Abstract 2104: Near-infrared fluorescent tumor histology for multiplexed phenotypic identification of immunosuppressive cells
Authors: Flor Amy , Vaccarello Annalise , Levin Matt , Snyder Helen , Schwartz David , Kron Stephen 
Published: August 2018

The purpose of our study was to develop near-infrared fluorophore-labeled antibodies to overcome autofluorescence interference in the visible spectrum, thereby enabling enhanced multiplexed identification of immune cells in human tumor tissue sections. Towards multiplexing, we conjugated each monoclonal primary antibody to a unique hapten tag. Detection of hapten-tagged primary antibodies was accomplished using high-affinity anti-hapten rabbit monoclonal secondary antibodies, which were each conjugated to a near-infrared fluorophore with Emax = 594, 650, 731, or 800 nm. For identification of immunosuppressive cells in tumor tissues, we used formalin-fixed, paraffin-embedded human tissue microarrays comprising malignant breast or prostate tumor core sections. Microarrays contained 12-60 patient biopsy cores with duplicate sections per case mounted on standard glass slides. Two antibody panels to detect immunosuppressive cell phenotypes were used in our study. The T regulatory panel targeted the antigens CD4, CD8, FOXP3, and LAG-3, allowing for phenotypic identification of CD4+ T helper cells, CD8+ cytotoxic T cells, CD4+ FOXP3+ Tregs, and highly immunosuppressive CD4+ FOXP3+ LAG-3+ Tregs. The macrophage panel targeted the antigens CD3, CD20, CD68, and CD163 for identification of CD3+ T cells, CD20+ B cells, CD68+ M1 macrophages, and highly immunosuppressive CD163+ M2 macrophages. Widefield fluorescence microscopy was used to image the stained tumor microarrays, utilizing a high-radiance mercury arc lamp, high-sensitivity digital CMOS camera, and single-band optical filter sets to detect near-infrared fluorescence. Triplicate images were taken per tissue core. Prior to image analysis, a spectral unmixing algorithm was created using a reference set of single-stained tissue slides in order to deconvolute minor spectral overlap of near-infrared fluorophores. The algorithm was then applied to the multiplexed digital raw images, and immunophenotyping analysis was conducted to enumerate cells of interest. Image analysis results indicated unique patterns of distribution of immune cells in tumor tissues correlated with tumor grade and stage. In breast cancer tissues, higher levels of LAG-3+ immunosuppressive cells were found in tumors of the aggressive, treatment-resistant "triple-negative" tumor subtype. In prostate cancer tissues, an increase in CD68+ macrophages and loss of immunostimulatory CD3+ T cells and CD20+ B cells were found to be associated with advanced tumor grade and Gleason score. The use of near-infrared fluorophores and hapten-tagged detection antibodies facilitated enhanced, rapid multiplexed phenotyping of immunosuppressive cells in tumor tissue. These findings demonstrate our approach to be a potentially paradigm-shifting technology for detection of immune infiltrates in patient samples.

Citation Format: Amy Flor, Annalise Vaccarello, Matt Levin, Helen Snyder, David Schwartz, Stephen Kron. Near-infrared fluorescent tumor histology for multiplexed phenotypic identification of immunosuppressive cells [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 2104.