Elevated ALDH Expression Impairs Dendritic Cell Function and Contributes to Immunotherapy Resistance in Bladder Cancer

Abstract

Immunotherapy has significantly improved cancer treatment, but a significant proportion of patients do not respond to therapy. This study investigates the role of aldehyde dehydrogenase 1A1 (Aldh1A1) and its metabolite retinoic acid (RA) in shaping the tumor microenvironment and influencing immunotherapy response in bladder cancer. Analysis of two murine bladder cancer cell lines, BBNF2 and BBNF9, revealed that BBNF9 tumors, which are resistant to anti-PD-1 therapy, express higher levels of Aldh1A1 compared to immunotherapy responsive BBNF2 tumors. In vitro studies demonstrated that RA impairs dendritic cell maturation, IL-12 production, and capacity to stimulate T cells, a process mediated by the retinoic acid receptor RXRα. To further elucidate the role of Aldh1A1 in immunotherapy resistance, Aldh1A1 was knocked out in BBNF9 cells using CRISPR-Cas9. Aldh1A1-deficient BBNF9 tumors exhibited increased dendritic cell infiltration, enhanced trafficking of cross-presenting cDC1s to tumor-draining lymph nodes, and reduced recruitment of immunosuppressive neutrophil subsets. Importantly, Aldh1A1 knockout sensitized BBNF9 tumors to anti-PD-1 therapy, characterized by increased T cell infiltration and exhaustion phenotypes. These findings provide mechanistic insights into how the Aldh1a1-RA axis modulates dendritic cell function and contributes to immunotherapy resistance in bladder cancer.