A new approach for immuno-oncology biomarker discovery: High-plex, spatial protein profiling based on NanoString digital quantification.

Abstract

27 Background: The immune response to cancer is shaped by the abundance and localization of immune cell populations, their activation status, and expression of immunomodulatory factors. To detect proteins at high multiplex with spatial resolution, NanoString optical barcoding technology was used to digitally profile protein expression in formalin fixed paraffin embedded (FFPE) samples and compared to traditional IHC. Methods: NanoString has enabled digital profiling of immuno-oncology protein targets, including immune cell markers and checkpoint proteins. Protein detection is enabled via primary antibodies (Abs) which are attached via a UV cleavable linker to DNA indexing oligos. FFPE samples are stained with a multiplex cocktail of labeled Abs, then DNA oligos are released by UV light exposure. Liberated oligos are then hybridized to optical barcodes for quantitation on a NanoString instrument. This technique enables quantitative, multiplex protein detection over 5 logs of dynamic range. IHC and NanoString spatial protein profiling were performed on alternating sections from blocks of tonsil, melanoma, and colorectal cancer. Sections were fluorescently labeled with panCK, Ki67, and Syto-83 to visualize morphology, and regions of interest (ROI) were selected for profiling using up to 30 oligo-tagged Abs. Results: NanoString counts strongly correlated with quantification of CD3, CD4, CD8, PanCK, Ki67, PD-1, and PD-L1 derived from IHC. To explore limits of detection, ROIs of 1, 2, 4, or 8 cells were profiled. Digital counts were detected above background at the single cell level and linearly correlated with cell count. Furthermore, quantification with two cell lineage markers and double positive cells were demonstrated using a 30-plex Ab cocktail. Conclusions: Multiplex, digital protein profiling with spatial resolution will enable deep characterization of immune responses in tumors. Additionally, single cell profiling enables inter-cellular characterization of variations in immune response. The strong correlation of NanoString data to IHC indicates the feasibility to spatially profile multiple key proteins with minimal consumption of patient tissue.