Modulating Phagocytosis Of Tumor-associated Macrophage By Co-delivery Nanoparticles To Improve Cancer Immunotherapy

Macrophages are one of the most abundant non-malignant cells in the tumor microenvironment.As an important member of the innate immune system,macrophages form the key defense system to protect the organism.On the one hand,macrophages can recognize and engulf pathogenic microorganisms or alive tumor cells to initiate innate immune response,which in turn activates adaptive immunity.On the other hand,macrophages manage to clear apoptotic cells through efferocytosis for maintaining tissue homeostasis.However,it should be noted that alive tumor cells overexpress CD47 on their surface to interact with signal regulatory proteinα(SIRPα)expressed on macrophages to suppress phagocytosis,which is one of the mechanisms of tumor immune escape.On the other hand,phagocytic clearance of apoptotic cells by macrophages is accompanied by a significant increase in anti-inflammatory cytokine production and the recruitment of regularogry T cells(Tregs),which collectively contribute to the formation of tumor-immunosuppressive microenvironment.Thus,facilitating the phagocytosis of alive tumor cells by macrophages or inhibiting efferocytosis of apoptotic tumor cells is a promising strategy for improved cancer immunotherapy.In this thesis,by taking advantage of the co-delivery capacity of nanoparticles,we constructed two co-delivery systems using mesoporous silica nanoparticles(MSNs)as the carrer to either promote the phagocytosis of macrophages to alive tumor cells or inhibit the efferocytosis of apoptotic tumor cells to strengthen the antitumor immune response of macrophages.We for the first time identified and confirmed that resiquimod(R848)can significantly promote macrophage engulfment of B16F10 tumor cells besides its recognized repolarization effect(4.5%vs 16.5%).And the combination of R848 and aSIRPαfurther increased the phagocytic ability of macrophages(increased by 1.3-fold).Based on this,we sought to employ MSNs as the carrier for co-delivery of R848 and aSIRPα(denoted as RMSN-aSIRPα)for macrophage-medicated cancer immunotherapy.RMSN-aSIRPαwas prepared by loading R848into the cavity of MSNs,and adsorbing aSIRPαon the surface.In B16F10 aggressive melanoma and 4T1 breast cancer animal models,the tumor growth inhibition rate of RMSN-aSIRPαreached 92.0%and 69.5%,respectively.The flow cytometric results indicated that after RMSN-aSIRPαadministrations,the abundance of M2-like macrophages significantly decreased and the ratio of M1/M2 increased from 0.46 to 1.4.The proportion of CD8~+T cells increased to12.5,which was three times higher than PBS treatment(3.8%).We constructed co-delivery nanoparticles to silmutaneously deliver chemotherapeutic drug doxorubicin(DOX)and efferocytosis inhibitor BMS77607 to increase apoptosis of tumor cells while inhibiting macrophage engulfment of apoptotic tumor cells.We loaded DOX and BMS777607 into the pores of MSNs in a nanoconfined manner(denoted as SC-MSN@D/B)to achieve codelivery and simultaneous release of the two drugs.In vitro experiments showed that SC-MSN@D/B nanoparticles effectively blocked the phagocytosis of apoptotic cells by macrophages and the inhibition rates reached 51.3%.In MC38 colorectal cancer model and 4T1breast cancer model,the tumor growth inhibition rate of SC-MSN@D/B reached 66.7%and57.5%,respectively.Immunofluorescence staining of tumor tissue showed that compared to the SC-MSN@D group,the intratumoral number of apoptotic tumor cells in the SC-MSN@D/B group was 2.4-fold higher.ELISA results showed that compared to the SC-MSN@D group,the level of IL-10 and TGF-βin the SC-MSN@D/B group decreased significantly,the level of IL-12 and TNF-αincreased 1.5-fold and 1.8-fold respectively,which resulted the proportion of M2-like TAMs and Tregs decreased,and the proportion of CD8~+T increased.In addition,the combination of SC-MSN@D/B and aPD-1 further improved the therapeutic effect and the inhibitory effect of lung metastasis in 4T1 orthotopic breast cancer model,as well as stronger anti-tumor memory response.