(555j) Programming Tumor-Clearing Macrophages with Targeted Gene Therapy

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 (M1) tumoricidal state to an immunosuppressive (M2) phenotype, which facilitates tumor growth and metastasis. Much effort has therefore been devoted to developing therapies that target tumor-associated mφs (TAMs) as an alternative to classic radio/chemotherapy. 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 mφs in situ into highly effective, tumor-clearing M1 mφs by delivering genes encoding transcription factors. Specifically, we used mannose receptor-targeted nanoparticles (NPs) to provide mφs with mRNAs encoding master regulators of mφs polarization - Interferon Regulatory Factor 5 (IRF5). To identify the critical changes in mφs gene expression 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 when NPs carrying mRNA encoding IRF5 (IRF5-NPs) were used treat interleukin 4 (IL-4) exposed ‘M2-like mφs’, it promoted signature genes associated with M1 mφs while suppressed signature genes associated with M2 mφs. These signature genes persisted even when mφs were re-challenged with IL-4 media.

In an ID8 cells-induced syngeneic mouse model of ovarian cancer, repeated intraperitoneal (i.p.) injection of IRF5-NPs significantly suppressed tumor growth in all tested mice and demonstrated survival benefits in 40% tested mice. To determine the mechanism of IRF5-NPs suppressing tumor growth in this model, we analyzed the immune cells population in mouse peritoneum through flow-cytometry. IRF5-NPs treatment suppressed the expansion of M2 mφs population in the peritoneum of ovarian tumor mice, while maintaining a constant M1 mφs population. In a more aggressive B16F10 lung metastasis mouse model, repeated intravenous (i.v.) injection IRF5-NPs delayed tumor growth by 50%. Based on histology analysis, complete blood count and serum chemistry analysis, we showed that repeated injection of NPs under therapeutic doses did not induce serious toxicity to healthy mice.

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 (1) providing a foundation for gene-modification systems that would enable physicians to obviate the suppressive tumor milieu. (2) It also has the potential to work synergistically with existing immunotherapies by creating a therapeutic window for cancer patients, thus stimulating a stronger overall immune response in patients who also receive immunotherapy. (3) Although our project focuses on mφs, genetic re-engineering using NPs could also be applied to reprogram other tumor-promoting cell types such as regulatory T cells, MDSCs. Thus, the approach could provide a basis for future initiatives involving collaborations at the interface of materials science, gene therapy, and immunology.