Although chimeric antigen receptor (CAR) T cell therapies have demonstrated considerable success in treating hematologic malignancies, they have simultaneously been plagued by a cytokine release syndrome (CRS) that can harm or even kill the cancer patient. We describe a CAR T cell strategy in which CAR T cell activation and cancer cell killing can be sensitively regulated by adjusting the dose of a low molecular weight adapter that must bridge between the CAR T cell and cancer cell to initiate tumor eradication. By controlling the concentration and dosing schedule of adapter administration, we document two methods that can rapidly terminate (<3 h) a pre-existing CRS-like toxicity and two unrelated methods that can pre-emptively prevent a CRS-like toxicity that would have otherwise occurred. Because all four methods concurrently enhance CAR T cell potency, we conclude that proper use of bispecific adapters could potentially avoid a life-threatening CRS while enhancing CAR T cell tumoricidal activity.