A Reversible Chemogenetic Switch for Chimeric Antigen Receptor T Cells
Introduction
As a revolutionary cancer treatment, the chimeric antigen receptor (CAR) T cell therapy suffers from complications such as cytokine release syndromes and T cell exhaustion. Their mitigation desires controllable activation of CAR-T cells that is achievable through regulatory display of CARs on the T cell surface.
Methods
By embedding the hepatitis C virus NS3 protease (HCV-NS3) in an anti-CD19 CAR between the anti-CD19 single-chain variable fragment (scFv) and the hinge domain, we showed that the display of anti-CD19 scFv on CAR-T cells was positively correlated to the presence of a clinical HCV-NS3 inhibitor asunaprevir (ASV).
Results
This novel CAR design that allows the display of anti-CD19 scFv on the T cell surface in the presence of ASV and its removal in the absence of ASV effectuates a practically recurring chemical switch for CAR-T cells. We demonstrated that the intact CAR on T cells was repeatedly turned on and off by controlling the presence of ASV. The dose-dependent manner of the intact CAR display on T cells with regard to the ASV concentration enables delicate modulation of CAR-T cell activation during cancer treatment. In a mouse model, we showed different treatment prospects when ASV was provided at different doses to mice that were infused with both human CD19+ lymphoma and the switchable CAR-T cells.
Conclusion
Unlike small molecules with well-defined pharmacokinetic/pharmacodynamic features, the unpredictability of CAR-T cell therapeutics faces unique treatment challenges regarding the dose control. The ability to regulate the activity and survival of these live drugs has dual benefits of promoting efficacy without abandoning safety. By introducing a recurring chemogenetic switch into the CAR that can be regulated through a small molecule, the problem turns into control of the dosage of the small molecule, which in the current work is a well-studied FDA approved HCV-NS3 inhibitor ASV. Using ASV to regulate activity of HCV-NS3 embedded in sCAR19, we show that full-length sCAR19 was displayed on its host CAR-T cell surface in an ASV-dose dependent manner. More importantly, we found that the removal of ASV resulted in gradual elimination of the CAR, and as fast as in 24 h the CAR level decreased to an insignificant level. Most biological characterization results prove that CAR-T cells with this recurring chemogenetic switch behave similarly to standard CAR-T cells and ASV regulates, with a dose dependent manner, the antitumor effect of switchable CAR-T cells both in vitro at the cellular level and in vivo in mice. Due to its recurring control nature, we believe this novel chemogenetic CAR switch will find critical applications in CAR-T cell therapy in mitigating serious side effects such as cytokine release syndromes and T cell exhaustion. Since ASV is an FDA-approved medication and sCAR19 in the current work was derived from an approved CAR-T therapeutic, the combined use of ASV and sCAR19 as a therapeutic can be potentially advanced quickly to undergo clinical investigations in the treatment of hematopoietic tumors such as B-cell lymphoblastic leukemia.