(114c) Dissection of Human T-cell Heterogeneity at Single-cell Resolution Using Mass Cytometry

T cells are important immune cells for fighting infection and cancer, and as such monitoring their behavior provides a critical step in understanding and engineering T-cell responses. T cells detect pathogens with exquisite specificity by recognizing short peptide fragments of pathogen-derived proteins, complexed with MHC molecules. It is estimated that there are ~10⁷ T-cell specificities in a human body, which ensures good epitope coverage for pathogen recognition. Upon antigen recognition and stimulation, T cells secrete an array of cytokines that orchestrate the action of other white blood cells for infection clearance, or directly inducing apoptosis of infected cells. Circulating T cells exhibit a range of differentiation stages based on their relative level of antigen experience. As a result of this highly heterogeneous nature, it is challenging to study T cells on a systems level, and ideally, incorporating readouts of multiplexed parameters would provide the most effective analysis.

Of particular interest, chronic cytomegalovirus (CMV) infection is known to elicit many changes across the T-cell compartment. By monitoring 40 parameters on single cells using mass spectrometry, we showed T-cell heterogeneity dynamically arranged in a 3D phenotypic and functional space, and is preferentially driven towards effector memory and late-stage differentiated subsets by CMV infection. We also showed that while CMV-seropositivity increased the diversity of cytokine combinations only in CD8⁺ T cells to reveal novel functional subsets, both CD8⁺ and CD4⁺ T cells showed a move towards greater degree of polyfunctionality. These CMV-associated patterns and fingerprints have potential use for diagnosis and biomarker screening of CMV infection, with the analytical strategy described here suitable across a spectrum of immune-modulating diseases.