Intratumoral depletion of regulatory T cells using CD25-targeted photodynamic therapy in a mouse melanoma model induces antitumoral immune responses

Microbubble-Protected Oncolytic Virotherapy Targeted by Sonoporation Induces Tumor Necrosis and T-Lymphocyte Infiltration in Humanized Mice Bearing Triple-Negative Breast Cancer

Oncolytic virotherapy has shown great promise in mediating targeted tumor destruction through tumor-selective replication and induction of anti-tumor immunity; however, obstacles remain for virus candidates to reach the clinic. These include avoiding neutralizing antibodies, preventing stimulation of the adaptive immune response during intravenous administration, and inducing sufficient apoptosis and immune activation so that the body's defense can work to eradicate systemic disease. We have developed a co-formulation of oncolytic viruses (OVs) with Imagent® lipid-encapsulated, perfluorocarbon microbubbles (MBs) to protect the OVs from the innate and adaptive immune system. Once inside the MB, the viral particles become acoustically active such that external ultrasound can target the delivery of the virus locally within the tumor. Humanized NSG female mice (Hu-CD34+ NSG-SGM3) engrafted in their flanks with MDA-MB-231-Luc triple-negative breast cancer (TNBC) cells were transduced with MB/OVs, with or without adjuvant Pembrolizumab treatment, and tumor sizes and tumor necrosis were assessed. The presence of CD8+ (cytotoxic T-cells), CD4+ (helper T-cells), and CD25+ (Tregs) tumor-infiltrating lymphocytes (TILs) was quantified in the tumor samples by immunohistochemistry. In an in vivo model of humanized mice engrafted with a human immune system, we observed significantly greater tumor necrosis and smaller tumor mass in human TNBC xenografts systemically treated with MB/OV complexes in the presence or absence of pembrolizumab adjuvant treatment, compared to controls. Additionally, we observed a low ratio of CD4+/CD8+ TILs and a high ratio of CD8+/CD25+ TILs in the MDA-MB-231 xenografts treated with MB/OVs complexes with or without pembrolizumab adjuvant treatment, compared to controls. Our study demonstrated the feasibility of using MBs to target OVs to TNBC through diagnostic ultrasound, which decreased tumor mass by increasing tumor necrosis and stimulated a local and systemic antitumoral immune response by increasing intratumoral CD8+ T-cytotoxic lymphocyte infiltration and decreasing CD25+ Treg cells.

Regulatory T cells in immune checkpoint blockade antitumor therapy

Regulatory T cells (Tregs), an essential component of the human immune system, are a heterogeneous group of T lymphocytes with the ability to suppress immune responses and maintain immune homeostasis. Recent evidence indicates that Tregs may impair antitumor immunity and facilitate cancer progression by weakening functions of effector T cells (Teffs). Consequently, targeting Tregs to eliminate them from tumor microenvironments to improve Teffs' activity could emerge as an effective strategy for cancer immunotherapy. This review outlines the biology of Tregs, detailing their origins, classification, and crucial markers. Our focus lies on the complex role of Tregs in cancer's development, progression and treatment, particularly on their suppressive role upon antitumor responses via multiple mechanisms. We delve into Tregs' involvement in immune checkpoint blockade (ICB) therapy, their dual effect on cancer immunotherapy and their potential biomarkers for ICB therapy effectiveness. We also summarize advances in the therapies that adjust Tregs to optimize ICB therapy, which may be crucial for devising innovative cancer treatment strategies.

The fusion of light and immunity: Advancements in photoimmunotherapy for melanoma

Metastatic melanoma is an aggressive skin cancer with high mortality and recurrence rates. Despite the clinical success of recent immunotherapy approaches, prevailing resistance rates necessitate the continued development of novel therapeutic options. Photoimmunotherapy (PIT) is emerging as a promising immunotherapy strategy that uses photodynamic therapy (PDT) to unleash systemic immune responses against tumor sites while maintaining the superior tumor-specificity and minimally invasive nature of traditional PDT. In this review, we discuss recent advances in PIT and strategies for the management of melanoma using PIT. PIT can strongly induce immunogenic cell death, inviting the concomitant application of immune checkpoint blockade or adoptive cell therapies. PIT can also be leveraged to selectively remove the suppressive immune populations associated with immunotherapy resistance. The modular nature of PIT therapy design combined with the potential for patient-specific antigen selection or drug co-delivery makes PIT an alluring option for future personalized melanoma care.

