UCLA

Existing approaches that quantify cytotoxic T cell responses rely on bulk or surrogate measurements which impede the direct identification of single activated T cells of interest. Single cell microscopy or flow cytometry methodologies typically rely on fluorescent labeling, which limits applicability to primary cells such as human derived T lymphocytes. Here, we introduce a quantitative method to track single T lymphocyte mediated cytotoxic events within a mixed population of cells using live cell interferometry (LCI), a label-free microscopy technique that maintains cell viability. LCI quantifies the mass distribution within individual cells by measuring the phase shift caused by the interaction of light with intracellular biomass. Using LCI, we imaged cytotoxic T cells killing cognate target cells. In addition to a characteristic target cell mass decrease following attack by a T cell, there was a significant increase in T cell mass relative to the mass of unresponsive T cells and controls. Measuring the mass change of activated human CD8+ T lymphocytes by LCI has significant promise both in assessing T cell cytotoxicity for applications in cancer immune therapy, as well as for analyzing the biological principles underlying T cell activation.