How molecular dynamics in CAR T cells explain their cancer-killing behavior

A study published in Science Advances shares new insights into how two of the most common types of chimeric antigen receptor (CAR) T cells kill cancer.

Investigators from Baylor College of Medicine, Texas Children’s Cancer Center and the Center for Cell and Gene Therapy at Baylor, Houston Methodist Hospital and Texas Children’s Hospital examined how molecular dynamics at the immune synapse—where CAR T cells bind to cancer cells—affect anticancer activity.

In this study, researchers aimed to understand how CAR T cells with different signaling domains work at the molecular and cellular levels to lay the foundation for designing CAR molecules that maximize antitumor activity beyond B cell malignancies.

“We looked at two different types of CAR T cells. The first, CD28.ζ-CART cells, are like sprinters. They kill cancer cells quickly and efficiently, but their activity is short-lived. The second, 4-1BB.ζ-CART cells, are like marathon runners. They kill cancer cells consistently over a long period,” said senior author Dr. Nabil Ahmed, professor of pediatrics—hematology and oncology at Baylor and Texas Children’s.

“We need to understand what’s happening at the molecular level so we can engineer CAR T cells to adapt their killing behavior to target hard-to-treat malignancies, such as solid tumors.” Ahmed is also a member of the Center for Cell and Gene Therapy and the Dan L Duncan Comprehensive Cancer Center.

Led by first author Dr. Ahmed Gad, postdoctoral associate in Ahmed’s lab, the research team examined molecular dynamics at the immune synapse. The team biopsied the CAR T cell immunological synapse by isolating the membrane lipid rafts—cholesterol-rich molecules on the cell surface where most molecular interactions between cells take place.

They found that CD28.ζ-CAR molecules shuttle through the immune synapse quickly, working within minutes to kill cancer cells. This enabled fast CAR T cell recovery and a mastery of “serial killing” of cancer cells. In contrast, researchers found that 4-1BB.ζ-CAR molecules linger in the lipid rafts and immune synapse. The 4-1BB.ζ-CAR T cells multiply and work together, resulting in sustained “collaborative” killing of tumor cells.

“Observing the distinct pattern of dynamics between single molecules helps us understand the big picture of how these products work,” Gad said. “Next, we are studying how to dynamically adapt these CAR T cells at the synapse level to make them more effective.”

“Tumors are very sophisticated. We need to adapt our tools to the biology of the disease. This may involve using multiple tools that work in different ways at different stages,” Ahmed added.