Engineered yeast deliver colorectal cancer immunotherapy

Saccharomyces cerevisiae var. boulardii is a yeast strain that has been designed for a new purpose: treating colorectal cancer. Researchers have previously engineered Escherichia coli bacteria that produce and release immune checkpoint inhibitors when injected into tumors in mice. In a new study, a team led by microbiologist Gautam Dantas at Washington University in St. Louis designed a system based on S. cerevisiae var. boulardii, (also called S. boulardii ) to make and deliver immune checkpoint inhibitors to gastrointestinal tumors in mice after it’s ingested ( Cell Chem. Biol. 2024, DOI: 10.1016/j.chembiol.2024.10.013 ) . Dantas’ team inserted plasmids into the yeast that encode miniature antibody variants, which then block PD-1, a checkpoint protein found on T cells. Cancer cells can shield themselves from the immune system by binding to checkpoint proteins. When checkpoint proteins or the ligands they bind to are blocked, T cells can destroy the tumors. Mice with