A lactate-SREBP2 signaling axis drives tolerogenic dendritic cell maturation and promotes cancer progression

Conventional dendritic cells (DCs) are essential mediators of antitumor immunity. As a result, cancers have developed poorly understood mechanisms to render DCs dysfunctional within the tumor microenvironment (TME). After identification of CD63 as a specific surface marker, we demonstrate that mature regulatory DCs (mregDCs) migrate to tumor-draining lymph node tissues and suppress DC antigen cross-presentation in trans while promoting T helper 2 and regulatory T cell differentiation. Transcriptional and metabolic studies showed that mregDC functionality is dependent on the mevalonate biosynthetic pathway and its master transcription factor, SREBP2. We found that melanoma-derived lactate activates SREBP2 in tumor DCs and drives conventional DC transformation into mregDCs via homeostatic or tolerogenic maturation. DC-specific genetic silencing and pharmacologic inhibition of SREBP2 promoted antitumor CD8+ T cell activation and suppressed melanoma progression. CD63+ mregDCs were found to reside within the lymph nodes of several preclinical tumor models and in the sentinel lymph nodes of patients with melanoma. Collectively, this work suggests that a tumor lactate-stimulated SREBP2-dependent program promotes CD63+ mregDC development and function while serving as a promising therapeutic target for overcoming immune tolerance in the TME.

Gli2 Facilitates Tumor Immune Evasion and Immunotherapeutic Resistance by Coordinating Wnt Ligand and Prostaglandin Signaling

Therapeutic resistance to immune checkpoint blockade has been commonly linked to the process of mesenchymal transformation (MT) and remains a prevalent obstacle across many cancer types. An improved mechanistic understanding for MT-mediated immune evasion promises to lead to more effective combination therapeutic regimens. Herein, we identify the Hedgehog transcription factor, Gli2, as a key node of tumor-mediated immune evasion and immunotherapy resistance during MT. Mechanistic studies reveal that Gli2 generates an immunotolerant tumor microenvironment through the upregulation of Wnt ligand production and increased prostaglandin synthesis. This pathway drives the recruitment, viability, and function of granulocytic myeloid-derived suppressor cells (PMN-MDSCs) while also impairing type I conventional dendritic cell, CD8 + T cell, and NK cell functionality. Pharmacologic EP2/EP4 prostaglandin receptor inhibition and Wnt ligand inhibition each reverses a subset of these effects, while preventing primary and adaptive resistance to anti-PD-1 immunotherapy, respectively. A transcriptional Gli2 signature correlates with resistance to anti-PD-1 immunotherapy in stage IV melanoma patients, providing a translational roadmap to direct combination immunotherapeutics in the clinic.

SIGNIFICANCE

Gli2-induced EMT promotes immune evasion and immunotherapeutic resistance via coordinated prostaglandin and Wnt signaling.

A SREBF2-dependent gene program drives an immunotolerant dendritic cell population during cancer progression

Dendritic cells (cDCs) are essential mediators of anti-tumor immunity. Cancers have developed mechanisms to render DCs dysfunctional within the tumor microenvironment. Utilizing CD63 as a unique surface marker, we demonstrate that mature regulatory DCs (mregDCs) suppress DC antigen cross-presentation while driving T _H 2 and regulatory T cell differentiation within tumor-draining lymph node tissues. Transcriptional and metabolic studies show that mregDC functionality is dependent upon the mevalonate biosynthetic pathway and the master transcription factor, SREBP2. Melanoma-derived lactate activates DC SREBP2 in the tumor microenvironment (TME) and drives mregDC development from conventional DCs. DC-specific genetic silencing and pharmacologic inhibition of SREBP2 promotes anti-tumor CD8 ⁺ T cell activation and suppresses melanoma progression. CD63 ⁺ mregDCs reside within the sentinel lymph nodes of melanoma patients. Collectively, this work describes a tumor-driven SREBP2-dependent program that promotes CD63 ⁺ mregDC development and function while serving as a promising therapeutic target for overcoming immune tolerance in the TME.

One Sentence Summary

The metabolic transcription factor, SREBF2, regulates the development and tolerogenic function of the mregDC population within the tumor microenvironment.

