Abstract PD5-12: Spatial mapping of the immune microenvironment in primary triple-negative breast cancer (TNBC) and association with neoadjuvant therapy response

Abstract

Abstract Background: Emerging data suggest that some patients with TNBC could benefit from the addition of immune-based therapy. This observation is in part due to the significant association between distinct tumor-infiltrating lymphocytes (TILs) and prognosis in TNBC. Efforts to comprehensively characterize the immune microenvironment of TNBCs are critically important to gain a better understanding of the immune landscape and how it influences response to both standard chemotherapy and immunotherapy. We previously assessed both stromal TILs (sTILs) and intraepithelial TILs (iTILs) from pre-treatment tumor samples from patients enrolled on a phase II study of neoadjuvant gemcitabine, carboplatin and iniparib (PrECOG 0105; NCT00813956). We found that both iTILS and sTILS significantly associated with pathologic response. Furthermore, we assessed a novel 'in silico flow cytometry' gene expression-based method, CIBERSORT, designed to assess overall immune content and deconvolute the relative levels of distinct leukocyte subsets in tumors. Specific leukocyte subsets significantly associated with pCR included activated memory CD4+ T cells, CD8+ T cells and M1 macrophages (all p<0.05). To validate these findings and further explore spatial mapping of these immune cell subsets we undertook this analysis. Methods: We performed SPARTA - Spatial Perception And Regional Tumor Analysis - a multiplexed immunohistochemistry-based technology with data visualization and analysis modules that is designed to capture clinically relevant information about the tumor microenvironment in 72 pre-treatment FFPE tumor sections from patients enrolled on PrECOG 0105. SPARTA was used to test and analyze the coordinated expression of PD-L1, PD-1, CD45RO, CD4, CD8 and HLA-DRA in the study cohort from whole slide scanned images. Pathologic response at the time of surgery was evaluated using the residual cancer burden index. Germline BRCA1 and BRCA2 status was known for all patients. Results: Of 72 samples, 67 were evaluable for SPARTA analysis. Within a subset of tumors separately profiled by both SPARTA (FFPE/IHC microscopy) and CIBERSORT (Frozen/RNA GEP), we found significant correlation for clinically relevant TIL subpopulations, including for CD8+ T cells (r=0.83, p<0.0001), and activated memory CD4+ T cells (r=0.78, p<0.0001). On average, the SPARTA frequency of CD8, PD-L1 and CD4 expressing cell types were higher in samples from the pCR group when compared to the no pCR group. Subpopulation analysis revealed that, on average, the frequency of CD4+HLA-DRA+ cells were higher in samples from the pCR group when compared to the no pCR group. Samples from the pCR group were associated with a higher local spatial density of CD45RO+HLA-DRA+CD4+ cells when compared to the no pCR group. Location- and proximity-based analyses are ongoing and will be presented. Analyses based on germline BRCA1/2 mutant versus wild-type status, as well as associations between tumor mutation burden and neoantigen burden will also be presented. Conclusions: Spatial mapping of the immune microenvironment in primary TNBC reveals distinct immune cell populations associated with response to neoadjuvant platinum-based therapy. Citation Format: Telli ML, Vinayak S, Khododoust MS, Gruber JJ, Ford JM, Sanchez P, Banayan N, Azimi S, Tumeh PC, Newman AM, Alizadeh AA. Spatial mapping of the immune microenvironment in primary triple-negative breast cancer (TNBC) and association with neoadjuvant therapy response [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr PD5-12.