A genome-wide CRISPR Screening identifies targets that drive Tolerogenic Dendritic Cells

Tolerogenic dendritic cells (TolDCs) are essential for immune tolerance and offer promise for treating autoimmune diseases. Despite the clinical evidence of their therapeutic potential, the key molecular pathways guiding their differentiation and tolerogenic phenotype remain elusive due to complex interactions identified in functional assays. Here we investigated the molecular profiles and regulatory programs underlying the functional status of tolerogenic dendritic cell populations in response to known tolerizing agents. We identified CD86 as a consistent and robust marker downregulated in tolerogenic state. Using CD86 blocking antibodies or CRISPR-mediated gene inactivation we demonstrated that CD86 is functionally required for TolDC-mediated suppression of T cell proliferation and cytokine secretion, establishing CD86 as both a consensus phenotypic and functional screening marker and a mechanistic regulator of tolerance. Leveraging CD86 as a scalable readout, we performed a pooled genome-wide CRISPR-Cas9 knockout screen to identify regulators of TolDC function. This approach uncovered UBE2L6 as a novel modulator that promotes the tolerogenic phenotype and restricts TolDC-mediated T cell activation. Mechanistically, UBE2L6 deficiency leads to coordinated upregulation of ISG15 and USP18, indicating a possible ISGylation-dependent pathway regulating CD86 expression and tolerogenic function. Together, this study identifies pathways that can be targeted to promote immune tolerance in immune-mediated inflammatory diseases.