CD8α Dendritic Cells Dictate Leukemia-Specific CD8 T Cell Fates.

APCs are essential for the orchestration of antitumor T cell responses. Batf3-lineage CD8α and CD103 dendritic cells (DCs), in particular, are required for the spontaneous initiation of CD8 T cell priming against solid tumors. In contrast, little is known about the APCs that regulate CD8 T cell responses against hematological malignancies. Using an unbiased approach, we aimed to characterize the APCs responsible for regulating CD8 T cell responses in a syngeneic murine leukemia model. We show with single-cell resolution that CD8α DCs alone acquire and cross-present leukemia Ags in vivo, culminating in the induction of leukemia-specific CD8 T cell tolerance. Furthermore, we demonstrate that the mere acquisition of leukemia cell cargo is associated with a unique transcriptional program that may be important in regulating tolerogenic CD8α DC functions in mice with leukemia. Finally, we show that systemic CD8α DC activation with a TLR3 agonist completely prevents their ability to generate leukemia-specific CD8 T cell tolerance in vivo, resulting instead in the induction of potent antileukemia T cell immunity and prolonged survival of leukemia-bearing mice. Together, our data reveal that Batf3-lineage DCs imprint disparate CD8 T cell fates in hosts with solid tumors versus systemic leukemia.