Sensitivity of in situ hybridization techniques using biotin- and 35S-labeled human papillomavirus (HPV) DNA probes

In order to evaluate the sensitivity of our modified in situ DNA hybridization technique using biotinylated probes, formalin fixed, paraffin embedded biopsies from 20 cervical lesions known to contain human papillomavirus (HPV) DNA were re-examined by the technique using both 35S-labeled- and biotinylated HPV DNA probes. The probe concentrations as well as the detection limits of biotin probing were screened by spotting known amounts of HPV 16 DNA on nylon filter, and allowed to hybridize with biotinylated HPV 16 DNA probe. By this method, 4 pg of HPV 16 DNA could be detected using a probe concentration of 0.2 micrograms/ml. HPV DNA could be demonstrated in all 20 biopsies with both hybridization techniques. However, signals in subrabasal cells were detected more frequently with biotin- than with 35S-labeled probes. Additional experiments were performed using three cervical cancer cell lines (with known copy numbers of HPV DNA), to assess the detection limits of HPV infections by the in situ hybridization techniques. The CaSki cells (500-600 HPV 16 copies/cell) were unequivocally positive with both labelling systems. HeLa cells (10-50 HPV 18 copies/cell) were positive with the biotin probing in 10/10 smears, as compared to 7/10 smears when 35S-labeled probes were used. Radioactive probing was inferior to biotinylated probing in detecting the signals in SiHa cells (1-2 HPV 16 copies/cell). This is because even weak background signals could mask true positive signals when 35S-labeled probes are used. In contrast, no background is generated with the biotinylated probes, detected with streptavidin-biotinylated alkaline phosphatase complex. In situ hybridization with biotinylated DNA probes is as sensitive as techniques using 35S-labeled probes for detecting HPV infections in routine cervical biopsies or smears.     

In situ hybridization detection of single-copy human papillomavirus on isolated cells, using a catalyzed signal amplification system: GenPoint

The performance and drawbacks of GenPoint, which is a catalyzed signal amplification system for immunohistochemistry, have been evaluated for its ability to reveal human papillomavirus (HPV) DNA detected by in situ hybridization with biotinylated DNA probes. For this aim, formalin-fixed cell deposits from carcinoma cells of the uterine cervix, CaSki, SiHa, and HeLa, containing, respectively, 600 copies of HPV DNA type 16, 1-2 copies of HPV DNA type 16, and 10-50 copies of HPV DNA type 18, were used, and the GenPoint method (consisting of successive incubations with peroxidase-conjugated streptavidin, biotinyl tyramide, and peroxidase-conjugated streptavidin) was compared to immunoenzymatic revelation procedures involving either a one-step reaction (streptavidin-alkaline phosphatase or streptavidin-peroxidase), or a three-step reaction (anti-biotin mouse monoclonal antibody, rabbit anti-mouse antiserum, and mouse APAAP complex). In these conditions, after analysis with a bright-field microscope, GenPoint appeared the most sensitive method of revelation, easily allowing detection of 1-2 copies of HPV DNA on isolated cells by in situ hybridization.     

PCR in situ hybridisation detection of HPV 16 in fixed CaSki and fixed SiHa cell lines.

AIMS--To investigate the feasibility of using fixed cells with the polymerase chain reaction (PCR) in situ hybridisation and to investigate possible reasons for reaction failure. METHODS--Fixed SiHa and CaSki cells were used in an experimental model of PCR in situ hybridisation for the detection of low and intermediate copy number viral infection in fixed cells. RESULTS--PCR in situ hybridisation was able to detect one to two copies of human papillomavirus (HPV) 16 in SiHa cells, using small fragment amplicons (120 base pairs), confirming the high detection sensitivity and flexibility of the technique. Problems were encountered with localisation of PCR amplified product in CaSki cells (200-300 copies of HPV 16 per cell) owing to diffusion of product post amplification. Overall, 40% of reactions were successful, which confirms the current unreliability of the technique. Within cell preparations, about 50% of cells contained amplified product. CONCLUSION--PCR in situ hybridisation represents the marriage of two revolutionary molecular pathological techniques. However, it is currently unreliable, with reaction failure common. Standardised, dedicated equipment is urgently required if the technique is to achieve universal acceptance. In the future, the technique may be used to detect chromosomal translocations in human tumours and to study cellular gene expression.     

