• PD-1 blockade has limited efficacy in reducing tumor burden and altering tumor-infiltrating immune cells in TNBC mice.
• Systemic immune activity is enhanced by PD-1 blockade, with increased T cells and dendritic cells in peripheral blood, potentially linked to inflammatory side effects.
• PD-1 blockade does not rescue hematopoietic damage induced by TNBC, indicating a limitation for long-term response.
• In tumor-free mice, PD-1 blockade increases hematopoietic stem/progenitor cells, suggesting potential benefits after tumor resection.