Abstract Mantle cell lymphoma (MCL) accounts for 6-8% of all non-Hodgkin lymphomas (NHLs). While substantial therapeutic advances have been achieved for other NHLs, MCL remains an incurable lymphoma, the reason of which is not known. MCL patients have a dismal prognosis with a median overall survival of 3-5 years. Standard of care includes ibrutinib, a small molecule inhibitor of the B-cell receptor (BCR)-proximal tyrosine kinase BTK. However, one-third of MCL patients do not respond to the drug. Even initially ibrutinib- sensitive patients invariably develop resistance; however, the mechanisms of ibrutinib-resistance are now clear. Since mechanistic insight into oncogenic BCR signaling in DLBCL and CLL enabled the development of highly effective treatment approaches, this proposal will address the mechanisms of oncogenic BCR- signaling in MCL. In an integrated functional analysis combining a genome-wide CRISPR-Cas9 library, gene expression profiling and BCR signal transduction studies, we have uncovered CEACAM1 as a central component of oncogenic BCR signaling that is essential in MCL but not in normal B cells or other B-cell malignancies. As a transmembrane protein, CEACAM1 is expressed on the surface of activated lymphocytes and carries two immunoreceptor tyrosine-based inhibitory motifs (ITIMs) on its cytoplasmic tail. Owing to recruitment of the inhibitory phosphatase SHP1 to the ITIMs, CEACAM1 functions as a regulator of T-cell receptor (TCR) signaling in T cells, however, its function in normal B cells and MCL is not known. Unexpectedly, our preliminary data showed that CEACAM1 function induced a net increase of BCR signaling, leading to increased survival and proliferation of MCL cells in vitro and in vivo. Our mechanistic studies revealed that CEACAM1 recruited the actin-binding protein filamin A to the plasma membrane microdomains and activated the BCR-proximal kinase LYN after antigen engagement. Furthermore, super- resolution confocal microscopy revealed that CEACAM1 promoted reorganization of the actin cytoskeletal network following BCR cross-linking. Leveraging the clinical grade Cell Therapeutics Facility at City of Hope, we designed and validated a novel CEACAM1 chimeric antigen receptor (CAR) engineered in primary human T cells. The CAR-T cells were highly active in eliminating CEACAM1+ MCL but lacked reactivity against other cell types. Based on our discovery of CEACAM1 as a critical BCR signaling component in MCL and the successful development of CEACAM1 CAR-T cells, we hypothesize that CEACAM1 functions as a central driver of oncogenic BCR activity and represents a novel therapeutic target in MCL. The following specific aims will test and refine the concept of CEACAM1-based therapies for MCL: Aim 1) Define the mechanistic role of CEACAM1 in oncogenic BCR signaling in MCL; Aim 2) Dissect the role of CEACAM1 in new genetic mouse models for MCL; Aim 3) Validation of CAR T-cell strategies targeting CEACAM1 in refractory MCL. Resul...