Insufficiency of compound immune checkpoint blockade to overcome engineered T cell exhaustion in pancreatic cancer

Achieving robust responses with adoptive cell therapy for the treatment of the highly lethal pancreatic ductal adenocarcinoma (PDA) has been elusive. We previously showed that T cells engineered to express a mesothelin-specific T cell receptor (TCR) accumulate in autochthonous PDA, mediate therapeutic antitumor activity, but fail to eradicate tumors in part due to acquisition of a dysfunctional exhausted T cell state. Here, we investigated the role of immune checkpoints in mediating TCR engineered T cell dysfunction in a genetically engineered PDA mouse model. The fate of engineered T cells that were either deficient in PD-1, or transferred concurrent with antibodies blocking PD-L1 and/or additional immune checkpoints, were tracked to evaluate persistence, functionality, and antitumor activity at day 8 and day 28 post infusion. We performed RNAseq on engineered T cells isolated from tumors and compared differentially expressed genes to prototypical endogenous exhausted T cells. Mouse CD8+Thy1.1+ T cells were activated in vitro with anti-CD3+anti-CD28 + rIL-2, transduced with a high affinity mesothelin-specific murine TCR (clone 1045) and transferred into a tumor-bearing, genetically engineered KPC mouse model of pancreatic cancer. TCR engineered T cells were sorted from tumors on day 8 and day 28 post transfer and gene expression was compared to naive T cells and engineered T cells prior to transfer (effector) using microarray.