Safety switches for adoptive cell therapy

Adoptive transfer of allogeneic and genetically modified T cells, such as CAR-T and TCR-T cells, can induce profound immune reactivity against cancer tissue. At the same time, these therapies are associated with severe off-target and on-target toxicities. For this reason, the development of genetic safety switches that can be used to control the activity of T cells in vivo has become an active field of research. With the spectrum of technologies developed, reversible control of cell products either by supply or removal of small molecules, by supply of protein-based regulators, or by physical stimuli such as light, ultrasound or heat, has become feasible. In this review, we describe the mechanistic classes of genetic safety switches, such as transcription-based or protein-based control of antigen receptors, split receptors, small molecule responsive antibodies, as well as universal remote controls, and discuss their advantages and limitations.