TGFB1 and neoplasm: Second, soluble inhibitory factors, such as TGF‐β, IL‐10, VEGF, and PD‐L1, impede T cell activation, proliferation, and effector functions, while promoting T cell exhaustion.[36] Additionally, physical barriers, including the dense extracellular matrix (ECM) and fibrotic stroma, significantly hinder the infiltration and spatial distribution of CAR‐T cells within tumor sites.[37] Collectively, these factors create a hostile environment that restricts CAR‐T cell infiltration, activation, and functional efficacy in solid tumors.