Photodynamic Therapy and Adaptive Immunity Induced by Reactive Oxygen Species: Recent Reports

Cancer is one of the most significant causes of death worldwide. Despite the rapid development of modern forms of therapy, results are still unsatisfactory. The prognosis is further worsened by the ability of cancer cells to metastasize. Thus, more effective forms of therapy, such as photodynamic therapy, are constantly being developed. The photodynamic therapeutic regimen involves administering a photosensitizer that selectively accumulates in tumor cells or is present in tumor vasculature prior to irradiation with light at a wavelength corresponding to the photosensitizer absorbance, leading to the generation of reactive oxygen species. Reactive oxygen species are responsible for the direct and indirect destruction of cancer cells. Photodynamically induced local inflammation has been shown to have the ability to activate an adaptive immune system response resulting in the destruction of tumor lesions and the creation of an immune memory. This paper focuses on presenting the latest scientific reports on the specific immune response activated by photodynamic therapy. We present newly discovered mechanisms for the induction of the adaptive response by analyzing its various stages, and the possible difficulties in generating it. We also present the results of research over the past 10 years that have focused on improving the immunological efficacy of photodynamic therapy for improved cancer therapy.

Combinational photodynamic and photothermal - based therapies for melanoma in mouse models

BACKGROUND

Melanoma is a highly metastatic skin cancer with limited response to current therapies in advanced patients. To overcome resistance, novel treatments based on photodynamic and photothermal therapies (PDT and PTT, respectively) have been developed to treat melanoma in preclinical murine models. Despite success inhibiting implanted tumors' growth, there has been limited evaluation of their long-term effectiveness in preventing metastasis, recurrence, or improving survival rates.

METHODS

Combined and multidrug therapies based on PDT and/or PTT to treat cutaneous malignant melanoma in the preclinical mouse model were reviewed from 2016 onwards. PubMed® was the database in which the search was performed using mesh search algorithms resulting in fifty-one studies that comply with strict inclusion rules of screening.

RESULTS

B16 melanoma-bearing C57BLACK6 mice model was the most used to evaluate immunotherapies, chemotherapies, and targeted therapies in combination with PDT and/or PTT. Combined therapies demonstrated a synergistic effect, resulting in intense antitumor activity. The most extensively studied protocol for developing metastatic models involved the intravenous administration of malignant cells, with some combined therapies being tested. Furthermore, the review presents the composition of the nanostructures utilized for delivering the drugs and light-responsive agents and the treatment plans for each combined approach.

CONCLUSIONS

The identified mechanisms to simulate metastatic melanoma models and the therapeutic combinations may aid in evaluating the systemic protection of combined PDT and PTT-based therapies, particularly in conducting short-term preclinical experiments. Such simulations could have relevance to clinical studies.

Efficient Synthesis of Chlorin e6 and Its Potential Photodynamic Immunotherapy in Mouse Melanoma by the Abscopal Effect

Photodynamic therapy (PDT) can eradicate not only cancer cells but also stimulate an antitumor immune response. Herein, we describe two efficient synthetic methodologies for the preparation of Chlorin e6 (Ce6) from Spirulina platensis and address the phototoxic effect of Ce6 in vitro along with antitumor activity in vivo. Melanoma B16F10 cells were seeded and phototoxicity was monitored by the MTT assay. The C57BL/6 mice were subcutaneously inoculated on the left and right flank with B16F10 cells. The mice were intravenously injected with Ce6 of 2.5 mg/kg and then exposed to red light (660 nm) on the left flank tumors 3 h after the injection. The immune response was studied by analyzing Interferon-gamma (IFN-γ), tumor necrosis factor-alpha (TNF-α), and Interleukin-2 (IL-2) of the right flank tumors through qPCR. Our results revealed that the tumor was suppressed not only in the left flank but also in the right flank, where no PDT was given. The upregulated gene and protein expression of IFN-γ, TNF-α, and IL-2 revealed antitumor immunity due to Ce6-PDT. The findings of this study suggest an efficient methodology of Ce6 preparation and the efficacy of Ce6-PDT as a promising antitumor immune response.

