Efficient generation of human cDC1-like cells to detect and enhance tumor-reactive T cells via CD4⁺ T cell help.

Classical type 1 dendritic cells (cDC1s) are crucial to anti-tumor immunity by cross-presenting tumor antigens and priming cytotoxic CD8⁺ T lymphocytes (CTLs). Licensing via CD4⁺ T cell help endows cDC1s with enhanced cross-presentation and CTL-priming capacity, making them a promising tool to improve adoptive T cell therapies. However, the scarcity of primary human cDC1s limits their in-depth translational investigation and application. Here, we describe a method to efficiently generate DCs in vitro from CD34⁺c-KIT⁺ progenitors in non-mobilized peripheral blood. This DC population is enriched for cDC1-like cells that respond to CD4⁺ T cell help by upregulation of key molecules involved in antigen cross-presentation and T cell costimulation. Upon CD4⁺ T cell-mediated licensing, the progenitor-derived DC promotes tumor-specific CTL priming and facilitates detection of rare tumor antigen-specific CD8⁺ T cells in blood and tumor tissues. This DC culture platform incorporating CD4⁺ T cell help provides a scalable system for immunomonitoring and optimizing adoptive T cell therapies in cancer.