Scientists have created innovative kinds of chimeric antigen-receptor (CAR) T cells, which are a form of cancer immunotherapy. These CAR T cells can be activated to different levels of intensity and then deactivated on demand using existing medications.
Researchers from Ludwig Cancer Research have engineered new variants of chimeric antigen-receptor (CAR) T cells, a cancer treatment proven effective in certain cases, which can be turned on to various intensities and deactivated as needed with already authorized drugs. The development and initial assessments of these CAR-T cells were guided by Melita Irving and Greta Maria Paola Giordano Attianese at the Lausanne Branch of the Ludwig Institute for Cancer Research, and their findings are published in this week’s edition of the Proceedings of the National Academy of Sciences.
“While CAR-T cells are currently utilized to treat a range of blood cancers, they face considerable challenges in treating solid tumors due to issues of safety and effectiveness,” stated Irving. “We have potentially resolved these concerns by integrating on and off switches into the CAR design that can be activated by drugs already approved for clinical use. This innovation is expected to accelerate the transition of these controllable CAR-T cells into clinical trials.”
CAR-T cells are designed to express synthetic receptors capable of recognizing specific molecular targets, or antigens, found on cancer cells through the use of antibody fragments as external sensors. When the CAR binds to its corresponding antigen on a cancer cell, it activates signaling pathways that unleash the T cell’s natural ability to eliminate tumor cells.
However, many antigens on solid tumors are also present on healthy cells, which raises the risk of “off-tumor, on-target” effects. This can lead to harmful immune reactions that are hard to manage and can be potentially fatal for the patient. Additionally, the harsh conditions surrounding solid tumors can often render anti-tumor T cells, including those with CARs, dysfunctional, a state referred to as “exhaustion.”
“The capability to remotely activate CAR-T cells to different extents with varying doses of an activating drug, and then deactivate them promptly when necessary, would enhance the safety profile of this therapy,” remarked Giordano Attianese. “Furthermore, controlling CAR-T cell activity remotely could help avoid T cell exhaustion, leading to more sustained patient responses to the treatment.”
This potential is supported by studies led by Ludwig Stanford’s Crystal Mackall, which indicate that allowing CAR-T cells breaks between active phases of targeting tumors can modify their gene expression, reverse exhaustion, and significantly improve their functional performance.
Traditional CARs utilize single-chain receptors that link the binding of tumor antigens directly to internal signals derived from essential proteins in T cells. These antigen-recognition parts of the CAR, extending from the engineered T cell like an antenna, typically come from the antigen-binding fragment of an antibody, which can be tailored to precisely target nearly any marker on tumor cells. The internal signaling components primarily derive from a protein called CD3-ζ, essential for activating T cells upon antigen interaction, and another part from co-stimulatory proteins like 4-1BB or CD28, which enhance T cell function and survival after they are activated.
To facilitate control over CAR activity, Irving, Giordano Attianese, and their team divided the antigen-detecting portion (the antibody fragment) and the activation component (CD3-ζ) into two different chains known as the ‘receptor chain’ and the ‘signaling chain’. Collaborating with Bruno Correia from the École Polytechnique Fédérale de Lausanne (EPFL), they also introduced an additional module capable of connecting the two chains using a cancer drug called venetoclax.
When venetoclax attaches to these external modules, it acts as a connector, bringing the two chains together to form an active CAR complex. The strength of the resulting CAR-T cell response is proportional to the dosage of the drug used. The researchers named this CAR design the “inducible-ON” (iON) CAR.
To ensure safety, though, it’s crucial that CAR-T cells can be quickly deactivated if they pose any risks to patients. Thus, the team added a drug-responsive component to the CD3-ζ signaling chain that can be triggered by another approved cancer drug, lenalidomide. When lenalidomide binds to this component, it signals the cell to degrade the receptor. The researchers demonstrated that their all-in-one iON/OFF CAR (iONØ-CAR) T cells could be activated by venetoclax and promptly turned off — within 4-6 hours — with lenalidomide.
Moving forward, the researchers intend to thoroughly evaluate the performance of their iON and iONØ-CARs against various tumor models. They will also investigate whether the remote control feature helps to prevent harmful overreactions from CAR-T cells and if intermittent rest periods can improve long-term tumor management.
Melita Irving is the head of the T cell engineering team within Ludwig Lausanne’s Human integrated tumor immunology discovery engine (Hi-TIDe).
The research conducted by the Irving lab received support from Ludwig Cancer Research, the Swiss National Science Foundation, the ISREC Foundation, the Prostate Cancer Foundation, and the Fondazione Teofilo Rossi di Montelera e di Premuda.