Current Challenges and Opportunities of Photodynamic Therapy against Cancer

BACKGROUND

Photodynamic therapy (PDT) is an established, minimally invasive treatment for specific types of cancer. During PDT, reactive oxygen species (ROS) are generated that ultimately induce cell death and disruption of the tumor area. Moreover, PDT can result in damage to the tumor vasculature and induce the release and/or exposure of damage-associated molecular patterns (DAMPs) that may initiate an antitumor immune response. However, there are currently several challenges of PDT that limit its widespread application for certain indications in the clinic.

METHODS

A literature study was conducted to comprehensively discuss these challenges and to identify opportunities for improvement.

RESULTS

The most notable challenges of PDT and opportunities to improve them have been identified and discussed.

CONCLUSIONS

The recent efforts to improve the current challenges of PDT are promising, most notably those that focus on enhancing immune responses initiated by the treatment. The application of these improvements has the potential to enhance the antitumor efficacy of PDT, thereby broadening its potential application in the clinic.

Insight into the Prospects for Tumor Therapy Based on Photodynamic Immunotherapy

Malignancy is one of the common diseases with high mortality worldwide and the most important obstacle to improving the overall life expectancy of the population in the 21st century. Currently, single or combined treatments, including surgery, chemotherapy, and radiotherapy, are still the mainstream regimens for tumor treatment, but they all present significant side effects on normal tissues and organs, such as organ hypofunction, energy metabolism disorders, and various concurrent diseases. Based on this, theranostic measures for the highly selective killing of tumor cells have always been a hot area in cancer-related fields, among which photodynamic therapy (PDT) is expected to be an ideal candidate for practical clinical application due to its precise targeting and excellent safety performance, so-called PDT refers to a therapeutic method mainly composed of photosensitizers (PSs), laser light, and reactive oxygen species (ROS). Photoimmunotherapy (PIT), a combination of PDT and immunotherapy, can induce systemic antitumor immune responses and inhibit continuing growth and distant metastasis of residual tumor cells, demonstrating a promising application prospect. This article reviews the types of immune responses that occur in the host after PDT treatment, including innate and adaptive immunity. To further help PIT-related drugs improve their pharmacokinetic properties and bioavailability, we highlight the potential improvement of photodynamic immunotherapy from three aspects: immunostimulatory agents, tumor-associated antigens (TAAs) as well as different immune cells. Finally, we focus on recent advances in various strategies and shed light on their corresponding mechanisms of immune activation and possible clinical applications such as cancer vaccines. Having discovered the inherent potential of PDT and the mechanisms that PDT triggers host immune responses, a variety of immunotherapeutic strategies have been investigated in parallel with approaches to improve PDT efficiency. However, it remains to be further elucidated under what conditions the immune effect induced by PDT can achieve tumor immunosuppression and to what extent PDT-induced antitumor immunity will lead to complete tumor rejection. Currently, PIT presents several outstanding intractable challenges, such as the aggregation ability of PSs locally in tumors, deep tissue penetration ability of laser light, immune escape, and biological toxicity, and it is hoped that these issues raised will help to point out the direction of preclinical research on PIT and accelerate its transition to clinical practice.

Targeting Microenvironment of Melanoma and Head and Neck Cancers in Photodynamic Therapy

Background:

Photodynamic therapy (PDT), in comparison to other skin cancers, is still far less effective for melanoma, due to the strong absorbance and the role of melanin in cytoprotection. The tumour microenvironment (TME) has a significant role in tumour progression, and the hypoxic TME is one of the main reasons for melanoma progression to metastasis and its resistance to PDT. Hypoxia is also a feature of solid tumours in the head and neck region that indicates negative prognosis.

Objective:

The aim of this study was to individuate and describe systematically the main strategies in targeting the TME, especially hypoxia, in PDT against melanoma and head and neck cancers (HNC), and assess the current success in their application.

Methods:

PubMed was used for searching, in MEDLINE and other databases, for the most recent publications on PDT against melanoma and HNC in combination with the TME targeting and hypoxia.

