(176d) Disruption of Tumor-Associated Immune Dysfunction Via Coupled Multicellular Networks

Macrophages play a critical role in maintaining the balance between homeostasis and protective inflammation by adopting either immunostimulatory (M1) or immunosuppressive (M2) phenotypes. Tumors and pathogens manipulate this balance by inducing the production of immunosuppressive stimuli, which shifts macrophages into a M2 phenotype, supporting tumor growth and pathogen survival. In addition, M2 macrophages have been reported to convert to an M1 phenotype given certain stimuli, which is termed “plasticity”. Despite the centrality of these phenomena to diverse disease processes, the mechanisms regulating macrophage “decision-making” vis-à-vis polarization remain poorly understood. Here, we describe several novel systems-level insights into how such dysfunctional immune network states are established, maintained, and potentially may be disrupted.

Since most macrophage polarization studies to date involve applying coherent stimuli (either pro-M1 or pro-M2 stimuli alone), and these stimuli rarely exist independently in vivo, we first investigated how macrophages integrate contradictory signals to “calculate” a response. Macrophages were exposed to combinatorial variations in dose of IL-10 and IL-12 (pro-M2 and pro-M1 stimuli, respectively), and macrophages were “activated” using bacterial endotoxin. We previously observed that M2-type responses increased with IL-10 dose and were largely independent of IL-12 co-treatment. Furthermore, we also showed that the removal of IL-10 was sufficient to restore an M1-type phenotype. Here, we identify a biochemical “node” within the macrophage intracellular network that mediates IL-10-driven M2 functions and also explains the reversion of macrophage phenotype from M2 to M1 upon removal of IL-10. We also identified a novel multicellular network through which IL-12 may indirectly promote commitment to M1 phenotypes via the pro-inflammatory mediator, IFNγ. This novel network-level model of macrophage polarization identifies several candidate nodes that may be targeted for restoring of an immune network state that promotes immunological clearance or control of cancer.

Finally, we have observed that under some conditions, distinct M1 and M2 states are induced in different cells within a single population. The probability of polarization towards an M2 state increased with IL-10 dose and was again independent of IL-12 co-treatment. These data represent the first evidence to date that macrophage polarization may be a stochastic process. We will present novel insights into the mechanisms underpinning this heterogeneity, and we will discuss connections between these phenomena and the dynamic evolution of macrophage phenotypes we have observed during tumor progression in vivo. These systems-level analyses of macrophage function provides new insights into innate immune function and will help to formulate therapeutic strategies for treating the many chronic diseases characterized by local immune dysfunction.