(441f) A Tissue-like Platform for Studying Dynamics of Macrophage Tumor Infiltration

Macrophages, a key component of the innate immune system, possess an intrinsic ability to infiltrate into tissues in response to chemokine gradients arising from local inflammation or infection. Macrophages play a particularly important role in cancer where they occupy a large percent of the solid tumor by mass. Ex vivo macrophages have been classified as naïve (M0), anti-tumor (M1), or pro-tumor (M2). Majority of macrophages found in the tumor exhibit an M2 phenotype. Ex vivo, stable M1 and M2 phenotypes are derived from M0 macrophages by addition of lipopolysaccharide/interferon-γ and interleukin-4 respectively.

In the current study, we sought to investigate the reasons behind the lack of clinical efficacy in cancer patients treated with intravenously injected M1 cell therapies. It is thought that these therapies work by tumor cell engulfment or direct killing by macrophages, or by secreting soluble cues to promote an anti-tumor immune environment. Beyond these biochemical considerations, injected M1 macrophages must physically migrate to tumors to execute their therapeutic benefit. However, the trafficking of macrophages to tumors has not been rigorously studied.

We hypothesized that trafficking capabilities of macrophages are impacted when naïve M0 macrophages are converted into an M1 phenotype for macrophage therapy. To test this, we developed a three-dimensional assay comprising a tumor spheroid and macrophages to quantify macrophage tumor transport. Cell migration, permeability, and kinetics of tumor entry were quantitatively defined and compared between macrophage phenotypes. Our results demonstrate that compared to M0 macrophages, M1 macrophages migrate less efficiently toward the tumor spheroid and exhibit a five-fold lower tumor permeability. Live imaging data combined with unsupervised machine learning algorithms reveal that macrophage migration correlates with their shape transitions. Our studies highlight the importance of transport considerations in determining the efficacy of cell therapies.

Significance of study

This study quantitatively demonstrates that the transport properties of macrophages in tumors depend on their phenotype. Beyond the current study, adoptive immune cell therapies are being investigated in the clinic. There exists an urgent need to characterize migration and accumulation of immune cells in tumors including T cells, macrophages, and neutrophils. The studies described here provide a foundation to pursue these queries.

In addition, the quantitative approach we developed by leveraging computational algorithms allowed us to probe an overlooked phenomenon in cell migration: single cell motility heterogeneity. This approach raises the prospect of opening new ways to understand immune cell transport. More broadly, we envision that our assay can be used to quantitatively compare different adoptive cell therapies from patient derived tumor organoid. This has the potential to move clinical oncology closer to personalized therapy. With an eye towards the future, our studies present a conceptual framework, an assay, and a quantitative approach that could accelerate development of in vitro disease models, as well as the adoption of cell therapies beyond cancer to diverse fields including neuroscience, developmental biology, and regenerative medicine.