Advanced Imaging Technique Reveals Immune Cell Metabolic States in Blood Samples

When patients are battling certain cancers or immune conditions, clinicians rely on white blood cells—predominantly immune cells—to gain insights into disease progression and treatment effects. Typically, peripheral blood mononuclear cells (PBMCs) are isolated from a blood draw and analyzed for the abundance of various cell types, along with some basic measures of their functioning. PBMCs also serve as the foundation for CAR T cell therapies, where a patient's immune cells are engineered to combat specific cancers.

In a study conducted by researchers at the Morgridge Institute for Research, a novel imaging technique called optical metabolic imaging (OMI) was demonstrated to characterize metabolic activity within immune cells derived from peripheral blood samples. The scientists claim that this technique could enhance disease diagnostics and the production of cell therapies when used in conjunction with current clinical methods.

Furthermore, classifying immune cells and their metabolic states in complex samples rather than in isolated forms provides more precise insights into the cell's behavior. The researchers hope that OMI could contribute to improved diagnosis and treatment of immune system-related disorders, such as blood cancers, systemic lupus erythematosus (SLE), sepsis, and cognitive decline.

Melissa Skala, PhD, an investigator in biomedical engineering at the Morgridge Institute and senior author of the study, highlighted that PBMCs can be easily isolated clinically and are already incorporated into clinical workflows. She posed the question of what additional information could be derived from these cells. The authors of the published paper in Biophotonics Discovery, titled "Autofluorescence lifetime imaging resolves cell heterogeneity within peripheral blood mononuclear cells," concluded that OMI could provide supplementary metabolic information to traditional PBMC measurements, which could improve disease monitoring and the development of immune therapies.

PBMCs consist of a diverse group of immune cells, including lymphocytes (T cells, B cells, and NK cells) and myeloid cells (monocytes). Previous methods for measuring immune cell metabolism involved isolating individual cell types or employing chemical labels to highlight the presence or absence of metabolites. Moreover, standard flow cytometry does not routinely assess cell metabolism, yet cell metabolic state can reveal unique cell subpopulations and functional states beyond surface markers.

The researchers achieved the first-ever accurate observation of the metabolic state of single immune cells within a complex PBMC sample using a nondestructive analysis. This technique allows for the continued use of samples following the analysis, as opposed to other methods that require adding reagents to the sample, which can be harmful to the cells.

The ability to learn more about immune cells and their function without causing cell destruction opens up opportunities for applications like assessing the fitness of immune cells before they are administered as a treatment. Melissa Skala added that PBMCs are often used as starting material for cell therapies, and assessing their fitness before processing could be beneficial.

The OMI technique, pioneered by the Skala lab, relies on intrinsic sources of contrast and is label-free, making it a nondestructive and highly accurate imaging method. By employing two long-wavelength photons that do not damage the material, OMI excites the inherent fluorescence of cell metabolism products, enabling researchers to determine whether PBMCs are metabolically active or quiescent.

In their reported study, the team achieved 93% accuracy in identifying quiescent and activated monocytes, respectively, and 88% accuracy in identifying natural killer (NK) cells in both states within 2 hours of cell stimulation. OMI demonstrates a label-free measurement of single-cell metabolism, identifying immune cell subsets and early activation states within PBMCs without the need for staining, enabling high-throughput metabolic screens.