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Chimeric antigen receptors (CARs) combine specificity of antibody to target antigen on cancer cells with the potent cytotoxic activity of T-cells without the need for MHC recognition. Chimeric antigen receptor (CAR) T-cells that were designed to express the single chain variable fragment binding domain of human anti-CEA antibody BW431/26 on mouse splenocytes were able to reduce CEA-expressing pancreatic adenocarcinoma tumor in CEA-transgenic (CEAtg) mice without significant off-target effects (Chmielewski et al., 2012). In this study, an anti-CEA CAR construct derived from murine anti-CEA antibody (T84.66) expressed on human T-cells targeted CEA+ colon carcinoma cells (LS174T/CEA and MC38CEA) with high specificity in vitro. When co-incubated with CEA-positive or CEA-negative mouse cancer cells, anti-CEA CAR expressed on mouse T-cells also specifically targeted CEA-positive cancer cells in vitro. Compared to mock T-cells control, anti-CEA CAR T-cells injected intravenously delayed subcutaneous MC38CEA tumor growth in CEA-transgenic mice (CEAtg). Lymphodepletion via cyclophosphamide injected before anti-CEA T-cells injection further delayed subcutaneous MC38CEA tumor growth and delayed orthotopic CEA+ breast carcinoma (E0771CEA) tumor growth in CEAtg mice. To improve the therapeutic potential of anti-CEA CAR T-cells, IL2 conjugated to humanized anti-CEA antibody (M5A-IL2, ICK) was interperitoneally injected after anti-CEA CAR T-cells into lymphodepleted CEAtg mice. A single injection of ICK after anti-CEA CAR T-cells delayed subcutaneous MC38CEA tumor growth even further. Two injections of ICK after anti-CEA T-cells delayed orthotopic E0771CEA tumor growth. Four injections of ICK after anti-CEA CAR T-cells eradicated subcutaneous MC38CEA tumors. These data show the therapeutic potential of anti-CEA CAR T-cells to target CEA-positive tumors. Citation Format: Seung Cha, Paul Yazaki, Christine Brown, John Shively. Treatment of CEA-positive solid tumors with anti-CEA chimeric antigen receptor T-cells in CEA transgenic mice [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2020 Oct 19-20. Philadelphia (PA): AACR; Cancer Immunol Res 2021;9(2 Suppl):Abstract nr PO083.

Microfibril-associated glycoprotein 2 (MAGP2) is a secreted protein associated with multiple cellular activities including the organization of elastic fibers in the extracellular matrix (ECM), angiogenesis, as well as regulating Notch and integrin signaling. Importantly, increases in MAGP2 positively correlate with poor prognosis for some ovarian cancers. It has been assumed that full-length MAGP2 is responsible for all reported effects; however, here we show MAGP2 is a substrate for the proprotein convertase (PC) family of endoproteases. Proteolytic processing of MAGP2 by PC cleavage could serve to regulate secretion and thus, activity and function as reported for other extracellular and cell-surface proteins. In support of this idea, MAGP2 contains an evolutionarily conserved PC consensus cleavage site, and amino acid sequencing of a newly identified MAGP2 C-terminal cleavage product confirmed functional PC cleavage. Additionally, mutagenesis of the MAGP2 PC consensus cleavage site or treatment with PC inhibitors prevented MAGP2 proteolytic processing. Finally, both cleaved and uncleaved MAGP2 were detected extracellularly and MAGP2 secretion appeared independent of PC cleavage, suggesting that PC processing occurs mainly outside the cell. Our characterization of alternative forms of MAGP2 present in the extracellular space not only enhances diversity of this ECM protein but also provides a previously unrecognized molecular mechanism for regulation of MAGP2 biological activity.