Sensitive in situ hybridization with catalyzed reporter deposition, streptavidin-Nanogold, and silver acetate autometallography: detection of single-copy human papillomavirus.

The usefulness of standard in situ hybridization for viral nucleic acid detection is occasionally limited by its sensitivity limit of 10 to 50 copies per cell. A modified version of the recently described signal amplification method, catalyzed reporter deposition (CARD), and its application to formalin-fixed cells and tissue sections is presented. Deposition of the reporter is facilitated by using horseradish peroxidase catalyzing the deposition of biotinylated tyramide on the location of the probe target. The biotin accumulation created is usually detected with streptavidin-labeled enzymes or fluorochromes. In the present investigation, this step was replaced by streptavidin-Nanogold and combined with silver acetate autometallography. This resulted in deep-black precipitation at positive in situ hybridized reaction sites. The sensitivity of this new approach was tested with a biotinylated, genomic probe specific for human papillomavirus (HPV)-16/18. SiHa cells, a cervical carcinoma-derived cell line with one to two HPV16 copies per cell, and 10 histologically confirmed cervical carcinomas were used for the study. All samples were previously HPV16 positive with solution polymerase chain reaction, but only two of the cervical carcinomas were positive with standard in situ hybridization with barely visible signals. When employing CARD-Nanogold, SiHa cells and 9 of 10 biopsies proved positive with marked signals. It is concluded that this nonisotopic method can detect single viral copies in situ in routinely fixed material and may have the potential to replace in situ polymerase chain reaction in many applications.     

Optimization of human papillomavirus genotype detection in cervical scrapes by a modified filter in situ hybridization test.

Optimal conditions for the screening of cervical scrapes for human papillomavirus (HPV) were investigated by using filter in situ hybridization. Since integrated and episomal HPV can be found, cell lines containing viral DNA in an integrated form (HPV in CaSki) or in an episomal state (BK virus-induced hamster tumor cells) were used for optimization experiments. An increase in sensitivity was achieved by alkaline denaturation and neutralization before the specimens were spotted onto the membrane. This increase was 5-fold for the episomal virus and 16-fold for the integrated virus in the model system, as compared with other methods. To evaluate this method on clinical material, 1,963 cervical scrapes were screened for the presence of HPV 6/11 and HPV 16. Nineteen scrapes were positive for HPV 6/11 or HPV 16; and in 1,810 scrapes, no HPV 6/11 or HPV 16 could be detected by the modified filter in situ hybridization technique. Scrapes from which the interpretation of the modified filter in situ hybridization results were equivocal (n = 71, 3.6%) or in which positivity was detected for both HPV 6/11 and HPV 16 (n = 63, 3.2%) were further analyzed by the DNA dot spot technique. Eight scrapes with an equivocal result and only one scrape showing a double positivity by the modified filter in situ hybridization technique could be confirmed in the dot spot assay. In the total group 12 scrapes were positive for HPV 6/11 DNA, 15 were positive for HPV 16 DNA, and 1 was positive for both HPV 6/11 and HPV 16 DNA. Southern blot analysis on modified filter in situ hybridization-positive and -negative scrapes revealed a 100% correlation.     

Use of Probemix and OmniProbe biotinylated cDNA probes for detecting HPV infection in biopsy specimens from the genital tract.

AIMS--To compare two commercially available pan probes for the identification of human papillomavirus (HPV) DNA expression in histological sections and to type the HPV positive cases. METHODS--97 formalin fixed, paraffin wax embedded biopsy specimens from the genital tract were tested for HPV positivity with in situ hybridisation using biotinylated cDNA pan probes--Probemix (Enzo) and OmniProbe (Digene). The HPV positive cases were further tested with HPV types 6/11, 16/18, and 31/33/35/51, and the HPV type was related to the histological diagnosis. Formalin fixed, HeLa cells (10-50 HPV 18 copies per cell) and SiHa cells (1-2 HPV 16 copies per cell) were used as reference cell lines. RESULTS--32% of the specimens gave positive nucleic signals with both Probemix and OmniProbe. Of these, 84% could be further characterised with regard to HPV types 6/11, 16/18, and 31/33/35/51; 4% of all cases were positive with either Probemix or OmniProbe. The concordance of these probes was high, 96% altogether. HeLa cells stained positive but SiHa cells did not. CONCLUSION--There is no difference between Probemix and OmniProbe for the general detection of HPV. The mean detection limit of these probes is about 20 copies a cell.     

