The Impact of Nanopulse Treatment on the Tumor Microenvironment in Breast Cancer: Overturning the Treg Immunosuppressive Dominance

Nanopulse treatment (NPT) is a high-power electric engineering modality that has been shown to be an effective local tumor treatment approach in multiple cancer models. Our previous studies on the orthotopic 4T1-luc breast cancer model demonstrated that NPT ablated local tumors. The treatment consequently conferred protection against a second live tumor challenge and minimized spontaneous metastasis. This study aims to understand how NPT mounts a potent immune response in a predominantly immunosuppressive tumor. NPT changed the local and systemic dynamics of immunosuppressive cells by significantly reducing the numbers of regulatory T cells (Tregs), myeloid-derived suppressor cells (MDSCs), and tumor-associated macrophages (TAMs) that contribute to the dominant immunosuppressive environment in the 4T1-luc mouse breast cancer model. The Treg suppression capacity and activation markers, including 4-1BB and TGFβ, were diminished post-treatment, and the Treg activation profile shifted from a predominantly activated (CD44+CD62L-) to a naïve (CD44-CD62L+) profile. Furthermore, we observed an increase in apoptosis among Tregs and TAMs followed by a concomitant M1-macrophage polarization of the surviving TAMs. Meanwhile, a continuing rise in the effector T cell (Teff) / Treg ratio and among resident memory CD8 T cells hinted at the expansion of antitumor specific cytotoxic T cells. Overall, these findings suggest that NPT is a potent tumor microenvironment (TME) modifier that can effectively reverse the tumor’s immunosuppressive barrier by decreasing MDSCs, TAMs and functionally suppressive Tregs. Thus, the TME modification by NPT confers cytotoxic T cell function and immune memory formation contributing to the tumor challenge rejection and reduction in metastasis risk. Future studies will investigate the underlying mechanisms of NPT-induced T cell immunity by determining the changes it creates among Treg and Teff T cell receptor (TCR) clonality in both mice and humans. Control studies on human blood indicated that ...