B7-H3 CAR T cell-based immunotherapy combined with Losartan to counteract desmoplasia for the treatment of Pancreatic Ductal Adenocarcinoma (PDAC)

ABSTRACT The need for an effective therapy for pancreatic ductal adenocarcinoma (PDAC) has prompted us to develop a novel combinatorial immunotherapy with T cells engineered with a B7-H3-specific chimeric antigen receptor (CAR).

We have selected this effector mechanism because it allows rapid generation of polyclonal T cells with tumor antigen-specificity and potent cytotoxic activity, as well as because of the HLA class I antigen independence of the recognition of tumor cells by CAR T cells.

We have selected B7-H3 as a target because the epitope recognized by our homemade monoclonal antibody (mAb) 376.96: i) has high expression on differentiated PDAC cells and PDAC cancer initiating cells (CICs) with limited heterogeneity. Therefore, B7-H3 CAR T cells are expected to eradicate both differentiated PDAC cells and PDAC CICs.

According to the cancer stem cell theory, the latter play a major role in disease recurrence and metastatic spread and need to be eradicated for a therapy to be effective; ii) is expressed in at least 70% of PDAC tumors with low if any heterogeneity; iii) has a restricted distribution in normal tissues, since it is minimally, if at all, detectable on epithelial cells of the stomach, salivary glands, and adrenal glands; and iv) is also expressed in tumor-associated fibroblasts and endothelial cells, therefore B7-H3 immunotargeting may disrupt the peritumoral stroma and inhibit neo-angiogenesis.

In previous studies we have shown that B7-H3 CAR T cells completely eliminate PDAC cells in vitro and have demonstrated the safety and efficacy of our B7-H3 CAR T cell therapy against PDAC in immunodeficient and immunocompetent mice. However, the latter models were limited by the lack of desmoplasia in the tumor microenvironment (TME).

Desmoplasia consisting of dense extracellular matrix and fibroblasts is a prominent feature of the TME in PDAC.

It favors tumor cell proliferation, promotes invasive properties and suppresses anti-tumor immune response by creating a hypovascular and hostile environment.

To overcome the limitations of the models used thus far, we will use two human PDAC cell lines which produce desmoplasia in mouse models.

Using these models, we will show that losartan can reduce desmoplasia by inhibiting TGF-B1, and can increase the extent of tumor infiltration by CAR T cells.

Therefore, our strategy is expected to increase the number of B7- H3 CAR T cells reaching their targets; as a result, their local anti-tumor activity will be enhanced.

Furthermore, since it is not known whether losartan has any negative impact on the functional properties of CAR T cells, we will corroborate our preliminary results that i) losartan does not affect the viability and/or functional activity of B7-H3 CAR T cells, but enhances the in vitro specific recognition and elimination of PDAC cells by B7-H3 CAR T cells; and ii) B7-H3 CAR T cells in combination with losartan are able to counteract the desmoplastic TME and completely eliminate human PDAC cells orthotopically grafted in immunodeficient mice.

The information obtained from the outlined studies will contribute to the optimization of the B7-H3 CAR T cell-based treatment for PDAC.