Vaccine and Gene Therapy Institute of Florida 1 article published in JoVE Immunology and Infection Cell-based Flow Cytometry Assay to Measure Cytotoxic Activity Alessandra Noto1, Pearline Ngauv1, Lydie Trautmann1 1Vaccine and Gene Therapy Institute of Florida This protocol describes a sensitive, cell-based cytotoxicity assay. By enumerating the decrease in frequency of live target CD4+ T cells in the presence of an increasing number of effector CD8+ T cells, this assay allows for the direct assessment of cytolytic activity of antigen-specific CD8+ T cells.