Immunogenicity study of human papillomavirus type 68b virus-like particles expressed in a Hansenula polymorpha strain

Objective To evaluate the immunogenicity of the recombinant human papillomavirus type 68b (HPV68b) virus-like particles(VLPs)in a mouse model. Methods The L1 protein of HPV type 68b was successful expressed in the Hansenula polymorpha strain (NVSI-68b-1). Processes including purification and reconstitution were performed to achieve pure HPV68b VLPs. The purity, morphology and immunogenicity of the purified HPV68b VLPs were further analyzed. The BALB/c mice were immunized with HPV68b VLPs formulated on aluminum adjuvant. Pseudovirus-neutralizing antibody (PsV NAb) assay was performed to detect the neutralizing antibodies in serum samples. Results The HPV 68b L1 VLPs were obtained as indicated by the results of SDS-PAGE, Western blot assay, HPLC, electron microscopy and dynamic light scattering with a high purity of 95%. Transmission electron microscopy and dynamic light scattering analysis revealed that the HPV68b L1 VLPs resembled the native virus with an average particle diameter of 50 nm. High levels of HPV68b-neutralizing antibodies were detected in serum samples from the mice immunized with HPV68b L1 VLPs. Moreover, a cross-protective efficacy of HPV68b L1 VLPs for HPV68a was observed. Conclusion This study suggested that the recombinant HPV68b VLPs expressed in a Hansenula polymorpha strain might be used as a potential candidate for the development of HPV vaccine. Key words: Hansenula polymorpha; HPV68; Cross-protection