Researchers engineered NK cells with a second CAR to act as a logic gate

Natural killer cells can now be modified by the University of Texas MD Anderson Cancer Center to have a second chimeric antigen receptor (CAR) that functions as a logic gate, requiring two signals to destroy a target cell. In preclinical studies, these next-generation CAR NK cells improved tumor specificity and increased anti-tumor activity by stopping a process that makes natural killer cells less effective and leads to tumors coming back.

This study, which was just published in Nature Medicine, showed that the physiological process trogocytosis, which results in the loss of tumor antigen, natural killer cell exhaustion, and fratricide—the killing of sibling CAR NK cells—contributes to tumor escape and subpar responses following CAR NK cell therapy.

Dr. Katy Rezvani, professor of Stem Cell Transplantation & Cellular Therapy, said, “We identified a novel mechanism of relapse following CAR NK cell therapy, and we also developed a strategy to mitigate this process.” “We engineered CAR NK cells with dual-targeting CARs that can ignore tumor antigens on the surface of their sibling natural killer cells acquired through trogocytosis and specifically kill tumor cells,” the authors write.

The study was directed by Rezvani and Ye Li, M.D., a graduate student in the Rezvani Lab.

Trogocytosis involves the transfer of surface proteins from a target cell to the surface of an immune cell, like an natural killer cell or T cell, to control the activity of those cells. Li and his colleagues used preclinical models to show that CAR activation promotes trogocytosis, which leads to the transfer of tumor antigens to CAR NK cells and their expression.

This causes CAR NK cell fratricide, in which the engineered cells target one another rather than the tumor, as well as a decrease in the target antigens on tumor cells. Self-targeting impairs metabolic function, depletes natural killer cells, and impairs the anti-tumor response.

The researchers confirmed that lower levels of the CD19 antigen on tumor cells and a higher likelihood of relapse were associated with higher levels of the CD19 antigen on CAR NK cells by analyzing clinical samples from patients with lymphoid malignancies treated with anti-CD19 CAR NK cells in a clinical trial.

The addition of an inhibitory CAR, which is made to recognize a marker specific to natural killer cells, prevented this process from taking place. As a result, CAR NK cells now receive a “don’t kill me” signal when interacting with their siblings, even if they have the tumor antigen on their surface. In preclinical models, these logic-gated CAR NK cells were better at focusing on and attacking just the tumor cells. This cut down on NK cell exhaustion and self-destruction and increased their ability to kill tumor cells.

“Following CAR NK therapy, it’s critical to prevent tumor escape because in some patients, this has resulted in relapse. We can increase the activity and functionality of CAR NK cells by preventing fratricide and exhaustion,” replied Rezvani. According to the researchers, we are eager to apply this research to the clinic because it could be used for any CAR-NK cell therapy.

The research extends earlier efforts by the Rezvani Lab to develop and enhance CAR NK cell therapies, including clinical trials for patients with leukemia and lymphoma and preclinical research to create CAR NK cells that can override immune suppression in glioblastoma. This study adds to what we know about CAR-NK biology and suggests that the dual-CAR approach needs to be tested in the clinic.