Results:

In PDT for melanoma and HNC, it is very important to control hypoxia levels, and amongst the different approaches, oxygen self-supply systems are often applied. Vascular targeting is promising, but to improve it, optimal drug-light interval, and formulation to increase the accumulation of the photosensitiser in the tumour vasculature, have to be established. On the other side, the use of angiogenesis inhibitors, such as those interfering with VEGF signalling, is somewhat less successful than expected and needs to be further investigated.

Conclusion:

The combination of PDT with immunotherapy by using multifunctional nanoparticles continues to develop and seems to be the most promising for achieving a complete and lasting antitumour effect.

Multifunctional Nanosystems Powered Photodynamic Immunotherapy

Photodynamic Therapy (PDT) with the intrinsic advantages including non-invasiveness, spatiotemporal selectivity, low side-effects, and immune activation ability has been clinically approved for the treatment of head and neck cancer, esophageal cancer, pancreatic cancer, prostate cancer, and esophageal squamous cell carcinoma. Nevertheless, the PDT is only a strategy for local control of primary tumor, that it is hard to remove the residual tumor cells and inhibit the tumor metastasis. Recently, various smart nanomedicine-based strategies are developed to overcome the barriers of traditional PDT including the drawbacks of traditional photosensitizers, limited tissue penetrability of light, inefficient induction of tumor cell death and tumor resistance to the therapy. More notably, a growing number of studies have focused on improving the therapeutic efficiency by eliciting host immune system with versatile nanoplatforms, which heralds a broader clinical application prospect of PDT in the future. Herein, the pathways of PDT induced-tumor destruction, especially the host immune response is summarized, and focusing on the recent progress of nanosystems-enhanced PDT through eliciting innate immunity and adaptive immunity. We expect it will provide some insights for conquering the drawbacks current PDT and expand the range of clinical application through this review.

Nanoparticle-Based Drug Delivery Systems for Photodynamic Therapy of Metastatic Melanoma: A Review

Metastatic melanoma (MM) is a skin malignancy arising from melanocytes, the incidence of which has been rising in recent years. It poses therapeutic challenges due to its resistance to chemotherapeutic drugs and radiation therapy. Photodynamic therapy (PDT) is an alternative non-invasive modality that requires a photosensitizer (PS), specific wavelength of light, and molecular oxygen. Several studies using conventional PSs have highlighted the need for improved PSs for PDT applications to achieve desired therapeutic outcomes. The incorporation of nanoparticles (NPs) and targeting moieties in PDT have appeared as a promising strategy to circumvent various drawbacks associated with non-specific toxicity, poor water solubility, and low bioavailability of the PSs at targeted tissues. Currently, most studies investigating new developments rely on two-dimensional (2-D) monocultures, which fail to accurately mimic tissue complexity. Therefore, three-dimensional (3-D) cell cultures are ideal models to resemble tumor tissue in terms of architectural and functional properties. This review examines various PS drugs, as well as passive and active targeted PS nanoparticle-mediated platforms for PDT treatment of MM on 2-D and 3-D models. The overall findings of this review concluded that very few PDT studies have been conducted within 3-D models using active PS nanoparticle-mediated platforms, and so require further investigation.

Inhibition of photodynamic therapy induced-immunosuppression with aminolevulinic acid leads to enhanced outcomes of tumors and pre-cancerous lesions

Photodynamic therapy (PDT) is a treatment option for tumors and pre-cancerous lesions, but it has immunosuppressive side effects that limit its effectiveness. Recent studies suggest that PDT-mediated immunosuppression occurs through a cyclooxygenase type 2 (COX-2) mediated pathway that leads to increases in regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs), which act as negative regulators of immune responses. Given this pathway, there are three main methods to block immunosuppression: i) Inhibiting the proliferation of Tregs, which can be achieved with the administration of cyclophosphamide or inhibitors of indoleamine 2,3-dioxygenase 1, an activator of Tregs; ii) inhibiting MDSCs by reducing hypoxia around the tumor to create an unfavorable environment or administering all-trans-retinoic acid, which converts MDSCs to a non-immunosuppressive state; and iii) inhibiting COX-2 through selective or non-selective COX-inhibitors. In the present review article, strategies that have shown increased efficacy of PDT in treating tumors and pre-cancerous lesions by blocking the immunosuppressive side effects are outlined and discussed.

