A comparison of early (E7) and late (L1) primer-mediated amplification of papillomaviral DNA in cervical neoplasia.

Studies have demonstrated that in 50-90% of cervical carcinomas, human papillomavirus (HPV) DNA sequences are covalently bound (integrated) to the chromosomal DNA. All evidence shows that when integration takes place disruption of the viral genome occurs downstream to the E7 open reading frame, which is invariably retained in functional form. Theoretically, this phenomenon could result in loss of HPV sequences (L1) not critical to the presumed tumourigenic functions and if so, could influence primer selection for HPV DNA detection in these tumours. A series of cervical carcinomas (CA, n = 133), adenocarcinomas in situ (ACIS, n = 28) and high grade squamous intraepithelial lesions (HSIL, n = 30) were analysed for HPV nucleic acids using primers designed to amplify the E7 and L1 regions. Primer sizes and sensitivities were adjusted to produce equivalent amplification efficiency. Of 191 cases studied, 134 (70%) scored positive for HPV16 or 18 with either the E7 or L1 primer set. Of these, 116 (87%) were positive with both primer pairs. There were no significant differences in proportions of HPV 16/18 positives or lesion types scoring positive exclusively with the E7 vs the L1 primer sets. However, HPV18 associated, E7 positive carcinomas were slightly less likely than HPV16 associated carcinomas to be L1 positive (P = 0.07). Although a high proportion of HPV16 and particularly HPV18 positive carcinomas have been associated with exclusively integrated HPV DNA, there is little evidence that this influences detection sensitivity with E7 vs L1 primers. The combination of E7 and L1 primers provided the maximum sensitivity in this study, with 18 of 134 cases scoring positive with only one primer set.