A prognostic neural epigenetic signature in high-grade glioma.

Neural-tumor interactions drive glioma growth as evidenced in preclinical models, but clinical validation is limited. We present an epigenetically defined neural signature of glioblastoma that independently predicts patients' survival. We use reference signatures of neural cells to deconvolve tumor DNA and classify samples into low- or high-neural tumors. High-neural glioblastomas exhibit hypomethylated CpG sites and upregulation of genes associated with synaptic integration. Single-cell transcriptomic analysis reveals a high abundance of malignant stemcell-like cells in high-neural glioblastoma, primarily of the neural lineage. These cells are further classified as neural-progenitor-cell-like, astrocyte-like and oligodendrocyte-progenitor-like, alongside oligodendrocytes and excitatory neurons. In line with these findings, high-neural glioblastoma cells engender neuron-to-glioma synapse formation in vitro and in vivo and show an unfavorable survival after xenografting. In patients, a high-neural signature is associated with decreased overall and progression-free survival. High-neural tumors also exhibit increased functional connectivity in magnetencephalography and resting-state magnet resonance imaging and can be detected via DNA analytes and brain-derived neurotrophic factor in patients' plasma. The prognostic importance of the neural signature was further validated in patients diagnosed with diffuse midline glioma. Our study presents an epigenetically defined malignant neural signature in high-grade gliomas that is prognostically relevant. High-neural gliomas likely require a maximized surgical resection approach for improved outcomes.

Biomonitoring of volatile organic compounds and organophosphorus flame retardands in commercial aircrews after "fume and smell events".

Health risks to humans after "fume and smell events", short-term incidents on aircrafts that are accompanied by unpleasant odour or visible smoke, remain a subject of controversy. We assessed exposure to volatile organic compounds (VOC) and organophosphorus compounds (OPC) by biomonitoring in 375 aircrew members after self-reported "fume and smell events" and in 88 persons of the general population. A total of 20 parameters were analysed in blood and urine by gas chromatography and mass spectrometry. Median levels of acetone in blood and urine and 2-propanol in blood were elevated in aircrews compared to controls (p < 0.0001). Additionally, elevated peak exposures, best estimated by the 95th percentiles, were observed in aircrews for n-heptane and n-octane in blood, and acetone, 2,5-hexanedione and o-cresol in urine. Only the maximum observed levels of 2,5-hexandione in urine (768 µg/L) and toluene in blood (77 µg/L) in aircrew members were higher than the current biological exposure indices (BEI® levels) (500 and 20 µg/L, respectively) of the American Conference of Governmental Industrial Hygienists (US-ACGIH) for workers occupationally exposed to n-hexane and toluene, two well-accepted human neurotoxicants. Low-level exposures to n-hexane and toluene could be also observed in controls. The majority of OPC parameters in urine, including those of neurotoxic ortho-isomers of tricresylphosphate, were below the limit of quantitation in both aircrews and controls. Our comparative VOC and OPC analyses in biological samples of a large number of aircrew members and controls suggest that exposures are similar in both groups and generally low.

A novel strategy to generate immunocytokines with activity-on-demand using small molecule inhibitors.

Cytokine-based therapeutics have been shown to mediate objective responses in certain tumor entities but suffer from insufficient selectivity, causing limiting toxicity which prevents dose escalation to therapeutically active regimens. The antibody-based delivery of cytokines significantly increases the therapeutic index of the corresponding payload but still suffers from side effects associated with peak concentrations of the product in blood upon intravenous administration. Here we devise a general strategy (named "Intra-Cork") to mask systemic cytokine activity without impacting anti-cancer efficacy. Our technology features the use of antibody-cytokine fusions, capable of selective localization at the neoplastic site, in combination with pathway-selective inhibitors of the cytokine signaling, which rapidly clear from the body. This strategy, exemplified with a tumor-targeted IL12 in combination with a JAK2 inhibitor, allowed to abrogate cytokine-driven toxicity without affecting therapeutic activity in a preclinical model of cancer. This approach is readily applicable in clinical practice.