Evaluation of In Vitro Phototoxicity of a Minibody-IR700 Conjugate Using Cell Monolayer and Multicellular Tumor Spheroid Models

Photodynamic therapy (PDT) is a treatment strategy that utilizes photosensitizers (PSs) and light of a specific wavelength to kill cancer cells. However, limited tumor specificity is still a drawback for the clinical application of PDT. To increase the therapeutic efficacy and specificity of PDT, a novel human minibody (MS5) that recognizes a cell surface receptor expressed on various cancer cells was labeled with the hydrophilic phthalocyanine PS IR700 to generate an MS5-IR700 conjugate that is activated by near-infrared (NIR) light. The phototoxicity of the conjugate was mainly tested against the PC3 prostate cancer cell line. The MS5-IR700 conjugate killed PC3 cells after NIR light irradiation as compared to untreated cells or cells treated with IR700 alone. Time-course analysis of cell viability revealed a high percentage of cell death during the first hour in PC3 cells exposed to the MS5-IR700 conjugate and NIR light irradiation. After irradiation, the MS5-IR700 conjugate-treated PC3 cells displayed cellular swelling, round shape, and rupture of the cell and nuclear membranes. In a co-culture model, the MS5-IR700 conjugate killed MS5-positive Ramos lymphoma cells specifically, while leaving MS5-negative cells unaffected. In line with the data obtained with the monolayer cultures, the MS5-IR700 conjugate also killed PC3 cancer cell spheroids. The treatment induced relocation of heat shock protein 70 and calreticulin to the cell surface, implying the induction of immunogenic cell death. Overall, the data suggest that the developed MS5-IR700 conjugate is a promising therapeutic agent that warrants further preclinical studies.

Regulatory T-Cells as an Emerging Barrier to Immune Checkpoint Inhibition in Lung Cancer

Immune checkpoint inhibitors (ICIs) have revolutionized the treatment paradigm for lung cancer in recent years. These strategies consist of neutralizing antibodies against negative regulators of immune function, most notably cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death protein 1 (PD-1), and PD-1 ligand 1 (PD-L1), thereby impeding the ability of tumor cells to escape immune surveillance. Though ICIs have proven a significant advance in lung cancer therapy, overall survival rates remain low, and lung cancer continues to be the leading cause of cancer-related death in the United States. It is therefore imperative to better understand the barriers to the efficacy of ICIs, particularly additional mechanisms of immunosuppression within the lung cancer microenvironment. Recent evidence suggests that regulatory T-lymphocytes (Tregs) serve as a central mediator of immune function in lung cancer, suppressing sterilizing immunity and contributing to the clinical failure of ICIs. Here, we provide a comprehensive summary of the roles of Tregs in lung cancer pathobiology and therapy, as well as the potential means through which these immunosuppressive mechanisms can be overcome.

Current Prospects for Treatment of Solid Tumors via Photodynamic, Photothermal, or Ionizing Radiation Therapies Combined with Immune Checkpoint Inhibition (A Review)

Photodynamic therapy (PDT) causes selective damage to tumor cells and vasculature and also triggers an anti-tumor immune response. The latter fact has prompted the exploration of PDT as an immune-stimulatory adjuvant. PDT is not the only cancer treatment that relies on electromagnetic energy to destroy cancer tissue. Ionizing radiation therapy (RT) and photothermal therapy (PTT) are two other treatment modalities that employ photons (with wavelengths either shorter or longer than PDT, respectively) and also cause tissue damage and immunomodulation. Research on the three modalities has occurred in different “silos”, with minimal interaction between the three topics. This is happening at a time when immune checkpoint inhibition (ICI), another focus of intense research and clinical development, has opened exciting possibilities for combining PDT, PTT, or RT with ICI to achieve improved therapeutic benefits. In this review, we surveyed the literature for studies that describe changes in anti-tumor immunity following the administration of PDT, PTT, and RT, including efforts to combine each modality with ICI. This information, collected all in one place, may make it easier to recognize similarities and differences and help to identify new mechanistic hypotheses toward the goal of achieving optimized combinations and tumor cures.

