Blocking of CEACAM-6 on myeloma cells increases cytotoxic activity of tumor-reactive CTL. (A,B) Perforin secretion of ex vivo isolated, purified CD8+ T cells from a representative (A) or 5 (cumulative) MM patients (B), cocultured with sorted autologous myeloma cells in a perforin Elispot assay. Inhibition of CEACAM-1, CEACAM-5, and CEACAM-8 on myeloma cells was conducted by specific mAbs. A significant increase of perforin-secreting CTL was achieved upon CEACAM-6 inhibition (black bar). Unblocked myeloma cells (con; white bar) served for comparison. Data are shown as mean ± SEM numbers of perforin spots. TC, T cells only. *P < .05 or (*)P < .1, statistically significant differences between test and respective control groups as calculated by two-sided Student t test.