Spatially resolved gene expression and tumour-microenvironment interactions across malignant transformation in IDH-mutant glioma

Isocitrate dehydrogenase (IDH)-mutant gliomas are the most common form of lower-grade diffuse gliomas affecting young adults. While these tumors initially appear relatively benign compared to their IDH-wildtype counterparts, they inevitably progress to malignancy. The underlying mechanisms of this progression have been largely unknown.

In a groundbreaking study, researchers examined a unique longitudinal cohort of two patients with IDH-mutant diffuse gliomas, each featuring matched WHO grade 2, 3, and 4 tumors. By employing spatial transcriptomics (NanoString GeoMx and 10X Visium), they were able to analyze the spatial organization of genes within these tumors.

Through differential expression analysis, gene ontology enrichment, and spatially variable gene analysis, the researchers were able to define the transcriptional programs responsible for the progression of these tumors. Surprisingly, they found that higher-grade tumors exhibited reduced proliferation at the infiltrative margin, as measured by Ki67 staining.

The spatial transcriptomic analysis revealed an enrichment of invasion-associated genes associated with increasing tumor grade. In an independent cohort analyzed through bulk RNA-seq, the expression of this spatially derived program did not surpass the predictive power of grade-only PFS or OS analysis.

These findings highlight the importance of developing new metrics that account for the spatial evolution of tumor progression that is not captured by bulk analyses. The researchers suggest that prioritizing the investigation of migration-, cytoskeletal-, and stress-associated programs could provide valuable insights into the mechanisms driving the inevitable malignant transformation of IDH-mutant gliomas.