Abstract P6-10-09: Multispectral immunofluorescence (mIF) to detect dynamic changes in PD-L1 expression, immune cell (IC) infiltration, and tumor-IC interactions in primary breast cancer (BC) immuno-oncology (I-O) clinical trials

Introduction: Anti-PD-1/L1 (atezolizumab) is effective in first-line, PD-L1-positive triple negative breast cancer, however it is becoming increasingly apparent that the majority of breast cancers will require novel I-O combination strategies. We describe a framework for use of multispectral immunofluorescence (mIF) as a high-dimensional biomarker to facilitate discovery in BC I-O clinical trials. Specifically, we propose a method for recapitulating the prognostic stromal tumor infiltrating lymphocyte (sTIL) score and PD-L1 status using mIF, but with higher resolution to detect dynamic changes. Furthermore, mIF provides spatial and phenotypic data on the cellular level, allowing for comprehensive characterization of tumor-IC interactions, which may provide insight into the mechanisms of action of I-O therapy. Methods: In a recent ESBC I-O pre-operative clinical trial, a regimen combining low-dose systemic chemotherapy (cyclophosphamide) with intralymphatic cytokine injections (IRX-2) was evaluated for pharmacodynamic immune activity, as measured by dynamic changes in ICs and PD-L1 status. Pre-treatment and resection tissues were analyzed for sTIL score (HE 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P6-10-09.