Receptor-based bioassay for functional IL-2 quantification.

IL-2 is a potent cytokine that promotes multiple immune cells proliferation and activation. Accordingly, IL-2 based immunotherapies are emerging to treat cancers or AIDS by enhancing T cell growth and function. Besides, IL-2 is indispensable in in vitro cultivation of immune cells which is a critical step of CAR-T or CAR-NK immunotherapies. In bulk manufacturing of recombinant IL-2, E. coli expression system has several advantages such as low cost and rapid growth. However, high level protein expression in prokaryotic organisms often results in inactive insoluble aggregates, also known as inclusion bodies. It is crucial and most challenging work to solubilize and refold the protein of interest from inclusion bodies to generate its bioactive form. While multiple spectrum method had been applied to monitor the refolding process, the question of how to measure the refolding efficiency from the perspective of its biological function remained unaddressed. Here we present a receptor-based sandwich ELISA method to evaluate the bioactive product in samples and provide a guidance for manufacturing bioactive rhIL-2 (recombinant human IL-2) with prokaryotic expression system. Compared to traditional antibody-based ELISA method, this novel approach truly measures the presence of functional rhIL-2 and also potentially allows the detection of rhIL-2 variants with modifications like PEGylation as it doesn't rely on the exact amino acid sequence.