Biogenic Selenium Nanoparticles Potentiate Anti-Mesothelin CAR-T Cell Therapy in a Syngeneic TNBC Model.

Triple-negative breast cancer (TNBC) remains a highly aggressive subtype lacking effective targeted therapies. Although chimeric antigen receptor (CAR)-T cell therapy has transformed the treatment of hematological malignancies, its efficacy in solid tumors is hindered by the immunosuppressive tumor microenvironment (TME). Here, we generated anti-mesothelin CAR-T cells and evaluated their antitumor activity against TNBC using the immunocompetent 4T1 murine model. To enhance therapeutic responses, we incorporated biogenic selenium nanoparticles (bSeNPs), biosynthesized using Lactobacillus reuteri, based on their known immunomodulatory and pro-apoptotic properties. An experimental study was conducted using female BALB/c mice (n = 15) bearing subcutaneous 4T1 TNBC tumors. Mice were randomized into CAR-T + bSeNPs, CAR-T alone, or PBS control groups (n = 5 each). CAR-T cells were generated using γ-retroviral transduction. Treatments were administered intratumorally following lymphodepletion. Tumor growth, histopathological changes, and qPCR-based analysis of apoptotic and immunosuppressive gene expression were assessed. Statistical analyses included one-way and two-way ANOVA with Tukey's post-hoc tests. Results demonstrated significant in vitro activity of anti-mesothelin CAR-T cells against 4T1 TNBC cells by exerting potent cytotoxicity, antigen-specific proliferation, and cytokine production. In vivo, both CAR-T monotherapy and combination therapy significantly reduced tumor growth compared with controls, with the combination group showing a consistent trend toward improved tumor control. Histopathology revealed reduced mitotic activity and angiogenesis in treated tumors. Gene expression analysis demonstrated decreased PD-L1, TGF-β1, and IL-10 expression, along with enhanced pro-apoptotic signaling in the combination group. This study highlights the therapeutic promise of anti-mesothelin CAR-T cells for TNBC, providing preliminary evidence that bSeNPs may enhance CAR-T cell function by modulating the TME. These findings support further investigation of nanoparticle-assisted strategies to improve CAR-T therapy for solid tumors.