A killer T cell clamps onto a tumour cell, releases its payload and leaves the neighbouring healthy cells alone. Immunologists have understood that much for years. What they could not do was watch the contact point itself at the scale where the real work happens, inside intact human cells, without the preparation wrecking the structure.
A team from Geneva’s university (UNIGE) working with Lausanne University Hospital (CHUV) now says it has done it. Their paper appeared in Cell Reports, with support from the ISREC Foundation TANDEM program.
Freeze first, then stretch
The method is cryo-expansion microscopy, or cryo-ExM. Cells are frozen at very high speed into a glass-like state in which water sets without forming crystals, so delicate structures are not torn apart. The sample is then swollen with an absorbent hydrogel, which pulls the interior far enough apart to be read in detail.
“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,” said Virginie Hamel, a senior lecturer in UNIGE’s Department of Molecular and Cellular Biology.
The team was candid about limits. Cryo-ExM cannot image living cells. The team says it is best suited to measuring brittle structures in three dimensions, cell after cell, and should sit beside live-cell super-resolution imaging rather than replace it.
A dome at the contact point
In human T cells the technique left the cell’s actin, microtubules and membranes intact, along with the finest protrusions. It also showed something the group had not expected: a dome-like space beneath activated T cells, dependent on adhesion.
“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 organization of the cell,” said Florent Lemaître, a postdoctoral researcher at UNIGE who led the writing as first author.
The cytotoxic granules, the packets that actually kill the target, came into focus as well. They are not uniform. Some hold a single core where the active molecules concentrate, others several.
From the dish to real tumours
The group then took the method out of the culture dish and applied it to human tumour samples. Benita Wolf, who co-led the work and splits her time between residency and research in CHUV’s clinical oncology department, said this makes it possible to see T lymphocytes infiltrating a tumour, and their killing machinery, at the nanometre scale.
That matters because immunotherapy works for some patients and fails for others, often without a clear reason. A picture of what a successful attack looks like physically, and what limits an unsuccessful one, gives researchers something concrete to compare. The authors frame their contribution as a reference framework for studying immune cells, one that could eventually help refine treatments in immuno-oncology. They stop short of claiming a therapy.
The paper states the gap plainly: “No single technique has so far combined near-native structural preservation, quantitative nanoscale resolution, multicolor molecular specificity, and whole-cell three-dimensional coverage.”
Sources
- First-ever 3D view shows how killer T cells destroy cancer
- University of Geneva reveals details of immune system's killer cells
