Barcoding of viable peripheral blood mononuclear cells with selenium and tellurium isotopes for mass cytometry experiments

Barcoding viable cells combined with pooled sample staining is an effective technique that eliminates batch effects from serial cell staining and facilitates uninterrupted data acquisition. We describe three novel and isotopically pure selenium-containing compounds (SeMals) that are useful cellular labeling tools. The maleimide-functionalized selenophenes (⁷⁶SeMal, ⁷⁷SeMal, and ⁷⁸SeMal) covalently react with cellular sulfhydryl groups and uniquely label cell samples. The SeMal reagents label viable and paraformaldehyde-fixed peripheral blood mononuclear cells (PBMC), are well resolved by the mass cytometer, and have little spill into adjacent channels. They appear non-toxic to viable cells at working concentrations. We used SeMal reagents in combination with four isotopically pure tellurium maleimide reagents (¹²⁴TeMal, ¹²⁶TeMal, ¹²⁸TeMal, and ¹³⁰TeMal) to label 21 individual PBMC samples with unique combinations of selenium and tellurium isotopes (seven donors with three replicates using a 7 isotope pick 2 combinatorial schema). The individually barcoded samples were pooled, stained with an antibody cocktail as a pool, and acquired on the mass cytometer as a single suspension. The single-cell data were de-barcoded into separate sample-specific files after data acquisition, enabling an uninterrupted instrument run. Each donor sample retained its unique phenotypic profile with excellent replicate reproducibility. Unlike current live cell barcoding methods, this approach does not require antibodies to surface markers, allowing for the labeling of all cells regardless of surface antigen expression. Additionally, since selenium and tellurium isotopes are not currently utilized in CyTOF antibody panels, this method expands barcoding options and frees up commonly used isotopes for more detailed cell profiling.