*3.2.1 Modulate or eradicate the fibrotic stroma*

Fibroblastic stroma can reduce the efficacy of ICT by promoting tumor development and employing immunosuppressive immune cells. Several strategies have been applied to modulate or eradicate the fibrotic stroma to improve the effectiveness of ICT. For instance, Xu et al. constructed a puerarin loaded nano emulsion (nanoPue) for the targeted delivery of puerarin to the sigma receptor over-expressing cancer-associated fibroblasts (CAFs) and cancer cells [30]. Reactive oxygen species (ROS) play critical roles in activation of CAFs and puerarin was applied to decrease ROS production in the activated myofibroblast. In the desmoplastic triple-negative breast cancer (TNBC) model, nanoPue greatly reduced CAFs in mice and deactivated the stromal microenvironment, leading to enhanced chemotherapy effect of encapsulated paclitaxel. Importantly, combination therapy of nanoPue and α-PD-L1-based ICT induced more apoptosis and exhibited a significantly robust antitumor effect in 4 T1 tumor model compared to α-PD-L1 or nanoPue monotherapy. This suggests that CAFs deactivation is a promising approach to regulate tumor stroma and improve

#### **Figure 3.**

*Modulate the immunosuppressive tumor microenvironment (TME) to boost the efficacy of immune checkpoint therapy (ICT). Treg: regulatory T cell; CAF: cancer-associated fibroblast; and MDSC: myeloid treated suppressor cell.*

the efficacy of ICT. In another study, Zhao et al. established cyclopamine (CPA) and paclitaxel (PTX) co-encapsulated polymeric micelles (M-CPA/PTX) to modulate desmoplastic stroma in pancreatic ductal adenocarcinoma (PDAC) and improve the efficacy of ICT [31]. The (M-CPA/PTX) plarform could regulated the tumor stroma to enhance intratumoral vasculature density, leading to increased tumor-infiltrating CTLs and decreased hypoxia. In a Kras model, the combination treatment of M-CPA/ PTX with α-PD-1-based ICT upregulated CD8<sup>+</sup> T cells and IFN-γ levels in tumor tissues and prolonged the survival of mice compared to monotherapy of M-CPA/PTX or and α-PD-1 alone. These findings demonstrated the potential of fibrotic stroma modulation in enhancing the therapeutic efficacy of ICT.
