Background: Glutathione (GSH) plays an important role in anti-oxidant defense and detoxification reactions. It is primarily synthesized in the liver by the transsulfuration pathway and exported to provide precursors for in situ GSH synthesis by other tissues. Deficits in glutathione have been implicated in aging and a host of diseases including Alzheimer's disease, Parkinson's disease, cardiovascular disease, cancer, Down syndrome and autism.

GVL against chronic phase CML (CP-CML) is potent, but it is less efficacious against acute leukemias and blast crisis CML (BC-CML). The mechanisms underlying GVL-resistance are unknown. Previously, we found that alloreactive T cell targeting of GVL-sensitive bcr-abl-induced mouse CP-CML (mCP-CML) required TCR:MHC interactions and that multiple and redundant killing mechanisms were in play. To better understand why BC-CML is resistant to GVL, we performed a comprehensive analysis of GVL against mouse BC-CML (mBC-CML) induced by the retroviral transfer of the bcr-abl and NUP98/HOXA9 fusion cDNAs. Like human BC-CML, mBC-CML was GVL-resistant, and this was not due to accelerated kinetics or a greater leukemia burden. To study T cell recognition and killing mechanisms, we generated a panel of gene-deficient leukemias by transducing bone marrow from gene-deficient mice. T cell target recognition absolutely required that mBC-CML cells express MHC and GVL against both mCP-CML and mBC-CML required leukemia expression of ICAM-1. We hypothesized that mBC-CML would be resistant to some of the killing mechanisms sufficient to eliminate mCP-CML, but we found instead that the same mechanisms were effective against both types of leukemia as GVL was similar against wild type or mBC-CML genetically lacking Fas, TRAIL-R, Fas/TRAIL-R, TNFR1/R2 or when donor T cells were perforin−/−. However, mCP-CML but not mBC-CML, relied on expression of PD-ligands to resist T cell killing, as only GVL against mCP-CML was augmented when leukemias lacked PD-L1/L2. Thus, mBC-CML cells have cell-intrinsic mechanisms distinct from mCP-CML cells that protect them from T cell killing.

Key Points Standard chemotherapy can still be used for new diagnosis of acute lymphoblastic leukemia in patients with SARS-CoV-2. Corticosteroid can be given safely to patients with SARS-CoV-2 presenting with acute respiratory distress syndrome and ALL.

Commercially available films minimize the importance of the psychosocial dimension of care, which can perpetuate stigma around psychosocial needs and interventions. These films can be used to encourage discussion about how to optimize psychosocial care in pediatric oncology so that such care is not abandoned in actual practice as it is, for entertainment purposes, on the screen.

Beckwith-Wiedemann syndrome (BWS) is an epigenetic overgrowth disorder and cancer predisposition syndrome caused by imprinting defects of chromosome 11p15.5-11p15.4. BWS should be considered in children with atypical presentations of embryonal tumors regardless of clinical phenotype. Risk of malignancy correlates with specific molecular subgroups of BWS making molecular subclassification important for appropriate cancer screening. We report the first case of concurrent embryonal tumors in a phenotypically normal child, leading to the diagnosis of BWS with paternal uniparental disomy and describe the molecular classification of BWS as it relates to malignancy risk, along with approach to management.

