High titer expression of antibodies using linear expression cassettes for early-stage functional screening

Modern antibody discovery workflows identify an immense volume of potential binding sequences from diverse sources, including in vivo immune repertoires, in vitro display libraries, and in silico computational designs. Prior research has shown that the production of these recombinant proteins typically relies on circular plasmid vectors, which necessitate labor-intensive cloning, transformation, and bacterial expansion steps. Although transient expression using linear DNA templates offers a theoretically faster alternative, the inherent susceptibility of these fragments to intracellular exonuclease degradation often severely limits the final protein titer. Conventional methodologies for small-scale synthesis frequently struggle to generate the concentrations of Immunoglobulin G (IgG) or Fragment antigen-binding (Fab) molecules required for rigorous functional screening. The absence of high-yield, rapid-turnaround expression platforms creates a significant bottleneck in the transition from sequence identification to experimental validation. This absence of evidence motivated the development of a robust system utilizing protected linear fragments to streamline the early-stage evaluation of candidate therapeutic molecules.

This research establishes a high-efficiency platform for the rapid synthesis of recombinant antibodies using Gibson assembled linear DNA fragments (GLFs). The investigators sought to overcome the historical yield limitations associated with linear expression cassettes by engineering novel protecting flanking sequences at both the 5' and 3' termini. By enhancing the intracellular stability of these DNA templates, the study aimed to achieve protein titers comparable to traditional plasmid-based systems without the associated time delays. The project focused on validating a scalable workflow that accommodates both 1 ml volumes for high-throughput screening and 30 ml volumes for more intensive biophysical characterization. Researchers intended to demonstrate that this approach could produce high-quality Immunoglobulin G (IgG) and Fragment antigen-binding (Fab) proteins suitable for a wide array of downstream applications. This methodology was designed to reduce the financial burden and logistical complexity of antibody discovery by eliminating the need for bacterial cloning and plasmid preparation.

The experimental workflow utilizes Gibson assembly to rapidly generate linear DNA fragments (GLFs) that incorporate essential promoter, coding, and polyadenylation elements. Scientists integrated specific protecting flanking sequences at the distal ends of these linear constructs to mitigate enzymatic degradation within the host cell environment. Small-scale expressions were conducted in 1 ml volumes using transient transfection techniques to facilitate the immediate evaluation of binding affinity and biological activity. For assays requiring larger quantities of material, the team scaled the process to 30 ml and implemented a rigorous dual-column purification strategy. This purification regimen employed Protein A affinity chromatography followed by Size Exclusion Chromatography (SEC) to ensure the removal of aggregates and achieve high levels of protein homogeneity. The researchers then performed a comparative analysis of the resulting titers and product quality against traditional circular plasmid expression systems across multiple functional assays.

The implementation of protected Gibson assembled linear DNA fragments (GLFs) yielded antibody concentrations approximately five to ten-fold higher than those achieved with previous linear expression methods. Purified recombinant antibody yields from the 1 ml expression scale provided sufficient material for rapid functional screening and activity measurements. Scaling the production to 30 ml successfully generated milligram quantities of high-quality protein, which is essential for sensitive assays and detailed structural studies. The data indicates that this linear system achieves nearly equivalent yields to conventional plasmid-based expression platforms while significantly shortening the production timeline. Using these protected cassettes effectively reduced the overall costs associated with reagent use and labor during the antibody discovery process. High-quality material produced via this method demonstrated consistent performance across various applications, confirming that the linear approach does not compromise the functional integrity of the synthesized proteins.

These findings suggest that linear expression cassettes represent a highly effective and efficient alternative to circular plasmid vectors for early-stage antibody discovery. The ability to generate high titers of IgG and Fab molecules rapidly enhances the capacity of researchers to screen large libraries of candidate sequences with greater precision. Integrating protected linear DNA into discovery pipelines can significantly accelerate the identification of potent therapeutic leads by removing the cloning bottleneck. This methodology provides a versatile and scalable solution that bridges the gap between initial sequence identification and comprehensive functional characterization. Future applications of this technology may further streamline the transition from computational design to experimental validation in the field of protein engineering. The researchers conclude that adopting this high-yield linear platform will likely improve the overall efficiency and cost-effectiveness of recombinant protein production in modern biotechnology.