Current Strategies to Enhance Anti-Tumour Immunity

Therapeutic Strategies to Enhance Tumor Antigenicity: Making the Tumor Detectable by the Immune System

Cancer immunotherapy has revolutionized the oncology field, but many patients still do not respond to current immunotherapy approaches. One of the main challenges in broadening the range of responses to this type of treatment is the limited source of tumor neoantigens. T cells constitute a main line of defense against cancer, and the decisive step to trigger their activation is mediated by antigen recognition. Antigens allow the immune system to differentiate between self and foreign, which constitutes a critical step in recognition of cancer cells and the consequent development or control of the malignancy. One of the keystones to achieving a successful antitumor response is the presence of potent tumor antigens, known as neoantigens. However, tumors develop strategies to evade the immune system and resist current immunotherapies, and many tumors present a low tumor mutation burden limiting the presence of tumor antigenicity. Therefore, new approaches must be taken into consideration to overcome these shortcomings. The possibility of making tumors more antigenic represents a promising front to further improve the success of immunotherapy in cancer. Throughout this review, we explored different state-of-the-art tools to induce the presentation of new tumor antigens by intervening at protein, mRNA or genomic levels in malignant cells.

AdAPT-001, an oncolytic adenovirus armed with a TGF-β trap, overcomes in vivo resistance to PD-L1-immunotherapy

Monoclonal antibodies targeting the programmed cell death protein-1/programmed cell death-ligand 1 (PD-1/PD-L1) and cytotoxic T lymphocyte-associated protein-4 (CTLA-4) axes have permanently changed the therapeutic landscape for multiple tumor types previously associated with a dismal prognosis such as melanoma, non-small cell lung cancer, renal cell carcinoma, bladder cancer, head and neck squamous cell carcinoma, MSI-high colorectal carcinoma, Merkel cell carcinoma, and Hodgkin lymphoma. However, only a subset of patients initially benefits from these inhibitors, and increasing clinical experience indicates that in a substantial proportion of initial responders, lethal secondary resistance ultimately develops months or years later. In this paper we evaluated combination therapy with a Phase 1 oncolytic adenovirus called AdAPT-001, armed with a TGF-β "trap" that binds to and neutralizes the immunosuppressive cytokine, TGF-β, and a checkpoint inhibitor, anti-PD-L1, in PD-L1 resistant tumors. The study, which was performed in an immunocompetent syngeneic ADS-12 mouse model, demonstrated that the combination of AdAPT-001 with PD-L1 blockade reversed PD-L1 resistance, potentially representing a future paradigm shift for patients that are primarily or secondarily resistant to checkpoint inhibitors.

Vaccine Can Induce CD4-Mediated Responses to Homocitrullinated Peptides via Multiple HLA-Types and Confer Anti-Tumor Immunity

Homocitrullination is the post translation modification (PTM) of the amino acid lysine to homocitrulline also referred to as carbamylation. This PTM has mainly been studied in relation to autoimmune diseases including rheumatoid arthritis. Homocitrullination of lysines alters their charge which can lead to generation of neoepitopes that are differentially presented by MHC-II and induce modification-specific immune responses. Homocitrullination is often considered a process which triggers autoimmune disease by bypassing self-tolerance however, we suggest that homocitrullination may also have an alternative role in immune responses including protection against cancer. Here we demonstrate that immune responses to homocitrullinated peptides from three different proteins can be induced via multiple HLA-types. Immunization of Balb/c or HLA-transgenic DR4 and DR1 mice can induce modification-specific CD4 mediated IFNγ responses. Healthy human donors show a clear repertoire for the homocitrullinated Vimentin peptide (Vim116-135^Hcit), with modification-specific and oligoclonal responses. Importantly, in vivo homocitrulline specific Vim116-135^Hcit,Cyk8 371-388^Hcit and Aldo 140-157^Hcit responses are able to confer an anti-tumor effect in the murine B16 melanoma model. The Vim116-135^Hcit anti-tumor response was dependent upon tumor expression of MHC-II suggesting the direct recognition of PTMs on tumor is an important anti-tumor mechanism. Cancer patients also have a CD4 repertoire for Vim116-135^Hcit. Together these results suggest that homocitrulline-specific immune responses can be generated in healthy mice and detected in human donors through a variety of HLA-restrictions. Immunization can induce responses to Vim116-135^Hcit,Aldolase 140-157^Hcit and Cyk8 371-388^Hcit which provide anti-tumor therapy across several HLA-types. Our results advance our understanding of homocitrulline-specific immune responses, with implications for a number of fields beyond autoimmunity, including tumor immune surveillance.

