Journal Article

Antigen-independent activation enhances the efficacy of 41BB co-stimulated CD22 CAR T cells

Ramones, Melissa, Engels, Boris, Barrett, David M., Perazzelli, Jessica, Young, Regina M., Abdel-Mohsen, Mohamed, Damra, Mohammad, Highfill, Steven L., Price, Andrew, Maggie Lu, Xueqing, June, Carl H., Standley, Daron M., Pajarillo, Raymone, Grupp, Stephan A., Shyu, Amy, Singh, Nathan, Maude, Shannon L., Gill, Saar, Ravikumar, Pranali, Liu, Ting, Burkhardt, Janis K., Frey, Noelle V., Granda, Brian, Christian, David A., Roy, Nathan H., Liu, Dongfang, Cummins, Katherine D., Ruella, Marco, Colomb, Florent, Zhao, Linlin, Lee, Yong Gu, Peng, Liaomin, Shestova, Olga, Brogdon, Jennifer L., Chun, Inkook, Lacey, Simon F.

2021

Overview

While CD19-directed CAR T cells can induce remissions in patients with B cell acute lymphoblastic leukemia (ALL), a large subset relapse with CD19-negative disease. Like CD19, CD22 is broadly expressed by B-lineage cells and thus serves as an alternative immunotherapy target in ALL. Here we present the composite outcomes of two pilot clinical trials (NCT02588456 and NCT02650414) of T cells bearing a 41BB-based CD22-targeting CAR in patients with relapsed or refractory ALL. The primary endpoint of these studies was to assess safety, and the secondary endpoint was anti-leukemic efficacy. We observed unexpectedly low response rates, prompting us to perform detailed interrogation of the responsible CAR biology. We found that shortening of the amino acid linker connecting the variable heavy and light chains of the CAR antigen-binding domain drove receptor homo-dimerization and antigen-independent signaling. In contrast to CD28-based CARs, autonomously signaling 41BB-based CARs demonstrated enhanced immune synapse formation, activation of pro-inflammatory genes and superior effector function. We validated this association between autonomous signaling and enhanced function in several CAR constructs, and based on these observations designed a new short-linker CD22 scFv for clinical evaluation. Our findings suggest that tonic 41BB-based signaling is beneficial to CAR function and demonstrate the utility of bedside-to-bench-to-bedside translation in the design and implementation of CAR T cell therapies.