Reprogramming the Tumor Microenvironment with a Membrane-Proximal AXL Antibody to Overcome Immune Checkpoint Blockade Resistance

Immune-cold tumors failed to respond to immunotherapy due to insufficient lymphocytes infiltration within tumor tissue. How to increase the objective response rate is an urgent challenge. Here, we report the development of a monoclonal antibody (6C5) that specifically targets the membrane-proximal epitope of receptor tyrosine kinase AXL, which modulates the anti-tumor immunity. Unlike traditional membrane-distal AXL antibodies, 6C5 significantly enhanced innate immune sensing by promoting macrophage-mediated antigen uptake and type I interferon production via the MyD88 pathway. This reshaped the tumor microenvironment , further boosting CD8+ T cell infiltration and effector function. However, AXL antibody treatment concurrently induced a suppressive subset of PD-1hiFoxp3-CD4+ T cell, attenuating antitumor responses. The combination of AXL Ab with dual immune checkpoint blockade (anti-PD-1 plus anti-CTLA-4) or PD-1-targeted IL-2 fusion protein therapy mitigated this immunosuppression, achieving potent tumor regression and durable immune memory. Our findings demonstrate that membrane-proximal AXL targeting antibody effectively converts immune-cold tumor microenvironment, overcoming resistance to both conventional and next-generation immune checkpoint inhibitors.