Women with high levels of human papilloma virus (HPV) type 16 in the cervix are more likely to have high-grade pre-cancerous lesions, according to the results of a cross-sectional study presented in the 20th May edition of AIDS. This confirms the results of previous studies showing a link between HPV viral loads and a risk of the progression of pre-cancer in the cervix.
However, the investigators did not see any relationship between the amount of HPV’s DNA that was incorporated into the human cells’ genetic material and the progression of cervical lesions. This suggests that measuring incorporation rates of HPV may not provide any additional information on the risk of progression.
HPV, or the wart virus, can lead to the development of abnormalities of the cells it infects in the cervix. These abnormalities can go on to cause cervical cancer. Infection with certain strains of the virus, such as type 16, is associated with a higher risk of progression to pre-cancerous lesions, often called squamous intraepithelial lesion (SIL) or cervical intraepithelial neoplasia (CIN), and to cervical cancer.
Women with HIV have an elevated risk of HPV infection, and the development of CIN and cervical cancer. Consequently, investigators from the Canadian Women’s HIV Study Group wished to find out whether they could predict which women were at risk of progressing to high-grade lesions and developing cancer.
The entire study group consisted of 1055 women, who were HIV-positive or HIV-negative but “at risk of sexually transmitted diseases.” However, this analysis was confined to 75 women, 58 of whom were HIV-positive and 17 HIV-negative.
The researchers measured the levels of HPV-16 in cervical washes using a technique called real-time polymerase chain reaction (PCR). After matching the HPV levels to the results from cervical smears, the investigators found that HPV-16 viral loads were higher in the six women with high-grade lesions or the six with low-grade lesions than the 44 with normal cervical cells (median 191,000,000 vs. 7,590,000 vs. 126,000 copies/µg DNA; p < 0.006).
“Our results suggest that HPV-16 DNA viral load is greater in women with cervical disease,” they conclude. However, there was a significant overlap in the viral loads by women at different stages of cervical disease. This "could limit the usefulness of viral load measurements" in predicting the risk of progression, they warn.
HPV, like HIV, can insert its genetic material into the DNA of the human cells it infects. As this was thought to be a marker of disease progression, the investigators modified the real-time PCR method to work out how much of the HPV had been incorporated or ‘integrated’ into the chromosomes of the human cells, and how much remained ‘episomal’, or unincorporated into the human DNA.
Surprisingly, they saw a similar trend to the total HPV-16 DNA for both integrated and episomal DNA (integrated: 89,100,000 vs. 1,260,000 vs. 58,900 copies/µg DNA; p = 0.02; episomal: 97,700,000 vs. 4,270,000 vs. 40,700 copies/µg DNA; p < 0.004). In contrast to their expectations, this suggested that women at an early stage of HPV infection have both integrated and episomal DNA in their cervical cells.
The investigators conclude: “Specimens from women without lesion ... contained a mixture of integrated and episomal forms, impeding the potential usefulness of these real-time PCR tests to predict CIN progression.”
Thirty-nine women also underwent colposcopy, when a ‘biopsy’ or a small sample of the cervix was taken and examined under a microscope. This more accurate method showed that eleven of the women had normal cervical cells. Of the 28 women with CIN, 16 had 'low-grade' CIN 1 and twelve had 'high-grade' CIN 2 or 3.
After including data from an additional 24 women with normal results from cervical smears, the investigators analysed the relationship between HPV-16 viral loads and severity of the pre-cancerous lesions. Taking age, race, CD4 cell count and HIV status into account, they confirmed that having high-grade CIN was associated with total HPV-16 viral load (odds ratio [OR] = 3.5; p = 0.02), as well as integrated (OR = 1.6; p = 0.05) and episomal (OR = 2.9; p = 0.02) viral loads.
Analysis of the colposcopy results also revealed a significant association between lesion severity and CD4 cell counts. Women with CIN 2 or 3 had lower CD4 cell counts than those with normal cervical samples (median 160 vs. 286 cells/mm3; p = 0.04). This suggests that immune suppression can be a risk factor for the development of pre-cancerous lesions in the cervix.
The investigators admit that their analysis may be limited both by the small number of participants included in the study, and the high proportion of HIV-positive women. “Most women recruited were infected with HIV or were at risk of HIV infection,” they write.
They also acknowledge that their findings should be confirmed in further trials to assess whether measuring intgrated DNA levels will be of use. “Prospective studies involving a greater number of HPV-16-infected women are needed to define the predictive value of the integrated HPV-16 load versus the total or episomal load for progression,” they conclude.