The therapeutic activity of checkpoint blockers and TLR agonists, which show some efficacy against malignancies, appears to at least partially result from the secretion of type I interferons by macrophages and dendritic cells. Thus, we hypothesized that type I interferon-inducible transcription factors, such as basic leucine zipper transcription factor ATF-like 2 (Batf2), might also play a role in tumor immunity. Recent studies have demonstrated that Batf2 may have unique and positive transcriptional activities. We therefore investigated the role of Batf2, especially its positive transcriptional activities via TLR signals, and evaluated its antitumor effect. We established mouse models with subcutaneously injected B16-F1 melanoma cells to assess the role of Batf2 in in vivo tumor development. Using knockout and chimeric mice, we found that mice deficient in Batf2 or Tlr7 have fewer IL-12 p40+ macrophages and activated CD8+ T cells within the tumor than wild-type control mice. In vitro studies revealed that, following stimulation with TLR7 ligands, such as R848 and tumor-derived RNA, macrophages from Batf2−/− mice had significantly less IL-12 p40 expression compared with wild-type controls. Because these data suggest that Batf2 might promote the transcription of IL-12 p40, we performed a functional analysis of BATF2 on IL-12 p40 promoters using the macrophage cell line RAW 264.7. We thus demonstrated that BATF2 interacts with NF-κB p50/p65 and promotes IL-12 p40 expression. Taken together, this study shows that TLR7 ligands induce Batf2, which interacts with p50/p65 and upregulates IL-12 p40 expression by tumor-associated macrophages; these changes precede the activation and accumulation CD8+ T cells within the tumor. Batf2 may be a promising candidate in treatment with immune checkpoint blockers and TLR agonists.

The antitumor effect of basic leucine zipper transcription factor ATF-like 2 through IL-12 p40 upregulation