title: The induction of APC with a distinct tolerogenic phenotype via contact-dependent STAT3 activation.
abstract: BACKGROUND
  Activation of the signal transducer and activator of transcription 3 (STAT3) within antigen presenting cells (APCs) is linked to abnormal APCs differentiation and function. We have previously shown that STAT3 is activated within APC by a novel contact-dependent mechanism, which plays a key role in mediating the immunomodulatory effects of hMSC. In order to better understand the underlying mechanisms that control APC maturation in a contact dependent manner, we extended our observation to tumor cells. Tumors were shown to secrete a variety of tumor-derived factors that activate STAT3 within infiltrating APCs. We now tested whether tumor cells can activate STAT3 within APC using the contact-dependent mechanism, in addition to soluble factors, and compared these two STAT3 activating pathways.
  
  
  RESULTS
  We demonstrate that in addition to tumor-derived secreted factors tumor cells activate STAT3 by a mechanism that is based on cell-cell interaction. We further demonstrate that these two STAT3 activating mechanisms differ in their JAK usage and their susceptibility to JSI-124 inhibition thereby representing two distinct pathways. Significantly, although both pathways activate STAT3, they modulate DCs maturation in a different manner that results in disparate phenotypic outcomes. Whereas the soluble-dependent pathway results in an immature phenotype, the contact-dependent pathway results in an apparently mature phenotype. Albeit their mature-like phenotype these latter cells express the tolerogenic markers ILT3 and ILT4 and possess T cell inhibitory activity.
  
  
  CONCLUSIONS
  This data suggests that, in at least certain cellular microenvironments, cell:cell interactions represent a novel way to activate STAT3 signaling, uncouple APC activation events and consequently regulate immunity and tolerance. Significantly, we have now demonstrated that this contact-dependent signaling pathway differs from that mediated by soluble factors and cytokines, inducing disparate phenotypic outcome, suggesting these two mechanisms have different and possibly complementary biological functions.
authors.affiliation: Goldyne Savad Institute of Gene Therapy, Hadassah-Hebrew University Medical Center, Jerusalem, Israel.
authors.forename: Devorah
authors.initials: D
authors.lastname: Gur-Wahnon
authors.forename: Zipora
authors.initials: Z
authors.lastname: Borovsky
authors.forename: Meir
authors.initials: M
authors.lastname: Liebergall
authors.forename: Jacob
authors.initials: J
authors.lastname: Rachmilewitz
mesh_terms: D000938:Antigen-Presenting Cells; D045744:Cell Line, Tumor; D018920:Coculture Techniques; D017077:Culture Media, Conditioned; D006801:Humans; D047468:Immunoprecipitation; D007371:Interferon-gamma / Q000037:antagonists & inhibitors / Q000378:metabolism; D016753:Interleukin-10 / Q000096:biosynthesis; D053614:Janus Kinase 2 / Q000378:metabolism; D010641:Phenotype; D010766:Phosphorylation; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D017077:Culture Media, Conditioned; D050796:STAT3 Transcription Factor; D014409:Tumor Necrosis Factor-alpha; D016753:Interleukin-10; D007371:Interferon-gamma; C507924:JAK2 protein, human; D053614:Janus Kinase 2