TLR7/8 agonist 3M-052 formulated in micelles induces local type I IFN response and antiviral immunity in zebrafish larvae

Micelle-based delivery systems provide a promising platform for vaccine adjuvants by encapsulating active compounds and enabling targeted delivery, thereby limiting systemic side effects. Here, we investigated the immune response, biodistribution, and antiviral effects of micelles loaded with the TLR7/8 agonist, 3M-052, in zebrafish (Danio rerio) larvae.

Fluorescently labelled micelles were injected to transgenic reporter zebrafish larvae, and localization of micelles as well as neutrophils, macrophages, or mxa-expressing, was monitored by live confocal microscopy. Host response was also assessed at the whole-body level by qRT-PCR. In addition, larvae were infected with a recombinant Sindbis Virus to monitor the localization of viral infection.

Micelles demonstrated progressive clearance from the injection site and promoted local recruitment of neutrophils and macrophages, indicating immune activation. Whole-larva analysis showed no significant upregulation of key immune genes following unloaded or 3M-052-loaded micelle injection. However, 3M-052-micelles triggered a transient and localized mxa response, confirming induction of a local type I interferon response. Furthermore, zebrafish larvae exhibited significantly reduced virus replication near the site of 3M-052-micelle injection.

These findings indicate that micelles effectively deliver 3M-052 and elicit a localized antiviral response without broad systemic immune activation.