IMMUNE REGULATION AND TOLERANCE II

A. Grohnert¹, C.C. Baan², P. Koumoutsakos¹, A. Peeters¹, W. Weimar³, M.J. Hoogduijn^4
1Internal Medicine - Transplantation Laboratory, Erasmus Medical Center, Rotterdam/NETHERLANDS, ²Internal Medicine, Erasmus MC, Rotterdam/NETHERLANDS, ³Surgery, Erasmus Medical Center, Rotterdam/NETHERLANDS, ⁴Internal Medicine, Room Ee559, Erasmus Medical center, Rotterdam/NETHERLANDS

Body: Introduction: Mesenchymal stem cells (MSC) and CD25⁺FoxP3⁺CD127^- regulatory T cells (Treg) exhibit immunosuppressive functions, which have induced interest in their application as cell therapy in transplantation patients. Currently it is unclear whether there is immunomodulatory interaction between allogeneic MSC and Treg. In the present study we investigated the interaction between MSC and Treg of healthy individuals and kidney transplant patients. Methods: MSC were isolated from perirenal fat tissue of kidney donors. Peripheral blood mononuclear cells (PBMC) and Treg were obtained from blood bank donors or kidney recipients 6 months after transplantation. The immunomodulatory capacity of MSC and Treg was studied in mixed lymphocyte reactions (MLR). Cytokine production was determined at genomic level by qPCR and at protein level by cytometric bead array (CBA). Results: MSC and Treg dose-dependently inhibited the proliferation of allo-activated PBMC of healthy controls. Within the PBMC population MSC and Treg predominantly inhibited the proliferation of CD4⁺ and CD8⁺ T cells. Treg (1:10) achieved 39% inhibition (p<0.01) and MSC (1:10) inhibited PBMC proliferation by 84% (p<0.01). Treg and MSC in combination (each 1:10) resulted in an almost complete inhibition of PBMC proliferation (93%, p<0.01). This phenomenon was also seen using donor MSC, donor-activated PBMC and Treg from kidney transplant patients (96% inhibition, p<0.01). The inhibition of allo-activated PBMC proliferation by MSC was associated with a strong increase in mRNA expression of indoleamine 2,3-dioxygenase (IDO, 10⁵-fold change) in MSC. No change in TGF-beta and IL-10 levels were found. Furthermore, we found that Treg increased TNF (2-fold) and decreased IL-2 protein levels (2-fold) in MLR, whereas MSC inhibited TNF production (8-fold) and induced a strong increase in IL-2 production (80-fold). Conclusion: Our data show that MSC and Treg do not inhibit each others immunomodulatory function. In fact, their interaction leads to a cumulative immunosuppressive effect in healthy controls and kidney transplant patients. The ability of MSC to exert inhibition of allo-activated PBMC strongly depends on IDO. Further, MSC-mediated IL-2 production by allo-activated PBMC provides an ideal climate for Treg function and induction and therefore indicates the potential of both cell types for immunosuppressive therapy.

Disclosure: All authors have declared no conflicts of interest.