Abstract 1582: A pre-existing inflammatory immune microenvironment predicts the clinical and immunological response of vulvar high-grade squamous intraepithelial lesions to therapeutic HPV16 peptide vaccination

Background: Vulvar High-grade Squamous Intraepithelial Lesion (vHSIL) is predominantly induced by high-risk Human Papilloma Virus type 16 (HPV16). In two independent trials, therapeutic vaccination against the oncoproteins of HPV16 with synthetic long peptides (SLP) resulted in vHSIL regression in about half of the patients after 12 months. Several studies have shown that the immune microenvironment influences therapy outcome. Therefore, a thorough investigation of the vHSIL immune microenvironment before and after SLP vaccination was performed, and its impact on clinical response was studied. Methods: Two novel multiplex immunofluorescence panels were designed and fully optimized for formalin-fixed paraffin-embedded tissue, one for T cells (CD3, CD8, Foxp3, Tim3, Tbet, PD-1, DAPI) and one for myeloid cells (CD14, CD33, CD68, CD163, CD11c, PD-L1, DAPI). Pre- and post-vaccination biopsies of 29 vHSIL patients, as well as 27 healthy vulva excisions, were stained, scanned with the Vectra multispectral imaging system, and automatically phenotyped and counted with inForm advanced image analysis software. Results: A pre-existing pro-inflammatory tumor microenvironment, marked by high numbers of CD4+ and CD8+ T cells expressing Tbet and/or PD-1 as well as CD14+ inflammatory macrophages, is a strong predictor for good clinical response to therapeutic HPV16 SLP vaccination. A clear stepwise increase in pre-vaccination infiltrating Tbet+, CD4+, CD8+ T cells and CD14+ macrophages, and decrease in Foxp3+ regulatory T cells was observed as response increased from non to partial to complete response. Moreover, the pre-vaccination immune microenvironment of complete responders resembled healthy vulva. Vaccination further increased infiltrating CD4+ and Tbet+ T cells and CD14+ macrophages, and decreased Foxp3+ regulatory T cells and CD68+CD163+ M2 macrophages in the complete and partial responders, but not in the non responders. Conclusion: Clinical responsiveness to therapeutic HPV16 SLP vaccination requires a pre-existing inflamed type 1 immune contexture in vHSIL. Hence, only patients with an inflamed microenvironment should be selected for monotherapy by therapeutic peptide vaccination, since this strategy is incapable of overcoming an immunologically cold tumor microenvironment. Citation Format: Ziena Abdulrahman, Noel F. de Miranda, Mariette I. van Poelgeest, Sjoerd H. van der Burg. A pre-existing inflammatory immune microenvironment predicts the clinical and immunological response of vulvar high-grade squamous intraepithelial lesions to therapeutic HPV16 peptide vaccination [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1582.