PDCD1 and neoplasm: To dissect the heterogeneity of anti-PD-1 immunotherapy responses in molecularly distinct GBM cohort of PN, CL, and MES subtypes, we developed a microfluidics-based 3D ‘GBM-on-a-Chip’ microphysiological system (Figure 2 and Figure 2—figure supplement 1) mimicking the subtype-specific in vivo GBM tumor niche.