A cytotoxic T cell imaged by cryo-expansion microscopy (cryo-ExM). The colourful dots at the centre are cytotoxic granules used to destroy infected or cancerous cells. Credit: @ F Lemaitre @ UNIGE.
A collaboration between UNIGE and CHUV-UNIL has revealed in 3D how T lymphocytes destroy cancer cells in the human body.
Cytotoxic T lymphocytes are the body’s specialised ‘killer’ cells, precisely eliminating infected or cancerous cells.
Their action relies on a specialised exchange zone called the ‘immune synapse’, where they release active molecules to destroy the target cell without damaging neighbouring ones.
Until now, the fine organisation of these structures remained difficult to observe.
A study conducted by the University of Geneva (UNIGE) and the Lausanne University Hospital (CHUV) has made it possible to visualise these mechanisms in three dimensions in a near-native state.
The study reveals how the molecular organisation of cytotoxic T cells underpins their function, opening new perspectives in immuno-oncology.
During infection or cancer, cytotoxic T lymphocytes attach to their target and establish an exchange zone known as the immune synapse, then release toxic molecules that trigger the death of the targeted cell.
This mechanism enables precise and controlled destruction, essential for protecting the body while avoiding damage to nearby healthy cells.
Although this process has been widely studied, its organisation at the nanometre scale in intact human cells remained difficult to access.
One of the main obstacles lies in sample preparation methods, which can alter fragile cellular structures.
Existing imaging approaches often involve trade-offs between resolution, observable volume, and preservation of structures.
A technique to see the invisible
To overcome these limitations, a study by UNIGE and CHUV-UNIL, supported by the ISREC Foundation TANDEM programme, relied on cryo-expansion microscopy (cryo-ExM).
Virginie Hamel, senior lecturer in the Department of Molecular and Cellular Biology at the Faculty of Science of UNIGE, said: “This technique involves instantaneously freezing cells at very high speed, placing them in a so-called vitreous state, where water solidifies without forming crystals and thus faithfully preserves biological structures.
“The samples are then physically expanded using an absorbent hydrogel, making it possible to observe their internal organisation with great precision while maintaining their near-native architecture.”
First author of the study, Florent Lemaître, post-doctoral researcher in the Department of Molecular and Cellular Biology at the Faculty of Science of UNIGE, said: “Our work reveals that at the point of contact between the immune cell and its target, the membrane forms a kind of dome, whose structure appears to be linked to adhesion interactions and to the internal organisation of the cell.”
The research team also visualised cytotoxic granules – responsible for destroying target cells – with an unprecedented level of detail.
The study shows that these structures can vary in their organisation, with one or more ‘cores’ concentrating the active molecules that enable the destruction of the target cell.
From cells to patients
Study co-lead Benita Wolf, chief resident and associate researcher in the Department of Clinical Oncology at CHUV, said: “We extended this approach to human tumour tissues, making it possible to directly observe T lymphocytes infiltrating tumours and their cytotoxic machinery at the nanometre scale.
“This allows us to study immune responses directly in their clinical context and to better understand the mechanisms that determine their effectiveness.”
By providing a three-dimensional and near-native view of these processes, this work establishes a reference framework for analysing how immune cells function.
It could help improve therapeutic strategies, particularly in immuno-oncology, by enabling a better understanding of the mechanisms that determine the effectiveness – or limitations – of the immune response.
The study is published in Cell Reports.
