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Abstract

Chimeric antigen receptor engineered (CAR) T cells have shown remarkable success in the treatment of hematologic cancers. However, this efficacy has yet to translate to treatment in solid tumors. Pancreatic ductal adenocarcinoma (PDA) is a fatal malignancy with poor prognosis. Treatment options are limited and commonly associated with severe side effects. We have developed and characterized a second generation CAR using the light and heavy chain sequence derived from a novel monoclonal antibody, TAB004, that specifically binds tumor-associated MUC1 (tMUC1) antigen. tMUC1 is overexpressed in >85% of all human PDA. We present data showing that the TAB004 derived CAR engineered T cells (tMUC1-CAR T cells) specifically binds tMUC1 on PDA cells and is cytotoxic against the majority of PDA cell lines in vitro. Importantly, tMUC1-CAR T cells do not bind or kill normal epithelial cells. We further demonstrate that the tMUC1-CAR T cells control the growth of orthotopic pancreatic tumors in vivo. PDAs are immunologically cold tumors with resistance to many standard treatment modalities, thus, it was not surprising that some of the PDA cell lines were refractory to CAR T cell treatment. qPCR analysis of several genes known to be associated with immune resistance revealed overexpression of indoleamine 2, 3-dioxygenases-1 (IDO1), Cyclooxygenase 1 and 2 (COX1 and COX2), Adenosine deaminases acting on RNA (ADAR1) and galectin-9 (Gal-9). We treated resistant PDA cells with a combination of CAR T cells and biological inhibitors of IDO1, COX1/2, ADAR1, and Gal-9. Results showed a significant enhancement of CAR T cell cytotoxicity against resistant PDA cells when inhibiting IDO1, COX1/2, and Gal-9 but not ADAR1 or COX2. In addition, we show that pre-treatment of resistant PDA cells with sub-optimal doses of standard chemotherapeutic drugs (paclitaxel, gemcitabine, or 5FU) significantly increased CAR T cell cytotoxic efficacy against resistant PDA cells. Overcoming CAR T cell resistance in PDA is a significant advancement in the field and may lead to future combination therapies that may be less toxic and more efficient against this lethal disease.

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