Toxicokinetics of homosalate in humans after dermal application: applicability of oral-route data for exposure assessment by human biomonitoring.

Homosalate (HMS) is a UV filter used in sunscreens and personal care products as a mixture of cis- and trans-isomers. Systemic absorption after sunscreen use has been demonstrated in humans, and concerns have been raised about possible endocrine activity of HMS, making a general population exposure assessment desirable. In a previous study, it was shown that the oral bioavailability of cis-HMS (cHMS) is lower than that of trans-HMS (tHMS) by a factor of 10, calling for a separate evaluation of both isomers in exposure and risk assessment. The aim of the current study is the investigation of HMS toxicokinetics after dermal exposure. Four volunteers applied a commercial sunscreen containing 10% HMS to their whole body under regular-use conditions (18-40 mg HMS (kg bw)-1). Parent HMS isomers and hydroxylated and carboxylic acid metabolites were quantified using authentic standards and isotope dilution analysis. Further metabolites were investigated semi-quantitatively. Elimination was delayed and slower compared to the oral route, and terminal elimination half-times were around 24 h. After dermal exposure, the bioavailability of cHMS was a factor of 2 lower than that of tHMS. However, metabolite ratios in relation to the respective parent isomer were very similar to the oral route, supporting the applicability of the oral-route urinary excretion fractions for dermal-route exposure assessments. Exemplary calculations of intake doses showed margins of safety between 11 and 92 (depending on the approach) after single whole-body sunscreen application. Human biomonitoring can reliably quantify oral and dermal HMS exposures and support the monitoring of exposure reduction measures.

Ultrahigh-Throughput, Real-Time Flow Cytometry for Rare Cell Quantification from Whole Blood.

We present an ultrahigh-throughput, real-time fluorescence cytometer comprising a viscoelastic microfluidic system and a complementary metal-oxide-semiconductor (CMOS) linear image sensor-based detection system. The flow cytometer allows for real-time quantification of a variety of fluorescence species, including micrometer-sized particles and cells, at analytical throughputs in excess of 400,000 species per second. The platform integrates a custom C++ control program and graphical user interface (GUI) to allow for the processing of raw signals, adjustment of processing parameters, and display of fluorescence intensity histograms in real time. To demonstrate the efficacy of the platform for rare event detection and its utility as a basic clinical tool, we measure and quantify patient-derived circulating tumor cells (CTCs) in peripheral blood, realizing that detection has a sensitivity of 6 CTCs per million blood cells (0.000006%) with a volumetric throughput of over 3 mL/min.

Identification, Organic Synthesis, and Sensitive Analysis of a cis-Homosalate-Specific Exposure Biomarker.

Homosalate (HMS) is an organic UV filter used in sunscreens and personal care products. Despite its widespread use and detection in environmental matrices, little is known regarding its exposure in humans. HMS is used as a mixture of cis- and trans-isomers, and we recently revealed major differences in human toxicokinetics, indicating the need to consider these isomers separately in exposure and risk assessments. In the course of these previous investigations of human HMS toxicokinetics, we identified two trans-HMS-specific and one cis-HMS-specific biomarker candidates. However, the latter lacks sensitivity due to only low amounts excreted in urine, prompting the search for another cis-HMS-specific biomarker. Our toxicokinetic investigations revealed a total of five isomers of HMS carboxylic acid metabolites (HMS-CA). Of these, only one was specifically formed from cis-HMS (HMS-CA 5), but its full identity in terms of constitution and configuration had, so far, not been elucidated. Here, we describe the synthesis of three HMS-CA isomers, of which the isomer (1R,3S,5S)/(1S,3R,5R)-3-((2-hydroxybenzoyl)oxy)-1,5-dimethylcyclohexane-1-carboxylic acid turned out to be HMS-CA 5. Taken together with two previously synthesized HMS-CA isomers, we were able to identify the constitution and configuration of all five HMS-CA isomers observed in human metabolism. We integrated the newly identified cis-HMS-specific metabolite HMS-CA 5 into our previously published human biomonitoring LC-MS/MS method. Intra- and interday precisions had coefficients of variation below 2% and 5%, respectively, and the mean relative recovery was 96%. The limit of quantification in urine was 0.02 µg L-1, enabling the quantification of HMS-CA 5 in urine samples for at least 96 h after sunscreen application. The extended method thus enables the sensitive and separate monitoring of cis- and trans-HMS in future human biomonitoring studies for exposure and risk assessment.

