IL-10 does not play a role in cutaneous Photofrin photodynamic therapy-induced suppression of the contact hypersensitivity response

Recent advances in light-triggered cancer immunotherapy

Light-triggered phototherapies, such as photodynamic therapy (PDT) and photothermal therapy (PTT), have shown strong therapeutic efficacy with minimal invasiveness and systemic toxicity, offering opportunities for tumor-specific therapies. Phototherapies not only induce direct tumor cell killing, but also trigger anti-tumor immune responses by releasing various immune-stimulating factors. In recent years, conventional phototherapies have been combined with cancer immunotherapy as synergistic therapeutic modalities to eradicate cancer by exploiting the innate and adaptive immunity. These combined photoimmunotherapies have demonstrated excellent therapeutic efficacy in preventing tumor recurrence and metastasis compared to phototherapy alone. This review covers recent advancements in combined photoimmunotherapy, including photoimmunotherapy (PIT), PDT-combined immunotherapy, and PTT-combined immunotherapy, along with their underlying anti-tumor immune response mechanisms. In addition, the challenges and future research directions for light-triggered cancer immunotherapy are discussed.

5-FU mediated depletion of myeloid suppressor cells enhances T-cell infiltration and anti-tumor response in immunotherapy-resistant lung tumor

Tumor microenvironment (TME) is a heterogeneous system consisting of both cellular and acellular components. The growth and progression of tumors rely greatly on the nature of TME, marking it as an important target in cancer immunotherapy. Lewis Lung Carcinoma (LLC) is an established murine lung cancer model representing immunologically 'cold' tumors characterized by very few infiltrated cytotoxic T-cells, high levels of Myeloid-Derived Suppressor Cells (MDSCs) and Tumor-Associated Macrophages (TAMs). Here, we report various strategies we applied to reverse the non-immunogenic character of this cold tumor by imparting: a) immunogenic cell death using Hypericin nanoparticle-based photodynamic therapy (PDT), b) repolarising TAM using a TLR7/8 agonist, resiquimod, c) immune checkpoint inhibition using anti-PD-L1 and d) depleting MDSCs using low-dose 5-fluorouracil (5-FU) chemotherapy. Interestingly, the nano-PDT, resiquimod or anti-PD-L1 treatment had no major impact on tumor growth, whereas low-dose 5-FU-mediated depletion of MDSCs showed significant anti-tumor effect, primarily caused by the increased infiltration of CD8⁺ cytotoxic T-cells (∼96%). Though we have tested combining PDT with resiquimod or 5-FU for any synergistic effect, low-dose 5-FU alone showed better response than combinations. In effect, we show that depletion of MDSCs using low-dose 5-FU was one of the best methods to augment infiltration of CD8⁺ cytotoxic T-cells into a cold tumor, which is resistant to conventional therapies including immune checkpoint inhibitors.

Oxidative Stress and Photodynamic Therapy of Skin Cancers: Mechanisms, Challenges and Promising Developments

Ultraviolet radiation is one of the most pervasive environmental interactions with humans. Chronic ultraviolet irradiation increases the danger of skin carcinogenesis. Probably, oxidative stress is the most important mechanism by which ultraviolet radiation implements its damaging effects on normal cells. However, notwithstanding the data referring to the negative effects exerted by light radiation and oxidative stress on carcinogenesis, both factors are used in the treatment of skin cancer. Photodynamic therapy (PDT) consists of the administration of a photosensitiser, which undergoes excitation after suitable irradiation emitted from a light source and generates reactive oxygen species. Oxidative stress causes a condition in which cellular components, including DNA, proteins, and lipids, are oxidised and injured. Antitumor effects result from the combination of direct tumour cell photodamage, the destruction of tumour vasculature and the activation of an immune response. In this review, we report the data present in literature dealing with the main signalling molecular pathways modified by oxidative stress after photodynamic therapy to target skin cancer cells. Moreover, we describe the progress made in the design of anti-skin cancer photosensitisers, and the new possibilities of increasing the efficacy of PDT via the use of molecules capable of developing a synergistic antineoplastic action.