Detection of human papillomavirus in reprocessed routine Papanicolaou smears by DNA hybridization

DNA dot blot hybridization was used for the detection of human papillomavirus (HPV) types 6, 11, 16, and 18 in reprocessed routinely collected Papanicolaou smears. DNA was extracted from the smears with alkaline lysis and applied onto a nitrocellulose filter. The specificity and sensitivity of the dot blot hybridization on reprocessed Papanicolaou smears were confirmed by Southern blot analysis of selected samples, using CaSki, SiHa cell lines as positive controls and HF 32 as negative controls. From 42 normal smears and 44 abnormal smears with koilocytosis present, 9 (21%) and 43 (98%), respectively, were positive for HPV 6/11/16 or 18. These results show that reprocessed Papanicolaou smears in combination with DNA hybridization have potential application in retrospective studies on the prevalence and distribution of HPV infection.     

Chromosomal integration sites of human papillomavirus DNA in three cervical cancer cell lines mapped by in situ hybridization

Metaphase chromosomes of three cervical cancer cell lines (HeLa, CasKi, SiHa) were subjected to in situ hybridizations with the DNA of human papillomaviruses (HPV) types 16 and 18, respectively. Previous studies have demonstrated multiple copies of HPV 18 DNA in HeLa and of HPV 16 DNA in CasKi cells, but only 1–2 HPV 16 copies in cells of the SiHa line. The viral DNA persists in an integrated state (Schwarz et al 1985). Analysis of the integration sites revealed at least 11 chromosomal sites of HPV 16 integration in CasKi cells. SiHa cells contain integrated HPV 16 DNA in the region q21–q31 of chromosome No. 13. In HeLa cells integration of HPV 18 occurred in chromosome No. 8, band q24. Thus, no evidence was obtained for the existence of preferential chromosomal regions for HPV integration. The data indirectly support a trans-acting function of HPV-mediated cell transformation.On leave of absence from the Institute of Infectious and Parasitic Diseases, Medical Academy, VI. Zaimov 26, 1504 Sofia, Bulgaria     

Detection of human papillomavirus DNA in formalin-fixed tissues by in situ hybridization after amplification by polymerase chain reaction.

The authors describe the detection of human papillomavirus (HPV) 16 DNA in paraffin-embedded, formalin-fixed tissues of cervical squamous intraepithelial lesions (SILs) by in situ hybridization after amplification by the polymerase chain reaction (PCR). Using conventional in situ hybridization and a biotin-labeled probe, variable numbers of superficial cells and none of the basal cells in the SILs showed detectable HPV 16 DNA. When the in situ assay was done after amplification, increased numbers of superficial cells had detectable HPV DNA, and the hybridization signal was much more intense. HPV DNA was also detected in basal and parabasal cells at the site of the lesion whereas not detectable in directly adjacent, normal squamous epithelium. Amplified HPV DNA was demonstrated in formalin-fixed SiHa cells using a biotin-labeled probe, demonstrating the ability to detect one copy of HPV 16 DNA. This technique should allow for direct visualization in cells of other DNA sequences of low copy number from achival specimens otherwise undetectable by conventional in situ hybridization analysis.     

Interphase cytogenetics using biotin and digoxigenin labelled probes I: relative sensitivity of both reporter molecules for detection of HPV16 in CaSki cells.

This study was undertaken to develop technology for the detection of nucleic acid using two different DNA probe reporter molecules, the ultimate aim being to differentially label two nucleic acids within the same nucleus. Digoxigenin and biotin were used to label DNA probes. The absolute and relative sensitivity of digoxigenin and biotin labelled DNA probes for detecting integrated human papilloma virus 16 (HPV16) was investigated in CaSki cells by non-isotopic in situ hybridisation (NISH). Several methods for the detection of labelled probes were also investigated. The optimal sensitivity of digoxigenin labelled probe was equivalent to that of biotin when alkaline phosphatase was used as the final detector. The median number of discrete viral signals discernible in each cell with the most sensitive detection system was seven to eight with both labelled probes. The average number of HPV16 genomes in each CaSki cell, derived by dot blot hybridisation, was about 270. The calculated absolute sensitivity of NISH for viral detection in this system is complex because of variation of signal size and number. Nevertheless, one signal per nucleus equates to as little as 30 to 40 viral copies, and probably much less. The ability to distinguish up to 15 discrete signals with both digoxigenin and biotin labelled probes in the nuclei of CaSki cells indicates that these methods will be useful in interphase cytogenetics in material routinely fixed in aldehyde.     

