Chimeric 4/9ICR Reprograms Immunosuppressive IL-4 Signals to Enhance B7-H3-Targeted CAR-T Cell Efficacy Against Triple-Negative Breast Cancer

In triple-negative breast cancer (TNBC), interleukin-4 (IL-4) is markedly enriched and serves as a pivotal regulator driving CAR-T cell exhaustion and resistance to immune checkpoint inhibition. To overcome IL-4-mediated immunosuppression, we engineered an inverted cytokine receptor (4/9ICR), in which the extracellular domain of IL-4 receptor α (IL-4Rα) was fused to the transmembrane and intracellular domains of IL-9Rα.

When co-expressed with a B7-H3-targeted CAR, 4/9ICR enables T cells to sequester suppressive IL-4 and convert IL-4 signals into IL-9-like activation, leading to robust phosphorylation of STAT1, STAT3, STAT4, and STAT5. In vitro, both murine and human CAR-4/9ICR-T cells exposed to IL-4 exhibited increased effector cytokine production and enhanced expression of stemness markers. Importantly, CAR-4/9ICR-T cells exerted enhanced tumor control, maintained cytotoxicity, and reduced exhaustion compared with conventional CAR-T cells in vivo.