Tumor hypoxia represses γδ T cell-mediated antitumor immunity against brain tumors

The anatomic location and immunologic characteristics of brain tumors result in strong lymphocyte suppression. Consequently, conventional immunotherapies targeting CD8 T cells are ineffective against brain tumors. Tumor cells escape immunosurveillance by various mechanisms and tumor cell metabolism can affect the metabolic states and functions of tumor-infiltrating lymphocytes. Here, we discovered that brain tumor cells had a particularly high demand for oxygen, which affected γδ T cell-mediated antitumor immune responses but not those of conventional T cells. Specifically, tumor hypoxia activated the γδ T cell protein kinase A pathway at a transcriptional level, resulting in repression of the activatory receptor NKG2D. Alleviating tumor hypoxia reinvigorated NKG2D expression and the antitumor function of γδ T cells. These results reveal a hypoxia-mediated mechanism through which brain tumors and γδ T cells interact and emphasize the importance of γδ T cells for antitumor immunity against brain tumors.

Hyper-Progressive Disease: The Potential Role and Consequences of T-Regulatory Cells Foiling Anti-PD-1 Cancer Immunotherapy

Antibody-mediated disruption of the programmed cell death protein 1 (PD-1) pathway has brought much success to the fight against cancer. Nevertheless, a significant proportion of patients respond poorly to anti-PD-1 treatment. Cases of accelerated and more aggressive forms of cancer following therapy have also been reported. Termed hyper-progressive disease (HPD), this phenomenon often results in fatality, thus requires urgent attention. Among possible causes of HPD, regulatory T-cells (Tregs) are of suspect due to their high expression of PD-1, which modulates Treg activity. Tregs are a subset of CD4⁺ T-cells that play a non-redundant role in the prevention of autoimmunity and is functionally dependent on the X chromosome-linked transcription factor FoxP3. In cancer, CD4⁺FoxP3⁺ Tregs migrate to tumors to suppress anti-tumor immune responses, allowing cancer cells to persist. Hence, Treg accumulation in tumors is associated with poor prognosis. In mice, the anti-tumor efficacy of anti-PD-1 can be enhanced by depleting Tregs. This suggests Tregs pose resistance to anti-PD-1 therapy. In this article, we review the relevant Treg functions that suppress tumor immunity and the potential effects anti-PD-1 could have on Tregs which are counter-productive to the treatment of cancer, occasionally causing HPD.

Hyper-Progressive Disease: The Potential Role and Consequences of T-Regulatory Cells Foiling Anti-PD-1 Cancer Immunotherapy

Antibody-mediated disruption of the programmed cell death protein 1 (PD-1) pathway has brought much success to the fight against cancer. Nevertheless, a significant proportion of patients respond poorly to anti-PD-1 treatment. Cases of accelerated and more aggressive forms of cancer following therapy have also been reported. Termed hyper-progressive disease (HPD), this phenomenon often results in fatality, thus requires urgent attention. Among possible causes of HPD, regulatory T-cells (Tregs) are of suspect due to their high expression of PD-1, which modulates Treg activity. Tregs are a subset of CD4+ T-cells that play a non-redundant role in the prevention of autoimmunity and is functionally dependent on the X chromosome-linked transcription factor FoxP3. In cancer, CD4+FoxP3+ Tregs migrate to tumors to suppress anti-tumor immune responses, allowing cancer cells to persist. Hence, Treg accumulation in tumors is associated with poor prognosis. In mice, the anti-tumor efficacy of anti-PD-1 can be enhanced by depleting Tregs. This suggests Tregs pose resistance to anti-PD-1 therapy. In this article, we review the relevant Treg functions that suppress tumor immunity and the potential effects anti-PD-1 could have on Tregs which are counter-productive to the treatment of cancer, occasionally causing HPD.

CD25-targeted antibody-drug conjugate depletes regulatory T cells and eliminates established syngeneic tumors via antitumor immunity

Background

Regulatory T cells (T_regs) contribute to an immunosuppressive tumor microenvironment. They play an important role in the establishment and progression of tumors with high T_regs infiltration and present a major obstacle to tumor eradication by immunotherapies. Numerous strategies have been attempted to deplete or block T_regs, although their success has been limited.