Detection of human papillomavirus in normal and dysplastic tissue by the polymerase chain reaction

Detection of human papilloma virus (HPV) types 16 and 18 in formalin-fixed, paraffin-embedded tissue by a new in vitro DNA amplification method, the polymerase chain reaction, was compared with detection with genomic DNA probes using in situ hybridization. The polymerase chain reaction replicates exponentially HPV DNA sequences present in a single 5- to 10-micron paraffin-embedded tissue section. The amplified sequences are detected with a DNA hybridization probe in a dot blot assay. The HPV polymerase chain reaction was able to detect on the average less than one HPV genome/cell as determined by tests of paraffin sections of cell pellets with known HPV genomic content. Cervical sections from 21 patients with HPV types 16, 18, or 31 as determined by in situ DNA hybridization were analyzed by the polymerase chain reaction. No disagreements between the two methods were detected. The sections comprising normal and dysplastic epithelium were further analyzed by the HPV polymerase chain reaction. The presence of virus correlated with the presence of dysplasia in the sections, though 3 of 10 normal sections contained HPV, and 1 of 21 sections with dysplasia lacked HPV 16 or 18. The polymerase chain reaction can specifically detect HPV 16 or 18 with high sensitivity from paraffin-embedded tissues.     

Evaluation of different DNA-DNA hybridisation techniques in detection of HPV 16 DNA in cervical smears and biopsies

The sensitivities of dot blot hybridisation and in situ filter hybridisation for the detection of HPV DNA were compared. Dot blot hybridisation was 10-50 times more sensitive than in situ filter hybridisation in detecting HPV 16 DNA in the cervical cancer cell lines SiHa and CaSki. Cervical smears collected from 51 women with a history of one or more abnormal cervical smears were tested by both hybridisation techniques for the presence of HPV 16 DNA; 11 were positive in the in situ filter hybridisation, 35 in the dot blot hybridisation. Thirty-five cervical biopsies available from this group of 51 women were processed for dot blot hybridisation. In 30 of the 35 cases the results of this hybridisation corresponded with the results of the dot blot hybridisation on the smears.     

A comparison of methods for the detection of human papillomavirus DNA by in situ hybridization with biotinylated probes on human carcinoma cell lines. Application to wart sections

We compared nine different techniques for the detection of biotinylated DNA-DNA HPV hybrids on HeLa cells with 10-50 copies of HPV 18 DNA per cell. CaSki cells with 600 copies of HPV 16 DNA per cell and tissue sections from frozen or paraffin-embedded biopsy specimens. The cell samples were either cell deposits or cytocentrifuged or cultured slides. In most cases, the samples (cell deposits and tissue sections) were denatured with hybridization mixture prepared under stringent conditions (Tm = -17 degrees C) containing biotinylated DNA probes (cloned HPV types 1, 2, 6, 11, 16 and 18), at 90 degrees C for 10 min. In other cases (cytocentrifuged or cultured cells), the denaturation was performed by HCl hydrolysis and mild heating at 50 degrees C; the probes were denatured separately by heating. All the samples were further incubated overnight at 37 degrees C. For HPV DNA detection, three amplification levels were used on cell deposits. Only the techniques involving a three-step reaction (a rabbit anti-biotin antibody - a biotinylated goat anti-rabbit antibody - a complex of streptavidin-alkaline phosphatase or streptavidin-gold or streptavidin-fluorescein) gave satisfactory results, on both cell lines. With the one step reaction (an avidin-horseradish peroxidase, or streptavidin-alkaline phosphatase or streptavidin-fluorescein complex), no labeling of HeLa cells was observed with any of the HPV probes, including HPV 18. The techniques involving four steps (avidin or streptavidin - anti-avidin goat antibody or anti-streptavidin rabbit antibody - a biotinylated anti-goat (or anti-rabbit) antibody - a complex of avidin-biotin-peroxidase or streptavidin-biotin-alkaline phosphatase or streptavidin-biotin-horseradish peroxidase) resulted in high background on both cell lines. For the reproducible detection of low copy number of HPV DNA (less than 50 copies) such as occur in HeLa cells our data suggested that the three-step technique with the streptavidin-alkaline phosphatase complex was the method of choice. The most intense labeling was always obtained with cell deposits and the technique was successfully applied to frozen and paraffin-embedded tissue sections from typical warts.     

