Mechanisms of PD-L1-Mediated Immune Evasion and Resistance to CAR-T Cell Therapy in Triple-Negative Breast Cancer

Abstract

Triple-negative breast cancer (TNBC) remains one of the most aggressive and therapeutically challenging subtypes of breast cancer. Despite recent advances in CAR-T cell immunotherapy, many TNBC patients develop resistance through upregulation of PD-L1 immune checkpoint molecules. This study investigates the molecular mechanisms underlying PD-L1-mediated immune evasion and identifies potential therapeutic strategies to overcome CAR-T resistance. Using single-cell RNA sequencing of tumor-infiltrating lymphocytes and patient-derived xenograft models, we demonstrate that tumor cells dynamically upregulate PD-L1 expression in response to CAR-T cell infiltration through activation of the JAK/STAT signaling pathway. Furthermore, we discover that hypoxic tumor microenvironment enhances PD-L1 stability via HIF-1α-mediated transcriptional regulation. Combination therapy targeting both PD-L1 checkpoint and HIF-1α pathway significantly improved CAR-T efficacy in preclinical models, reducing tumor burden by 85% compared to CAR-T monotherapy. Flow cytometry analysis revealed enhanced T cell activation, increased IFN-γ production, and reduced T cell exhaustion markers (TIM-3, LAG-3). These findings provide mechanistic insights into immune resistance and suggest a rational combination strategy to enhance CAR-T cell therapy outcomes in TNBC patients.