Figure 6. ABCB5⁺ MMICs preferentially inhibit T cell activation.

(A) Left panel: ³H-thymidine uptake (mean cpm±SD) and cell death (Annexin V-PE/7-AAD) staining (%, mean±SD; right panel) of human PBMCs cultured with or without PHA in the presence or absence of ABCB5⁺ or ABCB5⁻ malignant melanoma cells (MMC) (representative of n=3-6 independent experiments, respectively; *, P<0.05; NS, not significant). (B) Fold-differences (mean±SEM) of cytokine secretion by mitogen-stimulated PBMCs cultured in the presence of ABCB5⁺ versus ABCB5⁻ melanoma cells as determined by ELISPOT analysis (representative of n=4 independent experiments). Images of representative ELISPOT wells are shown. (C) Effects of B7.2 blockade in ABCB5⁺ or ABCB5⁻ melanoma cells on cocultured mitogen-stimulated PBMCs with regard to IL-10 production (mean spots per well±SEM, left panel) and Treg cell frequencies (% CD4⁺CD25⁺FoxP3⁺ triple-positive PBMCs±SEM, right panel). Results are representative of n=3-5 independent experiments, respectively. (D) IL-2 (left panel) and IL-10 (right panel) production by PBMCs cultured in the presence of patient-derived, syngeneic ABCB5⁺ versus ABCB5⁻ melanoma subpopulations, as determined by ELISA. Illustrated are mean cytokine concentrations (pg/ml) for n=3 replicate wells of n=6 independent experiments±SEM, respectively.