Core Framework & Diagram How Does the Tumor Transform Immune Cells?

Because the problem isn't only the 'brake' — T cells' 'engine' has been remodeled. PD-1 is the 'brake pedal'; releasing the brake should let the car move. But deeply exhausted T cells' engine (effector function-related gene chromatin) has been 'welded shut' by TOX and other epigenetic regulators — releasing the brake, the engine still won't start. This is why combining epigenetic interventions (like HDAC inhibitors to open chromatin) is the next important direction.

This is exactly the two-sidedness of releasing 'brakes.' PD-1 not only is the brake tumors apply to T cells — in normal physiological states, it also helps maintain peripheral immune tolerance, preventing T cells from attacking normal tissues. When PD-1 is blocked, T cell aggressiveness is fully unleashed. If this aggressiveness targets not only tumors but also thyroid, liver, lungs, and other self-tissues, 'immune-related adverse events' (irAEs) occur.

'Hot tumor' refers to abundant T cell infiltration in the TME; 'cold tumor' refers to almost no T cell infiltration. Clinically determined through tumor biopsy immunohistochemical staining (detecting CD8+ T cell density), gene expression profiling, and TMB (high TMB usually correlates with hot tumor). Pancreatic cancer, prostate cancer, brain glioma are typically cold; melanoma and MSI-H colorectal cancer are typically hot.

Pancreatic cancer is the extreme representative of 'cold tumor,' almost combining all 'unfavorable for immunotherapy' features: extremely low TMB (few mutations, rare neoantigens); extremely dense CAF stroma (TGF-β-driven massive collagen fibers physically blocking immune cells); extreme M2-TAM enrichment; high adenosine concentration (high CD73 expression); and large amounts of Treg infiltration. The most promising directions involve multiple combinations: CD40 agonists (re-activate TAM antigen presentation) + stroma degradation (target CAFs) + personalized neoantigen vaccines + checkpoint inhibitors.