Consensus polymerase chain reaction and enzyme-linked immunosorbent assay for human papillomavirus detection and typing in cervical specimens.

Human papillomavirus (HPV) infection is common in cervical intraepithelial neoplasia (CIN). This study investigates HPV detection and typing assay based on polymerase chain reaction amplification of L1 open reading frame with general primers GP5/GP6, followed by enzyme-linked immunosorbent assay detection with type-specific DNA probes. To determine the sensitivity of this assay, formalin-fixed CaSki cells were used as reference cell lines. Fifty copies of viral DNA diluted in DNA from 100,000 noninfected cells could be detected. This assay was also investigated for HPV detection and typing of 67 cervical specimens diagnosed with with CIN III or carcinoma in situ (CIS) and their adjacent squamous epithelium. The CIN III lesions were infected in approximately 80% of the samples, 81% in the neighboring CIN II, and 68% in CIN I. The HPV infection was even detectable in 54% of nondysplastic epithelium located near a CIN III lesion.     

Sensitivity of in situ detection with biotinylated probes of human papilloma virus type 16 DNA in frozen tissue sections of squamous cell carcinomas of the cervix.

The sensitivity of human papilloma virus type 16 (HPV-16) DNA detection by DNA in situ hybridization using biotinylated probes (bio-DISH) was estimated by performing this technique on snap-frozen tissue sections of 10 cervical squamous cell carcinomas containing increasing amounts of HPV-16 as determined by Southern blot hybridization. A protocol using serial sections for bio-DISH and DNA extraction was used. The number of positively stained cells and the detection limit were strongly dependent on the treatment of the sections with proteinase K prior to hybridization. At low proteinase K concentration (0.1 micrograms/ml), the detection limit appeared to be 30-40 HPV-16 DNA copies per carcinoma cell, whereas morphology was preserved. A high proteinase K concentration (1-5 micrograms/ml) often resulted in an increase in the number of positively stained cells but also in a poor morphology. The detection limit was improved to at least 20 HPV-16 DNA copies per carcinoma cell.     

Detection of amplified HPV 6 and 11 DNA in vulvar lesions by hot start PCR in situ hybridization.

We analyzed the distribution pattern of human papillomavirus (HPV) 6 and 11 DNA in vulvar lesions by in situ hybridization after amplification by the "hot start" polymerase chain reaction (PCR). HPV DNA was routinely detected in granular layer cells showing perinuclear halos and nuclear atypia by in situ hybridization with or without PCR. Cells that lack these changes rarely exhibited HPV DNA with standard in situ hybridization. After amplification, in situ analysis showed that many of the cells that lacked halos and atypia did contain HPV DNA and that the hybridization signal often localized to areas where there was a thickened granular layer. HPV DNA was not noted in the basal cells. The one copy of HPV 16 in SiHa cells was detectable after PCR with a single primer pair by in situ analysis only if the hot start modification was employed. Prior reports describing the PCR in situ methodology noted the need for from five to seven primer pairs. The hot start technique, which may be done by withholding the DNA polymerase until the temperature is sufficiently high to disfavor nontarget specific pathways, allowed the use of a single primer pair and showed that the degree of target-specific amplification, and not the size of the amplified product, determines the success of the PCR in situ technique.     

Use of multiple PCR primer sets for optimal detection of human papillomavirus.