Effective blue light photodynamic therapy does not affect cutaneous langerhans cell number or oxidatively damage DNA

BACKGROUND

Photodynamic therapy (PDT) using aminolevulinic acid (ALA) with blue light or red light is effective for treating actinic keratoses (AKs). However, immunosuppression follows red light PDT, raising the spectre of skin cancer promotion in treated skin.

OBJECTIVE

To determine whether broad-area short incubation (BASI)-ALA-PDT using blue light immunosuppression immunosuppresses treated skin.

METHODS

Patients were evaluated clinically and by standardized facial biopsies of non-AK skin before, 24 hours and 1 month after customary blue light BASI-ALA-PDT. All biopsies were stained for markers of epidermal atypia and Langerhans cells (LCs); and at 24 hours to detect oxidative DNA damage.

RESULTS

Patients had an 81% reduction in AKs and slight improvement in clinical and histologic signs of photoaging after 1 month. The biopsied chronically photodamaged skin without clinically detectable AKs showed no effect of PDT on the LC number, distribution, or morphology; and no oxidative DNA damage, in contrast to the changes reported after customary red light PDT.

CONCLUSION

Customary blue light BASI-ALA-PDT does not affect the LC number or produce oxidative DNA damage, the sequelae of red light PDT responsible for immunosuppression in treated skin.

Immunogenic cell death: can it be exploited in PhotoDynamic Therapy for cancer?

Immunogenic Cell Death (ICD) could represent the keystone in cancer management since tumor cell death induction is crucial as well as the control of cancer cells revival after neoplastic treatment. In this context, the immune system plays a fundamental role. The concept of Damage-Associated Molecular Patterns (DAMPs) has been proposed to explain the immunogenic potential of stressed or dying/dead cells. ICD relies on DAMPs released by or exposed on dying cells. Once released, DAMPs are sensed by immune cells, in particular Dendritic Cells (DCs), acting as activators of Antigen-Presenting Cells (APCs), that in turn stimulate both innate and adaptive immunity. On the other hand, by exposing DAMPs, dying cancer cells change their surface composition, recently indicated as vital for the stimulation of the host immune system and the control of residual ill cells. It is well established that PhotoDynamic Therapy (PDT) for cancer treatment ignites the immune system to elicit a specific antitumor immunity, probably linked to its ability in inducing exposure/release of certain DAMPs, as recently suggested. In the present paper, we discuss the DAMPs associated with PDT and their role in the crossroad between cancer cell death and immunogenicity in PDT.

Direct and indirect photodynamic therapy effects on the cellular and molecular components of the tumor microenvironment

Photodynamic therapy (PDT) is a novel cancer treatment. It involves the activation of a photosensitizer (PS) with light of specific wavelength, which interacts with molecular oxygen to generate singlet oxygen and other reactive oxygen species (ROS) that lead to tumor cell death. When a tumor is treated with PDT, in addition to affect cancer cells, the extracellular matrix and the other cellular components of the microenvironment are altered and finally this had effects on the tumor cells survival. Furthermore, the heterogeneity in the availability of nutrients and oxygen in the different regions of a tridimensional tumor has a strong impact on the sensitivity of cells to PDT. In this review, we summarize how PDT affects indirectly to the tumor cells, by the alterations on the extracellular matrix, the cell adhesion and the effects over the immune response. Also, we describe direct PDT effects on cancer cells, considering the intratumoral role that autophagy mediated by hypoxia-inducible factor 1 (HIF-1) has on the efficiency of the treatment.

The immunosuppressive side of PDT

Photodynamic therapy (PDT) is a promising novel therapeutic procedure for the management of a variety of solid tumors and many non-malignant diseases. PDT has been described as having a significant effect on the immune system, which may be either immunostimulatory or, in some circumstances, immunosuppressive. The immunosuppressive effects of PDT have nearly all been concerned with the suppression of the contact hypersensitivity reaction in mice. Here, we review the immunosuppressive aspects of PDT treatment and discuss some additional mechanisms that may be involved.