Harnessing self-assembling peptide nanofibers toprime robust tumor-specific CD8 T cell responses in mice

Induction of tumor-specific CD8 + T cell responses is known as a major challenge for cancer vaccine development; here we presented a strategy to improve peptide nanofibers-mounted antitumor immune responses. To this end, peptide nanofibers bearing class I (Kb)-restricted epitope (Epi-Nano) were formulated with polyethylene imine backbone (Epi-Nano-PEI), and characterized using morphological and physicochemicalcharacterizationtechniques. Nanofibers were studied in terms of their uptake by antigen-presenting cells (APCs), antigen cross-presentation capacity, and cytotoxic activity. Furthermore, nanofibers were assessed by their potency to induce NLRP3 inflammasome-related cytokines and factors. Finally, the ability of nanofibers to induce tumor-specific CD8 T cells and tumor protection were investigated in tumor-bearing mice. The formulation of Epi-Nano with PEI led to the formation of short strand nanofibers with a positive surface charge, a low critical aggregation concentration (CAC), and an increased resistancetoproteolytic degradation. Epi-Nano-PEI was significantly taken up more efficiently by antigen-presenting cells (APCs), and was more potent in cross-presentation when compared to Epi-Nano. Moreover, Epi-Nano-PEI, in comparison to Epi-Nano, efficiently up-regulated the expression of NLRP3, caspase-1, IL-1b, IL18 and IL-6. Cell viability analysis showed that formulation of PEI with Epi-Nano not only abolished its cytotoxic activity, but surprisingly induced macrophage proliferation. Furthermore, it demonstrated that Epi-Nano-PEI triggered robust antigen-specific CD8+ T cell responses, and induced maximum antitumor response (tumor growth inhibition and prolonged survival) in tumor-bearing mice that were significantly higher compared to Epi-Nano. Taken together, the formulation of Epi-Nano with PEI is suggested as a promising strategy to improve nanofibers-mounted antitumor immune response.

The Mechanism of Stimulating and Mobilizing the Immune System Enhancing the Anti-Tumor Immunity

Cancer immunotherapy is a kind of therapy that can control and eliminate tumors by restarting and maintaining the tumor-immune cycle and restoring the body's normal anti-tumor immune response. Although immunotherapy has great potential, it is currently only applicable to patients with certain types of tumors, such as melanoma, lung cancer, and cancer with high mutation load and microsatellite instability, and even in these types of tumors, immunotherapy is not effective for all patients. In order to enhance the effectiveness of tumor immunotherapy, this article reviews the research progress of tumor microenvironment immunotherapy, and studies the mechanism of stimulating and mobilizing immune system to enhance anti-tumor immunity. In this review, we focused on immunotherapy against tumor microenvironment (TME) and discussed the important research progress. TME is the environment for the survival and development of tumor cells, which is composed of cell components and non-cell components; immunotherapy for TME by stimulating or mobilizing the immune system of the body, enhancing the anti-tumor immunity. The checkpoint inhibitors can effectively block the inhibitory immunoregulation, indirectly strengthen the anti-tumor immune response and improve the effect of immunotherapy. We also found the checkpoint inhibitors have brought great changes to the treatment model of advanced tumors, but the clinical treatment results show great individual differences. Based on the close attention to the future development trend of immunotherapy, this study summarized the latest progress of immunotherapy and pointed out a new direction. To study the mechanism of stimulating and mobilizing the immune system to enhance anti-tumor immunity can provide new opportunities for cancer treatment, expand the clinical application scope and effective population of cancer immunotherapy, and improve the survival rate of cancer patients.