[Immunotherapy against gliomas]. / Immuntherapie gegen Gliome.

BACKGROUND: Gliomas represent the most frequent malignant primary brain tumors in adults. Despite multimodal treatment concepts involving surgery, irradiation and chemotherapy, the prognosis remains poor and they are incurable. Recent insights into the interactions between the immune system and the central nervous system as well as breakthroughs in the results of other cancer types have led to the fact that various immunotherapeutic approaches against gliomas have also been investigated and in some cases specifically developed. OBJECTIVE: This article provides an overview of the current status of different immunotherapeutic concepts against gliomas, highlighting the advantages, disadvantages, and challenges. Additionally, it provides an overview of currently ongoing immunotherapeutic clinical trials in Germany and neighboring countries. RESULTS: Previous randomized studies on antibodies against programmed cell death protein 1 (anti-PD1) immune checkpoint inhibition, viral treatment and peptide vaccination targeting the variant III of the epidermal growth factor receptor (EGFRvIII) in glioblastomas were negative with respect to survival benefits. Conversely, other immunotherapeutic approaches, such as multivalent or driver mutation-based vaccinations, cytokine-based therapy and cell therapy, demonstrated a robust scientific foundation, with at least early studies showing promising safety and pharmacodynamic effects on the tumors. DISCUSSION: Currently, immunotherapies against gliomas should only be applied within the framework of well-designed clinical studies. There are still many knowledge gaps regarding the mechanisms of action and resistance of various immunotherapies. Accompanying translational research is essential to address these gaps and develop more effective therapies.

Time-resolved single-cell transcriptomics defines immune trajectories in glioblastoma.

Deciphering the cell-state transitions underlying immune adaptation across time is fundamental for advancing biology. Empirical in vivo genomic technologies that capture cellular dynamics are currently lacking. We present Zman-seq, a single-cell technology recording transcriptomic dynamics across time by introducing time stamps into circulating immune cells, tracking them in tissues for days. Applying Zman-seq resolved cell-state and molecular trajectories of the dysfunctional immune microenvironment in glioblastoma. Within 24 hours of tumor infiltration, cytotoxic natural killer cells transitioned to a dysfunctional program regulated by TGFB1 signaling. Infiltrating monocytes differentiated into immunosuppressive macrophages, characterized by the upregulation of suppressive myeloid checkpoints Trem2, Il18bp, and Arg1, over 36 to 48 hours. Treatment with an antagonistic anti-TREM2 antibody reshaped the tumor microenvironment by redirecting the monocyte trajectory toward pro-inflammatory macrophages. Zman-seq is a broadly applicable technology, enabling empirical measurements of differentiation trajectories, which can enhance the development of more efficacious immunotherapies.

The Epigenetic Evolution of Glioma Is Determined by the IDH1 Mutation Status and Treatment Regimen.

