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

CEACAM1 has also been reported to interact with TIM-3 [21] and, thus, we studied the potential effects of CC1 on this interaction. However, we were unable to reproducibly detect CEACAM1-Ig or CEACAM1-His binding of TIM-3 and hence, the evaluation of CC1 in these assays was not feasible. Minimal binding of TIM-3 to CEACAM1-Ig or CEACAM1-His was observed in both cell-based assays using mouse reagents ( Figure 2C ) and protein-based assays using human reagents (data not shown). Since CEACAM1-TIM-3 interactions were shown to occur both in the cis (through the membrane distal N-terminal domains of the molecules) and trans (through their N-terminal domains), the development of additional assays to assess potential effects of CC1 on CEACAM1-TIM-3 interactions will be needed. The current data do not reveal the reason for the lack of detectable binding in our assays, while low affinity interactions are likely to play a role. In addition, as galectin-9 has been identified as another ligand for TIM-3 and is ubiquitously expressed in multiple tissues and cell types [32] , potential interference by galectin-9 in the cellbased assays cannot be ruled out. However, it should be noted that no prior studies have suggested modulation of CEACAM1-Tim-3 interactions by the CC1 Ab.