A HER2-targeting antibody-drug conjugate, trastuzumab deruxtecan (DS-8201a), enhances antitumor immunity in a mouse model

Trastuzumab deruxtecan (DS-8201a), a HER2-targeting antibody-drug conjugate with a topoisomerase I inhibitor exatecan derivative (DX-8951 derivative, DXd), has been reported to exert potent antitumor effects in xenograft mouse models and clinical trials. In this study, the immune system-activating ability of DS-8201a was assessed. DS-8201a significantly suppressed tumor growth in an immunocompetent mouse model with human HER2-expressing CT26.WT (CT26.WT-hHER2) cells. Cured immunocompetent mice rejected not only re-challenged CT26.WT-hHER2 cells, but also CT26.WT-mock cells. Splenocytes from the cured mice responded to both CT26.WT-hHER2 and CT26.WT-mock cells. Further analyses revealed that DXd up-regulated CD86 expression on bone marrow-derived DCs in vitro, and that DS-8201a increased tumor-infiltrating DCs and up-regulated their CD86 expression in vivo. DS-8201a also increased tumor-infiltrating CD8+ T cells and enhanced PD-L1 and MHC class I expression on tumor cells. Furthermore, combination therapy with DS-8201a and anti-PD-1 antibody was more effective than either monotherapy. In conclusion, DS-8201a enhanced antitumor immunity, as evidenced by the increased expression of DC markers, augmented expression of MHC class I in tumor cells, and rejection of re-challenged tumor cells by adaptive immune cells, suggesting that DS-8201a enhanced tumor recognition by T cells. Furthermore, DS-8201a treatment benefited from combination with anti-PD-1 antibody, possibly due to increased T cell activity and up-regulated PD-L1 expression induced by DS-8201a.

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