A Safer CAR-T Therapy with STOP-CAR Design

A novel chimeric antigen-receptor (CAR) T cell therapy has been developed at Ludwig Cancer Research and may achieve turning on and off as needed. The study, led by Melita Irving of the Ludwig Institute for Cancer Research's Lausanne Branch, George Coukos, the Branch's director, and Bruno Correia of the École Polytechnique Fédérale de Lausanne (EPFL), discusses a key problem with current CAR-T therapies of initiating aggressive immune responses against healthy cells in patients.

ON-switch CARs that activate T cells by small molecule-mediated heterodimerization in the presence of antigen have been reported to be achieved, but suffer from the short half-life of small molecules.

This study presents a computationally assisted design of a STOP-switch CAR-T cell control system in which antigen binding and T cell activation are encoded by recognition (R chain) and signaling (S chain), respectively. By inserting computationally designed protein pairs into the intracellular domains of the two CAR chains, these two chains can spontaneously form functional heterodimers, while the addition of small molecules can specifically disrupt the dimerization.

Thus, Stop-Car has the potential to temporarily modulate T-cell function, rather than completely eliminate it as in the case of a suicide switch.

To develop a clinically promising STOP-CAR, the authors attempted to utilize a chemically disruptable heterodimer (CDH) system that requires components of human-derived proteins and a minimal number of residue substitutions to reduce the risk of transgenic immune rejection in patients. For the design of CDH, they used well-folded spherical structural domains to reduce the possibility of interfering with T-cell signaling near the synapse, as well as clinically applicable small molecules with long half-lives and good tolerability in humans.

They first identified the BH3 structural domain of human Bcl-XL and BIM proteins as the starting point for CDH design, which they planned to insert into the S and R chains, respectively. Then, they conducted an extensive structural search to identify scaffolds with similar backbone motifs that are structurally compatible with the binding partner, transposing the BH3 binding motif to the structural white domain of this globular protein and designing at the interface residues to replace BIM with a human globular protein with high binding affinity.

The research group derived three candidate proteins, and identified human apolipoprotein E4, codenamed LD3, followed by incorporating CDH into the STOP-CAR design.

In conclusion, this research developed a high-affinity CDH system where the introduction of CDH into the heterodimeric STOP-CAR could specifically activate primary human T cells in the presence of the corresponding antigen, and the efficacy of STOP-CAR-T cells targeting PSMA or CD19 observed in the experiments was greater than or equal to their respective conventional 2G-CAR-T cells.

In particular, the activity of STOP-CAR-T cells specifically decreased when subjected to CDH interference by small-molecule drugs, and this modulation was dynamic, with their activity recovered upon removal of the drugs.

With inspiring research results, Dr. Melita Irving is invited by Creative Biolabs to talk about new discovery of her research team in an upcoming webinar. The subject of this free live webinar is Engineering strategies for improving adoptive T cell therapy against cancer, and the topics will cover the use of syngeneic tumor models to evaluate the ability of co-engineered murine CAR T cells to reprogram the TME and boost T cell function, the use of low-doses of irradiation to inflame cold tumors and render them responsive to rational combinatorial immunotherapy, and the novel STOP-CAR to integrate efficacy and safety directly into CAR design.

Creative Biolabs is a biotech company providing TCR and CAR T&NK cell immune therapy development services as well as ready-to-use TCR and CAR T&NK cell construction products, and has been dedicated to creating a robust webinar platform to share the latest insights on CAR T therapy.

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