Boosting tumor-specific immunity using PDT

Photodynamic therapy (PDT) is a cancer treatment with a long-standing history. It employs the application of nontoxic components, namely a light-sensitive photosensitizer and visible light, to generate reactive oxygen species (ROS). These ROS lead to tumor cell destruction, which is accompanied by the induction of an acute inflammatory response. This inflammatory process sends a danger signal to the innate immune system, which results in activation of specific cell types and release of additional inflammatory mediators. Activation of the innate immune response is necessary for subsequent induction of the adaptive arm of the immune system. This includes the priming of tumor-specific cytotoxic T lymphocytes (CTL) that have the capability to directly recognize and kill cells which display an altered self. The past decades have brought increasing appreciation for the importance of the generation of an adaptive immune response for long-term tumor control and induction of immune memory to combat recurrent disease. This has led to considerable effort to elucidate the immune effects PDT treatment elicits. In this review we deal with the progress which has been made during the past 20 years in uncovering the role of PDT in the induction of the tumor-specific immune response, with special emphasis on adaptive immunity.(VLID)219173

Effects of Low-Dose Hypericin-PDT on Murine BMDCs and subsequent induction of regulatory T Lymphocytes

Photodynamische Therapie (PDT) ist eine Krebstherapie, die auf einem nicht-toxischen Photosensitzer (PS), sichtbarem Licht und molekularem Sauerstoff basiert. Durch Reaktion des angeregten PS mit molekularem Sauerstoff führt dies zur Entstehung von sog. ‚reactive oxygen species‘. Hierdurch werden Tumorzellen durch direkte und indirekte Effekte zerstört. Indirekt unterstützt PDT die Einleitung einer entzündlichen Immunantwort und tumorspezifischer Immunreaktionen. Diesbezüglich wurden die Entstehung eines immunologischen Gedächtnisses nach PDT und die Erfordernis dendritischer Zellen (DC) für deren therapeutische Effizienz gezeigt. Die Induktion einer tumorspezifischen Immunantwort und einer Gedächtnisimmunität erfordert, dass die Toleranz gegenüber dem Tumor gebrochen wird. Nach unserer Hypothese verschiebt PDT-Behandlung die DC-vermittelte Induktion von Treg im Mikromilieu des Tumors in Richtung der Differenzierung von Effektor-T-Zellen und fördert so die Eliminierung von Tumorzellen. In dieser Studie wurden sowohl direkte Effekte von PDT mit Hypericin als PS auf DCs als auch die Kapazität behandelter DCs, Treg und Effektor-T-Zellen zu induzieren, evaluiert. DCs zeigten gesteigerte Proliferation nach PDT-Behandlung mit bis zu 100 nM Hypericin und zytotoxische Effekte ab einer Konzentration von mehr als 200 nM. Die Induktion von Treg durch PDT-DCs war bei niedriger Konzentration tendenziell verringert. Die Th1 und Th17 spezifischen Zytokine IFN-γ und IL-17A zeigten gleichbleibende IFN-γ Niveaus und gesteigerte IL-17A Sekretion in Ko-Kulturen, die mit 300 nM Hypericin-PDT behandelte DCs enthielten. Zusammenfassend zeigt diese Studie einen vorteilhaften Effekt von niedrig dosierter Hypericin-PDT auf die Lebensfähigkeit von DCs und deren proinflammatorische Kapazität, eine verringerte Induktion von Treg und die Erhaltung der normalen Differenzierung von Effektor-T-Zellen. Diese Effekte könnten die PDT-induzierte Antitumor-Immunität teilweise erklären.Photodynamic therapy (PDT) is a cancer treatment modality which is based on three components: a non-toxic photosensitizer (PS), visible light and molecular oxygen. Photoactivation of the PS leads to generation of reactive oxygen species. Subsequently, tumor cells are eliminated by direct and indirect effects. Indirectly, PDT facilitates the induction of an inflammatory response and tumor-specific immune reactions. In this context, generation of memory immunity and a requirement for dendritic cells (DC) for PDT efficiency has been shown. We hypothesized that PDT treatment might skew DC-mediated induction of Treg in the tumor-microenvironment towards effector T cell differentiation, thereby promoting elimination of the tumor. This study assessed direct effects of PDT using hypericin as PS on DCs on the one hand and the capacity of treated DCs to induce Treg and effector T cells on the other hand. DCs showed increased proliferation at concentrations up to 100 nM hypericin and a cytotoxic effect at concentrations higher than 200 nM in response to PDT. Induction of Treg by PDT-DCs displayed a tendency towards reduced Treg levels in response to low-dose treatment. Secretion of Th1 and Th17 signature cytokines IFN-γ and IL-17 showed consistent IFN-γ levels and increased IL-17A levels in co-cultures with 300 nM hypericin-PDT treated DCs. In summary, this study shows a beneficial effect of low-dose hypericin-PDT on DC viability and proinflammatory capacity. Furthermore, it points to diminished induction of Treg by PDT-DCs and maintenance of normal effector T cell induction. These effects could partially explain the anti-tumor immunity triggered by PDT

Synergy of Human Platelet-Derived Extracellular Vesicles with Secretome Proteins Promotes Regenerative Functions

Platelet-rich plasma is a promising regenerative therapeutic with controversial efficacy. We and others have previously demonstrated regenerative functions of human platelet lysate (HPL) as an alternative platelet-derived product. Here we separated extracellular vesicles (EVs) from soluble factors of HPL to understand the mode of action during skin-organoid formation and immune modulation as model systems for tissue regeneration. HPL-EVs were isolated by tangential-flow filtration (TFF) and further purified by size-exclusion chromatography (SEC) separating EVs from (lipo)protein-enriched soluble fractions. We characterized samples by tunable resistive pulse sensing, western blot, tandem mass-tag proteomics and super-resolution microscopy. We evaluated EV function during angiogenesis, wound healing, organoid formation and immune modulation. We characterized EV enrichment by TFF and SEC according to MISEV2018 guidelines. Proteomics showed three major clusters of protein composition separating TSEC-EVs from HPL clustering with TFF soluble fractions and TFF-EVs clustering with TSEC soluble fractions, respectively. HPL-derived TFF-EVs promoted skin-organoid formation and inhibited T-cell proliferation more efficiently than TSEC-EVs or TSEC-soluble fractions. Recombining TSEC-EVs with TSEC soluble fractions re-capitulated TFF-EV effects. Zeta potential and super-resolution imaging further evidenced protein corona formation on TFF-EVs. Corona depletion on SEC-EVs could be artificially reconstituted by TSEC late fraction add-back. In contrast to synthetic nanoparticles, which commonly experience reduced function after corona formation, the corona-bearing EVs displayed improved functionality. We conclude that permissive isolation technology, such as TFF, and better understanding of the mechanism of EV corona function are required to realize the complete potential of platelet-based regenerative therapies