Abstract 961: Intralesional injection of anti-PD-1 (pembrolizumab) results in increased T cell infiltrate in high risk DCIS

Background. Accumulating evidence shows a correlation between tumor-infiltrating lymphocytes (TILs), in particular the presence of CD8+ T cells, in cancer tissue and favorable prognosis in various malignancies. Less is know about the role of the immune microenvironment in the context of pre-malignant lesions such as ductal carcinoma in situ (DCIS). In a previous study of women with DCIS, we observed that high numbers of activated CD8+ T cells within the DCIS lesions were associated with good outcomes while low numbers associated with high risk features and poor outcomes. These results suggest that manipulating the immune microenviroment in DCIS, for example via checkpoint blockade, could potentially alter disease progression. Methods. We recently initiated a phase 1 pilot study to investigate changes in the immune microenvironment of high risk DCIS after intralesional injection of anti-PD-1 (pembrolizumab). Study participants were given 2 intralesional injections of pembrolizumab 3 weeks apart with surgery approximately 3 weeks after the 2nd dose. The study started with a dose of 2 mg/ml (1/100 of the standard 200 mg/ml iv dose), then escalated to 4mg/ml and 8 mg/ml, with 3 patients at each dose. FFPE tissue samples from pre-treatment biopsies and post-treatment surgical resections were immunostained using Opal reagent kits (Perkin Elmer) on a fully automated Ventana Discovery platform, imaged with a Vectra automated imaging system, and analyzed with inForm software (Perkin Elmer). A 7-plex panel, consisting of mAbs to CD3, CD8, CD68, PD-1, PD-L1, Ki67, and cytokeratins, was used. An algorithm for tumor/stroma segmentation developed in inForm was used to randomly select 7-10 high power fields (hpfs) for imaging. Cell phenotype maps were generated for each of these hpfs for each sample. Cell densities were determined per area of stroma, DCIS, or total tissue and averaged across all hpfs for a given case. Results. We are completing our 2nd cohort of patients, and there have been no adverse clinical events. The injections are easily administered and well tolerated. By MRI imaging, there was no change in the size of lesions after the treatment. All patients have proceeded to surgical resection. Following intralesional pembrolizumab injection, multiplex fIHC analyses indicated an increase in CD8+ T cells, which in some areas was striking. This increase was mainly observed within the epithelial DCIS regions, as opposed to a lesser increase in stromal CD8+ T cells. We also observed an increase in CD68+ macrophages. Conclusions. We have demonstrated the safety and feasibility of intralesional injection of an immune checkpoint inhibitor (pembrolizumab) in high risk DCIS. Further, we have shown that this immunotherapeutic intervention results in a change in the immune microenvironment, with an increase in both T cells and macrophages, even at a dose that is 1/100 of the standard intravenous clinical dose. Citation Format: Michael J. Campbell, Emma McCune, Jennifer Bolen, Scott VandenBerg, Jo Chien, Jasmine Wong, Laura Esserman. Intralesional injection of anti-PD-1 (pembrolizumab) results in increased T cell infiltrate in high risk DCIS [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 961.