Abstract 2562: Quantitative and functional immune reprogramming induced by a nanomedicine in breast cancer model

Abstract Nanoparticles (NPs) are emerging as a promising strategy in oncology, offering optimised drug delivery and the potential to modulate immune responses. In this study, we developed an innovative nanoparticle encapsulating docetaxel and functionalised with trastuzumab for precise targeting of HER2-positive tumours (called ANC for Antibody Nanoparticle Conjugate). Immunomodulatory effects were performed in C57BL/6 mice administered free docetaxel (1.6 mg-kg-1) and trastuzumab (135 ng-kg-1) by intraperitoneal injection (n = 29) or ANC (nanoparticles at the same docetaxel and trastuzumab doses as the free drugs, n = 40). Immune profiling was performed in blood (J0-J21) and tumor tissue (J21) to evaluate quantitative and functional changes in major lymphoid and myeloid subsets involved in antitumor immunity. Flow cytometric analyses included B cells, T cells (CD4+, CD8+), activated T-cell subsets, NK cells, regulatory T cells (Treg), myeloid-derived suppressor cells (MDSC), and regulatory B cells (Breg). In blood, no significant differences were observed between groups for B cells, NK cells, CD4+ or CD8+ T cells, or their activated subsets. A trend toward reduced Treg frequencies was detected in the ANC group compared with controls (p = 0.053), suggesting early systemic modulation of immunosuppressive activity. MDSC levels remained unchanged across all groups. In tumors, global B-cell levels were comparable between groups, but ANC-treated mice showed an increased proportion of Breg, indicating a potential local immunosuppression. NK-cell infiltration and activation tended to be higher in the ANC group (p ≈ 0.08), suggesting localized immune stimulation. No differences were detected for CD4+ T cells, whereas a reduction in CD8+ T-cell frequency was observed in ANC-treated tumors. Treg levels also showed a decreasing trend (p = 0.07), consistent with a partial reduction in immunoregulatory pressure within the tumor microenvironment. MDSC levels did not differ significantly between conditions. ANC formulation exhibited subtle yet biologically relevant immunomodulatory trends, including reduced Treg frequencies and increased activated NK cells within the tumor, potentially favoring antitumor responses. Conversely, the elevated Breg population in ANC-treated tumors may counterbalance these effects by promoting local immunosuppression. These findings suggest that ANC may fine-tune the tumor immune landscape without inducing major systemic alterations. Further investigation with extended cohorts and functional assays will be required to confirm these trends and clarify their implications for therapeutic efficacy. Citation Format: Mathilde Dacos, Léa Plantureux, Sarah Giacometti, Joseph Ciccolini, Raphaelle Fanciullino. Quantitative and functional immune reprogramming induced by a nanomedicine in breast cancer model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 2562.