Using multiple PCR primer sets, we tried to optimize the detection of human papillomavirus (HPV) in DNA samples isolated from 361 frozen biopsy specimens from patients with invasive cervical carcinomas. The HPVs detected were placed into three distinct groups, including group I/Inex at Telelab (Skien, Norway) and group Ineg and group II at the Norwegian Radium Hospital (Oslo, Norway). The consensus primer sets were Oli-1b-oli-2i, My09-My11, Gp5-Gp6, and Gp(5+)-Gp6+ from the HPV L1 gene and CpI-CpIIG from the E1 gene. Using these consensus primers together with the type-specific primers from E6-E7, we found that 355 patients (98%) were HPV positive. Type-specific primers for HPV types 11, 16, 18, 31, 33, and 35 detected more HPV-infected patients than the most sensitive consensus primer set, while the three consensus primer sets My, Gp/Gp+, and Cp together detected more HPV-positive patients than the type-specific primers. Testing of sensitivity of the PCR with SiHa cells serially diluted in lymphocytes (HPV-negative cells) indicated a detection limit of 6,300 HPV type 16 DNA copies with consensus primers (My, Gp+, and Cp) and 126 original HPV type 16 DNA copies with type-specific primers. Comparison of the amplification results for consensus L1 primers and type-specific E6-E7 primers indicated the presence of L1 deletions in 23 of 56 samples. The conclusion is that in PCR detection systems, multiple consensus primers and type-specific primers should be used in order to detect all patients harboring HPV.     

In situ DNA hybridization of cervical small cell carcinoma and adenocarcinoma using biotin-labeled human Papillomavirus probes.

A preferential association of human Papillomavirus (HPV) type 18 with cervical small cell carcinoma and adenocarcinoma has been identified by in situ and blot hybridization analysis using radionucleotide-labeled DNA and RNA probes. We attempted to detect HPV DNA in nine cases each of invasive cervical small cell carcinoma and adenocarcinoma using biotin-labeled probes to HPV types 6/11, 16/31/33/35, and 18 with a peroxidase-conjugated streptavidin detection system. HPV type 18 DNA was detected within four of nine small cell carcinomas and one of nine adenocarcinomas. HPV types 16/31/33/35 were detected in one additional case of cervical adenocarcinoma. All HPV-positive small cell and glandular tumors showed a distinctive, punctate, often juxtanucleolar pattern of nuclear staining which involved the majority of carcinoma cells throughout each neoplasm. This pattern of HPV DNA labeling has not been observed in any of the HPV-positive typical squamous carcinomas or condylomas hybridized at our institution. It is possible that punctate nuclear HPV DNA staining is a marker of viral integration into the host cell genome. We conclude that in situ DNA hybridization with biotinylated probes, although less sensitive than detection of virally transcribed RNA, still allows detection of relatively low copy numbers of HPV DNA in cervical small cell carcinomas and adenocarcinomas. Furthermore, the spatial precision of biotinylated probes may provide morphological information not obtainable using radionucleotide-labeled probes.     

Detection of human papillomavirus in cervical carcinoma: comparison of peroxidase, Nanogold, and catalyzed reporter deposition (CARD)-Nanogold in situ hybridization.

We compared three in situ hybridization (ISH) methods for their applicability and sensitivity in detecting human papillomavirus (HPV) in 61 cases (1 Grade 1, 18 Grade 2, 42 Grade 3) of routinely processed squamous cell cervical carcinoma. A commercially available biotinylated probe for HPV-16/18 was applied to serial sections and detected by conventional streptavidin-biotin-peroxidase ISH, streptavidin-Nanogold-silver ISH, and catalyzed reporter deposition (CARD)-Nanogold-gold ISH. The latter method involved signal amplification by peroxidase-catalyzed deposition of biotinylated tyramides at the hybridization sites, followed by detection of accumulated biotin by streptavidin-Nanogold made visible by autometallography. The HPV-16/18 detection rates for the three methods were 39.3, 44.3, and 65.6%, respectively. In all of the three ISH methods, a punctate staining pattern (single or multiple intranuclear spots of variable size), presumably indicating viral integration, was highly predominant among the positive cases. Two of the cases identified as positive by streptavidin-biotinperoxidase ISH were rated negative with streptavidin-Nanogold-silver ISH, whereas six cases that were clearly negative with streptavidin-biotinperoxidase ISH became positively stained with streptavidin-Nanogold ISH. All of these discordant cases were positive by the highly sensitive CARD-Nanogold-gold ISH. In addition, the high detection sensitivity of CARD-Nanogold-gold ISH was confirmed by its ability to detect single copies of HPV-16 in SiHa cells. In general, we found that the intense black reaction product from Nanogold autometallography gave superior contrast to that obtained with the peroxidase system. After tyramide signal amplification, the staining was so clearly visible that preparations could be readily screened under low magnification. Our findings precisely demonstrated the need for improved sensitivity in the in situ detection of HPV. The CARD-Nanogold-gold technology looks promising as a highly sensitive method for routine ISH in molecular pathology.