Tumor adaptation or selection is thought to underlie therapy resistance in glioma. To investigate longitudinal epigenetic evolution of gliomas in response to therapeutic pressure, we performed an epigenomic analysis of 132 matched initial and recurrent tumors from patients with IDH-wildtype (IDHwt) and IDH-mutant (IDHmut) glioma. IDHwt gliomas showed a stable epigenome over time with relatively low levels of global methylation. The epigenome of IDHmut gliomas showed initial high levels of genome-wide DNA methylation that was progressively reduced to levels similar to those of IDHwt tumors. Integration of epigenomics, gene expression, and functional genomics identified HOXD13 as a master regulator of IDHmut astrocytoma evolution. Furthermore, relapse of IDHmut tumors was accompanied by histologic progression that was associated with survival, as validated in an independent cohort. Finally, the initial cell composition of the tumor microenvironment varied between IDHwt and IDHmut tumors and changed differentially following treatment, suggesting increased neoangiogenesis and T-cell infiltration upon treatment of IDHmut gliomas. This study provides one of the largest cohorts of paired longitudinal glioma samples with epigenomic, transcriptomic, and genomic profiling and suggests that treatment of IDHmut glioma is associated with epigenomic evolution toward an IDHwt-like phenotype. SIGNIFICANCE: Standard treatments are related to loss of DNA methylation in IDHmut glioma, resulting in epigenetic activation of genes associated with tumor progression and alterations in the microenvironment that resemble treatment-naïve IDHwt glioma.

Biomonitoring of polycyclic aromatic hydrocarbons in firefighters at fire training facilities and in employees at respiratory protection and hose workshops.

Introduction: Polycyclic aromatic hydrocarbons (PAHs) are carcinogenic to humans and are formed by incomplete combustion. PAHs are always present during firefighting operations, and fire department members can be exposed to them in the workplace. Methods: In this study, we analyzed 1-hydroxypyrene (1-OHP) in 36 urine samples from nine firefighters, collected before and after fire training sessions, and 32 urine samples from eight employees at respiratory protection and hose workshops. To assess breakthrough PAH exposure through personal protective equipment and potential dermal uptake, some of the workshop employees wore cotton garments under their regular workwear. Cotton samples were then examined for the presence of 17 semi-volatile and low-volatility PAHs. Results: After firefighting exercises, we observed approximately a fivefold increase in mean 1-OHP concentrations in samples from firefighters, from 0.24 µg/L to 1.17 µg/L (maximum: 5.31 µg/L). In contrast, 1-OHP levels in workshop employees were found to be low, with the majority of urine samples yielding concentrations below the limit of quantification (LOQ: 0.05 µg/L, maximum: 0.11 µg/L). Similarly, low PAH levels were found on the workshop employees' cotton undergarments, with maximum concentrations of 250 and 205 ng/g for pyrene and benzo[a]pyrene, respectively. Discussion: In conclusion, significant increases in 1-OHP in urine were observed in firefighters after training sessions, whereas work-related exposure remained low among workshop employees.

Protocol for the expansion of mouse immune effector cells for in vitro and in vivo studies.

Reproducible and efficient expansion of different immune effector cells is required for pre-clinical studies investigating adoptive cell therapies against cancer. Here, we provide a protocol for the rapid expansion of mouse T cells, natural killer (NK) cells, and bone-marrow-derived macrophages (BMDMs). We describe steps for αCD3/αCD8 plate coating, isolating splenocytes, and expanding T cells and NK cells. Further, we detail procedures for bone marrow isolation and BMDM differentiation.

Direct isolation of small extracellular vesicles from human blood using viscoelastic microfluidics.

Small extracellular vesicles (sEVs; <200 nm) that contain lipids, nucleic acids, and proteins are considered promising biomarkers for a wide variety of diseases. Conventional methods for sEV isolation from blood are incompatible with routine clinical workflows, significantly hampering the utilization of blood-derived sEVs in clinical settings. Here, we present a simple, viscoelastic-based microfluidic platform for label-free isolation of sEVs from human blood. The separation performance of the device is assessed by isolating fluorescent sEVs from whole blood, demonstrating purities and recovery rates of over 97 and 87%, respectively. Significantly, our viscoelastic-based microfluidic method also provides for a remarkable increase in sEV yield compared to gold-standard ultracentrifugation, with proteomic profiles of blood-derived sEVs purified by both methods showing similar protein compositions. To demonstrate the clinical utility of the approach, we isolate sEVs from blood samples of 20 patients with cancer and 20 healthy donors, demonstrating that elevated sEV concentrations can be observed in blood derived from patients with cancer.

