Nanobody-Based Antiviral Strategies: From Passive Immunotherapy to Advanced Diagnostics

Abstract

The emergence and continuous evolution of viral pathogens pose major challenges to human and veterinary medicine. Conventional vaccines and antiviral drugs may not provide immediate protection during outbreaks, whereas conventional monoclonal antibodies are associated with high production costs, relatively large molecular size, limited tissue penetration, and complex manufacturing requirements. Nanobodies, also known as camelidderived single-domain antibodies or variable domains of heavy-chain antibodies, have emerged as promising next-generation biologics because of their small molecular size, high affinity, excellent solubility, remarkable thermal stability, and ability to recognize conserved or cryptic epitopes. These properties make nanobodies attractive candidates for passive antiviral immunotherapy and advanced diagnostic applications. Nanobodies can be generated through immunized camelid libraries, naïve or synthetic libraries, followed by phage, yeast, or ribosome display and recombinant expression. Their antiviral activity can involve inhibition of viral attachment, entry, membrane fusion, intracellular replication, assembly, and release. Protein engineering has further enabled multivalent, multispecific, Fc-fused, and albumin-binding nanobody formats to improve neutralization and pharmacokinetic properties. Nanobodies have been investigated against important human viruses, including severe acute respiratory syndrome coronavirus 2, influenza virus, respiratory syncytial virus, and HIV, as well as veterinary pathogens such as bovine viral diarrhea virus, foot-and-mouth disease virus, and Newcastle disease virus. Their integration into enzyme-linked immunosorbent assays, biosensors, molecular imaging, and lateralflow diagnostic platforms further expands their applications. This review summarizes the structural characteristics, generation, antiviral mechanisms, diagnostic and therapeutic applications, advantages, limitations, and future prospects of nanobodies, with particular emphasis on their relevance to human and veterinary viral diseases.