<p>Breast cancer remains one of the leading causes of cancer-related mortality among women worldwide. Immunotherapy, a promising therapeutic approach, often faces challenges due to the immunosuppressive tumor microenvironment. This study explores the innovative use of CRISPR-Cas9 technology in conjunction with FCPCV nanoparticles to target and edit the C-C Motif Chemokine Ligand 5 (CCL5) gene, aiming to improve the efficacy of breast cancer immunotherapy. Single-cell RNA sequencing (scRNA-seq) and TCGA-BRCA data identified CCL5 as a key immune-related gene in breast cancer. Using CRISPR-Cas9, sgRNA targeting CCL5 was designed and delivered to breast cancer cells and humanized mouse models via FCPCV nanoparticles. In vitro experiments demonstrated that FCPCV nanoparticles effectively silenced CCL5, enhanced CD8⁺ T cell activity, and increased the production of cytokines such as IFN-γ, TNF-α, and GZMB. In vivo studies revealed significant tumor suppression, improved immune microenvironment, and increased CD8⁺/CD4⁺ ratios in treated mice, without notable toxic side effects. These findings highlight the potential of CRISPR-Cas9 nanoparticle-mediated gene editing as a novel strategy for enhancing breast cancer immunotherapy, providing a new direction for personalized and effective cancer treatment.</p>