Anti-tumor activity of an αPD-L1-PE38 immunotoxin delivered by engineered Nissle 1917.

Although immune checkpoint inhibitors specifically targeting the PD-1/PD-L1 axis have exhibited remarkable clinical success, they are not uniformly effective across all patient cohorts. Immunotoxins, a novel class of cancer therapeutics, offering a promising alternative. PD-L1, which is also present in certain normal tissues, limits its suitability as an ideal target for immunotoxins. The probiotic strain of E. coli Nissle 1917 (EcN) could target and colonize to solid tumors, which positions it as a promising candidate for tumor tissue-specific delivery of anti-tumor proteins. In this study, we constructed a PD-L1-targeted immunotoxin, designated as αPD-L1-PE38, by fusing an anti-PD-L1 nanobody and a clinically validated PE38 toxin. This immunotoxin exhibited potent cytotoxic activity against tumor cells while showed slightly cytotoxic activity against normal cells. To effectively deliver the αPD-L1-PE38 to tumor tissues, we engineered the EcN strain to release the immunotoxin induced by L-arabinose. Upon induction, the immunotoxin was efficiently secreted, and exhibited robust anti-tumor activity mainly by inducing cell apoptosis both in vitro and in vivo. Furthermore, we enhanced the immunotoxin's affinity for PD-L1 by optimizing the linker between the nanobody and PE38 toxin. The engineered EcN expressing the optimized immunotoxin, achieved superior anti-tumor activity. Collectively, our study suggests that the delivery of immunotoxins through live bacteria to improve safety and efficacy is a promising option in cancer therapeutics.