Mechanism Of MS4A4A Regulating Macrophage M2 Polarization To Mediate Immune Escape In Colorectal Cancer

Background:The occurrence and development of tumors are the result of interaction with the immune microenvironment.The interaction between tumor cells and immune cells is an important factor in promoting tumor immune evasion,but the mechanism of tumor-associated macrophages regulating immune evasion of colorectal cancer cells(CRC)through M2 polarization has not been elucidated.Membrane Spanning 4-Domains A4A(MS4A4A)is specifically and highly expressed in TAMs,is associated with the function of dectin-1 receptors in macrophage lipid rafts,and is required for full activation of Syk-dependent signaling pathways.Studies have shown that MS4A4A may be a novel marker of M2 macrophages and is associated with poor prognosis in gastric and renal cancers.However,in CRC,the function of MS4A4A in TAM,the molecular mechanism involved in regulating the immune microenvironment,and the relationship with tumor development remain to be clarified.In this study,firstly,we aimed to study the expression and clinical significance of MS4A4A in CRC.Secondly,we will clarify the role and mechanism of MS4A4A in regulating TAM polarization and the immune microenvironment in promoting immune escape in CRC.Finally,we will explore the role of blocking MS4A4A in colorectal cancer immunity.Methods:(1)Using public databases and tissue immunofluorescence to analyze the localization and expression of MS4A4A in the tumor microenvironment of colorectal cancer,and to analyze the effect of MS4A4A expression on the survival and prognosis of patients with various types of solid tumors.(2)qRT-PCR and flow cytometry were used to investigate the expression of MS4A4A in macrophages with different polarization states in vitro,the effect of MS4A4A on M2 polarization and phagocytic function of macrophages,and the effect on the expression of CD8~+T lymphocytes exhaustion markers.(3)C57BL/6 mouse or BALB/c mouse subcutaneous tumor model was used to evaluate in vivo inhibition of MS4A4A or anti-MS4A4A monoclonal antibody therapy,and in vivo inhibition of MS4A4A or anti-MS4A4A monoclonal antibody combined with immune checkpoint inhibitor therapy on tumor growth inhibition effect.Intratumoral CD8~+T lymphocytes proliferative capacity,expression of effector factors and T cell exhaustion markers,and intratumoral M2 macrophage infiltration levels were assessed by flow cytometry and tissue immunofluorescence.(4)Use RNA-seq and database to screen the downstream signaling pathways that may be activated by MS4A4A in macrophages,and detect the expression of related proteins by western blot.Results:(1)MS4A4A is specifically highly expressed in TAM and is closely related to the poor prognosis of patients with various types of cancer.(2)MS4A4A can promote TAM polarization to M2 type and induce CD8~+T lymphocytes exhaustion.(3)In vivo inhibition of MS4A4A expression can delay colorectal cancer progression by reducing intratumoral M2 macrophage infiltration,and this tumor suppressor effect is dependent on the presence of CD8+ T lymphocytes.(4)Anti-MS4A4A monoclonal antibody treatment can significantly delay the growth of CRC.(5)MS4A4A promotes M2-type polarization of macrophages by activating JAK/STAT6 and PI3K/AKT signaling pathways.(6)In vivo inhibition of macrophage MS4A4A or anti-MS4A4A monoclonal antibody therapy can synergize with anti-PD-1 monoclonal antibody therapy.Conclusions:Our study shows that MS4A4A is a key factor in regulating M2 polarization within TAM,and targeting macrophage MS4A4A can inhibit TAM polarization to M2 type and reduce T cell exhaustion,thereby delaying tumor growth and enhancing anti-PD-1 mAb therapy effect.