EXTH-08. REPLACEMENT OF MICROGLIA BY BRAIN-ENGRAFTED MACROPHAGES PREVENTS MEMORY DEFICITS AFTER THERAPEUTIC WHOLE-BRAIN IRRADIATION

Abstract Microglia have a distinct origin compared to blood circulating myeloid cells. Under normal physiological conditions, microglia are maintained by self-renewal, independent of hematopoietic progenitors. Following genetic or pharmacologic depletion, newborn microglia derive from the local residual pool and quickly repopulate the entire brain. The depletion of brain resident microglia during therapeutic whole-brain irradiation fully prevents irradiation-induced synaptic loss and recognition memory deficits but the mechanisms driving these protective effects are unknown. Here, we demonstrate that after CSF-1R inhibitor-mediated microglia depletion and therapeutic whole-brain irradiation, circulating monocytes engraft into the brain and replace the microglia pool. These monocyte-derived brain-engrafted macrophages have reduced phagocytic activity compared to microglia from irradiated brains, but similar to locally repopulated microglia without brain irradiation. Transcriptome comparisons reveal that brain-engrafted macrophages have both monocyte and embryonic microglia signatures. These results suggest that monocyte-derived brain-engrafted macrophages represent a novel therapeutic avenue for the treatment of brain radiotherapy-induced cognitive deficits

Phylogeny of Species, Infraspecific Taxa, and Forms in Iris Subgenus Xiphium (Iridaceae), From the Mediterranean Basin Biodiversity Hotspot

Iris subgenus Xiphium is a small group of taxa that occur in the Mediterranean Basin, a long-recognized biodiversity hotspot. Phylogenetic relationships among these Iris were reconstructed based on sequence data from 110 nuclear markers (coding regions) and plastomes using Bayesian inference and maximum likelihood methods. Best trees based on plastome and combined datasets resolved Iris subgenus Xiphium and I. xiphium as not monophyletic while nuclear and all-gene (combined nuclear and plastid coding regions) datasets resolved the subgenus as monophyletic but I. xiphium as not monophyletic. Topology tests indicated the alternative hypothesis of a monophyletic subgenus is not rejected by the combined dataset while a monophyletic I. xiphium is rejected. Topology tests also showed the hypothesis of a polyphyletic subgenus is rejected by the nuclear and all-gene datasets, however, a monophyletic I. xiphium is not rejected by these two datasets. We hypothesize that the subgenus is monophyletic based on these analyses, morphology, and biogeography, and that uneven patterns of missing data is a likely reason for topological incongruence among datasets. A previously suggested informal group within the subgenus was supported. Patterns of relationships among species suggest multiple exchanges between the African and European continents but also the importance of the Strait of Gibraltar as a barrier to genetic exchange

Functional role of brain-engrafted macrophages against brain injuries.

BackgroundBrain-resident microglia have a distinct origin compared to macrophages in other organs. Under physiological conditions, microglia are maintained by self-renewal from the local pool, independent of hematopoietic progenitors. Pharmacological depletion of microglia during whole-brain radiotherapy prevents synaptic loss and long-term recognition memory deficits. However, the origin or repopulated cells and the mechanisms behind these protective effects are unknown.MethodsCD45low/int/CD11b+ cells from naïve brains, irradiated brains, PLX5622-treated brains and PLX5622 + whole-brain radiotherapy-treated brains were FACS sorted and sequenced for transcriptomic comparisons. Bone marrow chimeras were used to trace the origin and long-term morphology of repopulated cells after PLX5622 and whole-brain radiotherapy. FACS analyses of intrinsic and exotic synaptic compartments were used to measure phagocytic activities of microglia and repopulated cells. In addition, concussive brain injuries were given to PLX5622 and brain-irradiated mice to study the potential protective functions of repopulated cells after PLX5622 + whole-brain radiotherapy.ResultsAfter a combination of whole-brain radiotherapy and microglia depletion, repopulated cells are brain-engrafted macrophages that originate from circulating monocytes. Comparisons of transcriptomes reveal that brain-engrafted macrophages have an intermediate phenotype that resembles both monocytes and embryonic microglia. In addition, brain-engrafted macrophages display reduced phagocytic activity for synaptic compartments compared to microglia from normal brains in response to a secondary concussive brain injury. Importantly, replacement of microglia by brain-engrafted macrophages spare mice from whole-brain radiotherapy-induced long-term cognitive deficits, and prevent concussive injury-induced memory loss.ConclusionsBrain-engrafted macrophages prevent radiation- and concussion-induced brain injuries and cognitive deficits

CXCL14 Promotes a Robust Brain Tumor-Associated Immune Response in Glioma.

PurposeThe immunosuppressive tumor microenvironment present in the majority of diffuse glioma limits therapeutic response to immunotherapy. As the determinants of the glioma-associated immune response are relatively poorly understood, the study of glioma with more robust tumor-associated immune responses may be particularly useful to identify novel immunomodulatory factors that can promote T-cell effector function in glioma.Experimental designWe used multiplex immune-profiling, proteomic profiling, and gene expression analysis to define the tumor-associated immune response in two molecular subtypes of glioma and identify factors that may modulate this response. We then used patient-derived glioma cultures and an immunocompetent murine model for malignant glioma to analyze the ability of tumor-intrinsic factors to promote a CD8+ T-cell response.ResultsAs compared with isocitrate dehydrogenase (IDH)-mutant astrocytoma, MAPK-activated pleomorphic xanthoastrocytoma (PXA) harbored increased numbers of activated cytotoxic CD8+ T cells and Iba1+ microglia/macrophages, increased MHC class I expression, enrichment of genes associated with antigen presentation and processing, and increased tumor cell secretion of the chemokine CXCL14. CXCL14 promoted activated CD8+ T-cell chemotaxis in vitro, recruited tumor-infiltrating CD8+ T cells in vivo, and prolonged overall survival in a cytotoxic T-cell-dependent manner. The immunomodulatory molecule B7-H3 was also highly expressed in PXA.ConclusionsWe identify the MAPK-activated lower grade astrocytoma PXA as having an immune-rich tumor microenvironment and suggest this tumor may be particularly vulnerable to immunotherapeutic modulation. We also identify CXCL14 as an important determinant of the glioma-associated immune microenvironment, sufficient to promote an antitumor CD8+ T-cell response