Elimination of fibrin polymer formation or crosslinking, but not fibrinogen deficiency, is protective against diet-induced obesity and associated pathologies

BACKGROUND

Obesity predisposes individuals to metabolic syndrome, which increases the risk of cardiovascular diseases, non-alcoholic fatty liver disease (NAFLD), and type 2 diabetes. A pathological manifestation of obesity is the activation of the coagulation system. In turn, extravascular fibrin(ogen) deposits accumulate in adipose tissues and liver. These deposits promote adiposity and downstream sequelae by driving pro-inflammatory macrophage function through binding the leukocyte integrin receptor αM β2 .

OBJECTIVES

An unresolved question is whether conversion of soluble fibrinogen to a crosslinked fibrin matrix is required to exacerbate obesity-driven diseases.

METHODS

Here, fibrinogen-deficient/depleted mice (Fib- or treated with siRNA against fibrinogen [siFga]), mice expressing fibrinogen that cannot polymerize to fibrin (FibAEK ), and mice deficient in the fibrin crosslinking transglutaminase factor XIII (FXIII-) were challenged with a high-fat diet (HFD) and compared to mice expressing a mutant form of fibrinogen lacking the αM β2 -binding domain (Fib𝛾390-396A ).

RESULTS AND CONCLUSIONS

Consistent with prior studies, Fib𝛾390-396A mice were significantly protected from increased adiposity, NAFLD, hypercholesterolemia, and diabetes while Fib- and siFga-treated mice gained as much weight and developed obesity-associated pathologies identical to wildtype mice. FibAEK and FXIII- mice displayed an intermediate phenotype with partial protection from some obesity-associated pathologies. Results here indicate that fibrin(ogen) lacking αM β2 binding function offers substantial protection from obesity and associated disease that is partially recapitulated by preventing fibrin polymer formation or crosslinking of the wildtype molecule, but not by reduction or complete elimination of fibrinogen. Finally, these findings support the concept that fibrin polymerization and crosslinking are required for the full implementation of fibrin-driven inflammation in obesity.

Tumor-intrinsic NLRP3-HSP70-TLR4 axis drives premetastatic niche development and hyperprogression during anti-PD-1 immunotherapy

The tumor-intrinsic NOD-, LRR- and pyrin domain-containing protein-3 (NLRP3) inflammasome-heat shock protein 70 (HSP70) signaling axis is triggered by CD8⁺ T cell cytotoxicity and contributes to the development of adaptive resistance to anti-programmed cell death protein 1 (PD-1) immunotherapy by recruiting granulocytic polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) into the tumor microenvironment. Here, we demonstrate that the tumor NLRP3-HSP70 axis also drives the accumulation of PMN-MDSCs into distant lung tissues in a manner that depends on lung epithelial cell Toll-like receptor 4 (TLR4) signaling, establishing a premetastatic niche that supports disease hyperprogression in response to anti-PD-1 immunotherapy. Lung epithelial HSP70-TLR4 signaling induces the downstream Wnt5a-dependent release of granulocyte colony-stimulating factor (G-CSF) and C-X-C motif chemokine ligand 5 (CXCL5), thus promoting myeloid granulopoiesis and recruitment of PMN-MDSCs into pulmonary tissues. Treatment with anti-PD-1 immunotherapy enhanced the activation of this pathway through immunologic pressure and drove disease progression in the setting of Nlrp3 amplification. Genetic and pharmacologic inhibition of NLRP3 and HSP70 blocked PMN-MDSC accumulation in the lung in response to anti-PD-1 therapy and suppressed metastatic progression in preclinical models of melanoma and breast cancer. Elevated baseline concentrations of plasma HSP70 and evidence of NLRP3 signaling activity in tumor tissue specimens correlated with the development of disease hyperprogression and inferior survival in patients with stage IV melanoma undergoing anti-PD-1 immunotherapy. Together, this work describes a pathogenic mechanism underlying the phenomenon of disease hyperprogression in melanoma and offers candidate targets and markers capable of improving the management of patients with melanoma.

