Characterization of murine CEACAM1 in vivo reveals low expression on CD8(+) T cells and no tumor growth modulating activity by anti-CEACAM1 mAb CC1

McLeod, Robbie L.; Angagaw, Minilik H.; Baral, Toya Nath; Liu, Liming; Moniz, Raymond Joseph; Laskey, Jason; Hsieh, SuChun; Lee, Mike; Han, Jin-Hwan; Issafras, Hassan; Javaid, Sarah; Loboda, Andrey; Sadekova, Svetlana; O'Connor, Joann A.; Tse, Archie; Punnonen, Juha

To delineate a potential mechanism of CEACAM-1 blockade for anti-tumor therapy, the expression profile of surface CEACAM-1 in tumor infiltrates was comprehensively assessed using flow cytometry. Several mouse syngeneic tumor models, MBT2, MC38, CT26, and MB49, were used for the analyses to avoid a tumor type-specific bias. About 100 mm 3 of subcutaneous tumors were established 7-10 days post implant. The CEACAM1 expression was first measured from untreated tumors by flow cytometry ( Figure 1A ). In all cases, high level of CEACAM1 expression was observed on granulocytic (CD11b+ Ly6G+ Ly6Clow) and monocytic (CD11b+ Ly6G− Ly6C+) myeloid cells from all tumors tested ( Figure 1A , MB49 not shown). The frequency of CEACAM1-expressing CD4+ or CD8+ T cells and the expression level of CEACAM1 on these cells were low.