Photodynamic therapy-induced immunosuppression in humans is prevented by reducing the rate of light delivery

Photodynamic therapy (PDT) of non-melanoma skin cancers currently carries failure rates of 10-40%. The optimal irradiation protocol is as yet unclear. Previous studies showed profound immunosuppression after PDT, which may compromise immune-mediated clearance of these antigenic tumors. Slower irradiation prevents immunosuppression in mice, and may be at least as effective as high-fluence-rate PDT in preliminary clinical trials. The photosensitizers 5-aminolaevulinic acid and/or methyl aminolaevulinate were applied to discrete areas on the backs of healthy Mantoux-positive volunteers, followed by narrowband red light irradiation (632 nm) at varied doses and fluence rates. Delayed type hypersensitivity (Mantoux) reactions were elicited at test sites and control sites to determine immunosuppression. Human ex vivo skin received low- and high-fluence-rate PDT and was stained for oxidative DNA photolesions. PDT caused significant, dose-responsive immunosuppression at high (75 mW cm(-2)) but not low (15 or 45 mW cm(-2)) fluence rates. DNA photolesions, which may be a trigger for immunosuppression, were observed after high-fluence-rate PDT but not when light was delivered more slowly. This study demonstrates that the current clinical PDT protocol (75 mW cm(-2)) is highly immunosuppressive. Simply reducing the rate of irradiation, while maintaining the same light dose, prevented immunosuppression and genetic damage and may have the potential to improve skin cancer outcomes.

Photodynamic therapy: illuminating the road from cell death towards anti-tumour immunity

Photodynamic therapy (PDT) utilizes the destructive power of reactive oxygen species generated via visible light irradiation of a photosensitive dye accumulated in the cancerous tissue/cells, to bring about their obliteration. PDT activates multiple signalling pathways in cancer cells, which could give rise to all three cell death modalities (at least in vitro). Simultaneously, PDT is capable of eliciting various effects in the tumour microenvironment thereby affecting the tumour-associated/-infiltrating immune cells and by extension, leading to infiltration of various immune cells (e.g. neutrophils) into the treated site. PDT is also associated to the activation of different immune phenomena, e.g. acute-phase response, complement cascade and production of cytokines/chemokines. It has also come to light that, PDT is capable of activating 'anti-tumour adaptive immunity' in both pre-clinical as well as clinical settings. Although the ability of PDT to induce 'anti-cancer vaccine effect' is still debatable, yet it has been shown to be capable of inducing exposure/release of certain damage-associated molecular patterns (DAMPs) like HSP70. Therefore, it seems that PDT is unique among other approved therapeutic procedures in generating a microenvironment suitable for development of systemic anti-tumour immunity. Apart from this, recent times have seen the emergence of certain promising modalities based on PDT like-photoimmunotherapy and PDT-based cancer vaccines. This review mainly discusses the effects exerted by PDT on cancer cells, immune cells as well as tumour microenvironment in terms of anti-tumour immunity. The ability of PDT to expose/release DAMPs and the future perspectives of this paradigm have also been discussed.

Topical photodynamic therapy is immunosuppressive in humans

BACKGROUND

Visible light irradiation after application of a photosensitizer (topical photodynamic therapy; PDT) is increasingly used to treat nonmelanoma skin cancers and premalignant actinic keratoses. PDT can provide a cosmetically superior alternative to surgery, but carries failure rates of 10-40%. While some murine studies have suggested immune enhancement by PDT, others reported immunosuppressive effects, which may indicate impaired antitumour immunity and thus compromised tumour clearance.

OBJECTIVES

This study aimed to determine the in vivo immune effects of PDT in humans.

