Episode Summary

Chimeric antigen receptors, or CARs, repurpose the build-in targeting and homing signals of our immune system to direct T cells to find and eliminate cancers. Although CAR-T cells have transformed the care of liquid tumors in the circulating blood, like B cell leukemia and lymphoma, CAR-T therapy has shown limited efficacy against solid tumors. To unlock the full potential of CAR-T therapies, better receptor designs are needed. Unfortunately, the space of potential designs is too large to check one by one. To design better CARs, Dan and his co-author Camillia Azimi developed CAR Pooling, an approach to multiplex CAR designs by testing many at once with different immune costimulatory domains. They select the CARs that exhibit the best anti-tumor response and develop novel CARs that endow the T cells with better anti-tumor properties. Their methods and designs may help us develop therapies for refractory, treatment-resistant cancers, and may enable CAR-T cells to cure infectious diseases, autoimmunity, and beyond.

About the Author

• During his PhD in George Church’s lab at Harvard Medical School, Dan studied interactions between bacterial transcription and translation, built and measured libraries of tunable synthetic biosensors, and constructed a new version of the E. coli genome capable of incorporating new synthetic amino acids into its proteins. He also built a high-throughput microbial genome design and analysis software platform called Millstone.
• As a Jane Coffin Childs Postdoctoral Fellow at UCSF, Dan is currently applying these high-throughput synthetic approaches to engineer T cells for the treatment of cancer and autoimmune disease. He is also working in the Bluestone, Roybal, and Marson labs.

Key Takeaways

• By genetically engineering the chimeric antigen receptor (CAR), T cells can be programmed to target new proteins that are markers of cancer, infectious diseases, and other important disorders.
• However, to realize this vision, more powerful CARs with better designs are needed - current CAR-T therapies have their restraints, including limited performance against solid tumors and lack of persistence and long-term efficacy in patients.
• An important part of the CAR response is “costimulation,” which is mediated by the 4-1BB or CD28 intracellular domains in all CARs currently in the clinic. Better designs of costimulatory domains could unlock the next-generation of CAR-T therapies.
• Since there are so many possibilities for costimulatory domain designs, it’s difficult to test them all in the lab.
• Based on his experience in the Church Lab, Dan has developed tools to “multiplex” biological experiments; that is, to test multiple biological hypotheses in the same experiment and increase the screening power.
• Dan and his co-author Camillia Azimi developed “CAR Pooling”, a multiplexed approach to test many CAR designs at once.
• Using CAR Pooling, Dan tested 40 CARs with different costimulatory domains in pooled assays and identified several novel cosignaling domains from the TNF receptor family that enhance persistence or cytotoxicity over FDA-approved CARs.
• To characterize the different CARs, Dan also used RNA-sequencing.

Impact

• The CAR Pooling approach may enable new, potent CAR-T therapies that can change the game for solid tumors and other cancers that are currently tough to treat.
• Highly multiplexed approaches like CAR Pooling will allow us to build highly complex, programmable systems and design the future of cell engineering beyond CAR-T.
• In addition to new therapeutics, high-throughput studies will allow us to understand the “design rules” of synthetic receptors and improve our understanding of basic immunology.

Paper: Pooled screening of CAR T cells identifies diverse immune signaling domains for next-generation immunotherapies