Persistent high-risk Human Papillomavirus infection is the primary factor in cervical carcinogenesis. However, other host-related features are believed to play a role as well. Recent research suggests that the vaginal microbiome and the immune microenvironment play a significant role in the acquisition and persistence of Human Papillomavirus infection, as well as in the regression or progression of cervical intraepithelial lesions. Studies in this emerging field describe factors associated with this interaction, though the precise nature remains incompletely understood. In this narrative review, we aim to summarize the current literature on the topic and propose hypotheses and recommendations for future research and treatment strategies.

Cervical high-grade squamous intraepithelial lesions (cHSILs) develop as a result of a persistent high-risk human papilloma virus (hrHPV) infection. The natural course of cHSIL is hard to predict, depending on a multitude of viral, clinical, and immunological factors. Local immunity is pivotal in the pathogenesis, spontaneous regression, and progression of cervical dysplasia; however, the underlying mechanisms are unknown. The aim of this review is to outline the changes in the immune microenvironment in spontaneous regression, persistence, and responses to (immuno)therapy. In lesion persistence and progression, the immune microenvironment of cHSIL is characterized by a lack of intraepithelial CD3+, CD4+, and CD8+ T cell infiltrates and Langerhans cells compared to the normal epithelium and by an increased number of CD25+FoxP3+ regulatory T cells (Tregs) and CD163+ M2 macrophages. Spontaneous regression is characterized by low numbers of Tregs, more intraepithelial CD8+ T cells, and a high CD4+/CD25+ T cell ratio. A ‘hot’ immune microenvironment appears to be essential for spontaneous regression of cHSIL. Moreover, immunotherapy, such as imiquimod and therapeutic HPV vaccination, may enhance a preexisting pro-inflammatory immune environment contributing to lesion regression. The preexisting immune composition may reflect the potential for lesion regression, leading to a possible immune biomarker for immunotherapy in cHSILs.

Objective: A major side effect of cervical excision for high‐grade cervical intraepithelial neoplasia (CIN) is premature birth. A non‐invasive treatment for reproductive age women is warranted. The aim of the present study was to determine the efficacy of topical imiquimod in the treatment of high‐grade CIN, defined as a regression to ≤CIN 1, and to determine the clearance rate of high‐risk human papillomavirus (hr‐HPV), compared with surgical treatment and placebo.Methods: Databases were searched for articles from their inception to February 2023.The study protocol number was INPLASY2022110046. Original studies reporting the efficacy of topical imiquimod in CIN 2, CIN 3 or persistent hr‐HPV infections were included. The study followed the Preferred Reporting Items for Systematic Reviews and Meta‐analyses checklist.Results: Five studies were included (n = 463). Histological regression to ≤CIN 1 was 55% in imiquimod versus 29% in placebo, and 93% in surgical treatment. Imiquimod‐treated women had a greater odds of histological regression to ≤CIN 1 than placebo (odds ratio [OR] 4.17, 95% confidence interval [CI] 2.03–8.54). In comparison to imiquimod, surgical treatment had an OR of 14.81(95% CI 6.59–33.27) for histological regression to ≤CIN 1. The hr‐HPV clearance rate was 53.4% after imiquimod and 66% after surgical treatment (95% CI 0.62–23.77).Conclusions: The histological regression rate is highest for surgical treatment followed by imiquimod treatment and placebo.

Background: The complete response rate of cervical high-grade squamous intraepithelial lesion (cHSIL) patients to imiquimod immunotherapy is approximately 60%. Consequently, many patients are exposed to unnecessary adverse effects of imiquimod. On the other hand, conventional surgical large loop excision therapy is associated with increased risk of premature births in subsequent pregnancies. An in-depth analysis of the cHSIL immune microenvironment was performed in order to identify and develop a predictive biomarker for response to imiquimod, to maximize therapy efficacy and to avoid adverse effects in patients unlikely to respond. Methods: Biopsies of 35 cHSIL patients, before and 10 weeks on imiquimod treatment, were analyzed by two multispectral seven-color immunofluorescence panels for T cell and myeloid cell composition in relation to treatment response. Based on these results a simplified immunohistochemical detection protocol was developed. Samples were scanned with the Vectra multispectral imaging system and cells were automatically identified using machine learning. Results: The immune microenvironment of complete responders (CR) is characterized by a strong and coordinated infiltration by T helper cells (activated PD1⁺/type 1 Tbet⁺), M1-like macrophages (CD68⁺CD163^-) and dendritic cells (CD11c⁺) prior to imiquimod. The lesions of non-responders (NRs) displayed a high infiltration by CD3⁺FOXP3⁺ regulatory T cells. At 10 weeks on imiquimod, a strong influx of intraepithelial and stromal CD4⁺ T cells was observed in CR but not NR patients. A steep decrease in macrophages occurred both in CR and NR patients, leveling the pre-existing differences in myeloid cell composition between the two groups. Based on the pre-existing immune composition differences, the sum of intraepithelial CD4 T cell, macrophage and dendritic cell counts was used to develop a quantitative simplified one color immunohistochemical biomarker, the CHSIL immune biomarker for imiquimod (CIBI), which can be automatically and unbiasedly quantified and has an excellent predictive capacity (receiver operating characteristic area under the curve 0.95, p<0.0001). Conclusion: The capacity of cHSIL patients to respond to imiquimod is associated with a pre-existing coordinated local immune process, fostering an imiquimod-mediated increase in local T cell infiltration. The CIBI immunohistochemical biomarker has strong potential to select cHSIL patients with a high likelihood to experience a complete response to imiquimod immunotherapy.

Objective: To investigate the efficacy of imiquimod in women with residual or recurrent cervical intraepithelial neoplasia (rrCIN), compared with large loop excision of the transformation zone (LLETZ).Design: Randomised controlled non‐inferiority trial.Setting: One academic and one regional hospital in the Netherlands.Population: Thirty‐five women with rrCIN were included in the study between May 2016 and May 2021.Methods: Women were randomised to receive treatment with 5% imiquimod cream (12.5 mg) intravaginally (three times a week for a duration of 16 weeks) or a LLETZ procedure (standard treatment).Main outcome measures: The primary outcome was reduction to normal cytology at 6 months after starting treatment. Secondary outcomes were clearance of high‐risk human papilloma virus (hr‐HPV) in both groups and reduction to ≤CIN1 in the imiquimod group. Side effects were monitored.Results: Treatment success was 33% (6/18) in the imiquimod group versus 100% (16/16) in the LLETZ group (P < 0.001), whereas HPV clearance was 22% (4/18) in the imiquimod group versus 88% (14/16) in the LLETZ group (P < 0.001). After the randomisation of 35 women, the futility of treatment with imiquimod was proven and the trial was prematurely finished. In the follow‐up period, three patients remained without additional treatment, whereas all other patients underwent LLETZ, conisation or hysterectomy. In the LLETZ group none of the patients received additional treatment during 2 years of follow‐up.Conclusions: This is the first randomised controlled trial to show that topical imiquimod has a significantly lower success rate in terms of reduction to normal cytology and hr‐HPV clearance, compared with LLETZ, in women with rrCIN. Additionally, imiquimod has numerous side effects and after using imiquimod most women with rrCIN still required additional surgical treatment.