The human papillomavirus (HPV) vaccine has not been widely used in developing countries because of its high cost and multiple subtype restrictions. The present study aimed to develop an economical, convenient, and effective vaccine to produce neutralizing antibodies. Using late protein 1 (L1) from the HPV16 subtype as the target antigen (HPV16L1) and Pichia pastoris as the antigen release system, integrated P. pastoris expressing HPV16L1 (named yeast-HPV16L1) was prepared and vaccinated directly into mice by subcutaneous multipoint injection. After immunization was performed thrice, high titers (greater than 1:40,960) of specific anti-HPV16L1 antibodies were obtained in immune serum and were observed to continuously rise over time. The indirect hemagglutination test and indirect hemagglutination inhibition test were used to detect neutralizing antibody activity in vitro, and the results demonstrated the hemagglutination ability of the immune serum and the reduction in or loss of the hemagglutination ability if preneutralized antigen was added to the immune serum. The protection conferred by immune serum to tumor-bearing mice at the early stages was confirmed, but the neutralizing activity disappeared when the tumor reached a size of 1 mm3. The neutralization activity of the immune serum was confirmed both in vitro and in vivo.
Keywords: HPV; Pichia pastoris; immunization; neutralizing antibody; therapy.