The MIT.HTMID Research Projects are dependent on a continuous supply of viruses for experimental work directed at developing Human Tissue Models for Infectious Diseases. The purpose of the Virology Core to provide the authenticated and quantified viruses for the work. Authentication refers to defining: a) the source of the virus, b) the nucleotide sequence of the virus, c) the cell type used for passage and amplifiction, d) the passage number, e) the storage conditions. Quantified refers to defining the titers of infectious viruses by plaque assay or flow cytometry, or by quantifying viral RNA genomes by qRTPCR. In response to AI16022, we intend to test 2D and 3D human cerebral organoid cultures using several viruses; specifically, Dengue Virus, West Nile Virus, and Zika virus; moreover, we propose to use the 2D and 3D cultures to test the tropisms of a number of other neurotropic viruses using pseudotyped vesicular stomatitis viruses (VSV). The rigor of the MIT.HTMID Center will be enhanced significantly by performing careful validation and quantification of the virus preparations. The flaviviruses are significant for this project because of their neurotropic properties; moreover, the use of pseudotyped VSVs will enable the MIT.HTMID Center to safely evaluate select agent viruses using the nearphysiological cerebral organoids. Zika virus studies are significant because Zika has been linked to the development of fetal microcephaly. Dengue, Zika, and West Nile viruses are all members of the Flaviviridae family and are important pathogens that cause significant morbidity and mortality. Because the three flaviviruses have different infection phenotypes and pathogenesis outcomes, a comparison of virus replication in the 2D and 3D cultures will be extremely informative, and will provide ongoing positive and negative controls to enhance the rigor of the experimental work. The Virology Core will also be responsible for biosafety oversight so that all personnel in the MIT.HTMID Center follow guidelines required for using BSL2 and BSL3 viruses.