A Double-Edged Sword: The Dichotomous Roles of Dendritic Cell Subsets in Shaping CD8+ T Cell Immunity and Tolerance Within the Tumor Microenvironment

Dendritic cells (DCs) function as a double-edged sword in tumor immunity, capable of both activating and tolerizing CD8+ cytotoxic T lymphocytes (CTLs). While conventional type 1 dendritic cells (cDC1s) are well-established mediators of cross-presentation for initiating anti-tumor CTL responses, existing reviews—largely overlook the tolerogenic potential of cDC1s and the context-dependent immunostimulatory capacity of cDC2s, monocyte-derived DCs (moDCs), and plasmacytoid DCs (pDCs). Furthermore, no prior synthesis has systematically reconciled the divergent functions of DC subsets across steady-state versus inflammatory conditions, migratory versus resident phenotypes, and human versus mouse model systems. The tumor microenvironment (TME) and tumor-derived exosomes further drive DCs toward an immunosuppressive phenotype, facilitating immune escape. Here, we establish a multi-dimensional framework that dissects the dichotomous roles of diverse DC subsets in regulating CTL immunity and tolerance, resolving key biological contradictions—including recent in vivo evidence that cDC2s can cross-present immune-complexed antigens via a WDFY4-dependent pathway shared with cDC1s—an activity that complements, but does not replace, the cDC1-restricted cross-presentation of cell-associated antigens. We also provide a hierarchical analysis of strategies to restore DC-mediated anti-tumor activity, extending the DC–CTL regulatory paradigm to autoimmunity and solid organ transplantation. A comprehensive summary table categorizes DC-based therapeutic approaches by clinical development stage. By elucidating this dynamic balancing mechanism, we offer refined insights for optimizing cancer immunotherapy design and cross-disciplinary therapeutic applications.