aDISCO: A clearing method to enable 3D microscopy of large archival paraffin-embedded human tissue blocks.

Human surgery and autopsy specimens are routinely stored as formalin-fixed paraffin-embedded (FFPE) tissue blocks for decades, creating vast archives of healthy and diseased tissues. While tissue clearing and whole-mount microscopy enable 3D analysis, FFPE human tissue blocks are often unsuitable for clearing and immunolabeling due to their large size and extensive cross-linking. Here, we introduce "archival" DISCO (aDISCO), a clearing method designed to overcome these challenges. aDISCO achieves effective clearing and immunolabeling of large samples stored for 15 years or more. We applied aDISCO to human brain, spinal cord, peripheral nerve, skin, muscle, heart, kidney, liver, spleen, colon, and lung, using a broad range of antibodies. Combining aDISCO with deep learning-based analysis to study focal cortical dysplasia (FCD), we found disrupted cortical layering with both focal and global neuronal density variations, features likely to be overlooked by conventional histology. In summary, aDISCO delivers datasets suitable for deep learning-based processing, enabling the detection of subtle and sparse pathologies in large archival human tissue specimens.