PD-1 blockade elicits a systemic immune response but not in the tumor of TNBC mice

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer with limited treatment options due to the absence of hormone receptors and HER2 amplification. Immune checkpoint blockade, particularly targeting PD-1/PD-L1, has emerged as a promising therapeutic strategy. However, the response rate of TNBC patients to this monotherapy remains low. This study explores the systemic effect of PD-1 blockade on the immune and hematopoietic systems in 4T1 TNBC mice and demonstrates its limited efficacy in reducing the tumor burden and changing the number of tumor-infiltrating immune cells. However, PD-1 blockade increases systemic immune activity, as demonstrated by increased T cells and DCs in the peripheral blood, which may be associated with inflammatory side effects of this treatment. In addition, PD-1 blockade does not rescue the hematopoietic damage caused by TNBC, highlighting a limitation in long-term response. Furthermore, PD-1 blockade in tumor-free mice leads to an increase in hematopoietic stem/progenitor cells, suggesting that PD-1 blockade may yield better benefits post-tumor resection.