In this study, the researchers hypothesized that NK cells encoded with CAR that targets an overexpressed tumor-associated antigen would enhance tumor recognition and destruction by human NK cells. CAR-NK cells were directed against PSCA, common to pancreatic tumors in addition to gastric, bladder, prostate, and some lung cancers.
Here, NK cells are first isolated from donated umbilical cord blood from healthy newborns and genetically modified to express the desired CAR, plus PSCA. The City of Hope researchers also added a soluble IL-15, an immune signaling molecule crucial for optimal antitumor response, in addition to a “suicide gene.”
Multiple doses of CAR-NK cells are then manufactured, with continued cell expansion going from 10s of millions of cells from a single donor cord blood to a hundred billion or more CAR-NK cells within 16 days. The cells are then frozen and preserved for future use. When thawed, they were shown to retain viability and potency.
“Large-scale production should allow our product to be administered to anywhere between 10 and 20 patients once in clinic,” Teng said.
To test the potential effectiveness of CAR-NK cell therapy in the lab against pancreatic cancer, Teng and colleagues added their engineered CAR NK cells targeting PSCA (PSCA+ CAR NK), with soluble IL-15 (sIL-15) and a “suicide gene,” into a culture of pancreatic cancer cells (Capan-1). They compared the results against a control that did not include PSCA (PSCA- CAR NK), but did contain IL-15 and the “suicide gene,” into a culture of PANC-1 pancreatic tumor cells.
“We showed that the co-expression of sIL-15 with PSCA+ CAR NK cells significantly enhances their cytotoxic function against pancreatic tumor cells compared to PSCA- CAR NK cells without expression of sIL-15 determined by a real-time cytolysis assay over 3.5 days,” the researchers wrote in an abstract of their study.
Encouraged by these findings, Teng and colleagues developed a model of metastatic human pancreatic cancer in immunodeficient mice using the PSCA+ Capan-1 cell line. Mice were treated for 45 days.
Compared to cells only expressing IL-15, repeated infusions of human PSCA CAR NK cells from a viably frozen source resulted in a significantly prolonged survival in these mice, including no sign of metastatic disease.
“Only treatment with the PSCA CAR NK cells significantly suppressed tumor growth, protected the pancreas, and delivered from metastatic spread and prolonged survival of the mice, over either arm of the controls studied,” Teng said.
Analysis of the cells isolated from pancreas on Day 48 also showed the near absence of tumor cells and the persistence of NK cells.
“In summary, our in vitro and in vivo studies utilizing viably frozen human PSCA CAR NK cells co-expressing sIL-15 demonstrate significant efficacy in prolonging survival against a human pancreatic tumor cell line without evidence of systemic toxicity, providing a rational to move this novel form of cell therapy into the clinic for PSAC(+) solid tumors,” the researchers wrote in their abstract.
Warren Froelich is a contributing writer.