Influenza pandemics have had devastating impacts in the 20th and 21st centuries, resulting in millions of deaths. It is challenging to control the influenza virus through antiviral drugs due to its rapid evolution to evade the host immune system. The 3D8 single chain variable fragment (scFv) protein, known for its nuclease activity against DNA and RNA viruses, has demonstrated broad antiviral properties in various models. In this study, we investigated the impact of administration routes and dosages on the distribution of exogenously administered 3D8 scFv. Our results suggested that repeated intranasal (IN) injection primarily targets lung tissue, while intravenous (IV) administration ensures systemic distribution, including lung tissues via the bloodstream. Furthermore, we explored the efficacy of exogenous and endogenous 3D8 scFv in inhibiting influenza A virus (H1N1/PR8) replication in mouse models. Our findings revealed that while both approaches exhibited antiviral activity, with constitutive pre-infection expression of 3D8 scFv showed 100% survival, whereas mice receiving exogenous 3D8 scFv post-infection exhibited 33.3% survival. These findings highlight the potential of 3D8 scFv as a promising antiviral strategy against influenza and suggest its possible applications in transgenic livestock for future disease control.

Flaviviruses such as dengue virus (DENV) and Zika virus (ZIKV) co-circulate widely and cause significant morbidity, yet effective broad-spectrum antivirals are limited. This study evaluated the antiviral efficacy, cytotoxicity, and host transcriptional responses to the nucleic acid–hydrolyzing antibody fragment 3D8 scFv in mono- and co-infection models. RNA sequencing of A549 cells treated with 3D8 scFv revealed a dose-dependent activation of the MAPK–HSP70 stress response, with minimal transcriptomic disruption at antiviral concentrations. Comparative transcriptomic analysis identified distinct host signatures for ZIKV and DENV2, and machine learning classifiers accurately distinguished infection states (AUC > 0.95). In Vero E6 cells, prophylactic treatment with 3D8 scFv significantly reduced viral RNA, protein expression, and infectious particle production for both viruses, including during co-infection. Optimized post-entry treatment also demonstrated antiviral activity. Cytotoxicity assays confirmed good tolerability at effective concentrations. These findings indicate that 3D8 scFv inhibits viral replication through early cleavage of viral nucleic acids while inducing a limited protective stress response, supporting its development as a broad-spectrum antiviral candidate.