Methods

A CD25-targeted, pyrrolobenzodiazepine (PBD) dimer-based antibody–drug conjugate (ADC) was investigated for its ability to deplete T_regs and induce antitumor immunity. Antitumor activity of CD25-ADC either alone or in combination with an anti-programmed cell death protein 1 (PD-1) antibody was evaluated in CD25-negative syngeneic models that exhibit tumor infiltration of CD25-expressing T_regs, and its pharmacodynamics and pharmacokinetics were assessed.

Results

Single low doses of CD25-ADC resulted in potent and durable antitumor activity in established syngeneic solid tumor models and the combination of a suboptimal dose was synergistic with PD-1 blockade. Tumor eradication by the CD25-targeted ADC was CD8+ T cell-dependent and CD25-ADC induced protective immunity. Importantly, while CD25-ADC mediated a significant and sustained intratumoral T_regs depletion, accompanied by a concomitant increase in the number of activated and proliferating tumor-infiltrating CD8+ T effector cells, systemic T_regs depletion was transient, alleviating concerns of potential autoimmune side effects.

Conclusions

This study shows that a PBD dimer-based, CD25-targeted ADC is able to deplete T_regs and eradicate established tumors via antitumor immunity. This represents a novel approach to efficiently deplete T_regs via a very potent DNA damaging toxin known to induce immunogenic cell death. Moreover, this study provides proof of concept for a completely new application of ADCs as immunotherapeutic agents, as the main mode of action relies on the ADC directly targeting immune cells, rather than tumor cells. These strong preclinical data warrant the clinical evaluation of camidanlumab tesirine (ADCT-301), a PBD-based ADC targeting human CD25, either alone or in combination with checkpoint inhibitors in solid tumors with known T_regs infiltration. A phase I trial (NCT03621982) of camidanlumab tesirine in patients with selected advanced solid tumors is ongoing.

Susceptibility and Resistance Mechanisms During Photodynamic Therapy of Melanoma

Melanoma is the most aggressive malignant skin tumor and arises from melanocytes. The resistance of melanoma cells to various treatments results in rapid tumor growth and high mortality. As a local therapeutic modality, photodynamic therapy has been successfully applied for clinical treatment of skin diseases. Photodynamic therapy is a relatively new treatment method for various types of malignant tumors in humans and, compared to conventional treatment methods, has fewer side effects, and is more accurate and non-invasive. Although several in vivo and in vitro studies have shown encouraging results regarding the potential benefits of photodynamic therapy as an adjuvant treatment for melanoma, its clinical application remains limited owing to its relative inefficiency. This review article discusses the use of photodynamic therapy in melanoma treatment as well as the latest progress made in deciphering the mechanism of tolerance. Lastly, potential targets are identified that may improve photodynamic therapy against melanoma cells.

Photodynamic Therapy and Immunity: An Update

Dr. Thomas Dougherty and his Oncology Foundation of Buffalo were the first to support my (S.O.G.) research into the effects of photodynamic therapy (PDT) on the host immune system. The small grant I was awarded in 2002 launched my career as an independent researcher; at the time, there were few studies on the importance of the immune response on the efficacy of PDT and no studies demonstrating the ability of PDT to enhance antitumor immunity. Over the last decades, the interest in PDT as an enhancer of antitumor immunity and our understanding of the mechanisms by which PDT enhances antitumor immunity have dramatically increased. In this review article, we look back on the studies that laid the foundation for our understanding and provide an update on current advances and therapies that take advantage of PDT enhancement of immunity.

Antisense oligonucleotide targeting CD39 improves anti-tumor T cell immunity

Background

Cancer cells are known to develop mechanisms to circumvent effective anti-tumor immunity. The two ectonucleotidases CD39 and CD73 are promising drug targets, as they act in concert to convert extracellular immune-stimulating ATP to adenosine. CD39 is expressed by different immune cell populations as well as cancer cells of different tumor types and supports the tumor in escaping immune recognition and destruction. Thus, increasing extracellular ATP and simultaneously reducing adenosine concentrations in the tumor can lead to effective anti-tumor immunity.

