Tumor-associated Schwann cells Expressing LncRNAs Direct Immune Resistant Metabolic Microenvironment

One of the major obstacles of treating pancreatic ductal adenocarcinoma (PDAC) is the immune-resistant microenvironment, by which the mechanisms remains elusive. We demonstrated that tumor-associated Schwann cells (TAScs) play important roles in promoting an immune-resistant microenvironment. The abundance of TASc is correlated with the expression of negative immune checkpoints and infiltration of tumor-promoting immune cells. TASc-expressed Plasmacytoma Variant Translocation 1 (PVT1) is triggered by the tumor cell-produced Interleukin-6 (IL-6). Mechanistically, PVT1 modulates the RAF proto-oncogene serine/threonine-protein kinase (RAF1)-mediated phosphorylation of Tryptophan 2,3-dioxygenase (TDO2) in TASc, facilitating the enzymatic activities of TDO2 in catalyzing Tryptophan (Trp) to Kynurenine (Kyn). The release of Kyn in the microenvironment further modulates colony-stimulating factor 1 (CSF1) signaling, leading to the expansion of Myeloid-derived suppressor cells (MDSCs) and diminished infiltration of effector T-cells. Depletion of TASc-expressed PVT1 or TASc using small molecule inhibitor effectively sensitized PDAC to immunotherapy, signifying the important roles of TASc in PDAC immune resistance. 6-week-old tamoxifen-inducible KPC mice were administered a solution with- or without-tamoxifen (Sigma-Aldrich; cat#T5648) induction (20 mg/kg, i.p. injection, 5 consecutive days) (Madisen et al., 2010). At the age of 4 months, pancreases from KPC mice without tamoxifen induction or PDAC tumors from KPC mice with tamoxifen induction were suspended into single cell suspensions, described as follows: pancreases were digested as a single cell suspension using an enzyme mixture (250 U/mL Hyaluronidase Type I-S (Sigma; #H3506), 160 U/mL Collagenase Type I (Sigma; #C1639) in DMEM-F12). The tumor isolated from the KPC mice with Tamoxifen induction was digested as a single cell suspension using a mouse Tumor Dissociation kit (Miltenui Biotec Inc.; #130-096-730). After the lysis of red blood cells (RBC Lysis Buffer, BioLegend; #420302), single-cell suspensions were subjected to removal of the dead cells using a dead cell removal kit (Miltenyi Biotec; #130-090-101) and then blocked with anti-CD16/32 (BioLegend; #156604) for 20 min on ice. The cell suspensions were then stained with anti-nerve growth factor receptor Alexa Fluor488 conjugated antibody (Sigma; #MAB5592X) for 1 hrs at RT, and then subjected to cell sorting using the BD FACSMelody™ Cell Sorter. Total RNA from each sample was extracted using Trizol Reagent following standard protocols and mRNA sequencing was performed.