Researchers using single-cell RNA and TCR sequencing in longitudinal mouse tumor models identified a conserved gene expression 'expansion signature' that predicts CD8+ T cell clonal bursts prior to proliferation. The work, reported in Nature Communications from Tokyo University of Science, used TCR sequences as natural barcodes to track clones across multiple tumor sites and timepoints. A complementary analysis highlighted key genes that forecast intratumoral T cell expansion, offering a potential early biomarker to gauge and guide immunotherapy responses. The studies suggest single-cell and TCR-based profiling could inform patient selection and combination strategies by detecting immune activation before conventional clinical signals emerge.