p16ink4a expression decreases during imiquimod treatment of anal intraepithelial neoplasia in human immunodeficiency virus-infected men and correlates with the decline of lesional high-risk human papillomavirus DNA load

BACKGROUND: Human papillomavirus (HPV)-associated anogenital cancers and their precursor lesions occur in excess in human immunodeficiency virus (HIV)-infected patients despite the initiation of highly active antiretroviral therapy. In this context, a drastically increased relative risk for anal intraepithelial neoplasia (AIN) exists in HIV-infected men having sex with men (MSM). In a pilot study, imiquimod, a topical immune response modifier, has been reported to be beneficial in the treatment of AIN. OBJECTIVES: To investigate the role of several biomarkers as potential adjuncts in the course of imiquimod treatment for AIN, and to determine whether these markers correlate with the course of high-risk HPV DNA load during imiquimod therapy. METHODS: Immunohistochemical staining was performed for p16(ink4a), minichromosome maintenance protein (MCM), Ki67, proliferating cell nuclear antigen (PCNA) and p21(waf1) expression before and after 16 weeks of imiquimod treatment for AIN. High-risk HPV DNA load determinations were performed by real-time polymerase chain reaction with type-specific primers and probes for HPV types 16, 18, 31 and 33. RESULTS: Histopathological and virological analyses were performed in 21 HIV-infected MSM with histologically confirmed AIN. Eighteen (86%) patients had a complete histological clearance of AIN after imiquimod therapy. As previously shown, lesional high-risk HPV DNA load significantly decreased during imiquimod therapy. Moreover, a significant decline of p16(ink4a), Ki67, MCM and PCNA expression after treatment was observed, while p21(waf1) expression changed nonsignificantly after imiquimod therapy. A significant correlation between the course of high-risk HPV DNA load and p16(ink4a) expression was observed during imiquimod treatment of AIN, whereas the decline of high-risk HPV DNA load did not significantly correlate with MCM, Ki67, PCNA or p21(waf1) expression. CONCLUSIONS: The significant decrease in p16(ink4a) expression in correlation with the drop of lesional high-risk HPV load suggests that p16(ink4a) may be a useful adjunct for the evaluation of treatment response in HPV-associated malignancies and their precursor lesions.