A Novel Chimeric Antigen Receptor Against Prostate Stem Cell Antigen Mediates Tumor Destruction in a Humanized Mouse Model of Pancreatic Cancer

Abstract

Despite advances in the understanding of its molecular pathophysiology, pancreatic cancer remains largely incurable, highlighting the need for novel therapies. We developed a chimeric antigen receptor (CAR) specific for prostate stem cell antigen (PSCA), a glycoprotein that is overexpressed in pancreatic cancer starting at early stages of malignant transformation. To optimize the CAR design, we used antigen-recognition domains derived from mouse or human antibodies, and intracellular signaling domains containing one or two T cell costimulatory elements, in addition to CD3zeta. Comparing multiple constructs established that the CAR based on human monoclonal antibody Ha1-4.117 had the greatest reactivity in vitro. To further analyze this CAR, we developed a human pancreatic cancer xenograft model and adoptively transferred CAR-engineered T cells into animals with established tumors. CAR-engineered human lymphocytes induced significant antitumor activity, and unlike what has been described for other CARs, a second-generation CAR (containing CD28 cosignaling domain) induced a more potent antitumor effect than a third-generation CAR (containing CD28 and 41BB cosignaling domains). While our results provide evidence to support PSCA as a target antigen for CAR-based immunotherapy of pancreatic cancer, the expression of PSCA on selected normal tissues could be a source of limiting toxicity.

Improving Chimeric Antigen Receptor-Modified T Cell Function by Reversing the Immunosuppressive Tumor Microenvironment of Pancreatic Cancer

“…19,21,22 With the purpose of arming our CAR T cells to withstand the tumor milieu, we have generated a custom inverted cytokine receptor (ICR) that combines the exodomain of the IL-4 receptor fused with the endodomain of the IL-7 receptor (4/7 ICR). When co-expressed with CAR-PSCA to target pancreatic cancer, a disease characterized by elevated IL-4 levels and PSCA overexpression, 8,9,11,23,24 we achieved enhanced expansion and anti-tumor effects but only when transgenic T cells engaged with both cytokine (IL-4) and cognate antigen (PSCA). This not only demonstrates the potency of CAR/ICR T cells but also their safety as expansion upon exposure to antigen alone was limited.…”

“…This is particularly noteworthy given that PSCA has been shown to be expressed at low levels in some normal tissues. 9,25 Pancreatic cancer remains the fourth leading cause of cancer-related mortality in the USA with a 5-year overall survival of <5%. 26 More than 53,070 patients are diagnosed annually, and an estimated 41,780 individuals die from this disease each year.…”

“…Though several pancreatic cancer-targeted CARs have been developed (carcinoembryonic antigen [CEA], 33 mesothelin, 34 Her2/ neu, 35 and PSCA 9,12 ), the immunosuppressive tumor microenvironment, which can impair the proliferative capacity and in vivo persistence of the infused T cells poses a major challenge to successful immunotherapy. 19,21,22 To overcome this barrier, a number of groups have combined CAR T cells with other therapies designed to modulate the tumor microenvironment including checkpoint inhibitors and oncolytic viruses.…”

“…5,6 To extend this approach to pancreatic ductal adenocarcinoma (PDAC), we chose to target prostate stem cell antigen (PSCA), a 123-amino-acid glycosylphosphatidylinositol (GPI)-anchored cell-surface protein that is highly expressed by most pancreatic tumor cells with low basal expression in normal tissues. [7][8][9][10] Indeed, in a phase II clinical trial Wolpin et al 11 demonstrated that combining an anti-PSCA monoclonal antibody with standard chemotherapy (gemcitabine) was safe and improved the 6-month survival rate in patients with metastatic PDAC. As a therapeutic alternative, we developed a PSCA-directed CAR and demonstrated that transgenic cells were able to efficiently and selectively eliminate antigen-expressing tumors in both in vitro and in vivo xenograft mouse models.…”

PSCA and MUC1 in non-small-cell lung cancer as targets of chimeric antigen receptor T cells

“…Antibody-based, PSCA-targeted therapies, as well as a peptide vaccine, have been explored for the treatment of prostate cancer. [24][25][26][27][28] Furthermore, PSCA-targeting CAR T cells have been used to treat pancreatic cancer in humanized mice, 29 and clinical trials of anti-PSCA CAR T cells for the treatment of prostate, bladder and pancreatic cancers are ongoing (ClinicalTrials.gov Identifier, NCT02092948 and NCT02744287). It remains unknown, however, whether anti-PSCA CAR T cells could be used to treat NSCLC.…”