Central tolerance is established through negative selection of self-reactive thymocytes and the induction of T-regulatory cells (T_Rs). The role of thymic dendritic cells (TDCs) in these processes has not been clearly determined. In this study, we demonstrate thatin vivo, TDCs not only play a role in negative selection but in the induction of T_Rs. TDCs include two conventional dendritic cell (DC) subtypes, CD8^loSirpα^hi/+(CD8^loSirpα⁺) and CD8^hiSirpα^lo/−(CD8^loSirpα⁻), which have different origins. We found that the CD8^hiSirpα⁺DCs represent a conventional DC subset that originates from the blood and migrates into the thymus. Moreover, we show that the CD8^loSirpα⁺DCs demonstrate a superior capacity to induce T_Rsin vitro. Finally, using a thymic transplantation system, we demonstrate that the DCs in the periphery can migrate into the thymus, where they efficiently induce T_Rgeneration and negative selection.

Checkpoint blockade antibodies have been approved as immunotherapy for multiple types of cancer, but the response rate and efficacy are still limited. There are few immunogenic cell death (ICD)-inducing drugs available that can kill cancer cells, enhance tumor immunogenicity, increase the in vivo immune infiltration, and thereby boosting a tumor response to immunotherapy. So far, the ICD markers have been identified as the few immuno-stimulating characteristics of dead cells, but whether the presence of such ICD markers on tumor cells translates into enhanced antitumor immunity in vivo is still investigational. To identify anticancer drugs that could induce tumor cell death and boost T cell response, we performed drug screenings based on both an ICD reporter assay and T cell activation assay. We identified that teniposide, a DNA topoisomerase II inhibitor, could induce high mobility group box 1 (HMGB1) release and type I interferon signaling in tumor cells, and teniposide-treated tumor cells could activate antitumor T cell response both in vitro and in vivo. Mechanistically, teniposide induced tumor cell DNA damage and innate immune signaling including NF-κB activation and STING-dependent type I interferon signaling, both of which contribute to the activation of dendritic cells and subsequent T cells. Furthermore, teniposide potentiated the antitumor efficacy of anti-PD1 on multiple types of mouse tumor models. Our findings showed that teniposide could trigger tumor immunogenicity, and enabled a potential chemo-immunotherapeutic approach to potentiate the therapeutic efficacy of anti-PD1 immunotherapy.