Epigenetic neural glioblastoma enhances synaptic integration and predicts therapeutic vulnerability.

Neural-tumor interactions drive glioma growth as evidenced in preclinical models, but clinical validation is nascent. We present an epigenetically defined neural signature of glioblastoma that independently affects patients' survival. We use reference signatures of neural cells to deconvolve tumor DNA and classify samples into low- or high-neural tumors. High-neural glioblastomas exhibit hypomethylated CpG sites and upregulation of genes associated with synaptic integration. Single-cell transcriptomic analysis reveals high abundance of stem cell-like malignant cells classified as oligodendrocyte precursor and neural precursor cell-like in high-neural glioblastoma. High-neural glioblastoma cells engender neuron-to-glioma synapse formation in vitro and in vivo and show an unfavorable survival after xenografting. In patients, a high-neural signature associates with decreased survival as well as increased functional connectivity and can be detected via DNA analytes and brain-derived neurotrophic factor in plasma. Our study presents an epigenetically defined malignant neural signature in high-grade gliomas that is prognostically relevant.

Targeting the Siglec-sialic acid axis promotes antitumor immune responses in preclinical models of glioblastoma.

Glioblastoma (GBM) is the most aggressive form of primary brain tumor, for which effective therapies are urgently needed. Cancer cells are capable of evading clearance by phagocytes such as microglia- and monocyte-derived cells through engaging tolerogenic programs. Here, we found that high expression of sialic acid-binding immunoglobulin-like lectin 9 (Siglec-9) correlates with reduced survival in patients with GBM. Using microglia- and monocyte-derived cell-specific knockouts of Siglec-E, the murine functional homolog of Siglec-9, together with single-cell RNA sequencing, we demonstrated that Siglec-E inhibits phagocytosis by these cells, thereby promoting immune evasion. Loss of Siglec-E on monocyte-derived cells further enhanced antigen cross-presentation and production of pro-inflammatory cytokines, which resulted in more efficient T cell priming. This bridging of innate and adaptive responses delayed tumor growth and resulted in prolonged survival in murine models of GBM. Furthermore, we showed the combinatorial activity of Siglec-E blockade and other immunotherapies demonstrating the potential for targeting Siglec-9 as a treatment for patients with GBM.

Chimeric antigen receptor T cell-based targeting of CD317 as a novel immunotherapeutic strategy against glioblastoma.

BACKGROUND: Chimeric antigen receptor (CAR) T cell therapy has proven to be successful against hematological malignancies. However, exploiting CAR T cells to treat solid tumors is more challenging for various reasons including the lack of suitable target antigens. Here, we identify the transmembrane protein CD317 as a novel target antigen for CAR T cell therapy against glioblastoma, one of the most aggressive solid tumors. METHODS: CD317-targeting CAR T cells were generated by lentivirally transducing human T cells from healthy donors. The anti-glioma activity of CD317-CAR T cells toward various glioma cells was assessed in vitro in cell lysis assays. Subsequently, we determined the efficacy of CD317-CAR T cells to control tumor growth in vivo in clinically relevant mouse glioma models. RESULTS: We generated CD317-specific CAR T cells and demonstrate strong anti-tumor activity against several glioma cell lines as well as primary patient-derived cells with varying CD317 expression levels in vitro. A CRISPR/Cas9-mediated knockout of CD317 protected glioma cells from CAR T cell lysis, demonstrating the target specificity of the approach. Silencing of CD317 expression in T cells by RNA interference reduced fratricide of engineered T cells and further improved their effector function. Using orthotopic glioma mouse models, we demonstrate the antigen-specific anti-tumor activity of CD317-CAR T cells, which resulted in prolonged survival and cure of a fraction of CAR T cell-treated animals. CONCLUSIONS: These data reveal a promising role of CD317-CAR T cell therapy against glioblastoma, which warrants further evaluation to translate this immunotherapeutic strategy into clinical neuro-oncology.

A T-cell antigen atlas for meningioma: novel options for immunotherapy.

