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

Taken together, the present study demonstrates low expression of CEACAM1 on tumor infiltrating mouse T cells, while significant expression was observed on B cells, NK cells and MDSCs. This expression profile is similar to that observed in freshly isolated human tumors (Lee et al., manuscript in preparation/submitted). Evaluation of the potential role of CEACAM1 in anti-tumor responses in syngeneic tumor models using the anti-CEACAM1 mAb CC1 did not reveal any anti-tumor benefits of the mAb, as a monotherapy or in combination with an anti-PD-1 mAb. However, while the CC1 Ab has been widely used in prior in vivo studies, our data suggest that the mAb facilitates, rather than blocks, CEACAM1-CEACAM1 interactions. Therefore, further studies using blocking Abs will be required to thoroughly understand the role CEACAM1 in tumorigenesis and anti-tumor responses in vivo. The potential role of CEACAM1 on B cells, NK cells and MDSCs was not addressed in this study and will be the focus of future studies. Low or minimal expression of CEACAM1 on tumor infiltrating T cells suggests that the primary function of CEACAM1 in vivo is mediated via cells other than CD8+ T cells, and the potential role of CEACAM1 in immuno-oncology remains to be established.