Cytotoxic T-lymphocytes are specialized "killer cells" designed to eliminate infected or cancerous cells. Their action relies on a specialized exchange zone called the immune synapse, where they release active molecules to destroy a target cell without damaging neighboring ones. Until now, the fine organization of these structures has been difficult to observe. However, a study led by the University of Geneva (UNIGE) and the Lausanne University Hospital (CHUV) has visualized these mechanisms in 3D and in a near-natural state. The paper, published in the journal Cell Reports, demonstrates how the molecular organization of cytotoxic T-cells influences their function.
When an infection or cancer develops, cytotoxic T-lymphocytes attach to their target and form the immune synapse. They then secrete toxic molecules that trigger the death of the target cell. This mechanism ensures precise and controlled destruction, which is essential for protecting the body without harming healthy adjacent cells.
While this process has been extensively studied, accessing its organization at the nanometer level in intact human cells has been challenging. A major obstacle is sample preparation, as traditional methods can damage fragile cellular structures. Existing imaging techniques often involve a trade-off between resolution, observed volume, and structural preservation.
To overcome these limitations, the scientists utilized cryo-expansion microscopy (cryo-ExM). "This method involves flash-freezing cells at very high speeds, causing them to enter a so-called vitreous state where water solidifies without forming crystals, thus reliably preserving biological structures. The samples are then physically expanded using an absorbent hydrogel, allowing for high-precision observation of their internal structure while maintaining a near-native architecture," explains Virginie Hamel, a senior lecturer at the Department of Molecular and Cellular Biology.
"The work showed that at the point of contact between the immune cell and the target, the membrane forms a kind of dome, the structure of which is linked to adhesion interactions and the internal organization of the cell," notes Florent Lemaître, the study's first author. The research team also visualized cytotoxic granules—responsible for killing target cells—with unprecedented detail. The study revealed that these structures vary in organization; they can contain one or more "cores" where active molecules are concentrated to facilitate the destruction of the target cell.
"We applied this approach to human tumor tissues, allowing us to directly observe T-lymphocytes infiltrating the tumor and their cytotoxic mechanisms at the nanometer level. This provides an opportunity to study immune responses directly in a clinical context and better understand the mechanisms that determine their effectiveness," explains Bénita Wolf, the study's lead supervisor.
By providing 3D imagery of these processes in their natural environment, this work establishes a foundation for analyzing immune cell function. This could help improve therapeutic strategies, particularly in immuno-oncology, and lead to a better understanding of the mechanisms that define the effectiveness—or the limitations—of the immune response.
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