HPV in full thickness cervical biopsies: high prevalence in CIN 2 and CIN 3 detected by a sensitive PCR method

A new type-specific, sensitive, non-radioactive assay is described for the detection of human papillomavirus (HPV) DNA in tissues. Sequences within the E6 gene were amplified by the polymerase chain reaction (PCR), using primer pairs which clearly distinguish HPV types, including those with close sequence homology such as 6b and 11. The amplified DNA products were identified by non-radioactive oligonucleotide hybridization and restriction endonuclease mapping, and the method was sufficiently sensitive to detect between 3 and 5 SiHa cells (each containing 1-2 copies of HPV 16 DNA) amongst 10,000 non-HPV-containing cells. Frozen and archival paraffin sections were equally acceptable substrates for the reaction. The assay was applied to frozen sections of full thickness cervical epithelium from 60 cases of cervical intraepithelial neoplasia (CIN) and 24 normal cervical controls. HPV DNA was detected in 60 per cent of cases of CIN 3 and CIN 2, in 25 per cent of cases of CIN 1, and in none of the normal controls. Prevalence of HPV 16 was similar (approximately 50 per cent) in both CIN 2 and CIN 3, and in the whole series HPV 16 was almost five-fold more common than HPV 18. Low-risk HPV types were present in 5 per cent of CIN 1, but 0 per cent of CIN 2 and CIN 3 biopsies. The data emphasize the biological similarity of CIN 2 and CIN 3 lesions, and their divergence from CIN 1.