A machine used for measuring impurities in semiconductors is now used to analyze immune cells in far more detail than has been previously possible, researchers from Stanford University have shown.

The new technology, mass cytometry, builds on an established technology known as fluorescence-activated cell sorting, or FACS, which is in widespread use throughout the world. To learn how various internal processes differed from one cell type to the next, the researchers used mass cytometry to take simultaneous measurements of dozens of features located on and in cells (the existing technology typically begins to encounter technical limitations at about a half-dozen).

They simultaneously monitored 34 different substances found inside and on the surface of different cell types produced in human bone marrow, the place where all immune and blood cells (as well as blood disorders such as leukemia) originate.

By measuring large numbers of cell features all at once, the team was able to capture subtle transitions between cell states in a high-resolution snapshot of the entire blood-forming system, the researchers said. Scientists normally think of the blood and immune cells as differentiating in a series of discrete steps. However, the researchers showed that the transitions from one cell state to another are marked by gradually shifting levels of cell-surface markers and varying amounts and activation states of several intercellular molecules.

How it works

Instead of dyes, mass cytometry joins rare-earth metals to antibodies, which in turn detect cellular features and processes. Cells are paraded one by one through a tube and sprayed into a tiny chamber in which they are heated to about 13,000 degrees Fahrenheit and vaporized into successive clouds of atomic nuclei and loose electrons.

Next, the contents of each cloud (that was once a cell) are essentially flung against a wall with equal force. The lightest atoms arrive first, then the next-lightest and so forth. A detector counts the atoms as they land, and from this, the instrument can determine their mass. The mass cytometer tallies how many copies of each metal-tagged antibody were stuck to the cell and, therefore, how many copies of each molecular feature were present on, or in, the cell in the first place.

The researchers perturbed cells by exposing them to various substances, including signaling molecules that sometimes circulate in our own blood, as well as foreign materials, such as fragments of bacterial cell walls that are known to excite immune responses. Some of these stimulatory tests were done in the presence of dasatinib, a drug used to treat chronic myelogenous leukemia and certain cases of acute lymphoblastic leukemia. Dasatinib is in clinical trials for several other indications, including some solid cancers.

When the researchers used pervanadate to “release the brakes” on a universal pro-cell-survival behavior, dasatinib blocked action in every cell type except one: the immune sentinels called dendritic cells. The researchers said this new finding demonstrates mass cytometry’s capacity to ferret out tiny differences in cellular behavior that may help explain drugs’ side effects as well as to indicate potential new uses for existing drugs.

Ref: Sean C. Bendall, Erin F. Simonds, Peng Qiu, El-Ad D. Amir, Peter O. Krutzik, Rachel Finck, Robert V. Bruggner, Rachel Melamed, Angelica Trejo, Olga I. Ornatsky, Robert S. Balderas, Sylvia K. Plevritis, Karen Sachs, Dana Pe’er, Scott D. Tanner, and Garry P. Nolan, Single-Cell Mass Cytometry of Differential Immune and Drug Responses Across a Human Hematopoietic Continuum, Science, 2011; 332 (6030): 687-696 DOI: 10.1126/science.1198704