Purpose Diffuse Intrinsic Pontine Glioma is a fatal tumor traditionally treated with radiotherapy (RT) and previously characterized as having a non-inflammatory tumor immune microenvironment (TIME). FLASH is a novel RT technique using an ultra-fast dose-rate which is associated with decreased toxicity, effective tumor control and potential immune-sparing properties. However, the effect of FLASH on the DIPG tumor immune microenvironment (TIME) has not yet been explored. Methods Here, we perform single-cell RNA sequencing on immune cells isolated from an orthotopic syngeneic murine model of DIPG following the use of FLASH (90Gy/sec) or conventional (2Gy/min) dose-rate RT (CONV-RT), and compare to unirradiated tumor and normal brainstem. Results Sequencing of immune cells reveals 17 unique populations, most abundant of which is microglia. In the most activated microglia subtypes, both CONV-RT and FLASH show upregulation of type 1 interferon (IFN1) genes and pathway scores compared to unirradiated tumor. In macrophages (MACs) and dendritic cells (DCs), CONV-RT is significantly enriched for IFN1 while this response is less seen with FLASH. Further, FLASH shows an increase in CNS border-associated MACs and upregulation of a myeloid-derived suppressor cell (MDSC) signature in MONOs, less seen with CONV-RT. In the lymphocytes, FLASH yields a higher mature B cell proportion and upregulation of T-cell activation and trafficking markers compared to CONV-RT. Finally, we correlate our data with myeloid cells from cerebrospinal fluid of human DIPG patients and find overlap with our murine tumor- and treatment-associated markers. Conclusion Our work is the first to map CONV-RT and FLASH immune alterations with single-cell resolution in the DIPG TIME. We find that CONV-RT and FLASH sculpt the microglial compartment similarly while recruiting distinct non-resident myeloid subsets and mature B-cell fractions, highlighting the potential to combine each modality with unique immunotherapy regimens in this fatal disease.

BackgroundDiffuse intrinsic pontine gliomas (DIPG’s) are immunologically inert tumors with a median survival of 9–15 months. Radiation therapy (RT) is the mainstay treatment for DIPG but is associated with immunodepletion of the tumor microenvironment (TME) at high dose ranges. FLASH, or ultra-fast dose rate RT, represents a novel ablative technique that may spare TME immune responses while decreasing tumor burden. Here, we present single-cell immune profiling of DIPG tumors treated with FLASH, conventional dose rate RT (CONV) or no RT (SHAM).MethodsMurine H3.3K27M mutant DIPG cells were stereotactically injected and tumor induction confirmed by magnetic resonance imaging (MRI) 15 days later. DIPG-bearing mice were randomly assigned to one of three treatment groups (n=4/group), FLASH, CONV or SHAM. A fourth group with no tumor (NML) was included as a negative biological control. A modified linear accelerator was used to deliver 15 Gy of electron RT to the brainstem at dose rates of 90 Gy/second and 2 Gy/minute, for the FLASH and CONV groups, respectively. Four days post-RT, mice brainstems were harvested, homogenized, stained for CD45 and tagged with a hashtag antibody specific to each group. CD45+ immune cells were isolated and sequenced using the 10X Genomics chromium single-cell 3’ platform. After processing and alignment of the reads using CellRanger with default parameters, the data was quality checked and filtered before hashtag demultiplexing, unsupervised clustering and downstream analysis was implemented following the Seurat R package. Differential expression evaluated based on the non-parametric Wilcoxon rank sum test. Key genes determine by an adjusted p value of < 0.05 based on bonferroni correction and |avg log2FC| > 0.8.ResultsPreliminary analysis identifies 15 clusters with distinct CD45 immune phenotypes (figure 1). Differential gene expression analysis by hashtag antibody (treatment group) reveals 14 clusters differentially expressing key genes, including 3 clusters upregulated in DIPG compared to NML, and 2 clusters upregulated in irradiated tumors compared to SHAM and NML (figure 2). Notably, analysis demonstrates an individual cluster upregulated in FLASH versus all other groups (p = 3.07E-171). Further deconvolution of specific immune phenotypes represented by each cluster is ongoing.Abstract 91 Figure 1tSNE plot based on clustering of RNA signatures, grouped by RNAAbstract 91 Figure 2tSNE plot based on clustering of RNA signatures, grouped by hashtag antibodyConclusionsOur preliminary analysis shows differential immune responses among DIPG tumors compared to NML. We also find several immune cell subsets that are unique to DIPG treated with CONV or FLASH compared to unirradiated samples. Most notably, we identify a single immune cell subset that is exclusive to FLASH alone, indicating that FLASH elicits a unique immune response in murine DIPG.

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