Poster Presentation 6th Australian Health and Medical Research Congress 2012

Interferon-gamma and interleukin-17A modification enhance the immunomodulatory function of Mesenchymal Stem Cells (#406)

Kisha N Sivanathan 1 2 3 , Benjamin Thierry 4 , Stan Gronthos 3 5 , P.Toby Coates 1 2 3 6
  1. Transplantation Immunology Laboratory, Royal Adelaide Hospital, Adelaide, South Australia, Australia
  2. Department of Medicine, Universtiy of Adelaide, Adelaide, South Australia , Australia
  3. Centre for Stem Cell Research, Robinson Institute, University of Adelaide, Adelaide, South Australia , Australia
  4. Ian Wark Research Institute, University of South Australia, Adelaide, South Australia, Australia
  5. Mesenchymal Stem Cell Group, Department of Hematology, SA Pathology, Adelaide, South Australia, Australia
  6. Central Northern Adelaide Renal Transplantation Service, Royal Adelaide Hospital, Adelaide, South Australia, Australia

Mesenchymal stem cells (MSC) robustly inhibit mitogen or alloantigen-driven T cell responses in vitro. The in vivo effectiveness of MSC as a monotherapy under inflammatory conditions however remains controversial. This study therefore aimed to identify novel ex vivo strategies to derive highly immunosuppressive MSC populations. Human bone-marrow derived MSC co-cultured with alloantigen or mitogen phytohaemagglutinin (PHA)-stimulated T cells showed baseline dose-dependent inhibition of T cell proliferation in a [3]-thymidine incorporation assay. The exogenous addition of proinflammatory cytokines IFN- γ (100 U/ml) and IL-17A (50 ng/ml) in MSC-T cell co-cultures restored mitogen phytohaemagglutinin (PHA)-induced T cell proliferation while only IL-17A (5 ng/ml) showed reversal of MSC-inhibition on alloantigen-driven T cell responses. Interestingly, the 5 day preactivation of MSC with 500 U/ml IFN-γ (MSC-γ) or with 50 ng/ml IL-17A (MSC-17) derived a highly immunosuppressive population of cells compared to untreated-MSC (UT:MSC). In PHA assays, MSC-γ and MSC-17 inhibited T cell proliferation by 20.6 % (p=0.0120) and 37.6 % (p=0.0028) respectively. MSC-γ were more effective than MSC-17 at suppressing the alloantigen-driven T cell proliferation. Greater than 90 % MSC-γ expressed the T cell negative costimulatory molecule programmed death ligand-1 (PD-L1) demonstrated by flow cytometry. Neutralisation of PD-L1 in MSC-γ however failed to restore T cell proliferative responses suggesting a partial but non-exclusive role of PD-L1 in MSC-γ immunosuppression. MSC-17 on the other hand showed similar PD-L1 expression as UT:MSC. Furthermore, MSC-γ potentially induced T cell anergy evident by the reduction of T cell activation marker CD 25 by flow cytometry. Similar to UT:MSC, these proinflammatory cytokine modified MSC differentiated into adipocytes, osteocytes and chondrocytes. MSC-17 retained similar stem cell marker expression as UT:MSC. Although MSC-γ highly expressed MHC class II molecules, the absence of costimulatory molecule CD 80 and CD 83 expression indicate the inability of MSC-γ to function as T cell stimulators. Moreover, IFN-γ dose-dependently inhibited MSC growth but did not affect cell viability. On the contrary, IL-17A enhanced MSC proliferation compared to UT:MSC and MSC-γ. The enhancement of MSC growth potential implicates that MSC-17 are more beneficial to generate larger numbers of cells for in vivo infusion. In conclusion, MSC-γ and MSC-17 enhanced MSC immunosuppression on T cells. The modified cells also retained MSC stemness phenotype evident by the mesenchymal trilineage differentiation potential and the positive expression of stem cell markers. These ex vivo strategies to derived MSC-γ and MSC-17 could yield more potent cell therapy agents to ameliorate inflammatory responses and enable the MSC application as a monotherapy in vivo.