A humanized monoclonal immunoglobulin G4 (IgG4) antibody targeting the anti-carcinoembryonic antigen (CEA)-related cell adhesion molecule 1 (CEACAM1; CD66a), with potential immunomodulating and antineoplastic activities. Upon administration of anti-CEACAM1 monoclonal antibody CM-24, this agent binds to CEACAM1 on cancer cells and certain immune cells. This blocks the binding of CEACAM1-expressing cancer cells to CEACAM1-expressing immune cells and abrogates CEACAM1-mediated immunosuppression. This enhances the activation of cytotoxic T-lymphocytes (CTLs) and natural killer (NK) cells and increases CTL- and NK-mediated killing of CEACAM1-overexpressing cancer cells. CEACAM1, a member of the CEA family of proteins that plays a key role in cell migration, cell invasion, and cell adhesion, is overexpressed by a variety of cancer cell types. Its overexpression is correlated with both immunosuppression and poor prognosis.