Cytokine release syndrome (CRS) is the most common serious toxicity of CAR-T cell therapy, and its escalation is driven less by the CAR-T cells themselves than by a positive feedback loop: activated macrophages release IL-6, which binds soluble IL-6 receptor and signals through gp130 on cells like the vascular endothelium (trans-signaling), triggering yet more IL-6 and vascular leak. This 2D simulator renders that loop as a causal flow-network diagram — draggable nodes for CAR-T cells, tumor, macrophages, the IL-6 pool and the endothelium, connected by particle-flux edges whose density and speed encode the actual reaction rates — alongside live strip charts of IL-6, temperature and tumor burden and a stability gauge comparing the loop's gain against its clearance rate. Tune CAR-T dose, the trans-signaling gain that makes the loop self-reinforcing, and a tocilizumab (anti-IL-6R) dose that interrupts it, exactly as the real drug does in the clinic.