Methods

We designed locked nucleic acid (LNA)-modified antisense oligonucleotides (ASOs) with specificity for human or mouse CD39 that do not need a transfection reagent or delivery system for efficient target knockdown. Knockdown efficacy of ASOs on mRNA and protein level was investigated in cancer cell lines and in primary human T cells. The effect of CD39 knockdown on ATP-degrading activity was evaluated by measuring levels of ATP in tumor cell supernatants and analysis of T cell proliferation in the presence of extracellular ATP. The in vivo effects of CD39-specific ASOs on target expression, anti-tumor immune responses and on tumor growth were analyzed in syngeneic mouse tumor models using multi-color flow cytometry.

Results

CD39-specific ASOs suppressed expression of CD39 mRNA and protein in different murine and human cancer cell lines and in primary human T cells. Degradation of extracellular ATP was strongly reduced by CD39-specific ASOs. Strikingly, CD39 knockdown by ASOs was associated with improved CD8⁺ T cell proliferation. Treatment of tumor-bearing mice with CD39-specific ASOs led to dose-dependent reduction of CD39-protein expression in regulatory T cells (Tregs) and tumor-associated macrophages. Moreover, frequency of intratumoral Tregs was substantially reduced in CD39 ASO-treated mice. As a consequence, the ratio of CD8⁺ T cells to Tregs in tumors was improved, while PD-1 expression was induced in CD39 ASO-treated intratumoral CD8⁺ T cells. Consequently, CD39 ASO treatment demonstrated potent reduction in tumor growth in combination with anti-PD-1 treatment.

Conclusion

Targeting of CD39 by ASOs represents a promising state-of-the art therapeutic approach to improve immune responses against tumors.

Electronic supplementary material

The online version of this article (10.1186/s40425-019-0545-9) contains supplementary material, which is available to authorized users.

Recent advances in nanomaterial-based synergistic combination cancer immunotherapy

This review aims to summarize various synergistic combination cancer immunotherapy strategies based on nanomaterials.

Sox7 promotes high-grade glioma by increasing VEGFR2-mediated vascular abnormality

High-grade glioma (HGG) is highly angiogenic, but antiangiogenic therapy has transient clinical benefit in only a fraction of patients. Vascular regulators of these heterogeneous responses remain undetermined. We found up-regulation of Sox7 and down-regulation of Sox17 in tumor endothelial cells (tECs) in mouse HGG. Sox7 deletion suppressed VEGFR2 expression, vascular abnormality, hypoxia-driven invasion, regulatory T cell infiltration, and tumor growth. Conversely, Sox17 deletion exacerbated these phenotypes by up-regulating Sox7 in tECs. Anti-VEGFR2 antibody treatment delayed tumor growth by normalizing Sox17-deficient abnormal vessels with high Sox7 levels but promoted it by regressing Sox7-deficient vessels, recapitulating variable therapeutic responses to antiangiogenic therapy in HGG patients. Our findings establish that Sox7 promotes tumor growth via vessel abnormalization, and its level determines the therapeutic outcome of VEGFR2 inhibition in HGG. In 189 HGG patients, Sox7 expression was heterogeneous in tumor vessels, and high Sox7 levels correlated with poor survival, early recurrence, and impaired vascular function, emphasizing the clinical relevance of Sox7 in HGG.

The role and significance of VEGFR2+ regulatory T cells in tumor immunity

Tumor development is closely related to angiogenesis, and VEGFR2 plays an important role in tumor angiogenesis. It is broadly expressed in the blood vessels, especially in the microvessels of tumor tissues. Furthermore, VEGFR2 is detected on the surface of the cell membrane in various immune cells, such as dendritic cells, macrophages, and regulatory T cells (Tregs). Tregs, which are one of the key negative regulatory factors in tumor immune microenvironments, show high-level expression of VEGFR2 which participates in the regulation of immunosuppressive function. VEGFR2+ Tregs play a potent suppressive role in the formation of immunosuppressive microenvironments. A large number of reports have proven the synergistic effects between targeted therapy for VEGFR2 and immunotherapy. The depression of VEGFR2 activity on T cells can significantly reduce the infiltration of Tregs into the tumor tissue. Targeted therapy for VEGFR2+ Tregs also provides a new choice for the clinical treatment of malignant solid tumors. In this paper, the role and significance of VEGFR2+ Tregs in tumor immunity in recent years are reviewed.