Chimeric antigen receptor (CAR) T cells can be remarkably effective in treating leukemias and lymphomas, but there are no successful immunotherapies for neuroendocrine tumors (NETs) and gastrointestinal cancers (GICs) yet.

Researchers at Penn Medicine have discovered that CAR T cells directed to a tumor antigen, CDH17, a cell surface marker expressed on both NETs and GICs but also found on healthy tissues, eliminated GICs in several preclinical models without toxicity to normal tissues in multiple mouse organs, including the small intestine and colon. The results from this study, the first to target CDH17 in neuroendocrine tumors, suggest a new class of tumor associated antigens accessible to CAR T cells in tumors but sequestered from CAR T cells in healthy tissues.

In the study, published in Nature Cancer, researchers isolated a llama-derived nanobody, a small antibody, which led to the identification of CDH17. Targeting CDH17—which is mainly expressed in the intestinal system—with CDH17CAR T cells eliminated gastric, pancreatic, and colorectal cancers in animal models. While CDH17 is also expressed in normal intestinal epithelial cells, the CDH17CAR T cells did not attack the normal cells, likely because the CAR T cells cannot reach or bind to healthy tissue in the tight junction between normal intestine epithelial cells, creating a “masking” effect in healthy cells from CAR T attack.

“Our work demonstrates that CDH17CAR T cells can eliminate solid tumors like NETs and GICs, but do not damage healthy, normal tissues that also express CDH17, because CDH17 is sequestered and hidden between the normal cells,” says senior author Xianxin Hua, a professor in the Department of Cancer Biology in the Abramson Family Cancer Research Institute at Penn. “This opens avenues to explore a new class of tumor antigens that are also expressed in normal cells but protected by the CAR T cell attack, and is hopefully another important step in developing safer immunotherapies for solid tumors.”

There are about five million new cases of GICs annually worldwide, underscoring the need for scientific and clinical advancements.