Chimeric antigen receptor (CAR)-T cell therapy is a type of cancer immunotherapy that ‘trains’ a patient’s own immune system to eradicate their cancer. CAR-T cell therapy has attained 50-90% complete remission rates in some clinical trials, however the broader use of CAR-T cell therapy as a first-line treatment remains limited in part by life-threatening side effects that often require additional critical hospital care for patients. The ability to maximise anti-tumour efficacy whilst minimizing the risk of inflammatory toxicities is therefore integral to the continued improvement of CAR-T cell therapies. We aimed to investigate the currently undefined relationship between CAR oligomeric state and potency, with the intention of leveraging these findings to predictably control CAR activity.
In collaboration with computational modelling experts, we have developed de novo designed transmembrane (TM) domain sequences capable of controlling the oligomeric state of receptors. We subsequently designed CARs containing these novel TM sequences, termed ‘programmed’ CARs (proCARs), and validated their effector function in CD8+ primary mouse T cells. Using our panel of proCARs we have demonstrated that increases in oligomeric state correlates with an enhanced control of solid tumour growth in vivo, and cytotoxicity in vitro. Interestingly, cytokine secretion in response to target antigen was significantly reduced by all proCARs in comparison to CARs possessing a conventional CD28 TM domain. A strong positive correlation with proCAR oligomeric state and inflammatory cytokine secretion however was still evident.
These findings present an opportunity to deliberately control the safety and potency of CAR-T cell therapies by controlling for CAR oligomeric state through the TM domain. Furthermore, the absence of systematic optimization of CAR TM sequences in the field, combined with the simple modularity of our designs presents a compelling case for easy translation of our proCAR TMs into diverse clinical CAR-T cell designs.