Cancer Immunology

Lactate-SREBP2 Signaling Axis-Driven Tolerogenic Dendritic Cell Maturation and Its Role in Promoting Cancer Progression

Background

In cancer, conventional dendritic cells (DCs) are key mediators of anti-tumor immunity. However, cancer has evolved mechanisms that render DCs ineffective in the tumor microenvironment (TME), and these mechanisms are not yet fully understood. This study identifies CD63 as a specific surface marker, revealing that mature regulatory dendritic cells (mregDCs) migrate to tumor-draining lymph nodes (TDLNs) and inhibit DC antigen cross-presentation, while promoting the differentiation of T helper 2 (Th2) and regulatory T cells (Tregs). Transcriptomic and metabolic studies indicate that the function of mregDCs relies on the mevalonate (MVA) biosynthesis pathway and its dominant transcription factor SREBP2. The study found that lactate derived from melanoma activates SREBP2 in tumor DCs, driving the formation of mregDCs. Gene silencing specific to DCs and pharmacological inhibition of SREBP2 promote the activation of anti-tumor CD8+ T cells and inhibit melanoma progression. This study suggests that through the lactate-SREBP2 dependent signaling axis, tumors can promote the development and function of CD63+ mregDCs, making this pathway a potential therapeutic target to overcome immune tolerance in the TME.

Source

This research was co-authored by Michael P. Plebanek, Yue Xue, Y-Van Nguyen, Nicholas C. Devito, Xueying Wang, Alisha Holtzhausen, Georgia M. Beasley, Balamayooran Theivanthiran, and Brent A. Hanks. The authors are affiliated with the Duke University School of Medicine, Department of Pharmacology and Cancer Biology, Duke Cancer Institute, University of North Carolina at Chapel Hill Lineberger Comprehensive Cancer Center, and Duke University Department of Surgery. The article was published in the journal Science Immunology on May 10, 2024.

Research Process

Identification of Dendritic Cell Populations

Through single-cell RNA sequencing (scRNA-seq) analysis of dendritic cells (DCs) in the Braf^V600E^Pten^-/^-^ transgenic melanoma mouse model, the study identified a DC population enriched for immune regulatory and MVA biosynthesis pathway gene expression. Cells were isolated from TDLNs, non-draining lymph nodes (NDLNs), and non-tumor-associated control lymph nodes and subjected to fluorescence-activated cell sorting (FACS) and scRNA-seq analysis. Unsupervised clustering identified CDC1, CDC2, and mregDC subsets. The mregDC subset upregulated immune suppressive genes and SREBP2-driven MVA biosynthesis pathway genes.

Identification of CD63 Marker

The study further confirmed CD63 as a specific surface marker for mregDCs through flow cytometry and quantitative real-time polymerase chain reaction (qRT-PCR). CD63+ mregDCs were correlated with CDC2 marker CD172a expression while being higher than CDC1 marker XCR1 expression. By quantifying the expression of CD63+ mregDCs during tumor progression via flow cytometry, it was found that these cells accumulate in TDLNs and are negatively correlated with the frequency of CDC1s.

Immunoregulatory Function Analysis

Through co-culture experiments and flow cytometry analysis, the study found that CD63+ mregDCs exhibit reduced antigen-specific CD8+ T cell response ability compared to CD63- DCs but still have the capacity to directly present SIINFEKL peptide and activate OT-I T cells. Further experiments demonstrated that CD63+ mregDCs inhibit the antigen cross-presentation of neighboring DCs via soluble mediators. Additionally, CD63+ mregDCs significantly promote the differentiation of Th2 and Tregs through IDO1-dependent mechanisms.

Maturation Pathways and Metabolic Characteristics

High-resolution analysis sub-divided mregDCs into mregDC1s and mregDC2s, showing transcriptional similarity to CDC1s and CDC2s, respectively. CITE-seq analysis indicated the presence of mregDCs in both TDLNs and tumors, exhibiting transcriptional statuses akin to CDC1s or CDC2s. Employing single-cell energy metabolism measurement (SCENITH), the study found that mregDCs displayed higher levels of fatty acid oxidation (FAO) and energy generation capacity compared to CDC1s and CDC2s. Further validation revealed that pharmacological inhibition of SREBP2 or silencing of the Srebf2 gene led to a decrease in mregDCs and inhibited melanoma progression.

Validation in Human Tumor Models

Through immunofluorescence microscopy and scRNA-seq analysis, the study identified CD63+ mregDCs in sentinel lymph node tissues from melanoma patients. This DC population was enriched for cholesterol homeostasis gene expression. Spatial transcriptomic analysis showed that CD63+ mregDCs were primarily located near CD4+ T cells and Tregs in sentinel lymph node tissues.

Conclusion

The study shows that through the lactate-SREBP2 signaling axis, tumors can promote the generation and function of CD63+ mregDCs in the TME, inhibiting antigen cross-presentation and promoting Treg and Th2 differentiation, thereby creating an immune-tolerant environment. Pharmacological inhibition and gene silencing of SREBP2 demonstrated potential to reverse mregDCs-dependent immune evasion and inhibit tumor progression, highlighting this pathway as a potential target to overcome cancer immunotherapy resistance.