Unmodified T cells (dim grey) patrol without recognising the tumour's marker. CAR-T cells (glowing cyan, spiked) are the patient's T cells engineered with a chimeric antigen receptor that binds that marker directly, so they home in on cancer cells and kill them at a rate set by the dose.
dC/dt = g·C − k_kill·dose·E·C
kills(t) → cytokine += killRate·dose·buildup·dt
cytokine −= decay·cytokine·dt
buildup = 1.0 normally, 0.35 after cytokine blocker
- CAR-T dose — more engineered cells means faster, more thorough cancer-cell killing, but also a bigger burst of cytokines released as cells die simultaneously.
- Tumor growth rate — too low a dose lets surviving cancer cells regrow faster than CAR-T cells can clear them.
- Cytokine level — rises with the rate of cancer-cell death, not the total killed; crossing the red zone represents cytokine release syndrome (CRS) risk — fever, low blood pressure, organ stress.
- Cytokine blocker — an IL-6-blocking intervention (e.g. tocilizumab) given mid-treatment: it sharply cuts further cytokine buildup without turning off the CAR-T cells' cancer-killing effect.
This is the real clinical tradeoff behind CAR-T dosing: clinicians titrate dose and monitor cytokine trends closely, ready to intervene the moment the reaction starts escalating — without abandoning the therapy itself.