Local delivery of IL-15 and anti-PD-L1 nanobody by in vitro-transcribed circILNb elicits superior antitumor immunity in cold tumors

The clinical translation of combined immunocytokine (IC) and immune checkpoint inhibitor (ICI) is constrained by relapse of advanced malignancies, systemic toxicities, and prohibitive research and synthesis costs. In this study, the circCV-B3 vector is constructed to enable scarless circular RNA (circRNA) engineering. The circILNb, engineered via the circCV-B3 vector, enables co-encoding of interleukin-15 (IL-15) and anti-PD-L1 nanobody (Nb). The circILNb is purified by biotin-avidin purification system (BAPS) and is encapsulated within lipid nanoparticles (LNPs). Intratumoral circILNb administration achieves in situ protein expression, achieving local tumor control. Furthermore, dendritic cells (DCs) load circILNb and migrate to tumor-draining lymph node (tdLN), where they prime antigen-specific CD8+ T cell activation, eliciting a robust systemic immune response. These findings highlight the potential of circCV-B3 vector and BAPS as a methodology for circRNA engineering and substantiate circILNb as non-protein-based therapeutic strategy for tumor immunotherapy.