METHODS

Using healthy, Mantoux-positive volunteers, we irradiated discrete areas of the back with narrowband red light (630 nm; 37 J cm(-2)), with and without prior application of 5-aminolaevulinic acid (ALA) or methyl aminolaevulinate (MAL). Adjacent, untreated areas served as immunologically intact control sites. Delayed-type hypersensitivity responses to tuberculin purified protein derivative (Mantoux reactions) were then elicited in each of the irradiated, unirradiated and control sites, and the intensity of the reactions was quantitated with an erythema meter and by measurement of Mantoux diameter. By comparing Mantoux intensity at treated and control sites, immunosuppression was determined in each volunteer for each intervention.

RESULTS

We found that both MAL-PDT and ALA-PDT significantly suppressed Mantoux erythema (by 30% and 50%, respectively) and diameter (41% and 38%). Red light alone significantly suppressed diameter (22%) but not erythema (13%).

CONCLUSIONS

Topical PDT induced significant immune suppression, which could impair local antitumour immune responses and may thus contribute to treatment failure.

Expression of IL-10, TGF-beta(1) and TNF-alpha in Cultured Keratinocytes (HaCaT Cells) after IPL Treatment or ALA-IPL Photodynamic Treatment

BACKGROUND

Depending on the light dose and concentration of photosensitizer for photodynamic treatment (PDT), a multitude of dose-related events are demonstrable in PDT-treated cells. Sublethal doses may result in the alteration of cytokine release and consequently modify immune actions, rather than cause cell death.

OBJECTIVE

The purpose of this study was to investigate cytokine expression in cultured HaCaT cells after intense pulse light (IPL) treatment or PDT utilizing 5-aminolevulinic acid (ALA) and IPL at sublethal doses.

METHODS

Cultured HaCaT cells were treated with either IPL only (4, 8 and 12 J/cm(2)) or ALA-IPL PDT (100micromol/L of ALA; 0, 4, 8, and 12 J/cm(2) of IPL). The expression of IL-10, TGF-beta(1) and TNF-alpha was investigated by reverse transcription-polymerase chain reaction and enzyme linked immunosorbent assay.

RESULTS

IL-10 protein increased up to 5.95-fold after IPL treatment and up to 2.85-fold after PDT. TGF-beta(1) mRNA and protein showed slight increases after both IPL treatment and PDT, of which the latter induced slightly larger increases. TNF-alpha mRNA and protein showed no induction or reduction after PDT.

CONCLUSION

Increased expressions of IL-10 and TGF-beta(1) was observed after PDT. The induction of IL-10 may contribute to the anti-inflammatory effect, which explains the therapeutic benefit of PDT for inflammatory dermatoses, and that of TGF-beta(1) may be related to the therapeutic effect for psoriasis. The finding that IL-10 induction was more marked after IPL treatment than after PDT suggests that other mechanisms than IL-10 induction in keratinocytes after PDT may participate in the anti-inflammatory effect of PDT.

Immunosuppressive effects of photodynamic therapy by topical aminolevulinic acid

Photodynamic therapy (PDT) has been used for inflammatory skin disorders as well as superficial skin cancers such as solar keratosis and Bowen's disease. Whether PDT with topical application of aminolevulinic acid (ALA) and exposure to visible light has a similar immunosuppressive action to ultraviolet phototherapy was investigated using a murine contact hypersensitivity (CHS) model. The number of epidermal Langerhans cells (LC) was decreased with their morphological changes 1 day after PDT with the minimal level at 5 days and gradual recovery thereafter. Conversely, the number of CD11c(+) I-A(+) cells was significantly increased in the draining lymph nodes after PDT. This suggests that LC moved from PDT-treated skin, resulting in the decrement of epidermal LC and migration to lymph nodes. CHS response to DNFB applied on the PDT-treated skin with 20% ALA and 40 J/cm(2) visible light was significantly suppressed (local immunosuppression). When mice were treated with 80 J/cm(2) of PDT, CHS response to the antigen applied on untreated distant skin was also significantly suppressed (systemic immunosuppression). The locally or systemically immunosuppressed mice by PDT were attempted to sensitize again with DNFB on non-treated skin, but elicitation responses were significantly suppressed. However, these mice were able to be sensitized with another hapten, oxasolone. Thus, a hapten-specific immunological unresponsiveness (tolerance) was induced in mice by topical ALA-PDT. These findings suggest that PDT has a potential immunological contribution to clinical efficacy for inflammatory diseases identical to ultraviolet phototherapies.

