Recently, PAN Guangjin's team from Guangzhou Institutes of Biomedicine and Health (GIBH) of the Chinese Academy of Sciences developed a strategy for mass production of genetically engineered macrophages (GEMs) for the treatment of solid tumors, and developed a functionally enhanced anti-tumor GEMs, providing new ideas for the development and application of GEMs. The study was published in Molecular Therapy-Methods & Clinical Development.

Macrophages can be continuously recruited and reside in the tumor microenvironment (TME), playing an important role in the tumorigenesis process. Compared with other cell products such as T cells, and NK cells, macrophage holds more advantages in treating solid tumors because of their better tumor infiltration, which has attracted wide attention in the treatment of solid tumors in recent years.  

There are multiple immunosuppressive mechanisms in TME. Cancer therapies aiming to alter the immune-suppressive TME have been studied. GEMs have emerged as a novel strategy for regulating TME in the treatment of cancer. However, macrophage therapy is limited by cell source and difficult genetic modification. 

In this study, the researchers used human pluripotent stem cells (hPSCs) to induce and differentiate mature macrophages (iMacs) in vitro. Starting with 1 T150 dish of 106 hiPSCs, more than 10⁹ mature macrophages (iMacs) could be generated within one month, thus overcoming the limitations of cell source. 

By utilizing the infinite self-renewal characteristics of hPSCs, the researchers targeted the gene of IL12 into specific safe sites of iPSCs through gene editing, and then generated stable IL12-secreting GEMs (iMac_IL12). iMacs and iMacs_IL12 expressed macrophage-related markers and exhibited typical macrophage properties such as phagocytosis and polarization, and were similar to macrophages derived from human peripheral blood monocytes at the transcriptome level.  

Interleukin-12 (IL12) promotes immunity by stimulating NK cells and T cells and has great potential to alter TME. However, the half-life of IL12 is short and the side effects of systematic administration are large. In this study, the researchers observed that iMacs_IL12 can be recruited and stably maintained in solid tumor tissue when administered through intravenous transplantation in mice, thereby reducing their side effects. 

Besides, the researchers found that iMacs_IL12 can induce peripheral blood mononuclear cells (PBMCs) to produce IFN-γ to enhance immunity. In vitro and in vivo experiments showed that iMacs_IL12 has a positive effect on the maintenance, proliferation and activation of CD8⁺ T cells, and can inhibit T cell exhaustion, and iMac_IL12 significantly promotes the killing of T cells on tumor cell lines such as cervical cancer, glioma and lung cancer.  

In the mouse cell line-derived xenograft (CDX) model, iMac_IL12 combined with T cells can significantly inhibit the tumor growth and prolong the survival of mice. In the mouse tumor metastasis model, and can also significantly inhibit the tumor burden, prolong the survival of mice, and reduce the metastasis of tumor cells to major organs. 

In conclusion, the differentiated iMacs in this study can overcome the source barriers and avoid the safety and inefficiency of macrophages in gene editing. The GEMs demonstrate strong T cell-dependent antitumor effects, leading to a significant inhibition of tumor growth and systemic metastasis, ultimately improving the survival of mice. 

Schematic of antitumor effect by human pluripotent stem cell-derived IL12-secreting macrophages (Image by GIBH)