The Design and Cell-Free Protein Synthesis of a Pembrolizumab Single-Chain Variable Fragment

Background/Objectives: Cancer is a leading cause of death. However, recently developed immunotherapies have shown significant promise to improve cancer treatment outcomes and survival rates. Pembrolizumab, a cancer immunotherapy drug, enables a strong T-cell response specifically targeting cancer cells to improve patient outcomes in more than 16 types of cancer. The increasing demand for pembrolizumab, the highest selling drug in 2023, increases global dependence on drug production, which can be vulnerable to supply chain disruptions. Methods: Cell-free protein synthesis (CFPS) is a rapid in vitro protein production method that could provide the production of an immunotherapy drug in an emergency and could facilitate on-demand production of the therapeutic at the point of care if needed. Furthermore, CFPS has potential as a production platform of biosimilars, as the patent for pembrolizumab is set to expire in 2028. Results: This work presents the design, synthesis, and target-binding affinity of a novel single-chain variable fragment of pembrolizumab (Pem-scFv) using CFPS. The CFPS production of Pem-scFv also enables the direct optimization of synthesis reaction composition and expression conditions. The conditions of 30 °C, 35% (v/v) cell extract, and an oxidizing redox environment resulted in the highest Pem-scFv soluble yield of 442 µg/mL. An affinity assay demonstrated significant binding between the CFPS-produced Pem-scFv and the PD-1 target. Computational simulations of Pem-scFv folding and binding corroborate the experimental results.