Rapid and Cost-Effective Diagnostic Blot Assays Based on the Use of Plant-Produced Recombinant Antigens: Lessons Learned from the SARS-CoV-2 RBD Antigen

The ongoing demand for reliable, cost-effective, and scalable diagnostic solutions during the COVID-19 pandemic emphasized the need for innovative production platforms. In this study, we present a plant-based molecular farming (PMF) strategy for the production of the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein fused with an Fc region (RBDw-Fc). The RBDw-Fc antigen was transiently expressed in the <i>Nicotiana benthamiana</i> plant, achieving high yields and purity. Its functionality was assessed through antigen-antibody binding assays. The purified antigen was subsequently employed in the development of a rapid diagnostic blot assay capable of screening plasma EDTA samples from pre- and post-vaccinated as well as pre- and post-infected individuals, demonstrating high sensitivity and specificity. Our results show that the RBDw-Fc-based assay is effective for SARS-CoV-2 detection and offers considerable advantages in terms of production speed, scalability, and cost efficiency compared to traditional systems, such as cell-culture-based production. The assay delivers accurate results in just a few minutes, making it particularly suitable for clinical and resource-limited settings. This study highlights the versatility of PMF as a platform for producing high-quality reagents, with promising applications beyond SARS-CoV-2 diagnostics. The RBDw-Fc antigen-based method provides a model for the rapid, economical, and flexible development of screening tools for emerging infectious diseases and future pandemics.