CS-BLI for quantitative analysis of antitumor immune effector cell function. Luciferase-expressing MM.1S tumor cells (312-10 000/well) were plated with and without PBMCs (10 000/well). Luciferin was added and incubated for 30 minutes at 37°C, and bioluminescence was read on a Luminoscan luminometer. Signal for luc⁺ MM.1S cells remained linear across a range of cell numbers and was equal both in the presence or absence of PBMCs (A). PBMCs were isolated from a healthy donor, stimulated for 24 hours with 10 ng/mL IL-2, and cocultured with 5000 luc⁺ MM.1S target cells/well at increasing effector-to-target ratios. Tumor cell viability was assessed by CS-BLI after 4 hours of coculture. Decreased MM.1S viability was observed with increasing effector PBMC-to-tumor cell ratios (B). In addition, CS-BLI was compared with the traditional Cr release. Identical IL-2–simulated PBMCs and luc⁺ MM1S and OPM2 target cells were cocultured and evaluated with the CS-BLI method (C) and the Cr release (D) system (n = 4 for each condition). The 2 techniques led to consistent results, in terms of the effect of PBMCs on tumor cells. PBMCs for panels C and D were from the same donor but different from PBMCs used for panel B.