Human lung explants as a predictive platform for evaluating the on-target, off-tumor toxicity of T cell bispecifics.

T cell bispecifics (TCBs) are potent immunotherapies with proven efficacy in hematological cancers but limited success in solid tumors, where on-target, off-tumor toxicity has restricted their therapeutic index. Here, we establish a human lung explant model to assess TCB activity in matched tumors and normal adjacent tissues. Using a multi-modal approach combining flow cytometry, cytokine profiling, and multiplexed immunofluorescence, we show that EpCAM and FolR1 TCBs drive robust T cell activation and, critically, quantifiable epithelial cell killing above background levels. Normal lung explants exhibited consistently higher levels of killing than tumor counterparts, reflecting the on-target, off-tumor toxicities observed preclinically and clinically with the tested TCBs. Our findings establish lung explants as a predictive and clinically relevant preclinical model that uniquely enables simultaneous quantification of TCB-mediated T cell activation and target cell killing, recapitulating clinically observed toxicities and advancing the preclinical safety assessment of immunotherapies for solid tumors.