Researchers at Mayo Clinic in Rochester, Minnesota, and Astrolabe Diagnostics in Fort Lee, New Jersey, used a mass cytometry technology called CyTOF (from manufacturer Fluidigm) to qualitatively measure 31 proteins simultaneously in the tumor microenvironment of samples from patients with classic Hodgkin lymphoma. They found a great deal of heterogeneity among the 8 patients they studied, compared with a fairly uniform profile among the 7 control samples. The work was presented November 7, 2019, at the 34th Annual Meeting & Preconference Programs of the Society for Immunotherapy of Cancer, or SITC 2019, in National Harbor, Maryland.1

In cHL, a small number of cancer cells are surrounded by a large volume of inflammation. Because the cancer cells typically make up less than 5% of the tumor mass, conventional tools that are useful for studying other tumor types perform poorly in cHL. Among the immune cells present in the condition, some support the cancer, while others fight it, creating a complex ecosystem of many different types of cells. To fully appreciate the dynamic interactions involved, researchers need a tool that allows them to observe many different cell types in the same sample.

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Mass cytometry is a variation of flow cytometry in which heavy metal ion tags are used instead of fluorescent tags. The readout is by time-of-flight mass spectrometry, and there’s no overlap between the different metal ion tags. Compared with fluorescent tags, which are limited by the spectrum of light wavelengths, CyTOF allows for a much larger number of distinct tags to be used simultaneously.

“In a system like the immune system, when you have multiple different cell types and they are characterized by different proteins, you really need that complexity to resolve which cells are doing what,” said Jose Villasboas, MD, a hematology/oncology fellow at the Mayo Clinic. “Mass cytometry is, in my opinion, an ideal platform to resolve the complexity of the immune system.”

In flow cytometry, up to 5 to 8 tags can be used simultaneously, whereas in mass cytometry 30 or 40 different tags can be employed across the same sample.