administration of recombinant human interleukin (rhIL)-12. Serum levels of ANA were examined with an enzyme-linked immunosorbent assay kit. One patient with gastric carcinoma (patient 1, DC/tumour-fusion vaccine alone), one patient with breast cancer (patient 2, DC/tumour-fusion vaccine alone) and one patient with ovarian cancer (patient 3, DC/tumour-fusion vaccine + rhIL-12) showed significant elevations of serum ANA levels during treatment. In patient 1 malignant ascitic effusion resolved and serum levels of tumour markers decreased. Patients 2 and 3 remained in good physical condition during treatment for 24 and 9 months, respectively. Immunoblot analysis indicated antibody responses to autologous tumour cells after vaccination in patient 2. None of the treated patients showed clinical symptoms suggesting autoimmune disease. Patients with elevated serum levels of ANA had significantly longer treatment periods than those without it. Elevated serum levels of ANA after DC/tumour-fusion cell vaccine might be associated with anti-tumour immune response induced by the vaccination.

Autoimmune hepatic inflammation by vaccination of mice with dendritic cells loaded with well-differentiated hepatocellular carcinoma cells and administration of interleukin-12

Vaccination of mice with dendritic cells loaded with Hepa1-6, well-differentiated hepatocellular carcinoma cell line (DC/Hepa1-6), induced cytotoxic T lymphocytes against Hepa1-6. Liver-specific inflammation was generated by vaccination of mice with DC/Hepa1-6 and subsequent administration of interleukin (IL)-12. Vaccination with DCs loaded with MC38 or B16 and administration of IL-12 did not generate significant liver-specific inflammation. Splenic T cells from DC/Hepa1-6-vaccinated mice showed proliferative response by stimulation with S-100 protein of the liver and showed cytotoxic activity to hepatocytes. Hepatic mononuclear cells from DC/Hepa1-6 + IL-12-treated mice also showed cytotoxic activity to hepatocytes. Adoptive transfer of splenocytes from DC/Hepa1-6-vaccinated mice produced hepatic inflammation in recipient mice that had been pretreated with IL-12. IL-12 upregulated the expression of adhesion molecules and chemokines in the liver. In conclusion, CTLs responsive to hepatocytes induced by DC/Hepa1-6 and enhanced expression of adhesion molecules and chemokines in the liver by IL-12 would produce autoimmune hepatic inflammation.

Expression profile of genes coding for melanoma differentiation antigens and cancer/testis antigens in metastatic lesions of human cutaneous melanoma

Vaccination-based therapy of melanoma has so far mainly focused on monovalent approaches using either melanoma differentiation antigens or cancer/testis antigens. To study the complementarity of expression from these two families of antigens recognized by T-cells, we screened 47 metastatic lesions of cutaneous melanoma for the expression of three melanoma differentiation antigens and eight cancer/testis antigens using reverse transcription-polymerase chain reaction (RT-PCR). The melanoma differentiation antigens were expressed in a somewhat higher percentage of lesions (94% positive for at least one marker) than the cancer/testis antigens (91% positive for at least one marker). Nearly all the melanoma metastases (98%) expressed at least one of the markers tested. One melanoma metastasis was negative for all the markers. Two out of 47 lesions did not express any of the three differentiation markers but expressed one or more of the cancer/testis antigens, indicating some additional potential for these antigens compared with the melanoma differentiation antigens. Therefore, we conclude that polyvalent immunotherapy using multiple epitopes from both families of antigens might increase the eligibility of melanoma patients and the efficacy of the treatment.

