Abstract 4770: Programming tumor-clearing macrophages with targeted in situ gene therapy
Authors: Zhang Fan , Coon Miacheal E. , Parayath Neha N. , Stephan Sirrka B. , Pillai Smitha P. , Stephan Matthias T. 
Published: August 2019

Abstract
Macrophages (mϕs) are key immune effectors that infiltrate into tumor in high numbers. However, within the immunosuppressive tumor milieu, they undergo a switch from an activated tumoricidal (M1-like) state to an immunosuppressive (M2-like) phenotype, which facilitates tumor growth and metastasis. To date, only systemic cytokine blockade using antibodies or small molecule drugs has shown success in this arena; however, because these blockades have low response rate among patients and suppress all mϕs in the body, they also induce dangerous side effects.
Instead of ablating mϕs through cytokine inhibition, we genetically reprogramed suppressive M2-like mϕs in situ into highly effective, tumor-clearing M1-like mϕs by delivering genes encoding transcription factors. Specifically, we used nanoparticles to provide mϕs with mRNAs encoding master regulators of mϕs polarization - IRF5 (IRF5-NPs).
Our in vitro test demonstrated that IRF5-NPs can choreograph immediate, transient, robust IRF5 production, and induce dose-responsive activation of the IRF5 pathway in mϕs. To identify the critical gene expression changes associated with NPs treatment, we used genome-sequencing technology to analyze 770 genes in 19 different pathways and processes in myeloid cells. Our results demonstrated that IRF5-NPs treatment on M2-like mϕs promoted M1-like signature genes while suppressed M2-like signature genes.
In an ID8 cells-induced syngeneic mouse model of ovarian cancer, repeated intraperitoneal (i.p.) injection of IRF5-NPs regressed tumor growth and significantly increased their median survival from 60 days to 141 days. IRF5-NPs treatment decreased the suppressive mϕs population in the peritoneum of ovarian tumor mice and promoted inflammatory mϕs/monocytes population. This inflammatory cell population had similar gene profile to M1-like mϕs and the ability to produce inflammatory cytokines such as IL-12, TNFα, INFγ. Through biodistribution and toxicity study, we showed that the treatment effect was local and did not impose serious systemic side effects on the healthy mouse. We further showed that in a more aggressive B16F10 lung metastasis mouse model, repeated intravenous (i.v.) injection of IRF5-NPs prolonged the median survival for 30%.
This research is a pioneering effort to treat cancer by genetically reprogramming suppressive M2 mϕs. The results of the project could have a transformative effect on cancer therapeutics by providing a foundation for gene-modification systems that would enable physicians to obviate the suppressive tumor milieu.
Citation Format: Fan Zhang, Miacheal E. Coon, Neha N. Parayath, Sirrka B. Stephan, Smitha P. Pillai, Matthias T. Stephan. Programming tumor-clearing macrophages with targeted in situ gene therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4770.