Impact of CEACAM-6 on TCR signaling. (A) Polyclonally activated CD8+ T cells show reduced secretion of IFN-γ in response upon coculture with CEACAM-6–positive RPMI8226 myeloma cells assessed by IFN-γ Elispot assay of 1 representative of 3 MM patients. Mean ± SEM numbers of IFN-γ spots are shown for test wells containing only activated T cells (white bar), activated T cells in coculture with RPMI8226 myeloma cells (gray bar), or activated T cells in coculture with RPMI8226 myeloma cells on which CEACAM-6 was blocked before by CEACAM-6–specific mAbs (black bar). Cumulative data from all 3 tested patients are shown as % of IFN-γ secretion relative to corresponding wells containing TC only in (B). Each patient is represented by a different symbol. *P < .05 or (*)P < .1, statistically significant differences between test and respective control groups as calculated by 1-sided Student t test. (C) TCR signaling is reduced by CEACAM-6 on myeloma cells. The amount of different phosphorylated TCR-associated signaling molecules was assessed on CD8+ T cells from MM patients either cultured alone directly after ex vivo isolation (white bars) or after 5 minutes of coculture with untreated RPMI8226 myeloma cells (gray bars) or with RPMI8226 myeloma cells on which CEACAM-6 had been blocked by anti–CEACAM-6 mAb (black bars). Quantification of protein phosphorylation was conducted with phosphoprotein-specific antibodies by Luminex technology using 1 replicate per test group. One representative experiment of 3 is shown. Cumulative data from 3 tested patients are shown in (D) as % of fluorescence intensity relative to corresponding wells containing activated TC only. Mean ± SEM values from 3 independent experiments with different myeloma patients are shown. *Significant difference (P < .05) between TC treated with myeloma cells and T-cells treated with CEACAM-6 blocked myeloma cells (2-sided Student t test).