Physical state and copy numbers of HPV16 in oral asymptomatic infections that persisted or cleared during the 6-year follow-up

Abstract

Persistent human papillomavirus (HPV) infection is a key event in HPV-induced carcinogenesis. As part of the prospective Finnish Family HPV Study, we analysed the physical state and viral copy numbers of HPV16 in asymptomatic oral infections that either persisted or cleared during the 6-year follow-up. The persister group comprised 14 women and 7 men with 51 and 21 HPV16-positive brush samples. The clearance group included 41 women and 13 men, with 64 and 24 samples, respectively. Physical state and viral DNA load were assessed by using quantitative PCR for HPV16 E2 and E6 genes. E2/E6 ratio was calculated and HPV16 was classified as episomal, mixed or integrated with values of 0.93-1.08, <0.93 and 0, respectively. In both genders, the physical state of HPV16 was significantly different between the cases and controls (P<0.001). HPV16 was episomal in all men and 66 % (27/41) of women who cleared their infection. HPV16 was mixed and/or integrated in71 % and 57 %of the women and men persisters, respectively. The mean HPV16 copy number per 50 ng genomic DNA was nearly 5.5-fold higher in the women than in the men clearance group (P=0.011). Only in men, HPV16 copy numbers were higher in persisters than in the clearance group (P=0.039). To conclude, in both genders, persistent oral HPV16 infections were associated with the mixed or integrated form of HPV16, while in the clearance groups, episomal HPV16 predominated. This indicates that HPV16 integration is a common event even in asymptomatic oral infections, which might predispose the infected subjects to progressive disease.