Purification of Disassembled Capsid Protein by Hydroxyapatite Chromatography Enhances Virus-Like Particle Recovery

Virus-like particles (VLPs) are a promising modality with extensive applications in prophylactic and therapeutic vaccine design. Human Papillomavirus (HPV) vaccines are one such example where VLP vaccine applications have led to the successful reduction in HPV-associated diseases, such as cervical cancer. Current purification approaches utilize hydroxyapatite (HA) chromatography in bind-and-elute mode to purify HPV VLPs from host-cell impurities such as proteins and nucleic acids, though binding capacity for VLPs is low due to mass transfer limitations related to their large particle size. The intent of this work was to utilize VLP disassembly prior to HA chromatography in order to increase column yield and capacity. Since L1 protein subunits demonstrated weaker binding avidity for HA resin compared to VLPs, this enabled flow-through purification of L1 protein from strongly adsorbed host cell impurities. Mobile phase conditions were evaluated in batch partition screening experiments to determine the optimal conditions for L1 protein recovery with selective clearance of nucleic acid. Dynamic loading studies showed that while nucleic acid removal was equivalent to the VLP purification process, the flow-through process with disassembled L1 protein achieved higher L1 yield and column capacity. Optimal conditions were applied to HA flow-through purification for multiple HPV types with recombinant L1 protein expressed in yeast, demonstrating > 35% increased yield for six of eight types. The purified, disassembled proteins were subsequently reassembled and had comparable product attributes to the VLP purification process. The implementation of disassembly prior to purification also eliminates the requirement to perform a distinct final disassembly/reassembly process after isolating crude VLPs during purification.