The tumor microenvironment is a dynamic and complex system consisting of the tumor bed, surrounding stroma, vasculature, and immune infiltrate that self-organizes in response to contextual queues and polarizing factors. The nature and extent of this organization can determine if an immune response is beneficial, suppressed, or tumor promoting. Previous efforts have identified a gene expression signature (GES) that is composed of twelve chemokines and that is associated with the presence of ectopic lymph node structures (ELNS) within the tumor microenvironment. These ELNS are predictive of increased survival across a spectrum of solid tumors, and are thought to be foci of active antigen presentation, lymphocyte recruitment, and immune activation. Understanding how and why these structures form is paramount for improving existing immunotherapies and identifying novel treatment modalities. Most in vivo models utilize subcutaneous orthotopic inoculations that, while producing a tumorous mass, lack the surrounding context of a physiologically relevant microenvironment and completely lack ELNS. Alternatively, naturally occurring or chemically induced models offer a more physiologically relevant setting, but are often highly variable systems in which controlling experimental parameters becomes problematic. Here, we build upon insights gained from the GES using an implantable three-dimensional bioscaffold system to study the interaction of a developing tumor with endogenous immune infiltrates and implanted stroma. This allows for the introduction of carefully controlled microenvironmental elements in a more consistent mouse model. In this system, we can selectively interrogate individual chemokines using slow-release microparticles, and visualize immune infiltrates in real time using intravital microscopy. Concurrently, we use this system to parameterize an integrated mathematical model of the tumor microenvironment, which can then reinform our three-dimensional bioscaffold model. This dual-model system has identified an important role for three components of the GES--CCL19, CCL21, and CXCL13--in the induction of ELNS, and suggests that the type and extent of stromal activation can greatly enhance or prevent effective antitumor immunity. In particular, stromal activation using the lymphotoxin beta receptor ligand, LTα1β2, can induce organized aggregates of endogenous lymphocytes; significantly increase infiltration of T cells, B cells, and dendritic cells (all p<0.05); and prevent the growth of MC-38 colon carcinoma cells (p<0.001 by implant weight). In silico model runs parameterized by ex vivo microtaxis assays and in vivo ELNS formation assays predict that polarized activation of stromal cells is sufficient to compartmentalize lymphoid aggregates into discrete B cell and T cell zones and promote antitumor activity. Conversely, stromal activation in the presence of certain type-II promoting factors, such as all-trans retinoic acid, can result in the infiltration of suppressive populations that promote tumorigenesis. Taken together, this novel dual-model system of the tumor microenvironment suggests that the context of stromal activation in the tumor microenvironment can either promote effective antitumor immunity by inducing ELNS, or suppress antitumor immune response by recruiting suppressive populations.

Citation Format: Adam W. Mailloux, Falahat Rana, Yohsuke Yagawa, Mark Robertson-Tessi, Zhou L. Susan, Alexander R. A. Anderson, James J. Mulé. A dual in vivo and in silico system to model ectopic lymph node structure formation and antitumor immune response in the murine tumor microenvironment [abstract]. In: Proceedings of the AACR Special Conference: Advances in Modeling Cancer in Mice: Technology, Biology, and Beyond; 2017 Sep 24-27; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(10 Suppl):Abstract nr B17.