Understanding the Immune-Stroma Microenvironment in B Cell Malignancies for Effective Immunotherapy

Cancers, including lymphomas, develop in complex tissue environments where malignant cells actively promote the creation of a pro-tumoral niche that suppresses effective anti-tumor effector T cell responses. Research is revealing that the tumor microenvironment (TME) differs between different types of lymphoma, covering inflamed environments, as exemplified by Hodgkin lymphoma, to non-inflamed TMEs as seen in chronic lymphocytic leukemia (CLL) or diffuse-large B-cell lymphoma (DLBCL). In this review we consider how T cells and interferon-driven inflammatory signaling contribute to the regulation of anti-tumor immune responses, as well as sensitivity to anti-PD-1 immune checkpoint blockade immunotherapy. We discuss tumor intrinsic and extrinsic mechanisms critical to anti-tumor immune responses, as well as sensitivity to immunotherapies, before adding an additional layer of complexity within the TME: the immunoregulatory role of non-hematopoietic stromal cells that co-evolve with tumors. Studying the intricate interactions between the immune-stroma lymphoma TME should help to design next-generation immunotherapies and combination treatment strategies to overcome complex TME-driven immune suppression.

Enhancing the efficacy of immunotherapy using radiotherapy

Recent clinical breakthroughs in cancer immunotherapy, especially with immune checkpoint blockade, offer great hope for cancer sufferers - and have greatly changed the landscape of cancer treatment. However, whilst many patients achieve clinical responses, others experience minimal benefit or do not respond to immune checkpoint blockade at all. Researchers are therefore exploring multimodal approaches by combining immune checkpoint blockade with conventional cancer therapies to enhance the efficacy of treatment. A growing body of evidence from both preclinical studies and clinical observations indicates that radiotherapy could be a powerful driver to augment the efficacy of immune checkpoint blockade, because of its ability to activate the antitumor immune response and potentially overcome resistance. In this review, we describe how radiotherapy induces DNA damage and apoptosis, generates immunogenic cell death and alters the characteristics of key immune cells in the tumor microenvironment. We also discuss recent preclinical work and clinical trials combining radiotherapy and immune checkpoint blockade in thoracic and other cancers. Finally, we discuss the scheduling of immune checkpoint blockade and radiotherapy, biomarkers predicting responses to combination therapy, and how these novel data may be translated into the clinic.

E. coli nitroreductase NfsA is a reporter gene for non-invasive PET imaging in cancer gene therapy applications

The use of reporter genes to non-invasively image molecular processes inside cells has significant translational potential, particularly in the context of systemically administered gene therapy vectors and adoptively administered cells such as immune or stem cell based therapies. Bacterial nitroreductase enzymes possess ideal properties for reporter gene imaging applications, being of non-human origin and possessing the ability to metabolize a range of clinically relevant nitro(hetero)cyclic substrates. Methods: A library of eleven Escherichia coli nitroreductase candidates were screened for the ability to efficiently metabolize 2-nitroimidazole based positron emission tomography (PET) probes originally developed as radiotracers for hypoxic cell imaging. Several complementary methods were utilized to detect formation of cell-entrapped metabolites, including various in vitro and in vivo models to establish the capacity of the 2-nitroimidazole PET agent EF5 to quantify expression of a nitroreductase candidate. Proof-of-principle PET imaging studies were successfully conducted using ¹⁸F-HX4. Results: Recombinant enzyme kinetics, bacterial SOS reporter assays, anti-proliferative assays and flow cytometry approaches collectively identified the major oxygen-insensitive nitroreductase NfsA from E. coli (NfsA_Ec) as the most promising nitroreductase reporter gene. Cells expressing NfsA_Ec were demonstrably labelled with the imaging agent EF5 in a manner that was quantitatively superior to hypoxia, in monolayers (2D), multicellular layers (3D), and in human tumor xenograft models. EF5 retention correlated with NfsA_Ec positive cell density over a range of EF5 concentrations in 3D in vitro models and in xenografts in vivo and was predictive of in vivo anti-tumor activity of the cytotoxic prodrug PR-104. Following PET imaging with ¹⁸F-HX4, a significantly higher tumor-to-blood ratio was observed in two xenograft models for NfsA_Ec expressing tumors compared to the parental tumors thereof, providing verification of this reporter gene imaging approach. Conclusion: This study establishes that the bacterial nitroreductase NfsA_Ec can be utilized as an imaging capable reporter gene, with the ability to metabolize and trap 2-nitroimidazole PET imaging agents for non-invasive imaging of gene expression.

