The immune system's cancer-killing cells operate with a precision that scientists have long known about but never fully seen. A new study has changed that, capturing the process in three dimensions at a scale and level of detail not previously possible.
Researchers from the University of Geneva and the Lausanne University Hospital used an advanced imaging technique to observe cytotoxic T lymphocytes, the immune system's specialized "killer" cells, as they destroyed cancer cells inside real human tumors. Their findings, published in Cell Reports, reveal the fine internal structure of the moment when a T cell locks onto its target and delivers a lethal payload.
That moment happens at a structure called the immune synapse, a tightly controlled contact zone that forms between the T cell and its target. Through this interface, the T cell releases toxic molecules that trigger the destruction of the cancerous or infected cell. The key feature of the immune synapse is specificity: the toxic substances are directed at the target cell and largely spare neighboring healthy tissue. Scientists have understood this process in broad terms for years. What they lacked was a clear picture of its internal architecture at the nanometer scale.
Standard imaging methods make that difficult. Traditional sample preparation can distort delicate cellular structures. Existing techniques typically force researchers to choose between high resolution, a wide field of view, or preserving the cell's natural state. Getting all three at once has not been possible, until now.
The Geneva team used a method called cryo-expansion microscopy, or cryo-ExM. The approach involves freezing cells at very high speed, placing them in what researchers describe as a vitreous state, where water solidifies without forming crystals. That step preserves biological structures as they naturally exist. The samples are then physically expanded using an absorbent hydrogel, which makes it possible to examine internal organization with high precision while keeping the cell's architecture intact. "This technique involves instantaneously freezing cells at very high speed," explained Virginie Hamel, a senior lecturer at the University of Geneva's Department of Molecular and Cellular Biology. "The samples are then physically expanded using an absorbent hydrogel, making it possible to observe their internal organization with great precision while maintaining their near-native architecture."
What the technique revealed was what the researchers describe as molecular choreography, a highly organized arrangement inside the T cell that enables it to strike with accuracy. The three-dimensional view shows how the cell's internal components are positioned relative to the immune synapse and how that positioning supports the targeted release of toxic molecules.
The research was supported by the ISREC Foundation TANDEM program, which funds collaborative work between the University of Geneva and the Lausanne University Hospital. Scientists in the field of immuno-oncology have increasingly focused on T cells as a central tool in cancer treatment, including in CAR-T therapies that engineer patients' own immune cells to attack tumors. A clearer understanding of how cytotoxic T cells are organized and how that organization drives their function could help researchers design more effective immunotherapies or identify reasons why some T cell treatments fail.
The study adds structural detail to a process that sits at the center of the immune system's response to cancer, giving researchers a new baseline for work that could eventually influence how patients are treated.