Meningiomas are the most common primary intracranial tumors. Although most symptomatic cases can be managed by surgery and/or radiotherapy, a relevant number of patients experience an unfavorable clinical course and additional treatment options are needed. As meningiomas are often perfused by dural branches of the external carotid artery, which is located outside the blood-brain barrier, they might be an accessible target for immunotherapy. However, the landscape of naturally presented tumor antigens in meningioma is unknown. We here provide a T-cell antigen atlas for meningioma by in-depth profiling of the naturally presented immunopeptidome using LC-MS/MS. Candidate target antigens were selected based on a comparative approach using an extensive immunopeptidome data set of normal tissues. Meningioma-exclusive antigens for HLA class I and II are described here for the first time. Top-ranking targets were further functionally characterized by showing their immunogenicity through in vitro T-cell priming assays. Thus, we provide an atlas of meningioma T-cell antigens which will be publicly available for further research. In addition, we have identified novel actionable targets that warrant further investigation as an immunotherapy option for meningioma.

Targeted delivery of tumor necrosis factor in combination with CCNU induces a T cell-dependent regression of glioblastoma.

Glioblastoma is the most aggressive primary brain tumor with an unmet need for more effective therapies. Here, we investigated combination therapies based on L19TNF, an antibody-cytokine fusion protein based on tumor necrosis factor that selectively localizes to cancer neovasculature. Using immunocompetent orthotopic glioma mouse models, we identified strong anti-glioma activity of L19TNF in combination with the alkylating agent CCNU, which cured the majority of tumor-bearing mice, whereas monotherapies only had limited efficacy. In situ and ex vivo immunophenotypic and molecular profiling in the mouse models revealed that L19TNF and CCNU induced tumor DNA damage and treatment-associated tumor necrosis. In addition, this combination also up-regulated tumor endothelial cell adhesion molecules, promoted the infiltration of immune cells into the tumor, induced immunostimulatory pathways, and decreased immunosuppression pathways. MHC immunopeptidomics demonstrated that L19TNF and CCNU increased antigen presentation on MHC class I molecules. The antitumor activity was T cell dependent and completely abrogated in immunodeficient mouse models. On the basis of these encouraging results, we translated this treatment combination to patients with glioblastoma. The clinical translation is ongoing but already shows objective responses in three of five patients in the first recurrent glioblastoma patient cohort treated with L19TNF in combination with CCNU (NCT04573192).

Immunological and tumor-intrinsic mechanisms mediate the synergistic growth suppression of experimental glioblastoma by radiotherapy and MET inhibition.

The hepatocyte growth factor (HGF)/MET signaling pathway has been proposed to be involved in the resistance to radiotherapy of glioblastoma via proinvasive and DNA damage response pathways.Here we assessed the role of the MET pathway in the response to radiotherapy in vitro and in vivo in syngeneic mouse glioma models. We find that the murine glioma cell lines GL-261, SMA-497, SMA-540 and SMA-560 express HGF and its receptor MET and respond to exogenous HGF with MET phosphorylation. Glioma cell viability or proliferation are unaffected by genetic or pharmacological MET inhibition using tepotinib or CRISPR/Cas9-engineered Met gene knockout and MET inhibition fails to sensitize glioma cells to irradiation in vitro. In contrast, the combination of tepotinib with radiotherapy prolongs survival of orthotopic SMA-560 or GL-261 glioma-bearing mice compared with radiotherapy or tepotinib treatment alone. Synergy is lost when such experiments are conducted in immunodeficient Rag1-/- mice, and, importantly, also when Met gene expression is disrupted in the tumor cells. Combination therapy suppresses a set of pro-inflammatory mediators including matrix metalloproteases that are upregulated by radiotherapy alone and that have been linked to poor outcome in glioblastoma. Several of these mediators are positively regulated by transforming growth factor (TGF)-ß, and pSMAD2 levels as a surrogate marker of TGF-ß pathway activity are suppressed by combination treatment. We conclude that synergistic suppression of experimental syngeneic glioma growth by irradiation and MET inhibition requires MET expression in the tumor as well as an intact immune system. Clinical evaluation of this combined strategy in newly diagnosed glioblastoma is warranted.

