Dominant-acting CSF1R variants cause microglial depletion and altered astrocytic phenotype in zebrafish and adult-onset leukodystrophy.

Tissue-resident macrophages of the brain, including microglia, are implicated in the pathogenesis of various CNS disorders and are possible therapeutic targets by their chemical depletion or replenishment by hematopoietic stem cell therapy. Nevertheless, a comprehensive understanding of microglial function and the consequences of microglial depletion in the human brain is lacking. In human disease, heterozygous variants in CSF1R, encoding the Colony-stimulating factor 1 receptor, can lead to adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) possibly caused by microglial depletion. Here, we investigate the effects of ALSP-causing CSF1R variants on microglia and explore the consequences of microglial depletion in the brain. In intermediate- and late-stage ALSP post-mortem brain, we establish that there is an overall loss of homeostatic microglia and that this is predominantly seen in the white matter. By introducing ALSP-causing missense variants into the zebrafish genomic csf1ra locus, we show that these variants act dominant negatively on the number of microglia in vertebrate brain development. Transcriptomics and proteomics on relatively spared ALSP brain tissue validated a downregulation of microglia-associated genes and revealed elevated astrocytic proteins, possibly suggesting involvement of astrocytes in early pathogenesis. Indeed, neuropathological analysis and in vivo imaging of csf1r zebrafish models showed an astrocytic phenotype associated with enhanced, possibly compensatory, endocytosis. Together, our findings indicate that microglial depletion in zebrafish and human disease, likely as a consequence of dominant-acting pathogenic CSF1R variants, correlates with altered astrocytes. These findings underscore the unique opportunity CSF1R variants provide to gain insight into the roles of microglia in the human brain, and the need to further investigate how microglia, astrocytes, and their interactions contribute to white matter homeostasis.

An international technology platform for influenza vaccines.

Since 2008, the World Health Organization has provided seed grants to 11 manufacturers in low- and middle-income countries to establish or improve their pandemic influenza vaccine production capacity. To facilitate this ambitious project, an influenza vaccine technology platform (or "hub") was established at the Netherlands Vaccine Institute for training and technology transfer to developing countries. During its first two years of operation, a robust and transferable monovalent pilot process for egg-based inactivated whole virus influenza A vaccine production was established under international Good Manufacturing Practice standards, as well as in-process and release assays. A course curriculum was designed, including a two-volume practical handbook on production and quality control. Four generic hands-on training courses were successfully realized for over 40 employees from 15 developing country manufacturers. Planned extensions to the curriculum include cell-culture based technology for viral vaccine production, split virion influenza production, and generic adjuvant formulation. We conclude that technology transfer through the hub model works well, significantly builds vaccine manufacturing capacity in developing countries, and thereby increases global and equitable access to vaccines of high public health relevance.