Spatiotemporal Tracking of Brain-Tumor-Associated Myeloid Cells in Vivo through Optical Coherence Tomography with Plasmonic Labeling and Speckle Modulation

Abstract

By their nature, tumors pose a set of profound challenges to the immune system with respect to cellular recognition and response coordination. Recent research indicates that leukocyte subpopulations, especially tumor-associated macrophages (TAMs), can exert substantial influence on the efficacy of various cancer immunotherapy treatment strategies. To better study and understand the roles of TAMs in determining immunotherapeutic outcomes, significant technical challenges associated with dynamically monitoring single cells of interest in relevant live animal models of solid tumors must be overcome. However, imaging techniques with the requisite combination of spatiotemporal resolution, cell-specific contrast, and sufficient signal-to-noise at increasing depths in tissue are exceedingly limited. Here we describe a method to enable high-resolution, wide-field, longitudinal imaging of TAMs based on speckle-modulating optical coherence tomography (SM-OCT) and spectral scattering from an optimized contrast agent. The approach’s improvements to OCT detection sensitivity and noise reduction enabled high-resolution OCT-based observation of individual cells of a specific host lineage in live animals. We found that large gold nanorods (LGNRs) that exhibit a narrow-band, enhanced scattering cross-section can selectively label TAMs and activate microglia in an in vivo orthotopic murine model of glioblastoma multiforme. We demonstrated near real-time tracking of the migration of cells within these myeloid subpopulations. The intrinsic spatiotemporal resolution, imaging depth, and contrast sensitivity reported herein may facilitate detailed studies of the fundamental behaviors of TAMs and other leukocytes at the single-cell level in vivo, including intratumoral distribution heterogeneity and roles in modulating cancer proliferation.

A Spectral Demixing Model for Triplex In Vivo Imaging of Optical Coherence Tomography Contrast Agents

“…Future work will focus on conjugation of GNBPs, incorporating speckle reduction, 20 and utilizing widerbandwidth OCT light sources to allow for greater multiplexing with less reduction in axial resolution. 21 Building on previous OCT work demonstrating tracking of cancer cells, 22 lymph biomarkers, 23 and conjugation of antibodies to gold nanorods, 10 there are numerous preclinical and clinical opportunities enabled by this work. An example would be imaging the spatiotemporal dynamics of various immunocytes such as CD8+ T cells, NK cells, and tumor-associated macrophages in the tumor microenvironment of a live animal model and characterizing their cellular response to immunotherapies.…”

Integrating single-cell and spatial transcriptomics to elucidate intercellular tissue dynamics

“…Real-time tissue tracking of cellular subtypes is especially important to understanding the inner workings of the tumour microenvironment interface with immune cells. In this regard, optical coherence tomography has been used to track the migration of tumour-associated myeloid cells 145 , and CellGPS has been used with positron emission tomography to track human breast cancer cells loaded with radioisotope 146 . When paired with spatial transcriptomics, both of these live tracking techniques could be applied to cell types of interest from spatial data to elucidate cell kinetics in settings, such as metastatic progression and immune cell dynamics during cancer immunotherapy.…”

Molecular Immune Targeted Imaging of Tumor Microenvironment

“…While one disadvantage of OCT is that its contrast agents are far less developed than other modalities, recent progress has produced scattering nanomaterials that add the ability to molecularly target or otherwise track cells using imaging contrast agents 131 . In one immune cell tracking application, macrophages and activated microglia in orthotopically implanted brain tumors naturally took up large gold nanorods, which produce substantial OCT contrast 132 . Given the ability to dynamically track these myeloid cells within tumors down to single-cell resolutions, it may be possible to closely monitor intratumoral macrophage responses to chemo- and immunotherapies in the future.…”