923 Hedgehog signaling drives epithelial-to-mesenchymal transition, immune evasion, and anti-PD-1 resistance through coordinated upregulation of Wnt ligands and PGE2 synthesis

Background

Immunotherapy resistance has been correlated with epithelial-to-mesenchymal transition (EMT),1 2 however our understanding of tumor-intrinsic mechanisms driving this immune evasive phenotype is lacking. We have previously shown that Wnt ligands are upregulated in anti-PD-1 resistant melanomas,3 and postulated that upstream transcriptional regulation of select EMT pathways may underpin these findings. The hedgehog signaling (HH) transcription factor Gli2 promotes EMT.

Methods

Gli2 was constitutively activated (Gli2CA ) in a BRAFV600EPTEN-/- murine cell line via an N-terminal truncating mutation and silenced using CRISPR-Cas9. Multi-parameter flow cytometry and RNAseq was utilized to evaluate the impact of Gli2 on the tumor immune microenvironment. Anti-PD-1 resistance studies were performed in Gli2CA and control tumors. Bioinformatics studies were conducted using the melanoma TCGA and Hugo et al databases.2

Results

We found upregulation of Gli2 targets in patients with anti-PD-1-refractory metastatic melanoma as well as in an autochthonous BRAFV600EPTEN-/- melanoma model after escape from anti-PD-1. RNAseq and Western blot studies demonstrated Gli2CA to promote EMT and Wnt ligand production in addition to upregulated COX2 in BRAFV600EPTEN-/- melanoma. This finding was reversed by genetic ablation and pharmacologic inhibition of Gli2, implicating a previously undescribed role for Gli2 in modulating COX2. These data were consistent with a notable correlation between a Gli2 signature and a prostaglandin synthesis signature in human melanoma TCGA database. Flow cytometry analysis showed exclusion of cytolytic T and NK cells, a shift from cDC1s to cDC2s, and enhanced MDSC recruitment in Gli2CA tumors. Consistent with these findings, whole tumor RNAseq of Gli2CA tumors demonstrated a decrease in Cd3e, Prf1, and Xcr1 with a concomitant increase in Cxcl1, Cxcl2, Ccl2, Ptgs2, and Arg1 relative to control tumors. RNAseq of FACS-sorted DCs from Gli2CA tumors demonstrated a loss of cDC1-associated genes including Xcr1, Wdfy4, and Clec9a compared to DCs derived from control tumors. In-line with our previous results showing that Wnt5a promotes MDSC recruitment in a Yap-dependent manner,4 we found that Yap inhibition or Wnt5a deletion in the BRAFV600EPTEN-/-Gli2CA cell line diminished MDSC-recruiting chemokines. Further consistent with these findings, Gli2CA tumors resist anti-PD-1 antibody therapy.

Abstract 923 Figure 1

Gli2 in tumors promotes Wnt and prostaglandin signaling, generating an immunosuppressive microenvironment

Conclusions

Our data demonstrates that the HH transcription factor Gli2 drives the development of a tolerogenic tumor microenvironment unfavorable to anti-PD-1 immunotherapy by coordinating the upregulation of Wnt ligand expression and prostaglandin synthesis (figure 1). We propose that HH gene signatures are worthy of further study as a guide for selecting Wnt ligand and prostaglandin inhibitors in future immunotherapy studies.

Acknowledgements

The authors would like to acknowledge the Duke Cancer Institute Flow Cytometry Core.

References

Bagaev A, et al. Conserved pan-cancer microenvironment subtypes predict response to immunotherapy. Cancer Cell 2021.

Hugo W, et al. Genomic and transcriptomic features of response to anti-PD-1 therapy in metastatic melanoma. Cell 2016;165(1):35–44.

DeVito NC, et al. Pharmacological Wnt ligand inhibition overcomes key tumor-mediated resistance pathways to anti-PD-1 immunotherapy. Cell Rep 2021;35(5):109071.

Theivanthiran B, et al. A tumor-intrinsic PD-L1/NLRP3 inflammasome signaling pathway drives resistance to anti-PD-1 immunotherapy. J Clin Invest 2020;130(5):2570–2586.