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 evaluate the potential of CC1 to block its ligand interactions, we established protein-and cell-based ELISA assays. Mouse CEACAM1-CEACAM1 interaction was observed in both protein ELISA using recombinant CEACAM1 proteins and by cell ELISA (cELISA) using soluble protein and mouse CEACAM1-transfected cell lines (Figure 2A, 2B ). CEACAM1 has also been reported to interact with TIM-3 [21] and therefore, we aimed to analyze this interaction by cELISA using recombinant mouse CEACAM1 protein and mouse TIM-3 transfected cell line. In this assay format, we did not observe any direct CEACAM1-TIM3 interaction, while expression of TIM-3 was confirmed using anti-TIM-3 mAb ( Figure 2C ). We also attempted to analyze the potential CEACAM1-TIM3 interaction by other methods such as Biacore and protein ELISA using human recombinant proteins, while no interaction between these two proteins was observed in these assay formats either (data not shown).