Chemopreventative Thoughts for Photodynamic Therapy

The concept of skin cancer prevention with photodynamic therapy has evolved over the past few years to include large surface application of aminolevulinic acid or methyl aminolevulinate followed by light exposure to prevent the development of new lesions. Pre-clinical studies using various mouse models have shown that large surface photodynamic therapy can prevent the appearance of actinic keratoses, squamous cell carcinomas, and basal cell carcinomas. Recent clinical studies also suggest that large surface photodynamic therapy can prevent the development of actinic keratoses and possibly skin cancer.

Photodynamic therapy and anti-tumour immunity

Photodynamic therapy (PDT) uses non-toxic photosensitizers and harmless visible light in combination with oxygen to produce cytotoxic reactive oxygen species that kill malignant cells by apoptosis and/or necrosis, shut down the tumour microvasculature and stimulate the host immune system. In contrast to surgery, radiotherapy and chemotherapy that are mostly immunosuppressive, PDT causes acute inflammation, expression of heat-shock proteins, invasion and infiltration of the tumour by leukocytes, and might increase the presentation of tumour-derived antigens to T cells.

Systemic Suppression of the Contact Hypersensitivity by the Products of Protoporphyrin IX Photooxidation

Photodynamic therapy (PDT) is frequently accompanied by induction of systemic immunosuppression. Photochemical mechanisms underlying this effect are not completely understood. Here, we demonstrate the immunosuppressive activity of photooxidation products of protoporphyrin IX dimethyl ester (PPIX) in a murine model of contact hypersensitivity (CHS) to 2,4-dinitrofluorobenzene (DNFB). Intravenous injection of the preirradiated solution of PPIX to mice resulted in fluence-dependent suppression of the CHS. The samples of photodecomposed PPIX with suppressive effect on the CHS contained chlorin-type products, namely, two isomers of photoprotoporphyrin (pPP1 and pPP2) as main photoproducts. Concentration-dependent suppression of the CHS was also induced when purified pPP1 or pPP2 were injected to mice intravenously. These purified photoproducts exerted equal immunosuppressive activity. The highest suppression of the CHS was induced when pPP1 was injected 20 h before sensitization with DNFB. The lowest suppression was at its injection time 24 h before challenge. The pPP1-induced suppression of the CHS was adoptively transferable and was associated with generation of cells with suppressive functions. These suppressor cells inhibited the efferent phase of the CHS. Our results strongly indicate that induction of systemic immunosuppression by PDT with PPIX may proceed through photobleaching of photosensitizer and generation of photoprotoporphyrins, which can affect T cell immunity.

The immunological consequences of photodynamic treatment of cancer, a literature review

In this review we discuss the effect of photodynamic treatment (PDT) of solid tumors on the immune response. The effect on both the innate and adapted immune response is discussed. We have summarized the evidence that PDT causes or enhances an anti-tumor response. PDT is a local treatment in which the treated tumor remains in situ while the immune system is only locally affected and still functional in contrast with e.g. after systemic chemotherapy. We conclude that PDT of cancer is a way of in situ vaccination to induce a systemic antitumor response. In general, immune cells are found in the tumor stroma, separated from tumor cells by extracellular matrix and basal membrane-like structures. We hypothesize that PDT destroys the structure of a tumor, thereby enabling direct interaction between immune cells and tumor cells resulting in the systemic anti-tumor immune response.