A new study demonstrated the use of immortalized B-cell libraries to offer a path to develop therapeutics that adapt to viral evolution and showed how immortalized B-cells can undergo ex vivo directed evolution to generate antibody responses against emerging SARS-CoV-2 escape variants.
The study, conducted by Kling Bio, utilized immortalized B-cell libraries derived from human peripheral blood mononuclear cells (PBMCs) and tonsil tissue to identify B-cell clones with cross-reactive neutralization against SARS-CoV-2 variants. Immortalization was achieved via retroviral transduction with apoptosis inhibitors, resulting in the libraries retaining full immunoglobulin isotype representation, enabling broad functional screening.
The study was published in the journal Frontiers in Immunology.
“High efficiency immortalization and functional screening of B cells combined with directed evolution and protein engineering can accelerate the discovery of new therapeutics and provides an effective means to counter act the emergence of immune escape variants,” the investigators wrote.
High-throughput screening of 40,000 B-cells per library resulted in the identification of broadly neutralizing clones, including monoclonal antibodies with strong, robust activity against the Delta and BA5 variants. Ex vivo directed evolution further improved potency against emerging immune escape variants such as KP3 and XEC.
"Our proprietary B-cell platform technologies work together to unlock the full potential of the human immune system to stay ahead of evolving viral threats,” Kling Bio Chief Scientific Officer Stefano Gullà, said in a statement. “By combining high-throughput screening with ex vivo directed evolution, we can rapidly discover and optimize powerful antibodies in days, not months."
Results
“We produced immortalized B cell libraries from fresh human PBMCs and frozen human tonsil tissue by transduction with retrovirus carrying apoptosis inhibitor genes BCL-6 and BCL-xl genes and GFP as a marker of positive transduction. We observed immortalization efficiency by measuring the percentage GFP+ cells 4 days after transduction and found that 67.5% and 50.2% transduction efficiency for PBMC and tonsil derived libraries, respectively,” the investigators wrote.2
What You Need to Know
Kling Bio demonstrated that immortalized B-cells, derived from PBMCs and tonsil tissue, can undergo high-throughput screening and ex vivo directed evolution to generate antibodies that adapt to emerging SARS-CoV-2 escape variants.
Screening more than 40,000 B-cells led to monoclonal antibodies with strong cross-variant activity (eg, Delta, BA.5), and directed evolution further boosted potency against newer variants such as KP3 and XEC.
Kling Bio’s approach, which previously contributed to the RSV antibody Beyfortus, is positioned as a fast, scalable, and target-agnostic platform for infectious diseases, oncology, and beyond, supported by a new collaboration with Sanofi.
They note the differing immortalization efficiencies may have been to the handling of the 2 samples with the PBMCs were used fresh and the tonsil sample was obtained using frozen tissue.2
About the Platform
Kling Bio's platform has produced assets in oncology and infectious diseases, with additional programs focusing on solid tumors and neuroinflammation underway. The company points out the platform has already delivered the RSV antibody, Beyfortus (nirzevimab), marketed by Sanofi and AstraZeneca. The journal’s publication follows Kling Bio's recent announcement of a collaboration and license option agreement with Sanofi. The company is developing therapeutic platforms that combine high-efficiency B-cell immortalization with function-first screening to uncover novel antibody–antigen pairs. Kling Bio's method identifies highly specific antibodies directly from patients, enabling faster, target-agnostic, and de-risked drug development.1
“This breakthrough approach is not just a tool for today's pandemics; it is a transformative platform for developing next-generation infectious disease therapeutics and redefining how the world responds to future outbreaks,” Gullà said.1
References
1. Kling Bio Validates its Proprietary B-Cell Technology for Rapid Response Against Emerging Viral Variants. PR Newswire. September 9, 2025. Accessed September 9, 2025. https://www.prnewswire.com/news-releases/kling-bio-validates-its-proprietary-b-cell-technology-for-rapid-response-against-emerging-viral-variants-302549553.html
2. Marsman C, Heinen J, Clerico Mosina V, et al. Immune counter-evolution: immortalized B cell clones can undergo ex vivo directed evolution to counteract viral escape. Front Immunol. 2025;16:1648717. Published 2025 Aug 18. doi:10.3389/fimmu.2025.1648717
