CRISPR-based in situ engineering tumor cells to reprogram macrophages for effective cancer immunotherapy

Tumor-associated macrophages (TAMs) are abundant in the tumor microenvironment and promote the tumor progression via multiple mechanisms. CD47 is overexpressed in most malignant tumors and acts as a “don’t eat me” signal to inhibit phagocytosis. We utilized CRISPR/Cas9 technology to knock out CD47 to guarantee the long-lasting anti-tumor immune responses. However, the reprogrammed TAMs are vulnerable to the inhibitory cytokines and tend to be transformed back into TAMs, and CD47 blockade alone may not be sufficient to elicit effective immune responses. We combined CD47 blockade with an immune-activating cytokine IL-12 for synergistic anti-tumor efficacy by genetically engineering the tumor cells into factories of IL-12 to in situ reprogram TAMs. Firstly, we designed a selective responsiveness accelerated gene delivery system named HPT-PFs that was dual modified with hyaluronic acid (HA) and tumor microenvironment sensitive peptides (TMSP) to simultaneously deliver plasmids for CD47 knockout and IL-12 production. Due to tumor-specific transfection and excellent endosome escape ability of HPT-PFs vector, more than 27% of tumor cells lost CD47 expression after HPT-PFs mediated gene editing, thus eliciting the phagocytosis by macrophages. And higher than 500 ng/ml of IL-12 was produced by tumor cells after HPT-PFs mediated pIL-12 expression, indicating the successful engineering of tumor cells into factories of IL-12. In melanoma-bearing mice models, drastic elevation of M1-polarized TAMs and secretion of inflammatory cytokines were observed when combined CD47 knockout with IL-12 production, which led to significant inhibition of tumor growth. Our study suggested that combination of CRISPR-mediated CD47 blockade with IL-12 production in tumor cells could synergistically promote macrophage-mediated immunotherapy, paving the way for CRISPR-based in situ engineering tumor cells for effective immunotherapy.