In CAR-T cell therapy, synthetic chimeric antigen receptors (CARs) are engineered onto lymphocytes in order to make them more effective in attacking cancer. In an effort to better understand the underlying anti-cancer signaling pathways involved with CAR-T therapies, a new study published in Science Signaling uses phosphoproteomics to compare T cell signaling patterns in two different designs of CARs. The work is led by the Fred Hutchinson Cancer Research Center.
"There's been plenty of interest in targeting the T cells to cancer, but little has been known about the instructions that CARs give to the T cells," said study first author Alex Salter. "I wanted to study how the CARs deliver instructions to T cells."
The CARs, which function in tumor recognition, has multiple components. One key component is a T cell signaling unit called a costimulatory domain. The team sought to investigate the differences between CARs built with the two most-commonly used costimulatory domains: CD28 and 4-1BB.
Looking at human cancer cell cultures and mouse models, the team analyzed stimulation-induced phosphorylation events using mass spectrometry. Among their findings, the team observed that similar signaling pathways were initiated by both types of CARs, although the timing and intensity of the signal varied.
The CD28 CAR design showed faster and stronger activity and the 4-1BB CAR exhibited slower and milder activation. Further testing in a mouse lymphoma model showed that the 4-1BB CAR was more effective in clearing cancer cells. 4-1BB CAR T cells also showed greater expression of genes associated with T-cell memory, suggesting that the 4-1BB CAR signaling may give rise to T cells that can live longer and maintain their anti-cancer effects.
The team concluded that neither type of CAR domain is better than the other when it comes to treatment, but the results may provide insights to why some patients experience stronger side effects from CAR-T and why some relapse following treatment.
"We hope by developing a suite of targeted assays to phosphoproteins involved in T-cell signaling, we can help advance the immunotherapy field in developing more effective CAR T-cell therapies for patients," said study senior co-author Amanda Paulovich.