An Engineered IFNγ-Antibody Fusion Protein with Improved Tumor-Homing Properties.

Interferon-gamma (IFNγ) is one of the central cytokines produced by the innate and adaptive immune systems. IFNγ directly favors tumor growth control by enhancing the immunogenicity of tumor cells, induces IP-10 secretion facilitating (CXCR3+) immune cell infiltration, and can prime macrophages to an M1-like phenotype inducing proinflammatory cytokine release. We had previously reported that the targeted delivery of IFNγ to neoplastic lesions may be limited by the trapping of IFNγ-based products by cognate receptors found in different organs. Here we describe a novel fusion protein consisting of the L19 antibody, specific to the alternatively spliced extra-domain B of fibronectin (EDB), fused to a variant of IFNγ with reduced affinity to its cognate receptor. The product (named L19-IFNγ KRG) selectively localized to tumors in mice, showed favorable pharmacokinetic profiles in monkeys and regained biological activity upon antigen binding. The fusion protein was investigated in two murine models of cancer, both as monotherapy and in combination with therapeutic modalities which are frequently used for cancer therapy. L19-IFNγ KRG induced tumor growth retardation and increased the intratumoral concentration of T cells and NK cells in combination with anti-PD-1.

Exposure to polycyclic aromatic hydrocarbons assessed by biomonitoring of firefighters during fire operations in Germany.

BACKGROUND: Firefighters are exposed to a variety of hazardous substances including carcinogens such as polycyclic aromatic hydrocarbons (PAH) during firefighting. In order to minimize the uptake of such substances into the body, firefighters wear personal protective equipment. Only few data exist from real-life firefighting missions and under common although highly variable exposure scenarios such as fighting fires in residential buildings, outdoor, and vehicle fires. The aim of this study is to assess the levels of 1-Hydroxypyrene (1-OHP) as marker for incorporated PAH during firefighting operations in Germany using biomonitoring methods. METHODS: We analyzed urine samples for 1-OHP from 77 firefighters who reported firefighting operations (with and without creatinine adjustment). Urine samples were collected before (baseline) and, where applicable, after firefighting operations at three time points subsequent (2-4, 6-8, and 12 h). RESULTS: Compared to the baseline measurements, mean 1-OHP concentrations after firefighting missions were doubled (0.14 vs. 0.31 µg/L urine, 0.13 µg/g vs. 0.27 µg/g creatinine) and this increase was observed 2-4 h after firefighting. Firefighting in residential buildings (N = 54) and of outdoor and vehicle fires (N = 17) occurred most frequently, whereas blazes, vegetation fires, and fires in underground facilities (N = 6) were rarely encountered. For residential building fires, a 3-fold increase in mean 1-OPH concentrations was observed, whereas no increase could be observed for outdoor and vehicle fires. The highest increase was observed for firefighters with interior attack missions (0.11 µg/L vs. 0.48 µg/L 1-OHP) despite the use of self-contained breathing apparatus (SCBA). During the suppression of outdoor or vehicle fires using SCBA, again, no increase was observed. Although PAH are taken up during certain firefighting missions, the 1-OHP levels almost entirely remained (in 64 of the 77 reported missions) within the normal range of the German general population, i.e., below the reference levels (95th percentiles) of smokers (0.73 µg/g creatinine) and non-smokers (0.30 µg/g creatine). CONCLUSION: Under study conditions, properly applied protective clothing and wearing of SCBA led to a significant reduction of PAH exposure levels. But there are individual situations in which PAH are increasingly incorporated since the incorporation depends on several factors and can be extremely variable. In contrast to many workplaces with high occupational exposure levels, firefighters are not exposed to PAH on a daily basis. Nevertheless, the possibility of an individual increased cancer risk for a particular firefighter cannot completely be ruled out.