Bio-synthesized iron oxide nanoparticles for cancer treatment

Various living organisms, such as bacteria, plants, and animals can synthesize iron oxide nanoparticles (IONP). The mechanism of nanoparticle (NP) formation is usually described as relying on the reduction of ferric/ferrous iron ions into crystallized nanoparticulate iron that is surrounded by an organic stabilizing layer. The properties of these NP are characterized by a composition made of different types of iron oxide whose most stable and purest one appears to be maghemite, by a size predominantly comprised between 5 and 380 nm, by a crystalline core, by a surface charge which depends on the nature of the material coating the iron oxide, and by certain other properties such as a sterility, stability, production in mass, absence of aggregation, that have apparently only been studied in details for IONP synthesized by magnetotactic bacteria, called magnetosomes. In the majority of studies, bio-synthesized IONP are described as being biocompatible and as not inducing cytotoxicity towards healthy cells. Anti-tumor activity of bio-synthesized IONP has mainly been demonstrated in vitro, where this type of NP displayed cytotoxicity towards certain tumor cells, e.g. through the anti-tumor activity of IONP coating or through IONP anti-oxidizing property. Concerning in vivo anti-tumor activity, it was essentially highlighted for magnetosomes administered in different types of glioblastoma tumors (U87-Luc and GL-261), which were exposed to a series of alternating magnetic field applications, resulting in mild hyperthermia treatments at typical temperatures of 41-45 °C, leading to the full disappearance of these tumors without any observable side effects.

Response to the Rechallenge With Talimogene Laherparepvec (T-VEC) After Ipilimumab/Nivolumab Treatment in Patient With Cutaneous Malignant Melanoma Who Initially Had a Progression on T-VEC With Pembrolizumab

Talimogene laherparepvec (T-VEC) is approved for unresected stage III-IV malignant melanoma. T-VEC has a direct cytotoxic effect and enhances the antitumor immunity of host cells. Immune checkpoints inhibitors also enhance the immunity of host cells by increasing the recruitment of antigen-presenting cells or activation and restoration of T-cell functions. Both type of therapies can potentiate the effect of the other therapy. We are reporting a case of T-VEC rechallenge who initially progressed on T-VEC with pembrolizumab but then responded to T-VEC rechallenge after intervening ipilimumab/nivolumab. An 83-year-old man developed a subungual lesion of the left thumb and found to have AJCC V. 7 stage IIIb melanoma. Few months later, he developed axillary lymphadenopathy and multiple subcutaneous nodules (AJCC V. 7 stage IIIc). The patient was started on intralesional rose Bengal and pembrolizumab. After 4 cycles of pembrolizumab with rose Bengal, a positron-emission tomography/computerized tomography scan showed the progression of disease. He was started on T-VEC intralesional injections with concurrent pembrolizumab, however, after 3 T-VEC injections and 2 more cycles of pembrolizumab, there was the progression of disease. Subsequently, ipilimumab/nivolumab was started and patient responded partially. Ipilimumab/nivolumab was held due to toxicity. Eight weeks from the last dose of ipilimumab/nivolumab, he experienced locoregional progression and was rechallenged with T-VEC monotherapy. The patient showed a significant response after second T-VEC injection and continued to show response 6 months since rechallenge. After, initial progression on T-VEC with pembrolizumab, intervening immune checkpoints inhibitors may favorably modify the antitumor immunity and potentiate antitumor effect of T-VEC rechallenge.

Semaphorin Signaling in Cancer-Associated Inflammation

The inflammatory and immune response elicited by the growth of cancer cells is a major element conditioning the tumor microenvironment, impinging on disease progression and patients’ prognosis. Semaphorin receptors are widely expressed in inflammatory cells, and their ligands are provided by tumor cells, featuring an intense signaling cross-talk at local and systemic levels. Moreover, diverse semaphorins control both cells of the innate and the antigen-specific immunity. Notably, semaphorin signals acting as inhibitors of anti-cancer immune response are often dysregulated in human tumors, and may represent potential therapeutic targets. In this mini-review, we provide a survey of the best known semaphorin regulators of inflammatory and immune cells, and discuss their functional impact in the tumor microenvironment.