Background: Human induced pluripotent stem cell (iPSC)-derived cerebral organoids (COs) are novel in vitro models employed to investigate neurodegenerative disorders, neurotoxicity, and traumatic injury of the central nervous system (CNS) such as traumatic brain injury (TBI). A relatively recent development in the study of CNS trauma is the distinction between TBI, associated with contact sports, and blast injury, resulting from exposure to a pressure shockwave. Although both injury types have been identified in military service members, their etiology and pathophysiology can differ dramatically. The former is characterized histologically by the accumulation of a specific isoform of phosphorylated tau (pTau), while the latter is defined by prominent astrogliosis at the gray-white junction. Our study aims to investigate the suitability of cerebral organoids as laboratory models for traumatic brain and blast injury via histology, immunohistochemistry, and spatial transcriptomics. Methods: COs were developed from two commercially available iPSC lines for 188-190 days, designated Cell Lines 1 and 2. Each CO was embedded, cut, and stained with hematoxylin & eosin (H&E), glial fibrillary acid protein (GFAP), neurofilament protein (NFP), and pTau immunohistochemical stains. Organoid size was measured on digital slides obtained from a Leica CS2 Slide Scanner using QuPath (v0.4.3). pTau staining intensity assessed using Image J (v1.53). GFAP and NFP positivity per 3xHPFs (40x magnification) per organoid were manually counted. Spatial transcriptomics was performed on representative organoids via the 10x Visium platform by 10x Genomics; data was then visualized using Loupe Browser (v7.0.0). Cell identification was performed manually with a Boolean search for the top differentially expressed transcripts for each cell cluster referencing PanglaoDB. Manual cell calling was further refined using Seurat R toolkit (v4). Results: On histologic examination, there were no statistically significant differences in size, density of astrocytes/neurons by IHC, or pTau between cell lines; however, there was a trend towards smaller size, higher rates of staining with GFAP and NFP, and lower baseline pTau intensity in Cell Line 2 relative to Cell Line 1 (Fig 1a-c). In Cell Line 1, spatial transcriptomics demonstrated four clusters consistent with development from stem cells to neurons and interneurons (Fig 2). In contrast, Cell Line 2 demonstrated only 2 cell populations, transcriptomes of which are suggestive of neurons and astrocytes versus oligodendrocytes (Fig 3). Preliminary analysis with Seurat R clarified the identity of one population of Cell Line 2 as astrocytes and suggests that neuron clusters may be better classified as neuroepithelium in both lines. Conclusions: While there were no statistically significant differences in size or IHC staining between the cell lines investigated, spatial transcriptomics did identify a substantial difference in rate of maturation, which is critical for establishing baseline ‘maturity’ for future exposure studies. Additionally, the trend of increasing pTau accumulation in control Cell Line 1 organoids may obfuscate findings if used as a model for TBI studies. Future directions for this project include increasing sample size, expanding the cell lines under investigation, interrogating both IHC and transcriptomes at more time points during organoid development, and subjecting mature organoids to blast trauma in order to compare their performance to human cadaveric studies and animal models.