title: HLA expression and immunologic properties of differentiated and undifferentiated mesenchymal stem cells.
abstract: OBJECTIVE
  Mesenchymal stem cells (MSC) do not elicit alloreactive lymphocyte responses due to immune modulations. We investigated the immunologic properties of MSC after differentiation along three lineages: bone, cartilage, and adipose.
  
  
  RESULTS
  Flow cytometry showed that undifferentiated MSC express HLA class I but not class II, although HLA class II was present intracellularly as detected by Western blot. Addition of interferon gamma (IFN-gamma) for 48 hours induced greater than 90% of cells to express HLA class II. No lymphocyte response was induced by allogeneic irradiated MSC as stimulators. Results were similar using MSC pretreated with IFN-gamma. After growth of cells in medium to induce differentiation to bone, cartilage, or adipose for 6 or 12 days, the expression of HLA class I increased but no class II was detected on the cell surface. The ability to upregulate HLA class II on the cell surface after exposure to IFN-gamma for 48 hours was clearly diminished after the cells had been cultured in differentiation medium for 6 or 12 days, with only 10% of cells expressing HLA class II. Using MSC grown in osteogenic, chondrogenic, or adipogenic medium as stimulator cells, no lymphocyte alloreactivity was seen, even if differentiated MSC had been pretreated with IFN-gamma. MSC inhibit mixed lymphocyte cultures, particularly after osteogenic differentiation. This suppression was further enhanced by IFN-gamma.
  
  
  CONCLUSIONS
  Undifferentiated and differentiated MSC do not elicit alloreactive lymphocyte proliferative responses and modulate immune responses. The findings support that MSC can be transplantable between HLA-incompatible individuals.
authors.affiliation: Division of Clinical Immunology, Centre for Allogeneic Stem Cell Transplantation, Karolinska Institutet, Huddinge University Hospital, Stockholm, Sweden. Katrina.Leblanc@medhs.ki.se
authors.forename: Katarina
authors.initials: K
authors.lastname: Le Blanc
authors.forename: Charlotte
authors.initials: C
authors.lastname: Tammik
authors.forename: Kerstin
authors.initials: K
authors.lastname: Rosendahl
authors.forename: Eva
authors.initials: E
authors.lastname: Zetterberg
authors.forename: Olle
authors.initials: O
authors.lastname: Ringdén
mesh_terms: D000293:Adolescent; D000328:Adult; D002454:Cell Differentiation; D002648:Child; D005434:Flow Cytometry; D015395:Histocompatibility Antigens Class I / Q000032:analysis*; D000949:Histocompatibility Antigens Class II / Q000032:analysis*; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology; D008213:Lymphocyte Activation; D008648:Mesoderm / Q000166:cytology*; D008875:Middle Aged; D033581:Stem Cell Transplantation; D013234:Stem Cells / Q000276:immunology*
chemical_list: D015395:Histocompatibility Antigens Class I; D000949:Histocompatibility Antigens Class II; D007371:Interferon-gamma