Detection of human papillomavirus type 16/18 DNA in cervicovaginal cells by fluorescence based in situ hybridization and automated image cytometry

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Abstract
Automatic fluorescence image cytometry (AFIC) is a fast, sensitive, and reliable approach for screening slide‐based clinical specimens. In this study, we applied AFIC to identify cancer‐associated human papillomavirus (HPV) genotypes 16 and 18 in individual cells of cervical smears using a sensitive fluorescence based in situ hybridization (FISH) assay. HPV sequences were labeled by FISH and the cells imaged using an epi‐fluorescence microscope coupled to a low‐light color CCD camera. Before application to clinical specimens, AFIC was assessed using fluorescent calibration beads and cervical cancer cell lines containing known numbers of integrated HPV genomes per nucleus. Assessment showed that our AFIC had a linear response, was quantitatively accurate, and had the sensitivity to detect one HPV genome per nucleus: After acquisition of images, computer algorithms identified every cell nucleus (via a fluorescent DNA counterstain) and quantified the FISH signal per nucleus. AFIC was employed to screen 27 patient specimens for HPV 16/18, of which 12 were positive. The HPV status of the specimens positively correlated with the pathological diagnosis, and since AFIC automatically and correctly located every cell, it was possible to directly compare morphology and HPV status in the same cell. In conclusion, the combination of FISH and AFIC is a sensitive and quantitative method to detect high risk HPV sequences in cervical smears.