Abstract LB-221: Tumor microenvironment predicts aggressive breast cancer: Combination of HERV-K, immune checkpoint and activation status of CD8+ T cells

The purpose of this study is to identify useful predictive biomarkers of anti-tumor cytotoxic T cell and immune checkpoint response, to optimize targeted therapy, chemotherapy, and immunotherapy of breast cancer (BC). Immune checkpoint markers (14 circulating proteins) in BC patients were determined using a magnetic bead assay. CD27, PDL-2, LAG-3, and TIM-3 levels in the plasma, obtained from patients with invasive ductal carcinoma (IDC: n=32), ductal carcinoma in situ (DCIS: n=11), other invasive BC (n=12), prophylactic surgery (BRCA1: n=7, and BRCA2 mutations: n=4, benign phyllodes tumor: n=2) were significantly enhanced compared with healthy controls (n=12), which supports a highly immune suppressed environment. Also, these markers were compared at T1 (before surgery), T2 (6 months post-surgery), and T3 (18 months post-surgery). LAG-3, CD27 (p=0.012), 4-1BB, CD80, PD-L2, PD-L1 (p=0.045), and IDO all had a decreased plasma concentrations post-surgery (6 months or 18 months) compared with pre-surgery. Interestingly, significantly higher concentrations of BTLA, IDO, LAG-3, PD-L2, TIM-3, and PD-L1 were detected in BC patients that had higher titers of circulating human endogenous retrovirus type K (HERV-K) antibodies. We characterized the subset distribution and phenotype of the immune cells of various BC patients. CD4+ or CD8+ T cells collected from breast tissues including tumor tissues (T) or uninvolved normal breast tissues (N) were analyzed for CD4 and CD8. Higher percentages of CD8+ tumor infiltrating lymphocyte (TIL) cells were detected in N compared with autologous T. The percentage of CD38+/HLA-DR+ CD8+ T cells was low in the PBMCs compared to percentages in TILs. Activated T cells were only detected in TIL (40% to 99%; n=6) but not in their PBMCs from the same patients. Several studies have demonstrated that regulatory T cells (Tregs) within the tumor environment lead to a decrease in patient survival. Higher percentages of Treg cells were observed in aggressive BC and in TIL obtained from tumor tissues compared to TIL cells obtained from uninvolved tissues. HERV-K specific CD8 T cells (K-T cells) enhanced the percentage of CD8 T cells (62.5%; n=8) in patients with aggressive BC, and were able to kill their autologous tumor cells or mammospheres. Significantly reduced tumor weights and metastases were demonstrated in MDA-MB-231 mice treated with K-T cells. The lower percentage of CD8 T cells and higher percentage of Treg T cells we observed in breast tumor tissues, coupled with elevated concentrations of circulating immune checkpoint proteins in BC patients, suggests a highly immune suppressed environment in these aggressive tumors that could be minimized with anti-HERV-K therapy. Thus, HERV-K T cell therapies combined with blockade of immune checkpoints may be a new regimen for treating aggressive BC. Citation Format: Feng Wang-Johanning, Jia Li, Gary Johanning, Ming Li, Raghu Chivukula, Guoqing Wu. Tumor microenvironment predicts aggressive breast cancer: Combination of HERV-K, immune checkpoint and activation status of CD8+ T cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-221. doi:10.1158/1538-7445.AM2017-LB-221