In vitro and in vivo induction of a Th cell response toward peptides of the melanoma-associated glycoprotein 100 protein selected by the TEPITOPE program

The melanoma-associated Ag glycoprotein 100 was analyzed by the T cell epitope prediction software TEPITOPE. Seven HLA-DR promiscuous peptides predicted with a stringent threshold were used to load dendritic cells (DC), and induction of a proliferative response was monitored. PBMC of all nine donors including two patients with malignant melanoma responded to at least one of the peptides. The proliferative response was defined as a Th response by the selective expansion of CD4(+) cells, up-regulation of CD25 and CD40L, and IL-2 and IFN-gamma expression. Peptide-loaded DC also initiated a T helper response in vivo (i.e., tumor growth in the SCID mouse was significantly retarded by the transfer of PBMC together with peptide-loaded DC). Because the use of the TEPITOPE program allows for a prediction of T cell epitopes; because the predicted peptides can be rapidly confirmed by inducing a Th response in the individual patient; and because application of peptide-loaded DC suffices for the in vivo activation of helper cells, vaccination with MHC class II-binding peptides of tumor-associated Ags becomes a feasible and likely powerful tool in the immunotherapy of cancer.

Activation of lymphocytes by anti-CD3 single-chain antibody dimers expressed on the plasma membrane of tumor cells

Activation of cytotoxic T cells without MHC restriction was attempted by expressing single-chain antibodies (scFv) against CD3 on the surface of tumor cells. A chimeric protein consisting of a scFv of mAb 145.2C11, the hinge-CH2-CH3 region of human IgG1, and the transmembrane and cytosolic domains of murine CD80 formed disulfide-linked dimers on the plasma membrane of cells and specifically bound lymphocytes. Anti-CD3 scFv dimers expressed on the cell surface induced CD25 (IL-2 receptor alpha-chain) expression and proliferation of splenocytes. CT26 tumor cells engineered to express surface scFv dimers (CT26/2C11) also induced potent lymphocyte cytotoxicity with or without addition of exogenous IL-2. Splenocytes activated by CT26/2C11 cells also killed wild-type CT26 cells, indicating that activated splenocytes could kill bystander tumor cells. Immunization of BALB/c mice with irradiated CT26/2C11 cells did not protect against a lethal challenge of CT26 cells, suggesting that systemic immunity was not induced. However, the growth of CT26 tumors containing 50% CT26/2C11 cells was significantly retarded compared with CT26 tumors, whereas CT26/2C11 tumors did not grow in syngeneic mice. These results suggest that expression of anti-CD3 scFv dimers on tumors may form the basis for a novel therapeutic strategy for tumors that exhibit defects in antigen processing or presentation. Gene Therapy (2000) 7, 339-347.

Identification of a novel major histocompatibility complex class II-restricted tumor antigen resulting from a chromosomal rearrangement recognized by CD4(+) T cells

CD4(+) T cells play an important role in antitumor immune responses and autoimmune and infectious diseases. Although many major histocompatibility complex (MHC) class I-restricted tumor antigens have been identified in the last few years, little is known about MHC class II- restricted human tumor antigens recognized by CD4(+) T cells. Here, we describe the identification of a novel melanoma antigen recognized by an human histocompatibility leukocyte antigen (HLA)-DR1-restricted CD4(+) tumor-infiltrating lymphocyte (TIL)1363 using a genetic cloning approach. DNA sequencing analysis indicated that this was a fusion gene generated by a low density lipid receptor (LDLR) gene in the 5' end fused to a GDP-L-fucose:beta-D-galactoside 2-alpha-L-fucosyltransferase (FUT) in an antisense orientation in the 3' end. The fusion gene encoded the first five ligand binding repeats of LDLR in the NH2 terminus followed by a new polypeptide translated in frame with LDLR from the FUT gene in an antisense direction. Southern blot analysis showed that chromosomal DNA rearrangements occurred in the 1363mel cell line. Northern blot analysis detected two fusion RNA transcripts present only in the autologous 1363mel, but not in other cell lines or normal tissues tested. Two minimal peptides were identified from the COOH terminus of the fusion protein. This represents the first demonstration that a fusion protein resulting from a chromosomal rearrangement in tumor cells serves as an immune target recognized by CD4(+) T cells.