In the battle against infections and cancer, cytotoxic T lymphocytes play a critical role by binding to their targets and forming an immune synapse. This specialized connection enables them to release toxic substances that effectively eliminate harmful cells while minimizing damage to surrounding tissues.
Despite a foundational understanding of this process, researchers have faced significant challenges in visualizing its intricate details at the nanometer scale within intact human cells. Traditional sample preparation methods often distort delicate cellular components, leading to compromises in either resolution, field of view, or the preservation of the cell's natural structure.
Innovative Cryo-Expansion Microscopy Technique
To tackle these hurdles, a collaborative team from UNIGE and CHUV-UNIL, with support from the ISREC Foundation TANDEM program, employed a cutting-edge technique known as cryo-expansion microscopy (cryo-ExM). This method involves rapidly freezing cells to achieve a vitreous state, which preserves biological structures without crystal formation. Subsequently, the samples are expanded using an absorbent hydrogel, allowing for precise observation of their internal organization while maintaining their near-native architecture. Virginie Hamel, a Senior Lecturer at UNIGE, explains, "This technique enables us to explore cellular structures with remarkable accuracy."
The researchers discovered new structural characteristics at the immune cell's interaction point with its target. "Our findings indicate that the membrane forms a dome-like structure at the contact point, which is associated with adhesion interactions and the cell's internal organization," states Florent Lemaître, a postdoctoral researcher at UNIGE and lead author of the study. The team also examined cytotoxic granules--key players in cell destruction--with unprecedented clarity, revealing variations in structure and the presence of multiple "cores" where active molecules are concentrated.
Application to Human Tumor Samples
Extending their technique beyond isolated cells, the researchers applied their method to human tumor samples. Benita Wolf, Chief Resident and Associate Researcher at CHUV, noted, "This advancement allows for direct observation of T lymphocytes infiltrating tumors and their cytotoxic mechanisms at the nanometer scale, facilitating a better understanding of immune responses in clinical contexts."
By offering a three-dimensional and nearly native perspective of immune cell operations, this research provides a foundational framework for studying immune responses under real-world conditions. These insights could significantly enhance immuno-oncology treatments by elucidating the factors that drive effective immune attacks against cancer and identifying the limitations that may hinder these processes.