Human Multiple Myeloma and Breast Cancer Cells Evade Immune Rejection Through Expression of Carcinoembryonic Antigen-Related Cell Adhesion Molecule 6.

Abstract 2942

Tumor-specific cytotoxic T cells are common in tumor patients, but ineffectively react against autologous tumor cells. Here, we demonstrate in multiple myeloma and breast cancer that human tumor cells escape recognition by tumor-specific CD8+ T cells through carcinoembryonic antigen-related cell adhesion molecule-6 (CEACAM-6) expression. We demonstrate for the first time CEACAM-6 expression in primary and established myeloma and examined the effects of altered CEACAM expression on cytotoxic T cell activity and cytokine secretion against myeloma and breast cancer cells in vitro —, and in vivo, using a xenotransplant mouse model. Cytotoxic T cells from multiple myeloma patients reacted against myeloma antigens presented by dendritic cells, but not against autologous myeloma cells, which expressed CEACAM6. Gene knockdown or blocking of CEACAM6 on myeloma cells restored CD8+ T-cell reactivity against malignant plasma cells. SiRNA-mediated CEACAM6 knockdown or inhibition by specific mAbs also restored cytokine secretion, cytotoxic activity, and antigen-specific lysis of CEACAM6-positive breast cancer cells. Moreover, CEACAM-6 inhibition was a prerequisite for efficient treatment of xenotransplanted breast tumors by adoptive T cell transfer. CEACAM6 thus plays an important role in inhibiting CD8+ T-cell responses against hematological and epithelial human tumors. Therapeutic targeting of CEACAM6 may be a promising strategy for improving cancer immunotherapy.