Oncolytic viruses represent an emerging therapeutic approach for treating patients with solid tumours. One such virus, TILT-123 (Ad5/3-E2F-D24-hTNFα-IRES-hIL-2), is a serotype chimeric oncolytic adenovirus. TILT-123 is designed to encode tumour necrosis factor alpha and interleukin-2, aiming to induce T-cell infiltration and cytotoxicity within solid tumours. After several years of preclinical development, TILT-123 is now tested in phase I clinical trials either as a monotherapy, or in combination with other T-cell therapies across various solid tumour types. In a single-arm, multicentre phase I dose-escalation trial TUNIMO (NCT04695327), the safety of TILT-123 in patients with advanced solid cancers refractory to standard therapy was evaluated. During the intravenous phase of the study, researchers collected patient serum to identify potential predictive biomarkers associated with intravenous delivery of TILT-123.