Pharmacological Targeting of ALDH1a2 in Dendritic Cells Enhances Antigen Presentation, T Cell Activation and Anti-tumor immunity

Dendritic cell (DC) vaccines have been proposed as cancer immunotherapies due to their role as crucial antigen-presenting cells that regulate T cell functions. Despite considerable efforts to optimize ex vivo priming of DCs, DC vaccines have rarely been successful, suggesting the presence of unknown inhibitory factors. Here, we examined DC differentiation dynamics and discovered that ALDH1a2-produced retinoic acid (RA) acts as a bottleneck factor, initiating negative feedback to inhibit DC maturation. Removing this inhibition through either genetic knockout or pharmacological blockade using KyA33, an ALDH1a2 inhibitor we developed, significantly enhances DC maturation, phagocytosis, antigen presentation, and T cell activation, in part by downregulating glucose metabolism. KyA33 demonstrates favorable drug-like properties, including low toxicity, high membrane permeability, and low cell efflux rate. Its non-covalent binding to ALDH1A2 was also validated through X-ray crystallography. Importantly, application of KyA33 generates more robust DCs vaccines, promoting anti-tumor immunity through enhancing antigen-specific T cell responses. Our investigation highlights the intricate interplay between retinoid signaling, dendritic cell maturation, and immune metabolism, offering promising avenues for enhancing cancer immunotherapies. Overall design: To characterize BMDC subpopulations of high vs low maturation, two groups of BMDC were generated by bone marrow cell culture w/ and w/o retino acid and sorted by CD11c/MHC/CD86 using FACS. Three biological replicates were produced per group for bulk RNAseq analysis. To further characterize the role of Aldh1a2 in the process, BMDC from Aldh1a2 wild type and KO mice were generated for bulk RNAseq analysis. Two models were used to achieve the KO of Aldh1a2 in BMDC cells by Cre/Flox system, either CD11c-Cre to achieve DC specific KO and UBC-CreERT2 combined with tamoxifen to induce whole body Aldh1a2 KO. In both model, littermate mice without Cre are used as wild type control. Bulk RNA sequencing was performed to compare gene expression between Aldh1a2 KO and WT BMDCs in each model.