title: The production of human papillomavirus type 16 L1 vaccine product from Escherichia coli inclusion bodies.
abstract: The major capsid protein L1 of the human papillomavirus type 16 (HPV16) has been previously expressed recombinantly in Escherichia coli cells as inclusion bodies (IBs). The HPV16 L1 protein offers potential as a vaccine candidate against cervical cancer, but the reported E. coli process is limited in its ability to economically produce significant quantities of material. In this study, a scaleable laboratory process for the purification of recombinant His-tagged L1 protein and its processing to give an immunogenic product is developed. The performances of ion-exchange chromatography (IEX) and immobilised metal affinity chromatography (IMAC) for the purification of L1 protein in the presence of concentrated denaturant are compared. IEX was found to be superior to IMAC when taking into account the complexity of operation, cost of adsorbent, selectivity and purity of the final product. Following purification, reduction of denaturant concentration was performed by dilution to yield a product suitable for formulation. The simplicity and ease of scale-up of dilution makes it an attractive option for process scale production and superior to the existing approach employing dialysis. It was found that direct dilution of denaturant into suitable buffer can give rise to products which have neutralising conformational epitopes identified by strong antibody-binding properties, as assessed by ELISA with a conformational monoclonal antibody. Analysis of the results showed negative main effects of protein concentration and PEG addition on antibody-binding yields, but positive main effects of the addition of detergent and L-arginine to the buffer. The diluted product had antigenic properties as assessed by ELISA and may be formulated easily for use by diafiltration and the addition of adjuvant. This work demonstrates the feasibility of producing viral vaccines using E. coli and scaleable unit operations.